Scivo V. Pauran

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RADIOACTIVE 2012

PrefaceThanks be delegated to the Lord Almighty, For His blessings and wisdom i

was able to write this paper. In this paper I discuss about the radioactive. Radioactivity is a phenomenon that occurs naturally in a number of substances. Atoms of the substance spontaneously emit invisible but energetic radiations, which can penetrate materials that are opaque to visible light. The effects of these radiations can be harmful to living cells but, when used in the right way, they have a wide range of beneficial applications, particularly in medicine. This paper made to show the definition of radioactive, radioactive decay, the negative and positive impact by using radioactive, and the others.

I realize that this paper is not perfect, so I hope reader can give me some of critism or suggest. With this paper, I hope that we can better know more about radioactive, and can useful to other people.

Writer ,

Scivo V. Pauran

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Table of contents

Preface 1

Chapter 1 :

Background 3

Indetifying problem 6

Goals 7

Methodology 8

Abstract 9

Chapter 2 :

The definition of radioactive 11

Discovery of radioactive 14

Radioactive decay 17

Radioactive waste 35

Benefits of radiation 53

Radioactive impact 55

Chapter 3 :

Conclusion 57

Suggestion 58

Bibliography 59

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CHAPTER 1

1. BACKGROUND

Now, there are so many people in the world. One of the consequence of increasing human population is requirement of energy much more than before. Because it, many people try to find another

Radioactive is subtances that contain instability core. Radioactive is from “radio” or “radiare” which mean spout, shine and active. So, radioactive mean is a tool that have ability to spout spontaneously. It will produce three rays that have different length, and different effort of perforate. The three rays of radioactive are alfa (α), beta (β), and gamma (γ). An alpha particle consists of two protons and two neutrons and is identical to the nucleus of a helium atom. Because of its relatively large mass and charge, an alpha particle produces ions in a very localized area. An alpha particle loses some of its energy each time it produces an ion (its positive charge pulls electrons away from atoms in its path), finally acquiring two electrons from an atom at the end of its path to become a complete helium atom. An alpha particle has a short range (several centimeters) in air and cannot penetrate the outer layer of skin.

Beta particles can be either negative (negatron) or positive (positron). Negatrons are identical to electrons and originate in the nucleus of an atom that undergoes radioactive decay by changing a neutron into a proton. The only difference between a negative beta particle (negatron) and an electron is the ancestry. A beta particle originates in the nucleus whereas an electron is external to the nucleus. Unless otherwise specified, the term “beta particle” generally refers to a

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negatron. A positron is emitted from an atom that decays by changing a proton into a neutron. Beta particles are smaller and more penetrating than alpha particles, but their range in tissue is still quite limited. When its energy is spent, a negatron attaches itself to an atom and becomes an ordinary electron, while a positron collides with an ambient electron and the two particles annihilate each other, producing two gamma rays. When a negatron passes close to the nucleus of an atom, the strong attractive Coulomb force causes the beta particle to deviate sharply and lose energy at a rate proportional to the square of the acceleration. This energy manifests itself as photons termed Bremsstrahlung. The amount of beta energy converted into photons is directly proportional to the energy of the beta particle. This effect is only significant for high-energy beta particles generally passing through very dense materials such as lead, i.e., those with higher atomic numbers and so more protons in the nucleus.

Gamma rays are electromagnetic radiation given off by an atom as a means of releasing excess energy. They are bundles (quanta) of energy that have no charge or mass and can travel long distances through air (up to several hundred meters), body tissue, and other materials. A gamma ray can pass through a body without hitting anything, or it may hit an atom and give that atom all or part of its energy. This normally knocks an electron out of the atom, ionizing it. This electron then uses the energy it receives from the gamma ray to create additional ions by knocking electrons out of other atoms. Because a gamma ray is pure energy, it no longer exists once it loses all its energy. The capability of a gamma ray to do damage is a function of its energy, where the distance between ionizing events is large on the scale of the nucleus of a cell. Additional forms of ionizing radiation beyond the three types shown in the figure above include neutrons, protons, neutrinos, muons, pions, heavy charged particles, X-rays and others. Essentially all radioactive materials at the Hanford Site originated from neutron interactions with uranium fuel to produce plutonium. Byproducts of this process include fission products (most of which are in the high-level waste currently in on-site storage), activation products in the containment and reactor coolant materials, and various radioactive wastes. However, the radioactive hazards that remain at the Hanford Site are largely those associated with the three general types of radiation shown above, so the discussion here is limited to these three.

When ionising radiations (alpha, beta, gamma or X-rays) pass through matter they pass on some or all of their energy to the material by ionising and exciting the atoms of the material through the processes described above. The damage done by this depends both on the energy deposited and the amount of material involved. The radiation damage increases as the amount of energy deposited increases and decreases if it is spread throughout a greater amount of material. The radiation absorbed dose is therefore defined as the energy absorbed divided by the mass of material involved. One Joule of energy absorbed in each kilogram of material is defined as an absorbed dose of one gray (written 1 Gy). Usually we are dealing with

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doses smaller than this so we use units of one thousandth of a gray, or one milligray (written 1 mGy).

The concept of absorbed dose applies to all types of material but, when we need to assess the effect on biological tissues, we also need to take account of the fact that some types of radiation are more harmful than others. For example, because they are so densely ionising, alpha particles are about twenty times as effective at killing cells as beta particles, gamma rays or X-rays. Therefore when measuring the dose to biological tissues we use a quantity called equivalent dose which is defined as the absorbed dose multiplied by a radiation weighting factor. This radiation weighting factor is 20 for alpha particles but 1 for beta particles, gamma rays and X-rays. Confusingly, although equivalent dose has essentially the same units as absorbed dose, it is given a different special name of the sievert (written Sv) or millisievert (mSv). Since we never have to deal with alpha particles in medical applications it happens that the equivalent dose (in Sv or mSv) is always numerically the same as the absorbed dose (in Gy or mGy).

There is one final complication to measuring the effect of radiation on a person; not all tissues in the body are equally sensitive to radiation damage. For example the bone marrow is particularly susceptible to damage whereas the skin is relatively insensitive. Therefore, in situations where different parts of the body might receive different doses, it is usual to calculate a weighted sum of the equivalent doses to each organ. The organ weighting factors take account of the susceptibility of each organ to damage. Thus bone marrow gets a larger weighting factor than skin. This weighted sum of organ doses is called the effective dose. Because the weighting factors for all organs in the body add up to one, if every organ receives the same equivalent dose the effective dose will be the same as the equivalent dose. Therefore the effective dose can be thought of as the uniform whole body dose which would have the same effect (in terms of the risk of doing harm) as the actual non-uniform dose. Effective dose is measured in units of sievert (Sv) or millisieverts (mSv) just the same as equivalent dose.

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2. IDENTIFYING PROBLEM What the definitions of radioactive? Why radioactive can radiatte some rays? What are the benefits of using radioactive? How’s the impact of using radioactive?

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3. GOALS To make many people more understand about radioactive Shows to readers about radioactive decay and radioactive waste Make people know about health risk of radiation of radioactive Shows the readers negative and positive impact of using radioactive To finish the assignment english paper from Mr. Henry S. Nelwan

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4. METHODOLOGY

On making this paper, the writer use some literature, which can help the writer to find data for this paper, or use international network, the writer some methods, there is:

Interview

Study library (from books)

Browsing internet

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5. ABSTRACT

This paper contains a decription about radioactive ranging from history, mode of radioactive decay, kinds of radioactive waste, benefits, and the impact of using radioactive. Starting from the definition of radioactive that radioactive is a subtances that have instability core. It have ability to produce some rays that have different length, and different penetrate ability. And the rays are have good benefits for humans life, but it have bad impact if the radiation of it has radiatte our body to much. Some of the rays are alpha, beta and gamma.

Radioactivity was discovered in 1896 by the French physicist, Henri Becquerel working in Paris. The story of the discovery is a fascinating one which is worth telling in some detail. It gives interesting insights into how quickly and easily fundamental experiments could be done 100 years ago, compared with the lengthy processes of modern scientific research.

By the end of 1896 Becquerel’s interest in his new discovery seems to have waned as he could see little more of interest to do and Röntgen’s X-rays seemed to have many more applications. However in 1897 he was joined by a young research student, Marie Curie, who wished to study for her doctorate. Marie soon discovered that another element, thorium, also exhibited the same emission of Becquerel rays as uranium and she suggested the term ‘radioactivity’ for the phenomenon. She also discovered the important fact that the radioactivity was a property of the atoms themselves and it was not changed by any physical or chemical processes through which the material went. She was later joined by her husband, Pierre, and together they discovered that the mineral pitchblende contained two even stronger radioactive substances, which they called polonium and radium. After years of painstaking purification they were able to separate sufficient polonium and radium to demonstrate that these were both previously unknown elements. In 1903 Henri Becquerel, Marie Curie and Pierre Curie were jointly awarded the Nobel prize in physics for their work on radioactivity. Later Marie Curie was also awarded the 1911 Nobel prize in Chemistry for her discovery of radium.

From above, we know that radioactive is a subtances that have instability core. It means, the radioactive is not immortal. It will gone when the substances are complete to radiatte every rays in it. This event is call radioactive decay. Radioactive decay is collections of multiple process where the core of an atom that not stable radiatte subatomic particles (particles of radioation). Radioactive decay consist in a nucleus that we call “parents”, and it will result a new nucleus that smaller than the “parents” and we call it “daughter”.

Beside the new nucleus that made from “parents”, radioactive decay also produce the another output is the rays. Some of the rays are dangerous for human, it called radioactive waste. Radioactive wastes are wastes that contain radioactive

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material. It make some change to DNA structure and if it radiatte to long to human body, it can causing a cancer or another disease. And sometimes the disease will have impact to next generations, because that radiation has changed the sturcture of DNA and RNA polimerate. But the radioactive have some positif impact for human life. The example is radioactive used in the field of medical, like detect heart damage. It used Tc-99 that injected into a vein and will be absorbed primarily by the damaged tissue in certain organs, such as heart, liver and lungs contrast Ti-201 will mainly be absorbed by healthy tissue in the heart organ.

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CHAPTER 2

1. The definition of RadioactiveRadioactive is a substance that have instability core. It have ability to produce

some rays that have different length, and different penetrate ability. Alpha particles, beta particles, gamma rays and X-rays are examples of ionizing radiation which are so called because as they pass through matter they pass some of their energy to the atoms of the material, resulting in electrons being knocked out of the atom, the process of ionisation, or raised to higher energy levels, excitation. Sometimes this effect is harmful (for example causing damage to living cells) but sometimes it is the basis by which the radiations can be usefully detected. It is therefore important to understand the different ways in which these radiations interact in order to appreciate their uses and hazards.

Alpha particlesFigure 15 illustrates the passage of an alpha particle through matter. Because

alpha particles (made up of 2 protons and 2 neutrons) are comparatively heavy and doubly charged, they cause a great deal of ionisation as they collide with atomic electrons in the material, knocking them out of their atoms. Because they are so much heavier than an electron they do this without deviating from a straight path, but each collision results in a small loss of energy to the alpha particle, so that it steadily slows down. The density of ionisation tends to increase towards the end of the particle’s path. Occasionally an alpha particle may suffer a collision with an atomic nucleus, but this is comparatively rare because the nucleus is so small. However if an alpha particle does hit a nucleus it will be deviated significantly from its forward path and will also send the nucleus recoiling in a different direction. The recoil nucleus can then go on to cause additional ionisation in the material.

Because the ionisation produced is so dense, the alpha particle will soon lose all its energy as a result of many electron collisions and rapidly come to a stop. The distance travelled before it finally stops is called the particle’s range. The range depends on the particle’s energy and the material through which it travels, but for an alpha particle it is always very short. For example an alpha particle with an energy of 1 MeV will have a range of 5 mm in air and only 7 microns in tissue. From this it is clear that an alpha particle source outside the body will do little harm, because all the alpha particles will be absorbed in the superficial layers of the skin which are dead anyway. However if an alpha source was allowed to get inside the body its radiation would be absorbed in a few cells and could produce very damaging effects. This is why alpha emitting radionuclides, such as 238Pu, are so dangerous if inhaled. Alpha emitters are not used in medicine.

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Beta particlesFigure 16 illustrates the passageof a beta particle through matter. Because

beta particles (electrons) are lighter and only singly charged, they produce less dense ionisation than alpha particles and are much more easily deviated from astraight line as they ionise atoms in the material through which theypass. Frequently the collisions with an atomic electron are sufficiently violent to cause the beta particle to deviate through a large angle and then the atomic electron with which it collided acquires enough energy to move off on its own. This electron is called a delta ray and it goes on to produce further ionisation. Occasionally, if a betaparticle happens to encounter an atomic nucleus in a material of high atomic number, it will be deviated very violently and in doing so gives off bremsstrahlung X-rays (from the German for breaking radiation).

After a very zig-zag track, beta particles will eventually come to rest and so, like alpha particles, they exhibit a definite range. However, since they produce less dense ionisation, they slow down more gradually than alpha particles and will have a longer range. For example, 600 keV is a typical beta particle energy; this is the maximum energy of beta particles from 131I decay and the average energy from decay of 90Sr and its daughter 90Y. A 600 keV beta particle has a range of 2.5 metres in air or 3 mm in tissue. Because all beta sources emit a range of beta particle energies, rather than just a single energy, there will always be a spread in the range of particles emitted. The number of beta particles therefore falls off quite rapidly with thickness of material traversed, until none remain after a thickness equal to the range of the maximum energy present.

If a beta source is close to, or even inside, the body its radiation will be absorbed within a few millimetres of the source. This means that all the energy is absorbed in local tissues and, since beta particles are moderately ionizing, there is potential for damaging effects to these tissues. In diagnosis this may be looked upon as a hazard to be minimised, but it can be put to good use in therapeutic applications. For example the high energy beta particles emitted from the decay of 90Sr (and its daughter 90Y) can be used in an external applicator for therapeutic doses to surface tissues. The beta particles from 131I are also used in therapy of the thyroid. Since iodine is concentrated by thyroid tissue a patient administered with radioactive iodine 131I will receive a larger radiation dose to the thyroid than to other organs.

Nuclides such as 3H, which emit low energy beta particles, result in a smaller radiation dose which means that, in small amounts, they may be safely administered internally for in-vivo diagnostic studies. However, since the beta particles will not escape from the patient, measurements of the activity present must be made by collecting blood or urine samples and then counting these in the laboratory. Even then detecting the low energy beta particles is not easy and the samples must be intimately mixed with the detecting medium in a liquid scintillation counter. Slightly higher energy beta particles, such as those from 35S, are useful for autoradiography. When tissue containing 35S is placed on a photographic film, the beta particles will

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only blacken the film locally, producing an image of the activity distribution in the sample.

Gamma rays and X-raysGamma rays and X-rays are not particles like alpha and beta, but are examples

of electromagnetic radiation (like high energy light) and consequently interact with matter in a rather different way. Figure 17 illustrates the passage of several gamma rays through matter. Unlike alpha and beta, where each particle undergoes many individual interactions, each gamma ray only encounters one, or possibly two, interactions and many gamma rays pass through with no interaction at all.

Gamma rays and X-rays do not produce ionisation directly, but instead they do so by first producing secondary electrons. These arise from two types of process; scattering and absorption. Scattering occurs through the process of compton scattering in which a gamma ray interacts with a free electron in the material. The gamma ray passes some of its energy to the electron and continues on its way as scattered radiation with a lower energy and travelling in a different direction (for example rays 1 and 4 in figure 17). There are two possible absorption processes in which the gamma ray disappears altogether. Photoelectric absorption occurs when a gamma ray gives up all of its energy at once to an atomic electron which is then ejected from the atom (rays 3 and 6 in figure 17). Gamma rays with energy greater than 1 MeV can also be absorbed by pair production, in which an electron and positron pair are spontaneously produced (ray 7 in figure 17). The positron will subsequently annihilate with an atomic electron producing two gamma rays of 511 keV. After any of these processes the secondary electrons produced go on to produce ionisation of the material, just like a beta particle. Unlike alpha and beta particles, which are stopped after many interactions, gamma rays and X-rays each undergo only a few interactions. Gamma rays do not therefore have a definite range, but instead the intensity of a gamma ray beam is attenuated by a combination of scattering and absorption processes so that it falls off steadily with distance. The distance required to halve the number of the gamma rays is called the half-value layer (HVL). This is analogous to the half-life of radionuclide decay and the same exponential mathematics apply. In figure 17 the incident radiation consists of ten gamma rays entering at the left. During passage through one half value layer of the material 3 of these are absorbed and 2 scattered leaving an attenuated beam containing only 5 gamma rays. In the next half value layer, half of these would again disappear. The half value layer depends on the energy of the radiation and the nature of the material. For a gamma ray of 140 keV the HVL in lead is 0.25 mm. Therefore 0.25 mm of lead shielding will reduce the intensity of 140 keV radiation to half its original value, 0.5 mm will reduce it to one quarter, 1 mm (4 HVLs) to one sixteenth and 3 mm (12 HVLs) by a factor of 1/4096. In tissue the HVL is much greater, being 47 mm for 140 keV gamma rays. Thus if a radionuclide such as 99mTc, which emits 140 keV gamma rays, is present inside a person it is clear that sufficient numbers of gamma rays will be able to penetrate body tissues to permit external detection of the whereabouts of the radionuclide for diagnostic imaging

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purposes. Gamma rays that do not escape will distribute their energy throughout several organs, leading to a distributed radiation dose which is much less damaging than the local doses from beta emitters. This is why pure gamma emitting radionuclides such as 99mTc are so useful for diagnostic imaging purposes.

2. The discovery of radioactive

Radioactivity was discovered in 1896 by the French physicist, Henri Becquerel working in Paris. The story of the discovery is a fascinating one which is worth telling in some detail. It gives interesting insights into how quickly and easily fundamental experiments could be done 100 years ago, compared with the lengthy processes of modern scientific research. Becquerel had succeeded his father as Professor of Physics at the Museum of Natural History in Paris. There he continued his father’s investigations into the phenomenon of phosphorescence; the emission of visible light by certain substances when they are activated by exposure to a bright light source. He had assisted his father with many experiments on phosphorescence and knew that a preparation containing crystals of uranium and potassium would glow when exposed to sunlight and that this stopped quickly when it was taken into the dark. On 20 January 1896 Becquerel attended a lecture at the French Academy of Science in Paris at which he heard Henri Poincaré describe the recent discovery of X-rays by Wilhelm Röntgen. Poincaré demonstrated how, when a beam of electrons was accelerated across a vacuum tube, visible light was emitted from the spot where the electron beam hit the glass wall (just like in a modern TV tube). This was another example of phosphorescence (although nowadays we would call it fluorescence) which others had observed before. The new discovery which Röntgen had made in 1895 was that some hitherto unknown invisible radiation was also emitted from the same spot. These became known as X-rays (X standing for the unknown). Röntgen had found that they were able to penetrate solid material and cast shadows of metal objects on photographic paper. Hearing this description, Becquerel presumed that the X-rays were associated with the phosphorescence and he wondered whether his phosphorescent crystals might also emit X-rays. He therefore conducted several experiments to check this. In each experiment he wrapped a photographic plate in light tight paper and placed some of his crystals on the outside of the paper. This was then exposed to sunlight for several hours. Sure enough, when the plate was developed it had become blackened where the crystals had been. He found that if a thin piece of metal was placed between the crystals and the plate then this cast a shadow. These results seemed to confirm his assumption that X-rays were part of phosphorescence and he reported these results to the French Academy of Science on 24 February 1896. Continuing his experiments, Becquerel prepared some more samples on 26 and 27 February but the weather was poor and there was insufficient sunlight to activate his crystals, so did not use them. Instead he left the crystals lying

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on the wrapped photographic plate but in a dark drawer. By Sunday 1 March the sun still had not shone in Paris, but Becquerel decided to develop his plates anyway, expecting to find only very weak images. Instead he was amazed to find an image just as intense as when the crystals has been exposed to bright sunlight. He immediately did further experiments which confirmed that the crystals could blacken a photographic plate whether or not they were made to phosphoresce. He realised that he had accidentally discovered an entirely new phenomenon which he attributed to some form of long lasting phosphorescence emitting invisible radiation. He presented Introduction to Radioactivity Page 3 R.S.Lawson October 1999 his findings to a meeting of the French Academy of Sciences the very next day on 2 March 1896 and a written version of this was published within 10 days. By the end of the year he had published six more papers on his further investigations into these ‘Becquerel rays’ confirming that they derived from the uranium in his crystals and that they did not noticeably diminish in intensity even after several months. It is interesting to speculate what might have happened if Becquerel had chosen a different phosphorescent crystal for his experiments. He could just as easily have chosen zinc sulphate from his father’s large collection of phosphorescent materials, and then he would not have found any effect on the photographic plate because zinc is not radioactive like uranium. In that case the discovery of radioactivity might well have been left to an Englishman. On 23 February 1896 Silvanus Thompson, in London, had independently performed the same experiment as Becquerel, exposing uranium crystals to sunlight whilst placed on a wrapped photographic plate. By the time that Thompson wrote to the president of the Royal Society in London to describe his results, Becquerel’s initial findings had already been reported to the French Academy of Sciences. Hearing this, Thompson did no further work on the subject and thus missed the opportunity to beat Becquerel to his fortuitous discovery of 1 March. That is why we now measure radioactivity in units of megabecquerels rather than megathompsons. By the end of 1896 Becquerel’s interest in his new discovery seems to have waned as he could see little more of interest to do and Röntgen’s X-rays seemed to have many more applications. However in 1897 he was joined by a young research student, Marie Curie, who wished to study for her doctorate. Marie soon discovered that another element, thorium, also exhibited the same emission of Becquerel rays as uranium and she suggested the term ‘radioactivity’ for the phenomenon. She also discovered the important fact that the radioactivity was a property of the atoms themselves and it was not changed by any physical or chemical processes through which the material went. She was later joined by her husband, Pierre, and together they discovered that the mineral pitchblende contained two even stronger radioactive substances, which they called polonium and radium. After years of painstaking purification they were able to separate sufficient polonium and radium to demonstrate that these were both previously unknown elements. In 1903 Henri Becquerel, Marie Curie and Pierre Curie were jointly awarded the Nobel prize in physics for their work on radioactivity. Later Marie Curie was also awarded the 1911 Nobel prize in Chemistry for her

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discovery of radium. Radioactivity had also captured the interest of another student, Ernest Rutherford, who was then studying in Cambridge under professor J J Thomson. He continued this interest after he moved to McGill University in Montreal, where he discovered that the Becquerel rays contained two different components which he simply called alpha and beta. The alpha rays were easily stopped by thin card whereas the beta rays would pass through card but were stopped by sheets of metal. Becquerel and the Curies showed that the beta rays were identical to electrons (newly discovered by J J Thomson). Subsequently a third, even more penetrating, component of the radiation was discovered by Paul Villard in Paris and these were naturally called gamma rays. Further investigations by Rutherford, working with the chemist Frederick Soddy, showed that the intensity of radioactive emission of many materials reduced exponentially with time, but that they sometimes converted into other materials which were themselves radioactive. By 1902 Rutherford had concluded that the atom, previously thought to be indestructible, was spontaneously disintegrating and changing from one element into another. This heretical idea was not readily accepted by many scientists who though that it sounded too much like alchemy. However, by 1907 Rutherford and Soddy had identified several separate series of naturally occurring radioactive transformations in which each element successively changed into the next one down the chain, until they eventually ended up as non-active lead. In 1907 Rutherford moved to Manchester where he was appointed professor of physics, and in 1908 he proved that alpha rays were in fact ionised helium atoms. In 1911 two of his researchers, Hans Geiger and Ernest Marsden, performed a classic experiment in which they allowed alpha particles to scatter off a gold foil and found that some of them bounced straight back. The results of this experiment led Rutherford to deduce that there was a small nucleus at the centre of each atom. Our modern understanding of the nature of the atom and the process of radioactive decay stem largely from the theories developed by Ernest Rutherford and Niels Bohr during this period in Manchester.

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3. Radioactive decay

Radioactive decay is the process by which an atomic nucleus of an unstable atom loses energy by emitting ionizing particles (ionizing radiation). The emission is spontaneous, in that the atom decays without any physical interaction with another particle from outside the atom. Usually, radioactive decay happens due to a process confined to the nucleus of the unstable atom, but, on occasion (as with the different processes of electron capture and internal conversion), an inner electron of the radioactive atom is also necessary to the process.

Radioactive decay is a stochastic (i.e., random) process at the level of single atoms, in that, according to quantum theory, it is impossible to predict when a given atom will decay. However, the chance that a given atom will decay is constant over time. For a large number of identical atoms (of the same nuclide), the decay rate for the collection is predictable to the extent allowed by the law of large numbers, and is easily calculated from the measured decay constant of the nuclide (or equivalently from the half-life).

The decay, or loss of energy, results when an atom with one type of nucleus, called the parent radionuclide, transforms to an atom with a nucleus in a different state, or a different nucleus, either of which is named the daughter nuclide. Often the parent and daughter are different chemical elements, and in such cases the decay process results in nuclear transmutation. In an example of this, a carbon-14 atom (the "parent") emits radiation (a beta particle, antineutrino, and a gamma ray) and

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transforms to a nitrogen-14 atom (the "daughter"). By contrast, there exist two types of radioactive decay processes (gamma decay and internal conversion decay) that do not result in transmutation, but only decrease the energy of an excited nucleus. This results in an atom of the same element as before but with a nucleus in a lower energy state. An example is the nuclear isomer technetium-99m decaying, by the emission of a gamma ray, to an atom of technetium-99.

Nuclides produced by radioactive decay are called radiogenic nuclides, whether they themselves are stable or not. There exist stable radiogenic nuclides that were formed from short-lived extinct radionuclides in the early solar system. The extra presence of these stable radiogenic nuclides (such as Xe-129 from primordial I-129) against the background of primordial stable nuclides can be inferred by various means. Presently-radioactive nuclides are from three sources: many naturally-occurring radionuclides are short-lived radiogenic nuclides that are the daughters of ongoing radioactive primordial nuclides (types of radioactive atoms that have been present since the beginning of the Earth and solar system). Other naturally-occurring radioactive nuclides are cosmogenic nuclides, formed by cosmic ray bombardment of material in the Earth's atmosphere or crust. Finally, some primordial nuclides are radioactive, but are so long-lived that they remain present from the primordial solar nebula. For a summary table showing the number of stable nuclides and of radioactive nuclides in each category, see radionuclide.

Radioactivity was discovered in 1896 by the French scientist Henri Becquerel, while working on phosphorescent materials. During experiments to see if phosphorescent materials would expose photographic materials through black paper in the manner of the recently-discovered X-rays, which produced fluorescense, Becquerel used a phosphorescent uranium salt and eventually found that it blackened the plate through paper wrapping, in a desk drawer over a weekend, even without application of light, or production of its phosphorescence. These penetrating radiations, accidently discovered emanating from uranium minerals, were first called Becquerel rays.

The SI unit of radioactive activity is the becquerel (Bq), in honor of the scientist. One Bq is defined as one transformation (or decay) per second. Since sensible sizes of radioactive material contains many atoms, a Bq is a tiny measure of activity; amounts giving activities on the order of GBq (gigabecquerel, 1 x 109 decays per second) or TBq (terabecquerel, 1 x 1012 decays per second) are commonly used.

ExplanationThe neutrons and protons that constitute nuclei, as well as other particles that

approach close enough to them, are governed by several interactions. The strong nuclear force, not observed at the familiar macroscopic scale, is the most powerful

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force over subatomic distances. The electrostatic force is almost always significant, and, in the case of beta decay, the weak nuclear force is also involved.

The interplay of these forces produces a number of different phenomena in which energy may be released by rearrangement of particles in the nucleus, or else the change of one type of particle into others. These rearrangements and transformations may be hindered energetically, so that they do not occur immediately. In certain cases, random quantum vacuum fluctuations are theorized to promote relaxation to a lower energy state (the "decay") in a phenomenon known as quantum tunneling. Radioactive decay half-life of nuclides has been measured over timescales of 59 orders of magnitude, from 3 x 10-27 second (for helium-2) to longer than 2.4 x 1032 seconds (for tellurium-128). The limits of these timescales are set by the sensitivity of instrumentation only, and there are no known natural limits to how brief or long a decay half life for radioactive decay of a radionuclide may be.

The decay process, like all hindered energy transformations, may be analogized by a snowfield on a mountain. While friction between the ice crystals may be supporting the snow's weight, the system is inherently unstable with regard to a state of lower potential energy. A disturbance would thus facilitate the path to a state of greater entropy: The system will move towards the ground state, producing heat, and the total energy will be distributable over a larger number of quantum states. Thus, an avalanche results. The total energy does not change in this process, but, because of the law of entropy, avalanches happen only in one direction and that is toward the "ground state" — the state with the largest number of ways in which the available energy could be distributed.

Such a collapse (a decay event) requires a specific activation energy. For a snow avalanche, this energy comes as a disturbance from outside the system, although such disturbances can be arbitrarily small. In the case of an excited atomic nucleus, the arbitrarily small disturbance comes from quantum vacuum fluctuations. A radioactive nucleus (or any excited system in quantum mechanics) is unstable, and can, thus, spontaneously stabilize to a less-excited system. The resulting transformation alters the structure of the nucleus and results in the emission of either a photon or a high-velocity particle that has mass (such as an electron, alpha particle, or other type).

DiscoveryRadioactivity was discovered in 1896 by the French scientist Henri Becquerel,

while working on phosphorescent materials. These materials glow in the dark after exposure to light, and he suspected that the glow produced in cathode ray tubes by X-rays might be associated with phosphorescence. He wrapped a photographic plate in black paper and placed various phosphorescent salts on it. All results were

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negative until he used uranium salts. The result with these compounds was a blackening of the plate. These radiations were called Becquerel Rays.

It soon became clear that the blackening of the plate did not have anything to do with phosphorescence, because the plate blackened when the mineral was in the dark. Non-phosphorescent salts of uranium and metallic uranium also blackened the plate. It was clear that there is a form of radiation that could pass through paper that was causing the plate to become black.

At first it seemed that the new radiation was similar to the then recently-discovered X-rays. Further research by Becquerel, Ernest Rutherford, Paul Villard, Pierre Curie, Marie Curie, and others discovered that this form of radioactivity was significantly more complicated. Different types of decay can occur, producing very different types of radiation. Rutherford was the first to realize that they all occur with the same mathematical exponential formula (see below), and Rutherford and his student Frederick Soddy were first to realize that many decay processes resulted in the transmutation of one element to another.

The early researchers also discovered that many other chemical elements besides uranium have radioactive isotopes. A systematic search for the total radioactivity in uranium ores also guided Marie Curie to isolate a new element polonium and to separate a new element radium from barium. The two elements' chemical similarity would otherwise have made them difficult to distinguish.

Danger of radioactive subtancesThe dangers of radioactivity and radiation were not immediately recognized.

Acute effects of radiation were first observed in the use of X-rays when electrical engineer and physicist Nikola Tesla intentionally subjected his fingers to X-rays during 1896. He published his observations concerning the burns that developed, though he attributed them to ozone rather than to X-rays. His injuries healed later.

The genetic effects of radiation, including the effect on cancer risk, were recognized much later. During 1927, Hermann Joseph Muller published research showing genetic effects, and in 1946 was awarded the Nobel prize for his findings.

Before the biological effects of radiation were known, many physicians and corporations had begun marketing radioactive substances as patent medicine, glow-in-the-dark pigments, and radioactive quackery. Examples were radium enema treatments, and radium-containing waters to be drunk as tonics. Marie Curie protested this sort of treatment, warning that the effects of radiation on the human body were not well understood (Curie later died from aplastic anemia, which was likely caused by exposure to ionizing radiation). By the 1930s, after a number of

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cases of bone necrosis and death in enthusiasts, radium-containing medical products had been largely removed from the market.

Types of decayAs for types of radioactive radiation, it was found that an electric or magnetic

field could split such emissions into three types of beams. For lack of better terms, the rays were given the alphabetic names alpha, beta, and gamma, still in use today. While alpha decay was seen only in heavier elements (atomic number 52, tellurium, and greater), the other two types of decay were seen in all of the elements.

In analyzing the nature of the decay products, it was obvious from the direction of electromagnetic forces produced upon the radiations by external magnetic and electric fields that alpha rays carried a positive charge, beta rays carried a negative charge, and gamma rays were neutral. From the magnitude of deflection, it was clear that alpha particles were much more massive than beta particles. Passing alpha particles through a very thin glass window and trapping them in a discharge tube allowed researchers to study the emission spectrum of the resulting gas, and ultimately prove that alpha particles are helium nuclei. Other experiments showed the similarity between classical beta radiation and cathode rays: They are both streams of electrons. Likewise gamma radiation and X-rays were found to be similar high-energy electromagnetic radiation.

The relationship between types of decays also began to be examined: For example, gamma decay was almost always found associated with other types of decay, occurring at about the same time, or afterward. Gamma decay as a separate phenomenon (with its own half-life, now termed isomeric transition), was found in natural radioactivity to be a result of the gamma decay of excited metastable nuclear isomers, in turn created from other types of decay.

Although alpha, beta, and gamma were found most commonly, other types of decay were eventually discovered. Shortly after the discovery of the positron in cosmic ray products, it was realized that the same process that operates in classical beta decay can also produce positrons (positron emission). In an analogous process, instead of emitting positrons and neutrinos, some proton-rich nuclides were found to capture their own atomic electrons (electron capture), and emit only a neutrino (and usually also a gamma ray). Each of these types of decay involves the capture or emission of nuclear electrons or positrons, and acts to move a nucleus toward the ratio of neutrons to protons that has the least energy for a given total number of nucleons (neutrons plus protons).

Shortly after discovery of the neutron in 1932, it was discovered by Enrico Fermi that certain rare decay reactions yield neutrons as a decay particle (neutron emission). Isolated proton emission was eventually observed in some elements. It

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was also found that some heavy elements may undergo spontaneous fission into products that vary in composition. In a phenomenon called cluster decay, specific combinations of neutrons and protons (atomic nuclei) other than alpha particles (helium nuclei) were found to be spontaneously emitted from atoms, on occasion.

Other types of radioactive decay that emit previously seen particles were found, but by different mechanisms. An example is internal conversion, which results in electron and sometimes high-energy photon emission, even though it involves neither beta nor gamma decay. This type of decay (like isomeric transition gamma decay) did not transmute one element to another.

Rare events that involve a combination of two beta-decay type events happening simultaneously (see below) are known. Any decay process that does not violate conservation of energy or momentum laws (and perhaps other particle conservation laws) is permitted to happen, although not all have been detected. An interesting example (discussed in a final section) is bound state beta decay of rhenium-187. In this process, an inverse of electron capture, beta electron-decay of the parent nuclide is not accompanied by beta electron emission, because the beta particle has been captured into the K-shell of the emitting atom. An antineutrino, however, is emitted.

Radionuclides can undergo a number of different reactions. These are summarized in the following table. A nucleus with mass number A and atomic number Z is represented as (A, Z). The column "Daughter nucleus" indicates the difference between the new nucleus and the original nucleus. Thus, (A − 1, Z)

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means that the mass number is one less than before, but the atomic number is the same as before

Mode of decay Particaping particles Daughter nucleusDecays with emission of nucleos :Alpha decay An alpha particle emitter from nucleus (A-4, Z-2)Proton emission A proton ejected from nucleus (A − 1, Z − 1)Neutron emission A neutron ejected from nucleus (A − 1, Z)Double proton emission

Two protons ejected from nucleus simultaneously

(A − 2, Z − 2)

Spontaneous fission

Nucleus disintegrates into two or more smaller nuclei and other particles

___

Cluster decay Nucleus emits a specific type of smaller nucleus (A1, Z1) smaller than, or larger than, an alpha particle

(A − A1, Z − Z1) + (A1, Z1)

Different modes of beta decay :β− decay A nucleus emits an electron and an electron

antineutrino(A, Z + 1)

Positron emission (β+ decay)

A nucleus emits a positron and an electron neutrino

(A, Z − 1)

Electron capture A nucleus captures an orbiting electron and emits a neutrino; the daughter nucleus is left in an excited unstable state

(A, Z − 1)

Bound state beta decay

A nucleus beta decays to electron and antineutrino, but the electron is not emitted, as it is captured into an empty K-shell;the daughter nucleus is left in an excited and unstable state. This process is suppressed except in ionized atoms that have K-shell vacancies.

(A, Z + 1)

Double beta decay A nucleus emits two electrons and two antineutrinos

(A, Z + 2)

Double electron capture

A nucleus absorbs two orbital electrons and emits two neutrinos – the daughter nucleus is left in an excited and unstable state

(A, Z − 2)

Electron capture with positron emission

A nucleus absorbs one orbital electron, emits one positron and two neutrinos

(A, Z − 2)

Double positron emission

A nucleus emits two positrons and two neutrinos

(A, Z − 2)

Transitions between states of the same nucleus :

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Isomeric transition

Excited nucleus releases a high-energy photon (gamma ray)

(A, Z)

Internal conversion

Excited nucleus transfers energy to an orbital electron and it is ejected from the atom

(A, Z)

Radioactive decay results in a reduction of summed rest mass, once the released energy (the disintegration energy) has escaped in some way (for example, the products might be captured and cooled, and the heat allowed to escape). Although decay energy is sometimes defined as associated with the difference between the mass of the parent nuclide products and the mass of the decay products, this is true only of rest mass measurements, where some energy has been removed from the product system. This is true because the decay energy must always carry mass with it, wherever it appears (see mass in special relativity) according to the formula E = mc2. The decay energy is initially released as the energy of emitted photons plus the kinetic energy of massive emitted particles (that is, particles that have rest mass). If these particles come to thermal equilibrium with their surroundings and photons are absorbed, then the decay energy is transformed to thermal energy, which retains its mass.

Decay energy therefore remains associated with a certain measure of mass of the decay system invariant mass. The energy of photons, kinetic energy of emitted particles, and, later, the thermal energy of the surrounding matter, all contribute to calculations of invariant mass of systems. Thus, while the sum of rest masses of particles is not conserved in radioactive decay, the system mass and system invariant mass (and also the system total energy) is conserved throughout any decay process.

Decay chains and multiple modesThe daughter nuclide of a decay event may also be unstable (radioactive). In this case, it will also decay, producing radiation. The resulting second daughter nuclide may also be radioactive. This can lead to a sequence of several decay events. Eventually, a stable nuclide is produced. This is called a decay chain.An example is the natural decay chain of 238U, which is as follows:

decays, through alpha-emission, with a half-life of 4.5 billion years to thorium-234

which decays, through beta-emission, with a half-life of 24 days to protactinium-234

which decays, through beta-emission, with a half-life of 1.2 minutes to uranium-234

which decays, through alpha-emission, with a half-life of 240 thousand years to thorium-230

which decays, through alpha-emission, with a half-life of 77 thousand years to radium-226

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which decays, through alpha-emission, with a half-life of 1.6 thousand years to radon-222

which decays, through alpha-emission, with a half-life of 3.8 days to polonium-218

which decays, through alpha-emission, with a half-life of 3.1 minutes to lead-214

which decays, through beta-emission, with a half-life of 27 minutes to bismuth-214

which decays, through beta-emission, with a half-life of 20 minutes to polonium-214

which decays, through alpha-emission, with a half-life of 160 microseconds to lead-210

which decays, through beta-emission, with a half-life of 22 years to bismuth-210

which decays, through beta-emission, with a half-life of 5 days to polonium-210

which decays, through alpha-emission, with a half-life of 140 days to lead-206, which is a stable nuclide.

Some radionuclides may have several different paths of decay. For example, approximately 36% of bismuth-212 decays, through alpha-emission, to thallium-208 while approximately 64% of bismuth-212 decays, through beta-emission, to polonium-212. Both the thallium-208 and the polonium-212 are radioactive daughter products of bismuth-212, and both decay directly to stable lead-208.

Occurrence and applicationsAccording to the Big Bang theory, stable isotopes of the lightest five elements

(H, He, and traces of Li, Be, and B) were produced very shortly after the emergence of the universe, in a process called Big Bang nucleosynthesis. These lightest stable nuclides (including deuterium) survive to today, but any radioactive isotopes of the light elements produced in the Big Bang (such as tritium) have long since decayed. Isotopes of elements heavier than boron were not produced at all in the Big Bang, and these first five elements do not have any long-lived radioisotopes. Thus, all radioactive nuclei are, therefore, relatively young with respect to the birth of the universe, having formed later in various other types of nucleosynthesis in stars (in particular, supernovae), and also during ongoing interactions between stable isotopes and energetic particles. For example, carbon-14, a radioactive nuclide with a half-life of only 5730 years, is constantly produced in Earth's upper atmosphere due to interactions between cosmic rays and nitrogen.

Radioactive decay has been put to use in the technique of radioisotope labeling, which is used to track the passage of a chemical substance through a complex system (such as a living organism). A sample of the substance is synthesized with a high concentration of unstable atoms. The presence of the

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substance in one or another part of the system is determined by detecting the locations of decay events.

On the premise that radioactive decay is truly random (rather than merely chaotic), it has been used in hardware random-number generators. Because the process is not thought to vary significantly in mechanism over time, it is also a valuable tool in estimating the absolute ages of certain materials. For geological materials, the radioisotopes and some of their decay products become trapped when a rock solidifies, and can then later be used (subject to many well-known qualifications) to estimate the date of the solidification. These include checking the results of several simultaneous processes and their products against each other, within the same sample. In a similar fashion, and also subject to qualification, the rate of formation of carbon-14 in various eras, the date of formation of organic matter within a certain period related to the isotope's half-life may be estimated, because the carbon-14 becomes trapped when the organic matter grows and incorporates the new carbon-14 from the air. Thereafter, the amount of carbon-14 in organic matter decreases according to decay processes that may also be independently cross-checked by other means (such as checking the carbon-14 in individual tree rings, for example).

Radioactive decay ratesThe SI unit of radioactive activity is the becquerel (Bq), in honor of the scientist.

One Bq is defined as one transformation (or decay) per second. Since sensible sizes of radioactive material contains many atoms, a Bq is a tiny measure of activity; amounts on the order of GBq (gigabecquerel, 1 x 109 decays per second) or TBq (terabecquerel, 1 x 1012 decays per second) are commonly used. Another unit of radioactivity is the curie, Ci, which was originally defined as the amount of radium emanation (radon-222) in equilibrium with one gram of pure radium, isotope Ra-226. At present it is equal, by definition, to the activity of any radionuclide decaying with a disintegration rate of 3.7 × 1010 Bq. The use of Ci is currently discouraged by the SI.

The decay rate, or activity, of a radioactive substance are characterized by:Constant quantities:-. The half-life t1/2, is the time taken for the activity of a given amount of a radioactive substance to decay to half of its initial value.

-. The mean lifetime τ, "tau" the average lifetime of a radioactive particle before decay.

-. The decay constant λ, "lambda" the inverse of the mean lifetime.

Although these are constants, they are associated with statistically random behavior of populations of atoms. In consequence predictions using these constants are less accurate for small number of atoms.

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In principle the reciprocal of any number greater than one — a half-life, a third-life, or even a (1/√2)-life — can be used in exactly the same way as half-life; but the half-life t1/2 is adopted as the standard time associated with exponential decay.-. Total activity A, is number of decays per unit time of a radioactive sample.-. Number of particles N, is the total number of particles in the sample.-. Specific activity SA, number of decays per unit time per amount of substance of the sample at time set to zero (t = 0). "Amount of substance" can be the mass, volume or moles of the initial sample.

Where a0 is the initial amount of active substance — substance that has the same percentage of unstable particles as when the substance was formed.

Activity measurementsThe units in which activities are measured are: becquerel (symbol Bq) = one

disintegration per second; curie (Ci) = 3.7 × 1010 Bq. Low activities are also measured in disintegrations per minute (dpm).

Universal law of radioactive decayRadioactivity is one very frequent example of exponential decay. The law

however is only statistical - not exact. In the following formalism, the number of nuclides or nuclide population N, is of course a descrete variable (a natural number) - but for any physical sample N is so large (amounts of L = 1023, avagadro's constant) that it can be treated as a continuous variable. Differential calculus to set up differential equations for modelling the behaviour of the nuclear decay.

One-decay process

Consider the case of a nuclide A decaying into another B by some process A → B (emission of other particles, like electron neutrinos νe and electrons e– in beta decay, are irrelevant in what follows). The decay of an unstable nucleus is entirely random and it is impossible to predict when a particular atom will decay. However, it is equally likely to decay at any time. Therefore, given a sample of a particular radioisotope, the number of decay events −dN expected to occur in a small interval of time dt is proportional to the number of atoms present N, that is

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Particular radionuclides decay at different rates, so each has its own decay constant

λ. The probability of decay −dN/N is proportional to an increment of time, dt:

The negative sign indicates that N decreases as time increases, as each decay event follows one after another. The solution to this first-order differential equation is the function:

where N0 is the value of N at time .This equation is of particular interest; the behaviour of numerous important quantities can be found from it (see below). Although the parent decay distribution follows an exponential, observations of decay times will be limited by a finite integer number of N atoms and follow Poisson statistics as a consequence of the random nature of the process.We have for all time t:NA + NB = Ntotal = NA0,where Ntotal is the constant number of particles throughout the decay process, clearly equal to the initial number of A nuclides since this is the initial substance.If the number of non-decayed A nuclei is:

then the number of nuclei of B, i.e. number of decayed A nuclei, is

Chain-decay processesChain of two decays

Now consider the case of a chain of two decays: one nuclide A decaying into another B by one process, then B decaying into another C by a second process, i.e. A → B → C. The previous equation cannot be applied to a decay chain, but can be generalized as follows. The decay rate of B is proportional to the number of nuclides of B present, so again we have:

but care must be taken. Since A decays into B, then B decays into C, the activity of A adds to the total number of B nuclides in the present sample, before those B nuclides decay and reduce the number of nuclides leading to the later sample. In other words, the number of second generation nuclei B increases as a result of the first generation nuclei decay of A, and decreases as a result of its own decay into the third generation nuclei C. The proportionality becomes an equation:

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adding the increasing (and correcting) term obtains the law for a decay chain for two nuclides:

The equation is not

since this implies the number of atoms of B is only decreasing as time increases, which is not the case. The rate of change of NB, that is dNB/dt, is related to the changes in the amounts of A and B, NB can increase as B is produced from A and decrease as B produces C.Re-writing using the previous results:

The subscripts simply refer to the respective nuclides, i.e. NA is the number of nuclides of type A, NA0 is the initial number of nuclides of type A, λA is the decay constant for A - and similarly for nuclide B. Solving this equation for NB gives:

Naturally this equation reduces to the previous solution, in the case B is a stable nuclide (λB = 0):

as shown above for one decay. The solution can be found by the integration factor method, where the integrating factor is eλ

Bt. This case is perhaps the most useful,

since it can derive both the one-decay equation (above) and the equation for multi-decay chains (below) more directly.

Chain of any number of decaysFor the general case of any number of consecutive decays in a decay chain,

i.e. A1 → A2 ··· → Ai ··· → AD, where D is the number of decays and i is a dummy index (i = 1, 2, 3, ...D), each nuclide population can be found in terms of the previous population, using the above result in a recursive form:

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The general solution to the recursive problem are given by Bateman's equations

Alternative decay modes

In all of the above examples, the initial nuclide decays into only one product. Consider the case of one initial nuclide which can decay into two products, that is A → B + C. We have for all time t:

NA + NB + NC = Ntotal = NA0,

in which,

so the relations follow in parallel:

indicating that the total decay constant is that of A, given by:

λA = λB + λC.

Solving this equation for NA:

When measuring the production of one nuclide, one can only observe the total decay constant λA. The decay constants λB and λC determine the probability for the decay to result in products B or C as follows:

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These perhaps seemingly disjionted results are consistent:

Corollaries of the decay laws

The solutions to the above differential equations are sometimes written using quantities related to the number of nuclide particles N in a sample, where L is Avagadro's constant,6.023×1023, and Ar is the relative atomic mass number, and the amount of the substance is in moles.

The activity: A = λN. The amount of substance: n = N/L. The mass: M = Arn = ArN/L.

Collecting these results together for convenience: N = A/λ = Ln = LM/Ar.

Equivalent ways to write the decay solutions, then, are as follows:

One-decay processes

The solution

can be written:

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Notice how we can simply replace each quantity (on both sides of the equation), since they are directly proportional to N and so the constants cancel (constant at least for a particular nuclide).

Chain-decay processes

For the two-decay chain,

its almost as simple:

Decay timing: definitions and relations

Time constant and mean-life

For the one-decay solution A → B:

the equation indicates that the decay constant λ has units of t-1, and can thus also be represented as 1/τ, where τ is a characteristic time of the process called the time constant.

In a radioactive decay process, this time constant is also the mean lifetime for decaying atoms. Each atom "lives" for a finite amount of time before it decays, and it may be shown that this mean lifetime is the arithmetic mean of all the atoms' lifetimes, and that it is τ, which again is related to the decay constant as follows:

This form is also true for two-decay processes simultaneously A → B + C, inserting the equivalent values of decay constants (as given above)

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into the decay solution leads to:

Half-life

A more commonly used parameter is the half-life. Given a sample of a particular radionuclide, the half-life is the time taken for half the radionuclide's atoms to decay. For the case of one-decay nuclear reactions:

the half-life is related to the decay constant as follows: set N = N0/2 and t = T1/2 to obtain

This relationship between the half-life and the decay constant shows that highly radioactive substances are quickly spent, while those that radiate weakly endure longer. Half-lives of known radionuclides vary widely, from more than 1019

years, such as for the very nearly stable nuclide 209Bi, to 10−23 seconds for highly unstable ones.

The factor of ln(2) in the above relations results from the fact that concept of "half-life" is merely a way of selecting a different base other than the natural base e for the lifetime expression. The time constant τ is the e -1 -life, the time until only 1/e remains, about 36.8%, rather than the 50% in the half-life of a radionuclide. Thus, τ is longer than t1/2. The following equation can be shown to be valid:

Since radioactive decay is exponential with a constant probability, each process could as easily be described with a different constant time period that (for example) gave its "(1/3)-life" (how long until only 1/3 is left) or "(1/10)-life" (a time period until only 10% is left), and so on. Thus, the choice of τ and t1/2 for marker-times, are only for convenience, and from convention. They reflect a fundamental principle only in so much as they show that the same proportion of a given radioactive substance will decay, during any time-period that one chooses.

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Mathematically, the nth life for the above situation would be found in the same way as above — by setting N = N0/n, and substituting into the decay solution to obtain

Changing decay rates

The radioactive decay modes of electron capture and internal conversion are known to be slightly sensitive to chemical and environmental effects which change the electronic structure of the atom, which in turn affects the presence of 1s and 2s electrons that participate in the decay process. A small number of mostly light nuclides are affected. For example, chemical bonds can affect the rate of electron capture to a small degree (in general, less than 1%) depending on the proximity of electrons to the nucleus in beryllium. In 7Be, a difference of 0.9% has been observed between half-lives in metallic and insulating environments. This relatively large effect is because beryllium is a small atom whose valence electrons are in 2s atomic orbitals, which are subject to electron capture in 7Be because (like all s atomic orbitals in all atoms) they naturally penetrate into the nucleus.

Rhenium-187 is a more spectacular example. 187Re normally beta decays to 187Os with a half-life of 41.6 × 109 y, but studies using fully ionised 187Re atoms (bare nuclei) have found that this can decrease to only 33 y. This is attributed to "bound-state β- decay" of the fully ionised atom — the electron is emitted into the "K-shell" (1s atomic orbital), which cannot occur for neutral atoms in which all low-lying bound states are occupied.

A number of experiments have found that decay rates of other modes of artificial and naturally-occurring radioisotopes are, to a high degree of precision, unaffected by external conditions such as temperature, pressure, the chemical environment, and electric, magnetic, or gravitational fields. Comparison of laboratory experiments over the last century, studies of the Oklo natural nuclear reactor (which exemplified the effects of thermal neutrons on nuclear decay), and astrophysical observations of the luminosity decays of distant supernovae (which occurred far away so the light has taken a great deal of time to reach us), for example, strongly indicate that decay rates have been constant (at least to within the limitations of small experimental errors) as a function of time as well.

Recent results suggest the possibility that decay rates might have a weak dependence (0.5% or less) on environmental factors. It has been suggested that measurements of decay rates of silicon-32, manganese-54, and radium-226 exhibit small seasonal variations (of the order of 0.1%), proposed to be related to either solar flare activity or distance from the sun. However, such measurements are highly susceptible to systematic errors, and a subsequent paper has found no evidence for

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such correlations in six other isotopes, and sets upper limits on the size of any such effects.

4. Radioactive waste

Radioactive wastes are wastes that contain radioactive material. Radioactive wastes are usually by-products of nuclear power generation and other applications of nuclear fission or nuclear technology, such as research and medicine. Radioactive waste is hazardous to human health and the environment, and is regulated by government agencies in order to protect human health and the environment.

Radioactivity diminishes over time, so waste is typically isolated and stored for a period of time until it no longer poses a hazard. The period of time waste must be stored depends on the type of waste. Low-level waste with low levels of radioactivity per mass or volume (such as some common medical or industrial radioactive wastes) may need to be stored for only hours, days, or months, while high-level wastes (such as spent nuclear fuel or by-products of nuclear reprocessing) must be stored for thousands of years. Current major approaches to managing radioactive waste have been segregation and storage for short-lived wastes, near-surface disposal for low and some intermediate level wastes, and deep burial or transmutation for the long-lived, high-level wastes.

A summary of the amounts of radioactive wastes and management approaches for most developed countries are presented and reviewed periodically as part of the International Atomic Energy Agency (IAEA) Joint Convention on the Safety of Spent Fuel Management and on the Safety of Radioactive Waste Management.

The nature and significance of radioactive waste

Radioactive waste typically comprises a number of radioisotopes: unstable configurations of elements that decay, emitting ionizing radiation which can be harmful to humans and the environment. Those isotopes emit different types and levels of radiation, which last for different periods of time.

Physics

The radioactivity of all nuclear waste diminishes with time. All radioisotopes contained in the waste have a half-life—the time it takes for any radionuclide to lose half of its radioactivity—and eventually all radioactive waste decays into non-radioactive elements (i.e., stable isotopes). Certain radioactive elements (such as

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plutonium-239) in “spent” fuel will remain hazardous to humans and other creatures for hundreds of thousands of years. Other radioisotopes remain hazardous for millions of years. Thus, these wastes must be shielded for centuries and isolated from the living environment for millennia. Some elements, such as iodine-131, have a short half-life (around 8 days in this case) and thus they will cease to be a problem much more quickly than other, longer-lived, decay products, but their activity is therefore much greater initially. The two tables show some of the major radioisotopes, their half-lives, and their radiation yield as a proportion of the yield of fission of uranium-235.

The shorter a radioisotope's half-life, the more radioactive a sample of it will be. The opposite also applies; for instance, 96% of the element Indium in nature is the In-115 radioisotope, but it is considered non-toxic in pure metal form and mainly like a stable element because its multi-trillion-year half-life means that a relatively minuscule portion of its atoms decay per unit of time. The energy and the type of the ionizing radiation emitted by a radioactive substance are also important factors in determining its threat to humans.The chemical properties of the radioactive element will determine how mobile the substance is and how likely it is to spread into the environment and contaminate humans.This is further complicated by the fact that many radioisotopes do not decay immediately to a stable state but rather to radioactive decay products within a decay chain before ultimately reaching a stable state.

Pharmacokinetics

Exposure to high levels of radioactive waste may cause serious harm or death. Treatment of an adult animal with radiation or some other mutation-causing effect, such as a cytotoxic anti-cancer drug, may cause cancer in the animal. In humans it has been calculated that a 5 sievert dose is usually fatal, and the lifetime risk of dying from radiation-induced cancer from a single dose of 0.1 sieverts is 0.8%, increasing by the same amount for each additional 0.1 sievert increment of dosage. Ionizing radiation causes deletions in chromosomes. If a developing

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organism such as an unborn child is irradiated, it is possible a birth defect may be induced, but it is unlikely this defect will be in a gamete or a gamete-forming cell. The incidence of radiation-induced mutations in humans is undetermined, due to flaws in studies done to date.

Depending on the decay mode and the pharmacokinetics of an element (how the body processes it and how quickly), the threat due to exposure to a given activity of a radioisotope will differ. For instance iodine-131 is a short-lived beta and gamma emitter, but because it concentrates in the thyroid gland, it is more able to cause injury than caesium-137 which, being water soluble, is rapidly excreted in urine. In a similar way, the alpha emitting actinides and radium are considered very harmful as they tend to have long biological half-lives and their radiation has a high relative biological effectiveness, making it far more damaging to tissues per amount of energy deposited. Because of such differences, the rules determining biological injury differ widely according to the radioisotope, and sometimes also the nature of the chemical compound which contains the radioisotope.

Sources of waste

Radioactive waste comes from a number of sources. The majority of waste originates from the nuclear fuel cycle and nuclear weapons reprocessing. However, other sources include medical and industrial wastes, as well as naturally occurring radioactive materials (NORM) that can be concentrated as a result of the processing or consumption of coal, oil and gas, and some minerals, as discussed below.

Nuclear fuel cycle

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1). Front end

Waste from the front end of the nuclear fuel cycle is usually alpha-emitting waste from the extraction of uranium. It often contains radium and its decay products.

Uranium dioxide (UO2) concentrate from mining is not very radioactive - only a thousand or so times as radioactive as the granite used in buildings. It is refined from yellowcake (U3O8), then converted to uranium hexafluoride gas (UF6). As a gas, it undergoes enrichment to increase the U-235 content from 0.7% to about 4.4% (LEU). It is then turned into a hard ceramic oxide (UO2) for assembly as reactor fuel elements.

The main by-product of enrichment is depleted uranium (DU), principally the U-238 isotope, with a U-235 content of ~0.3%. It is stored, either as UF 6 or as U3O8. Some is used in applications where its extremely high density makes it valuable, such as the keels of yachts, and anti-tank shells. It is also used with plutonium for making mixed oxide fuel (MOX) and to dilute, or downblend, highly enriched uranium from weapons stockpiles which is now being redirected to become reactor fuel.

2). Back end

The back end of the nuclear fuel cycle, mostly spent fuel rods, contains fission products that emit beta and gamma radiation, and actinides that emit alpha particles, such as uranium-234, neptunium-237, plutonium-238 and americium-241, and even sometimes some neutron emitters such as californium (Cf). These isotopes are formed in nuclear reactors.

It is important to distinguish the processing of uranium to make fuel from the reprocessing of used fuel. Used fuel contains the highly radioactive products of fission (see high level waste below). Many of these are neutron absorbers, called neutron poisons in this context. These eventually build up to a level where they absorb so many neutrons that the chain reaction stops, even with the control rods completely removed. At that point the fuel has to be replaced in the reactor with fresh fuel, even though there is still a substantial quantity of uranium-235 and plutonium present. In the United States, this used fuel is stored, while in countries such as Russia, the United Kingdom, France, Japan and India, the fuel is reprocessed to remove the fission products, and the fuel can then be re-used. This reprocessing involves handling highly radioactive materials, and the fission products removed from the fuel are a concentrated form of high-level waste as are the chemicals used in the process. While these countries reprocess the fuel carrying out single plutonium cycles, India is the only country known to be planning multiple plutonium recycling schemes.

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3). Fuel composition and long term radioactivity

Long-lived radioactive waste from the back end of the fuel cycle is especially relevant when designing a complete waste management plan for spent nuclear fuel (SNF). When looking at long term radioactive decay, the actinides in the SNF have a significant influence due to their characteristically long half-lives. Depending on what a nuclear reactor is fueled with, the actinide composition in the SNF will be different.

An example of this effect is the use of nuclear fuels with thorium. Th-232 is a fertile material that can undergo a neutron capture reaction and two beta minus decays, resulting in the production of fissile U-233. The SNF of a cycle with thorium will contain U-233. Its radioactive decay will strongly influence the long-term activity curve of the SNF around 1 million years. A comparison of the activity associated to U-233 for three different SNF types can be seen in the figure on the top right.

The burnt fuels are thorium with reactor-grade plutonium (RGPu), thorium with weapons-grade plutonium (WGPu) and Mixed Oxide fuel (MOX). For RGPu and WGPu, the initial amount of U-233 and its decay around 1 million years can be seen. This has an effect in the total activity curve of the three fuel types. The absence of U-233 and its daughter products in the MOX fuel results in a lower activity in region 3 of the figure on the bottom right, whereas for RGPu and WGPu the curve is maintained higher due to the presence of U-233 that has not fully decayed.

The use of different fuels in nuclear reactors results in different SNF composition, with varying activity curves.

4). Proliferation concerns

Since uranium and plutonium are nuclear weapons materials, there have been proliferation concerns. Ordinarily (in spent nuclear fuel), plutonium is reactor-grade plutonium. In addition to plutonium-239, which is highly suitable for building nuclear weapons, it contains large amounts of undesirable contaminants: plutonium-240, plutonium-241, and plutonium-238. These isotopes are difficult to separate, and more cost-effective ways of obtaining fissile material exist (e.g. uranium enrichment or dedicated plutonium production reactors).

High-level waste is full of highly radioactive fission products, most of which are relatively short-lived. This is a concern since if the waste is stored, perhaps in deep geological storage, over many years the fission products decay, decreasing the radioactivity of the waste and making the plutonium easier to access. The undesirable contaminant Pu-240 decays faster than the Pu-239, and thus the quality of the bomb material increases with time (although its quantity decreases during that time as well). Thus, some have argued, as time passes, these deep storage areas have the potential to become "plutonium mines", from which material for nuclear

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weapons can be acquired with relatively little difficulty. Critics of the latter idea point out that the half-life of Pu-240 is 6,560 years and Pu-239 is 24,110 years, and thus the relative enrichment of one isotope to the other with time occurs with a half-life of 9,000 years (that is, it takes 9000 years for the fraction of Pu-240 in a sample of mixed plutonium isotopes, to spontaneously decrease by half—a typical enrichment needed to turn reactor-grade into weapons-grade Pu). Thus "weapons grade plutonium mines" would be a problem for the very far future (>9,000 years from now), so that there remains a great deal of time for technology to advance to solve it.

Pu-239 decays to U-235 which is suitable for weapons and which has a very long half-life (roughly 109 years). Thus plutonium may decay and leave uranium-235. However, modern reactors are only moderately enriched with U-235 relative to U-238, so the U-238 continues to serve as a denaturation agent for any U-235 produced by plutonium decay.

One solution to this problem is to recycle the plutonium and use it as a fuel e.g. in fast reactors. In pyrometallurgical fast reactors, the separated plutonium and uranium are contaminated by actinides and cannot be used for nuclear weapons.

Nuclear weapons decommissioning

Waste from nuclear weapons decommissioning is unlikely to contain much beta or gamma activity other than tritium and americium. It is more likely to contain alpha-emitting actinides such as Pu-239 which is a fissile material used in bombs, plus some material with much higher specific activities, such as Pu-238 or Po.

In the past the neutron trigger for an atomic bomb tended to be beryllium and a high activity alpha emitter such as polonium; an alternative to polonium is Pu-238. For reasons of national security, details of the design of modern bombs are normally not released to the open literature.

Some designs might contain a radioisotope thermoelectric generator using Pu-238 to provide a long lasting source of electrical power for the electronics in the device.

It is likely that the fissile material of an old bomb which is due for refitting will contain decay products of the plutonium isotopes used in it, these are likely to include U-236 from Pu-240 impurities, plus some U-235 from decay of the Pu-239; due to the relatively long half-life of these Pu isotopes, these wastes from radioactive decay of bomb core material would be very small, and in any case, far less dangerous (even in terms of simple radioactivity) than the Pu-239 itself.

The beta decay of Pu-241 forms Am-241; the in-growth of americium is likely to be a greater problem than the decay of Pu-239 and Pu-240 as the americium is a

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gamma emitter (increasing external-exposure to workers) and is an alpha emitter which can cause the generation of heat. The plutonium could be separated from the americium by several different processes; these would include pyrochemical processes and aqueous/organic solvent extraction. A truncated PUREX type extraction process would be one possible method of making the separation. Naturally occurring uranium is not fissile because it contains 99.3% of U-238 and only 0.7% of U-235.

Legacy waste

Due to historic activities typically related to radium industry, uranium mining, and military programs, there are numerous sites that contain or are contaminated with radioactivity. In the United States alone, the Department of Energy states there are "millions of gallons of radioactive waste" as well as "thousands of tons of spent nuclear fuel and material" and also "huge quantities of contaminated soil and water." Despite copious quantities of waste, the DOE has stated a goal of cleaning all presently contaminated sites successfully by 2025. The Fernald, Ohio site for example had "31 million pounds of uranium product", "2.5 billion pounds of waste", "2.75 million cubic yards of contaminated soil and debris", and a "223 acre portion of the underlying Great Miami Aquifer had uranium levels above drinking standards." The United States has at least 108 sites designated as areas that are contaminated and unusable, sometimes many thousands of acres. DOE wishes to clean or mitigate many or all by 2025, however the task can be difficult and it acknowledges that some may never be completely remediated. In just one of these 108 larger designations, Oak Ridge National Laboratory, there were for example at least "167 known contaminant release sites" in one of the three subdivisions of the 37,000-acre (150 km2) site. Some of the U.S. sites were smaller in nature, however, cleanup issues were simpler to address, and DOE has successfully completed cleanup, or at least closure, of several sites.

It is a common misconception that nuclear waste has to be stored in a cave after its 20-year decommissioning process.

Medical

Radioactive medical waste tends to contain beta particle and gamma ray emitters. It can be divided into two main classes. In diagnostic nuclear medicine a number of short-lived gamma emitters such as technetium-99m are used. Many of these can be disposed of by leaving it to decay for a short time before disposal as normal waste. Other isotopes used in medicine, with half-lives in parentheses, include:

Y-90, used for treating lymphoma (2.7 days) I-131, used for thyroid function tests and for treating thyroid cancer (8.0 days)

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Sr-89, used for treating bone cancer, intravenous injection (52 days) Ir-192, used for brachytherapy (74 days) Co-60, used for brachytherapy and external radiotherapy (5.3 years) Cs-137, used for brachytherapy, external radiotherapy (30 years)

Industrial

Industrial source waste can contain alpha, beta, neutron or gamma emitters. Gamma emitters are used in radiography while neutron emitting sources are used in a range of applications, such as oil well logging.

Naturally occurring radioactive material (NORM)

Processing of substances containing natural radioactivity is often known as NORM. A lot of this waste is alpha particle-emitting matter from the decay chains of uranium and thorium. The main source of radiation in the human body is potassium-40 (40K), typically 17 milligrams in the body at a time and 0.4 milligrams/day intake. Most rocks, due to their components, have a certain, but low, level of radioactivity. Usually ranging from 1 milli-Sievert to 13 milli-Sievert (mSv) annually depending on location, average radiation exposure from natural radioisotopes is 2.0 mSv per person a year worldwide. Such is most of typical total dosage (with mean annual exposure from other sources amounting to 0.4 mSv from cosmic rays, 0.007 mSv from the legacy of past atmospheric nuclear testing along with the Chernobyl disaster, 0.0002 mSv from the nuclear fuel cycle, and, averaged over the whole populace, 0.6 mSv medical tests and 0.005 mSv occupational exposure).

1). Coal

Coal contains a small amount of radioactive uranium, barium, thorium and potassium, but, in the case of pure coal, this is significantly less than the average concentration of those elements in the Earth's crust. The surrounding strata, if shale or mudstone, often contain slightly more than average and this may also be reflected in the ash content of 'dirty' coals. The more active ash minerals become concentrated in the fly ash precisely because they do not burn well. The radioactivity of fly ash is about the same as black shale and is less than phosphate rocks, but is more of a concern because a small amount of the fly ash ends up in the atmosphere where it can be inhaled. According to U.S. NCRP reports, population exposure from 1000-MWe power plants amounts to 490 person-rem/year for coal power plants and 4.8 person-rem/year for nuclear plants during normal operation, the latter being 136 person-rem/year for the complete nuclear fuel cycle.

2). Oil and gas

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Residues from the oil and gas industry often contain radium and its daughters. The sulfate scale from an oil well can be very radium rich, while the water, oil and gas from a well often contain radon. The radon decays to form solid radioisotopes which form coatings on the inside of pipework. In an oil processing plant the area of the plant where propane is processed is often one of the more contaminated areas of the plant as radon has a similar boiling point to propane.

Classification of radioactive waste

Uranium tailingsUranium tailings are waste by-product materials left over from the rough

processing of uranium-bearing ore. They are not significantly radioactive. Mill tailings are sometimes referred to as 11(e)2 wastes, from the section of the Atomic Energy Act of 1946 that defines them. Uranium mill tailings typically also contain chemically hazardous heavy metal such as lead and arsenic. Vast mounds of uranium mill tailings are left at many old mining sites, especially in Colorado, New Mexico, and Utah.

Low-level waste

Low level waste (LLW) is generated from hospitals and industry, as well as the nuclear fuel cycle. Low-level wastes include paper, rags, tools, clothing, filters, and other materials which contain small amounts of mostly short-lived radioactivity. Materials that originate from any region of an Active Area are commonly designated as LLW as a precautionary measure even if there is with only a remote possibility of being contaminated with radioactive materials. Such LLW typically exhibits no higher radioactivity than one would expect from the same material disposed of in a non-active area, such as a normal office block.

Some high-activity LLW requires shielding during handling and transport but most LLW is suitable for shallow land burial. To reduce its volume, it is often compacted or incinerated before disposal. Low-level waste is divided into four classes: class A, class B, class C, and Greater Than Class C (GTCC).

Intermediate-level wasteIntermediate-level waste (ILW) contains higher amounts of radioactivity and in

some cases requires shielding. Intermediate-level wastes includes resins, chemical sludge and metal reactor nuclear fuel cladding, as well as contaminated materials from reactor decommissioning. It may be solidified in concrete or bitumen for disposal. As a general rule, short-lived waste (mainly non-fuel materials from reactors) is buried in shallow repositories, while long-lived waste (from fuel and fuel reprocessing) is deposited in geological repository. U.S. regulations do not define this category of waste; the term is used in Europe and elsewhere.

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High-level waste

High-level waste (HLW) is produced by nuclear reactors. It contains fission products and transuranic elements generated in the reactor core. It is highly radioactive and often thermally hot. HLW accounts for over 95 percent of the total radioactivity produced in the process of nuclear electricity generation. The amount of HLW worldwide is currently increasing by about 12,000 metric tons every year, which is the equivalent to about 100 double-decker buses or a two-story structure with a footprint the size of a basketball court. A 1000-MW nuclear power plant produces about 27 tonnes of spent nuclear fuel (unreprocessed) every year.

Transuranic waste

Transuranic waste (TRUW) as defined by U.S. regulations is, without regard to form or origin, waste that is contaminated with alpha-emitting transuranic radionuclides with half-lives greater than 20 years and concentrations greater than 100 nCi/g (3.7 MBq/kg), excluding high-level waste. Elements that have an atomic number greater than uranium are called transuranic ("beyond uranium"). Because of their long half-lives, TRUW is disposed more cautiously than either low- or intermediate-level waste. In the U.S., it arises mainly from weapons production, and consists of clothing, tools, rags, residues, debris and other items contaminated with small amounts of radioactive elements (mainly plutonium).

Under U.S. law, transuranic waste is further categorized into "contact-handled" (CH) and "remote-handled" (RH) on the basis of radiation dose measured at the surface of the waste container. CH TRUW has a surface dose rate not greater than 200 Roentgen equivalent man per hour (to millisievert/hr), whereas RH TRUW has a surface dose rate of 200 Röntgen equivalent man per hour (2 mSv/h) or greater. CH TRUW does not have the very high radioactivity of high-level waste, nor its high heat generation, but RH TRUW can be highly radioactive, with surface dose rates up to 1000000 Röntgen equivalent man per hour (10000 mSv/h). The U.S. currently disposes of TRUW generated from military facilities at the Waste Isolation Pilot Plant.

Prevention of waste

Due to the many advances in reactor design, it is today possible to reduce the radioactive waste by a factor of 100. This can be done by using new reactor types such as Generation IV reactors. This reduction of nuclear waste is possible because these new reactor types are capable of burning the lower actinides.

Management of waste

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Of particular concern in nuclear waste management are two long-lived fission products, Tc-99 (half-life 220,000 years) and I-129 (half-life 17 million years), which dominate spent fuel radioactivity after a few thousand years. The most troublesome transuranic elements in spent fuel are Np-237 (half-life two million years) and Pu-239 (half-life 24,000 years). Nuclear waste requires sophisticated treatment and management to successfully isolate it from interacting with the biosphere. This usually necessitates treatment, followed by a long-term management strategy involving storage, disposal or transformation of the waste into a non-toxic form. Governments around the world are considering a range of waste management and disposal options, though there has been limited progress toward long-term waste management solutions.

In second half of 20th century, several methods of disposal of radioactive waste were investigated by nuclear nations. Which are;

"Long term above ground storage", not implemented. "Disposal in outer space", not implemented. "Deep borehole disposal", not implemented. "Rock-melting", not implemented. "Disposal at subduction zones", not implemented. "Ocean disposal", done by USSR, UK, Switzerland, USA, Belgium, France,

Netherland, Japan, Sweden, Russia, New Zealand, Germany, Italy and South Korea. (1954-93) It's not permitted by international agreements.

"Sub seabed disposal", not implemented, not permitted by international agreements.

"Disposal in ice sheets", rejected in Antarctic Treaty "Direct injection", done by USSR and USA.

Initial treatment of waste

1). Vitrification

Long-term storage of radioactive waste requires the stabilization of the waste into a form which will neither react nor degrade for extended periods of time. One way to do this is through vitrification. Currently at Sellafield the high-level waste (PUREX first cycle raffinate) is mixed with sugar and then calcined. Calcination involves passing the waste through a heated, rotating tube. The purposes of calcination are to evaporate the water from the waste, and de-nitrate the fission products to assist the stability of the glass produced.

The 'calcine' generated is fed continuously into an induction heated furnace with fragmented glass. The resulting glass is a new substance in which the waste products are bonded into the glass matrix when it solidifies. This product, as a melt, is poured into stainless steel cylindrical containers ("cylinders") in a batch process.

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When cooled, the fluid solidifies ("vitrifies") into the glass. Such glass, after being formed, is highly resistant to water.

After filling a cylinder, a seal is welded onto the cylinder. The cylinder is then washed. After being inspected for external contamination, the steel cylinder is stored, usually in an underground repository. In this form, the waste products are expected to be immobilized for a long period of time (many thousands of years).

The glass inside a cylinder is usually a black glossy substance. All this work (in the United Kingdom) is done using hot cell systems. The sugar is added to control the ruthenium chemistry and to stop the formation of the volatile RuO4 containing radioactive ruthenium isotopes. In the west, the glass is normally a borosilicate glass (similar to Pyrex), while in the former Soviet bloc it is normal to use a phosphate glass. The amount of fission products in the glass must be limited because some (palladium, the other Pt group metals, and tellurium) tend to form metallic phases which separate from the glass. Bulk vitrification uses electrodes to melt soil and wastes, which are then buried underground. In Germany a vitrification plant is in use; this is treating the waste from a small demonstration reprocessing plant which has since been closed down.

2). Ion exchange

It is common for medium active wastes in the nuclear industry to be treated with ion exchange or other means to concentrate the radioactivity into a small volume. The much less radioactive bulk (after treatment) is often then discharged. For instance, it is possible to use a ferric hydroxide floc to remove radioactive metals from aqueous mixtures. After the radioisotopes are absorbed onto the ferric hydroxide, the resulting sludge can be placed in a metal drum before being mixed with cement to form a solid waste form. In order to get better long-term performance (mechanical stability) from such forms, they may be made from a mixture of fly ash, or blast furnace slag, and Portland cement, instead of normal concrete (made with Portland cement, gravel and sand).

3). Synroc

The Australian Synroc (synthetic rock) is a more sophisticated way to immobilize such waste, and this process may eventually come into commercial use for civil wastes (it is currently being developed for US military wastes). Synroc was invented by the late Prof Ted Ringwood (a geochemist) at the Australian National University. The Synroc contains pyrochlore and cryptomelane type minerals. The original form of Synroc (Synroc C) was designed for the liquid high level waste (PUREX raffinate) from a light water reactor. The main minerals in this Synroc are hollandite (BaAl2Ti6O16), zirconolite (CaZrTi2O7) and perovskite (CaTiO3). The

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zirconolite and perovskite are hosts for the actinides. The strontium and barium will be fixed in the perovskite. The caesium will be fixed in the hollandite.

Long term management of waste

The time frame in question when dealing with radioactive waste ranges from 10,000 to 1,000,000 years, according to studies based on the effect of estimated radiation doses. Researchers suggest that forecasts of health detriment for such periods should be examined critically. Practical studies only consider up to 100 years as far as effective planning and cost evaluations are concerned. Long term behavior of radioactive wastes remains a subject for ongoing research projects.

1). Above-ground disposal

Dry cask storage typically involves taking waste from a spent fuel pool and sealing it (along with an inert gas) in a steel cylinder, which is placed in a concrete cylinder which acts as a radiation shield. It is a relatively inexpensive method which can be done at a central facility or adjacent to the source reactor. The waste can be easily retrieved for reprocessing.

2). Geologic disposal

The process of selecting appropriate deep final repositories for high level waste and spent fuel is now under way in several countries with the first expected to be commissioned some time after 2010. The basic concept is to locate a large, stable geologic formation and use mining technology to excavate a tunnel, or large-bore tunnel boring machines (similar to those used to drill the Channel Tunnel from England to France) to drill a shaft 500–1,000 meters below the surface where rooms or vaults can be excavated for disposal of high-level radioactive waste. The goal is to permanently isolate nuclear waste from the human environment. Many people remain uncomfortable with the immediate stewardship cessation of this disposal system, suggesting perpetual management and monitoring would be more prudent.

Because some radioactive species have half-lives longer than one million years, even very low container leakage and radionuclide migration rates must be taken into account. Moreover, it may require more than one half-life until some nuclear materials lose enough radioactivity to cease being lethal to living things. A 1983 review of the Swedish radioactive waste disposal program by the National Academy of Sciences found that country’s estimate of several hundred thousand years—perhaps up to one million years—being necessary for waste isolation “fully

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justified.” Aside from dilution, chemically toxic stable elements in some waste such as arsenic remain toxic for up to billions of years or indefinitely.

Sea-based options for disposal of radioactive waste include burial beneath a stable abyssal plain, burial in a subduction zone that would slowly carry the waste downward into the Earth's mantle, and burial beneath a remote natural or human-made island. While these approaches all have merit and would facilitate an international solution to the problem of disposal of radioactive waste, they would require an amendment of the Law of the Sea.

“Sea” means all marine waters other than the internal waters of States, as well as the seabed and the subsoil thereof; it does not include sub-seabed repositories accessed only from land.”

The proposed land-based subductive waste disposal method disposes of nuclear waste in a subduction zone accessed from land, and therefore is not prohibited by international agreement. This method has been described as the most viable means of disposing of radioactive waste, and as the state-of-the-art as of 2001 in nuclear waste disposal technology. Another approach termed Remix & Return would blend high-level waste with uranium mine and mill tailings down to the level of the original radioactivity of the uranium ore, then replace it in inactive uranium mines. This approach has the merits of providing jobs for miners who would double as disposal staff, and of facilitating a cradle-to-grave cycle for radioactive materials, but would be inappropriate for spent reactor fuel in the absence of reprocessing, due to the presence in it of highly toxic radioactive elements such as plutonium.

Deep borehole disposal is the concept of disposing of high-level radioactive waste from nuclear reactors in extremely deep boreholes. Deep borehole disposal seeks to place the waste as much as five kilometers beneath the surface of the Earth and relies primarily on the immense natural geological barrier to confine the waste safely and permanently so that it should never pose a threat to the environment. The Earth's crust contains 120 trillion tons of thorium and 40 trillion tons of uranium (primarily at relatively trace concentrations of parts per million each adding up over the crust's 3 * 1019 ton mass), among other natural radioisotopes. Since the fraction of nuclides decaying per unit of time is inversely proportional to an isotope's half-life, the relative radioactivity of the lesser amount of human-produced radioisotopes (thousands of tons instead of trillions of tons) would diminish once the isotopes with far shorter half-lives than the bulk of natural radioisotopes decayed.

3). Transmutation

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There have been proposals for reactors that consume nuclear waste and transmute it to other, less-harmful nuclear waste. In particular, the Integral Fast Reactor was a proposed nuclear reactor with a nuclear fuel cycle that produced no transuranic waste and in fact, could consume transuranic waste. It proceeded as far as large-scale tests, but was then canceled by the US Government. Another approach, considered safer but requiring more development, is to dedicate subcritical reactors to the transmutation of the left-over transuranic elements.

An isotope that is found in nuclear waste and that represents a concern in terms of proliferation is Pu-239. The estimated world total of plutonium in the year 2000 was of 1,645 MT, of which 210 MT had been separated by reprocessing. The large stock of plutonium is a result of its production inside uranium-fueled reactors and of the reprocessing of weapons-grade plutonium during the weapons program. An option for getting rid of this plutonium is to use it as a fuel in a traditional Light Water Reactor (LWR). Several fuel types with differing plutonium destruction efficiencies are under study. See Nuclear transmutation.

Transmutation was banned in the US in April 1977 by President Carter due to the danger of plutonium proliferation, but President Reagan rescinded the ban in 1981. Due to the economic losses and risks, construction of reprocessing plants during this time did not resume. Due to high energy demand, work on the method has continued in the EU. This has resulted in a practical nuclear research reactor called Myrrha in which transmutation is possible. Additionally, a new research program called ACTINET has been started in the EU to make transmutation possible on a large, industrial scale. According to President Bush's Global Nuclear Energy Partnership (GNEP) of 2007, the US is now actively promoting research on transmutation technologies needed to markedly reduce the problem of nuclear waste treatment.

There have also been theoretical studies involving the use of fusion reactors as so called "actinide burners" where a fusion reactor plasma such as in a tokamak, could be "doped" with a small amount of the "minor" transuranic atoms which would be transmuted (meaning fissioned in the actinide case) to lighter elements upon their successive bombardment by the very high energy neutrons produced by the fusion of deuterium and tritium in the reactor. A study at MIT found that only 2 or 3 fusion reactors with parameters similar to that of the International Thermonuclear Experimental Reactor (ITER) could transmute the entire annual minor actinide production from all of the light water reactors presently operating in the United States fleet while simultaneously generating approximately 1 gigawatt of power from each reactor.

4). Re-use of waste

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Another option is to find applications for the isotopes in nuclear waste so as to re-use them. Already, caesium-137, strontium-90 and a few other isotopes are extracted for certain industrial applications such as food irradiation and radioisotope thermoelectric generators. While re-use does not eliminate the need to manage radioisotopes, it reduces the quantity of waste produced.

The Nuclear Assisted Hydrocarbon Production Method, Canadian patent application 2,659,302, is a method for the temporary or permanent storage of nuclear waste materials comprising the placing of waste materials into one or more repositories or boreholes constructed into an unconventional oil formation. The thermal flux of the waste materials fracture the formation, alters the chemical and/or physical properties of hydrocarbon material within the subterranean formation to allow removal of the altered material. A mixture of hydrocarbons, hydrogen, and/or other formation fluids are produced from the formation. The radioactivity of high-level radioactive waste affords proliferation resistance to plutonium placed in the periphery of the repository or the deepest portion of a borehole.

Breeder reactors can run on U-238 and transuranic elements, which comprise the majority of spent fuel radioactivity in the 1000-100000 year time span.

5). Space disposal

Space disposal is an attractive notion because it permanently removes nuclear waste from the environment. It has significant disadvantages, not least of which is the potential for catastrophic failure of a launch vehicle which would spread radioactive material into the atmosphere and around the world. The high number of launches that would be required (because no individual rocket would be able to carry very much of the material relative to the total which needs to be disposed of) makes the proposal impractical (for both economic and risk-based reasons) using current rockets, resulting in some suggestions for developing a mass driver for disposal instead. To further complicate matters, international agreements on the regulation of such a program would need to be established.

National management plans

Most countries are considerably ahead of the United States in developing plans for high-level radioactive waste disposal. Sweden and Finland are furthest along in committing to a particular disposal technology, while many others reprocess spent fuel or contract with France or Great Britain to do it, taking back the resulting plutonium and high-level waste. “An increasing backlog of plutonium from reprocessing is developing in many countries... It is doubtful that reprocessing makes economic sense in the present environment of cheap uranium.”

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In many European countries (e.g., Britain, Finland, the Netherlands, Sweden and Switzerland) the risk or dose limit for a member of the public exposed to radiation from a future high-level nuclear waste facility is considerably more stringent than that suggested by the International Commission on Radiation Protection or proposed in the United States. European limits are often more stringent than the standard suggested in 1990 by the International Commission on Radiation Protection by a factor of 20, and more stringent by a factor of ten than the standard proposed by the US Environmental Protection Agency (EPA) for Yucca Mountain nuclear waste repository for the first 10,000 years after closure.

The U.S. EPA’s proposed standard for greater than 10,000 years is 250 times more permissive than the European limit. The U.S. EPA proposed a legal limit of a maximum of 3.5 milli-Sieverts (350 millirem) each annually to local individuals after 10,000 years, which would be up to several percent of the exposure currently received by some populations in the highest natural background regions on Earth, though the U.S. DOE predicted that received dose would be much below that limit. Over a timeframe of thousands of years, after the most active short half-life radioisotopes decayed, burying U.S. nuclear waste would increase the radioactivity in the top 2000 feet of rock and soil in the United States (10 million km2) by ≈ 1 part in 10 million over the cumulative amount of natural radioisotopes in such a volume, but the vicinity of the site would have a far higher concentration of artificial radioisotopes underground than such an average.

1). Mongolia

After serious opposition had risen about plans and negotiations between Mongolia with Japan and the United States of America to build nuclear waste facilities in Mongolia, Mongolia stopped all negotiations in September 2011. These negotiations started after U.S. Deputy Secretary of Energy Daniel B. Poneman visited Mongolia in September, 2010. Talks were held in Washington DC between officials of Japan, the United States and Mongolia in February 2011. After this the United Arab Emirates (UAE), which wanted buy nuclear fuel from Mongolia, joined in the negotiations. The talks were kept secret, and although The Mainichi Daily News reported on it in May. Mongolia officially denied the existence of these negotiations. But alarmed by this news, Mongolian citizens protested against the plans, and demanded the government withdraw the plans and disclose information. The Mongolian President Tsakhia Elbegdorj issued a presidential order on Sept. 13 banning all negotiations with foreign governments or international organizations on nuclear waste storage plans in Mongolia.

2). Illegal dumping

Authorities in Italy are investigating a 'Ndrangheta mafia clan accused of trafficking and illegally dumping nuclear waste. According to a turncoat, a manager

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of the Italy’s state energy research agency Enea paid the clan to get rid of 600 drums of toxic and radioactive waste from Italy, Switzerland, France, Germany, and the US, with Somalia as the destination, where the waste was buried after buying off local politicians. Former employees of Enea are suspected of paying the criminals to take waste off their hands in the 1980s and 1990s. Shipments to Somalia continued into the 1990s, while the 'Ndrangheta clan also blew up shiploads of waste, including radioactive hospital waste, and sending them to the sea bed off the Calabrian coast. According to the environmental group Legambiente, former members of the 'Ndrangheta have said that they were paid to sink ships with radioactive material for the last 20 years.

Accidents involving radioactive waste

A few incidents have occurred when radioactive material was disposed of improperly, shielding during transport was defective, or when it was simply abandoned or even stolen from a waste store. In the Soviet Union, waste stored in Lake Karachay was blown over the area during a dust storm after the lake had partly dried out. At Maxey Flat, a low-level radioactive waste facility located in Kentucky, containment trenches covered with dirt, instead of steel or cement, collapsed under heavy rainfall into the trenches and filled with water. The water that invaded the trenches became radioactive and had to be disposed of at the Maxey Flat facility itself. In other cases of radioactive waste accidents, lakes or ponds with radioactive waste accidentally overflowed into the rivers during exceptional storms. In Italy, several radioactive waste deposits let material flow into river water, thus contaminating water for domestic use. In France, in the summer of 2008 numerous incidents happened; in one, at the Areva plant in Tricastin, it was reported that during a draining operation, liquid containing untreated uranium overflowed out of a faulty tank and about 75 kg of the radioactive material seeped into the ground and, from there, into two rivers nearby; in another case, over 100 staff were contaminated with low doses of radiation.

Scavenging of abandoned radioactive material has been the cause of several other cases of radiation exposure, mostly in developing nations, which may have less regulation of dangerous substances (and sometimes less general education about radioactivity and its hazards) and a market for scavenged goods and scrap metal. The scavengers and those who buy the material are almost always unaware that the material is radioactive and it is selected for its aesthetics or scrap value. Irresponsibility on the part of the radioactive material's owners, usually a hospital, university or military, and the absence of regulation concerning radioactive waste, or a lack of enforcement of such regulations, have been significant factors in radiation exposures. For an example of an accident involving radioactive scrap originating from a hospital see the Goiânia accident.

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Transportation accidents involving spent nuclear fuel from power plants are unlikely to have serious consequences due to the strength of the spent nuclear fuel shipping casks.

On 15 December 2011 top government spokesman Osamu Fujimura of the Japanese government admitted that nuclear substances were found in the waste of Japanese nuclear facilities. Although Japan did commit itself in 1977 to these inspections in the safeguard agreement with the IAEA, the reports were kept secret for the inspectors of the International Atomic Energy Agency. Japan did start discussions with the IAEA about the large quantities of enriched uranium and plutonium that were discovered in nuclear waste cleared away by Japanese nuclear operators. At the press conference Fukimora said: "Based on investigations so far, most nuclear substances have been properly managed as waste, and from that perspective, there is no problem in safety management," But according to him, the matter was at that moment still investigated.

5. Benefits Of Radiation

Radiation and radioactive materials can be used by humans in a number of ways. This page merely touches the surface of the subject by giving examples of the uses in:

Agriculture

The increase in the volume and quality of grains and cereals has been vastly improved by selectively growing superior strains labeled by radioactive isotopes. These improvements are helping to alleviate famine in third world countries.

Environmental Measurements

The movement of pollutants through the environment (its included ground waters and rivers) can be accurately measured by the use of radioactive tracers.

Eradication of Pests

A number of pest flies are no longer the problem that they were in California since their numbers have been cut drastically following the release of sterile male flies in the region.

Food

Food, such as beef and chicken, that has been sterilized by irradiation has a longer shelf life and is free of E. coli as a bacterium that has killed several children as a result of eating poorly cooked fast food hamburgers. An extension of food

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irradiation could save the lives of many children and would be particularly useful in developing countries where refrigeration is not available.

Generation of Electricity

Over 440 nuclear plants around the world contribute some 16% of the world's electrical energy needs. 109 plants in the U.S. contributed 22% of the US's consumption of electricity in 2000.

Medical Diagnostics

The use of radiation in the medical world extends from X-rays, through magnetic resonance imaging (MRI), to the use of radioactive tracers to diagnose such varied conditions as faulty thyroid glands or bone problems. The use of radioactive tracers often takes the place of invasive surgical diagnosis.

Oil Drilling

Isotopes are used to measure the quality of steam before it is injected into almost defunct oil wells to force out residual supplies.

Polymerization of Plastics

Plastics can be polymerized by radiation instead of damaging heat treatments. The polymerized plastics are used in such applications as car dashboards, which would, otherwise, crack badly under heat in the summer.

Quality Control of Metal Parts

The integrity of metal parts such as aircraft engine turbine blades can be verified by radiophotography on a conveyor belt instead of having to destroy a sampling of blades to ensure they are intact.

Research in Biology

The use of radioactive tracers allows the non-invasive tracking of elements and drugs through the body for both metabolic studies and medicine.

Space Power

When small amounts of power are needed in space in regions in which solar power is inefficient (on the dark side or when large solar panels are impossible), plutonium batteries are ideal producers of compact energy.

Treatment of Cancers

Cancerous cells can be selectively killed by the use of radioactivity, either in the form of directed beams, as for breast cancer, or as radioactive bullets that are designed to migrate directly to the cancerous cells that need killing. The only

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alternative, chemotherapy, which involves the use of invasive drugs, is a very difficult alternative for the patient.

And the list of beneficial uses of radiation goes on and on. Our society depends on its assistance in so many aspects of our daily life.

6. Radioactive Impact

Sense or meaning of the definition of radioactive contamination is an environmental pollution caused by radioactive dust from the explosion of atomic reactors and atomic bombs. The most dangerous of the radioactive contamination of the nuclear radiation such as alpha, beta and gamma are very harmful to living things around it. Moreover neutron particles produced is also dangerous. Radioactive substances commonly foundenvironmental contaminants is a carcinogen Sr-90 bone and I-131.

Radiation from radioactvie substance can ionitate particles or molecule essence that it pass off, include cells of plants, animals, and humans. This energy of ionizing comparable with radiation energy. Penetrate ability of particles are not equal, and dependent to it energy. Using radiation can with external as well as internal ways. Effect of radiation can causes upsets in body cells, that can happen in short time, or long time of radiation. Effects of radiation are classificate to two effects, that are :

Somatic effects

Somatic effects of radiation influence in somatic cells, and the effect of radiation just working in the body of human that got radiation, and will not working on next generation of the human.

1). Somatic effect nonstocostic. The character of this effect generally happen in body tissue. The impact is tissue function will lost.

2). Somatic effects stocostic. The character of this effect is if the effect received by human body can firm into the high dose of radiation or low dose.

Genetic effects

This effect can influence germinal cells and emerge in heritage of human that got radiation. Low dose or radiation can causing change on DNA structure and occur gen mutation and emerge off in several heritage.

If there are living beings are exposed to dangerous radiation nuclear atom will usually occure because of gene mutation changes the structure and pattern of chemical substances that damage the cells of living organisms both plants and

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animals or animals. Effects as well as a result of radiation caused by radioactive substances in the human race as follows below:

Dizziness Decreased appetite or loss Diarhea Body heat or fever Weight loss Blood cancer or leukemia Increased heart rate or pulse Endurance is reduced so susceptible to disease caused by a number of

white blood cells is reduced

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CHAPTER 31. Conclusion

Radioactive is an event when an atom with instability core radiatte some rays to create new atom with more stable core. The rays are alpha, beta , and gamma. The rays have different length and penetrate ability. The rays also have multiple characteristic, and it’s make them have different benefits for human life. Radioactive decay is a part of radiation by radioactive. It mean an atom that have instability core will divided to some kind of substances as the product of radioactive decay. This product usually divided to two substances, they are atom and radiation ray.

In radioactive processes, particles or electromagnetic radiation are emitted from the nucleus. The most common forms of radiation emitted have been traditionally classified as alpha (a), beta (b), and gamma (g) radiation. Nuclear radiation occurs in other forms, including the emission of protons or neutrons or spontaneous fission of a massive nucleus. Of the nuclei found on Earth, the vast majority is stable. This is so because almost all short-lived radioactive nuclei have decayed during the history of the Earth. There are approximately 270 stable isotopes and 50 naturally occurring radioisotopes (radioactive isotopes). Thousands of other radioisotopes have been made in the laboratory. Radioactive decay will change one nucleus to another if the product nucleus has a greater nuclear binding energy than the initial decaying nucleus. The difference in binding energy (comparing the before and after states) determines which decays are energetically possible and which are not. The excess binding energy appears as kinetic energy or rest mass energy of the decay products.

Radioactive have negative and positif impact. So, we must be wise to manage the energy of radioactive. If we can’t manage, there will be a big disaster to us and people around us.

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2. Suggestion

After you read my paper about radioactive, now i’ll give you, the reader some suggestion :

Radioactive is very important for our live, but also can gave us adverse consequences, so carefull when you using it.

Don’t too close to areas that have high concetrate of radioactive. Now you know more about radioactive, so be wise to use it. Use radioactive to generally importance, and to humans prosperity.

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Bibliography

http://en.wikipedia.org/ http://ingebinzoez.wordpress.com/ http://imperfectionists.wordpress.com/ http://www.aboutnuclear.org/ http://yudhipri.wordpress.com/ An Introduction to Radioactivity-Richard Lawson.pdf ATOMIC STRUCTURE AND RADIOACTIVE DECAY.pdf Radioaktivitas.pdf Radioactive_decay.pdf www.pencemaranlimbah.com www.departemenkesehatan.com www.limbahradioaktif.com www.radioaktif.com

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