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RADIOACTIVE POLLUTION
Radiation is the emission or transmission of energy in the form
of waves or particles through space or through a material medium. This includes:
Electromagnetic radiation, such as radio waves, microwaves, infrared, visible
light, ultraviolet, x-rays, and gamma radiation (γ)
Particle radiation, such as alpha radiation (α), beta radiation (β), and neutron radiation
Acoustic radiation, such as ultrasound, sound, and seismic waves (dependent on a
physical transmission medium)
Gravitational radiation, radiation that takes the form of gravitational waves, or ripples
in the curvature of space time.
Radioactivity is the emission of ionizing
radiations or particles caused by the spontaneous
disintegration of atomic nuclei. e.g. spontaneous
emission of proton (α-particles), electrons (β-
particles) and gamma rays (short wave
electromagnetic waves) due to disintegration of
atomic nuclei of some elements.
Radioactive Pollution is defined as the release of
ionizing radiations or particles into the
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environment by human activities which may represent
significant health risk to the living thing and also to the
environment. The human activities that involve
activities with radioactive materials such as mining,
handling and processing of radioactive materials,
handling and storage of radioactive waste, as well as the
use of radioactive reactions to generate energy (nuclear
power plants), nuclear explosions etc.
Types of Radiations
Radiation is often categorized as either ionizing or non-ionizing depending on the energy of
the radiated particles. Ionizing radiation carries more than 10 eV, which is enough
to ionize atoms and molecules, and break chemical bonds.
1. Ionizing radiations
Radiations with sufficiently high energy
can ionize atoms. Ionization is the process by which an
atom or a molecule acquires a negative or positive charge
by gaining or losing electrons, often in conjunction with
other chemical changes. The resulting electrically
charged atom or molecule is called an ion.
Ionizing radiations have high penetration power and
cause breakage of macro molecules. They include X-rays,
cosmic rays and atomic radiations (radiations emitted by
radioactive elements).
Because living cells and, more importantly, the DNA in
those cells can be damaged by this ionization, exposure to ionizing radiation is considered
to increase the risk of cancer.
Most ionizing radiation originates from radioactive materials and space (cosmic rays-
which are generated by stars and certain celestial events such as supernova explosions),
and as such is naturally present in the environment, since most rocks and soil have small
concentrations of radioactive materials.
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Ionizing radiation has many practical uses in medicine, research and construction, but
presents a health hazard if used improperly. Exposure to radiation causes damage to
living tissue; high doses result in Acute radiation syndrome (ARS), with skin burns, hair
loss, internal organ failure and death, while any dose may result in an increased chance of
cancer and genetic damage;
The molecular damage may produce short range (immediate) of long range (delayed)
effects.
(i) Short range effects include burns, impaired metabolism, dead tissues and death of
the organisms.
(ii) Long range effects are mutations (changing of structure of genes), increased
incidence of tumors and cancer, shortening of life-span and developmental changes.
(iii) The mutated gene can persist in living organisms and may affect their progeny.
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The actively dividing cells such as Embryo, fetus, cells of skin, intestinal lining, bone
marrow and gamete forming cells are more sensitive to radiations.
Some species of animals and plants preferentially accumulate specific radioactive
materials. For example, oysters deposit 65Zn, fish accumulate 55Fe, and marine animals
selectively deposit 90Sr.
Types of radiation particles:
α-particles
They consist of two protons and two neutrons bound together. Alpha particles
are helium-4 nuclei i.e. Alpha particles are helium nuclei. The best known source of
Alpha particles is Alpha decay of heavier atoms.
Alpha particles don’t travel very fast (compared to beta particles) because they have
such a large mass. Their low speed means that they tend to collide with plenty of other
atoms and cause a lot of ionization on their way. An alpha particle can ionize thousands
of air particles before it slows down. All these collisions mean that they lose energy
quickly, so they have a short range in the air.
Alpha particles can be blocked by a piece of paper and human skin. They interact with
matter strongly due to their charges and combined mass, and at their usual velocities
only penetrate a few centimeters of air, or a few millimeters of low density material
(such as the thin mica). This means that alpha particles from ordinary alpha decay do
not penetrate the outer layers of dead skin cells and cause no damage to the live tissues
below. Some very high energy alpha particles compose about 10% of cosmic rays, and
these are capable of penetrating the body and even thin metal plates. However, they are
of danger only to astronauts, since they are deflected by the Earth's magnetic field and
then stopped by its atmosphere.
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Alpha radiation is dangerous when alpha-emitting radioisotopes are ingested or
inhaled (breathed or swallowed). This brings the radioisotope close enough to
sensitive live tissue for the alpha radiation to damage cells.
β-particles
A beta particle, also called beta ray or beta radiation, is a high-energy, high-
speed electron or positron emitted by the radioactive decay of an atomic nucleus during
the process of beta decay. There are two forms of beta decay, β− decay and β+ decay,
which produce electrons and positrons respectively.
Beta decay of a neutron transforms it into a proton by the emission of an electron
accompanied by an antineutrino i.e. An unstable atomic nucleus with an excess
of neutrons may undergo β− decay, where a neutron is converted into a proton, an
electron, and an electron antineutrino (the antiparticle of the neutrino). β− decay
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commonly occurs among the neutron-rich fission byproducts produced in nuclear
reactors.
Or
conversely a proton is converted into a neutron by the emission of a positron (positron
emission) with a neutrino, thus changing the nuclide type i.e. Unstable atomic nuclei with
an excess of protons may undergo β+ decay, also called positron decay, where a proton is
converted into a neutron, a positron, and an electron neutrino.
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Neither the beta particle nor its associated (anti-) neutrino exist within the nucleus prior to
beta decay, but are created in the decay process. By this process, unstable atoms obtain a
more stable ratio of protons to neutrons.
Of the three common types of radiation given off by radioactive materials, alpha, beta
and gamma, beta has the medium penetrating power and the medium ionizing power.
Being composed of charged particles, beta radiation is more strongly ionizing than
gamma radiation.
Beta particles can penetrate through skin, while can be blocked by some pieces of glass
and metal. Beta particles which are about 100 times more penetrating than alpha particles.
Beta particles can be used to treat health conditions such as eye and bone cancer and are
also used as tracers. Strontium-90 is the material most commonly used to produce beta
particles.
Beta particles are also used in quality control to test the thickness of an item, such
as paper, coming through a system of rollers.
Beta-plus (or positron) decay of a radioactive tracer isotope is the source of the positrons
used in positron emission tomography (PET scan).
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PET scan machine
γ- Rays or radiations
Gamma (γ) radiation consists of photons with a wavelength less than 3x10−11 meters and are
electromagnetic waves with very high frequencies and energy (greater than 1019 Hz and 41.4
keV). Gamma radiation emission is a nuclear process that occurs to rid an
unstable nucleus of excess energy after most nuclear reactions. Alpha and Beta decay are
almost always accompanied by Gamma Decay. Both alpha and beta particles have an electric
charge and mass, and thus are quite likely to interact with other atoms in their path. Gamma
radiation, however, is composed of photons, which have neither mass nor electric charge
and, as a result, penetrates much further through matter than either alpha or beta radiation.
Gamma rays can penetrate easily to human skin and damage cells on its way through,
reaching far, and can only be blocked by a very thick, strong, massive piece of concrete.
A nucleus which is in an excited state may emit one or more photons (packets of
electromagnetic radiation) of discrete energies. The emission of gamma rays does not alter
the number of protons or neutrons in the nucleus but instead has the effect of moving the
nucleus from a higher to a lower energy state (unstable to stable).
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Gamma ray emission frequently follows beta decay, alpha decay, and other nuclear decay
processes.
Gamma rays and X-rays are both electromagnetic radiation and they overlap in
the electromagnetic spectrum; the terminology varies between scientific disciplines.
Gamma rays are ionizing radiation and are thus biologically hazardous. Due to their high
penetration power, they can damage bone marrow and internal organs. Unlike alpha and beta
rays, they pass easily through the body and thus pose a formidable radiation
protection challenge, requiring shielding made from dense materials such as lead or concrete.
However, they are less ionizing than alpha or beta particles, which are less penetrating.
Natural sources of gamma rays on Earth include gamma decay from naturally
occurring radioisotopes such as potassium-40, and also as a secondary radiation from various
atmospheric interactions with cosmic ray particles. Some rare terrestrial natural sources that
produce gamma rays that are not of a nuclear origin are lightning strikes and terrestrial
gamma-ray flashes, which produce high energy emissions from natural high-energy voltages.
A large fraction of such astronomical gamma rays are screened by Earth's atmosphere.
Notable artificial sources of gamma rays include fission, such as occurs in nuclear reactors,
as well as high energy physics experiments, such as neutral pion decay and nuclear fusion.
Gamma radiation is often used to kill living organisms, in a process called irradiation.
Applications of this include the sterilization of medical equipment, the removal of decay-
causing bacteria from many foods and the prevention of the sprouting of fruit and vegetables
to maintain freshness and flavor. Despite their cancer-causing properties, gamma rays are
also used to treat some types of cancer, since the rays also kill cancer cells.
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2. Non-ionizing radiations
Non-ionizing radiation is described as a series of energy waves composed of oscillating
electric and magnetic fields traveling at the speed of light.
The kinetic energy of particles of non-ionizing radiation is too small to produce charged ions
when passing through matter. For non-ionizing electromagnetic radiation, the associated
particles (photons) have only sufficient energy to change the rotational, vibrational or
electronic valence configurations of molecules and atoms. Thus Non-ionizing (or non-
ionising) radiation refers to any type of electromagnetic radiation that does not carry
enough energy per quantum (photon energy) to ionize atoms or molecules. Instead of
producing charged ions when passing through matter, non-ionizing
electromagnetic radiation has sufficient energy only for excitation, the movement of an
electron to a higher energy state.
Near ultraviolet, visible light, infrared, microwave, radio waves, and low-frequency radio
frequency (long wave) are all examples of non-ionizing radiation. By contrast, far ultraviolet
light, X-rays, gamma-rays, and all particle radiation from radioactive decay are ionizing.
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The region at which radiation becomes considered as "ionizing" is not well defined, since
different molecules and atoms ionize at different energies.
Visible and near ultraviolet electromagnetic radiation may induce photochemical reactions,
or accelerate radical reactions. Near ultraviolet radiation, although technically non-ionizing,
may still excite and cause photochemical reactions in some molecules.
The energy of particles of non-ionizing radiation is low, and instead of producing charged
ions when passing through matter, non-ionizing electromagnetic radiation has only sufficient
energy to change the rotational, vibrational or electronic valence configurations of molecules
and atoms. This produces thermal effects.
Even "non-ionizing" radiation is capable of causing thermal-ionization if it deposits enough
heat to raise temperatures to ionization energies. These reactions occur at far higher energies
than with ionization radiation, which requires only single particles to cause ionization.
The possible non-thermal effects of non-ionizing forms of radiation on living tissue have
only recently been studied. Much of the current debate is about relatively low levels of
exposure to radio frequency (RF) radiation from mobile phones and base stations producing
"non-thermal" effects. Some experiments have suggested that there may be biological effects
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at non-thermal exposure levels, but the evidence for production of health hazard is
contradictory and unproven.
Non-Ionizing radiation originates from various sources: Natural origin (such as sunlight or
lightning discharges etc.) and man made (seen in wireless communications, industrial,
scientific and medical applications). The NIR spectrum is divided into two main regions:
optical radiations and electromagnetic fields. The optical radiations are centred around
visible light; those with higher energies are termed UV radiation and those with lower
energies IR radiation. Sources of UV radiation are the sun, arc welding, oxy-gas welding,
sun lamps, lasers (UV), sterilization (germicidal) lamps, low pressure gas discharge lamps,
high pressure discharge lamps. Sources of IR radiation are from hot processes such as
steelmaking, glassmaking, welding, and also lasers (IR). Microwaves are used in
telecommunications, radar/satellite links, mobile phones, microwave ovens, TV transmitters.
RF is used in radio communications, visual display units, television sets. Extremely low-
frequency (ELF) electric and magnetic fields (EMFs) surround electrical machinery, home
appliances, electric wiring, and high-voltage electrical transmission lines and transformers.
Non-ionizing radiations affect only those components which absorb them and have low
penetrability.