19216425 folio fizik radioactivity

8/3/2019 19216425 Folio Fizik Radioactivity

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Radioactivity - Introduction

All substances aremade of atoms.These have elect rons (e) around the

outside, and anucleus in the middle.

The nucleus consists of

protons (p) and neut rons (n), and is

extremely small.(Atoms arealmost ent irelymade ofempty spac e!)

In some typ es of atom, the nucleus is

unstable, and will decay into a mo restable atom. This radioactive decay iscom pletely spontaneous.

You can heat the substance up, or subject

it tohigh pressure or strong magneticfields - in fact, do whate veryou like to it -

and you won't affect the rate ofdecay inthe slightest.

This form of Lithium is not radioactive

- it's just an example of asimple atom.Most radi oactive substances have

many mo reparticles in their nucleus.

When an uns table nucleus decays, the rearethree ways that it can do so.It may give out:-

an alpha par ticle (we use the symbol )

a beta par ticle (symbol )

a gamma ray (symb ol )

Many radioactive substances emit par ticles and parti cles as well asrays.

In fact, you won't find apure source; anything that gives off rays will alsogive off and/or too.


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Types of Radioactive Rays

Alp ha

Alpha radiat ion is a heavy, very shor t-range particle and is actually an

ejected helium nucleus. Some cha racte ristics of alpha radiation are:

Most alpha radiation is not able to penetrate human skin.

Alpha -emitting materials can be harmful to humans ifthe materials are

inhaled, swallowed, or absorbed through open wou nds.

A variety of instrumen tshas been designed to measure alpha

radiati on. Special training in the use of the seinstrumen tsis essential

for making accura temeasuremen ts.

A thin-w indow Geige r-Mueller (GM) probe can detect the presence of

alpha radiation.

Instruments cannot detect alpharadiat ion through even a thin layer of

water, dust, paper, or other material, beca use alpha radiation is not

penetrating.

Alpha radiat ion travels only a short dis tance (a few inches) in air, but is

not an external haza rd.

Alpha radiat ion is not able to penetrate clot hing.

Exampl es of some alpha emitters: radium, radon, uranium, thorium .

Alpha Particles

Alpha par ticles arema de of 2protons and 2 neut rons.

This means that they have a cha rge of +2, and a mass of 4

(the mass ismeasured in "atomic mass units", where each

proton & neutron=1)

Alpha par ticles are relatively slow and heavy.

They have a low penetrating power - you can stop them

with just asheet ofpape r.

Becaus ethey have alarge cha rge, alpha particles ionise oth eratoms strongly.
http://www.darvill.clara.net/nucrad/ionise.htmhttp://www.darvill.clara.net/nucrad/ionise.htmhttp://www.darvill.clara.net/nucrad/ionise.htmhttp://www.darvill.clara.net/nucrad/ionise.htm


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BetaBeta radiation is a light, short -range particle and is actually an ejected

elec tron. Some characteristics ofbe taradiat ion are:

Beta radiation may travel several feet in air and is mod eratelypenetrating.

Beta radiation can penetrate human skin to the "ge rminal layer,"

wherenew skin cells areproduced. Ifhigh levels ofbe ta-emit ting

contaminants areallowed to remain on the skin for aprolonged period

of time, they may cause skin injury.

Beta-emitt ing contaminants may be harmful ifdeposited inte rnall y.

Most beta emitt ers can be detected with a survey instrument and a

thin-window GMprobe (e.g .,"panc ake" type). Some be taemitt ers,howeve r,produce very low-ene rgy, poorly penetrating radiat ion thatmay be difficult or impossible to detect. Examples of these difficult- to-detect beta emitters arehydroge n-3 (tritium), carbon- 14, and sulfur-35.

Clot hing provides some protection against beta radiatio n.

Exampl es of some purebeta emitters: strontium- 90, carbon- 14, tritium,

and sulfu r-35. Beta Particles

Beta particles have a charge of min us 1, and a mass ofabout 1/2000th of a proton. This means that beta

parti cles arethe same as an elect ron.

They arefast, and light.

Beta particles have a medium penetrating power - they

arestopped by a sheet of aluminium orplastics such as

Persp ex.

Beta particles i onise ato ms that they pass, but not asst rongly asAlpha particles do.


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Gam ma

Gam ma radiati onand x rays arehighly penetrating elect romagneticradiati on. Some characteristics of these radiations are:

Gam ma radiati on or x rays areable to travel many feet in air and many

inches inhuman tissue. They readilypenetrate most materials and are

sometimes called "penetrating" radiation .

X rays arelike gam marays. X rays, too, arepenet rati ngradiation.

Sealed rad ioactive sou rces and machines that emit gamma radiationand x rays respectively constitute mainly an exte rnal hazard to

huma ns.

Gam ma radiati onand x rays areelect romagnetic radiation like visible

light, radiowaves, and ultraviolet light. These elec tromagnetic

radiati ons differ only in the amount of ene rgy they have. Gamma rays

and x rays arethe most ene rgetic of these.

Dense mate rialsareneeded for shielding from gam maradiat ion.

Clot hing provides little shielding from penetrati ng radiation, but will

prevent contamination ofthe skin by gam ma-emitt ing rad ioactivematerials.

Gam ma radiati on is easily detected by survey meters with a sodium

iodide detector probe.

Gam ma radiati onand/ orcharacteristic x rays frequently accompany the

emission ofalpha and beta radiation during radioactive decay.Exampl es of some gam maemitters: iodine-131, cesium -137, cobalt-60,radium -226, and technetium -99m.

Gam ma Rays


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Gam ma rays arewaves, not particles. This means that

they have no mass and no charge.

Gam ma rays have a high penetrating power - it takes a

thick sheet of me tal such as lead, or conc rete to

reduce them sign ificantl y.

Gam ma rays do not directly ionise otheratoms,

althou gh they may cause atoms to emit other parti cles

which will then cause ionisatio n.

We don't find puregamma sources - gamma rays areemitted alongside alpha orbeta

particles. Strictly speaking, gamma emissi on isn't'radioact ive decay' bec ause it does n'tcha nge the sta te of the nucleus, it just carries away some ene rgy.

Rad ioactive dec ay

Radioactive decay is the proce ss in which an unstable atomic nucleus

spontaneously losesene rgy by emitting ionizing par ticles and radiation. This

decay, or loss of ene rgy, results inan atom of one type, called the parent

nuc lide transfo rming to an atom of a different type, called the daughter

nuc lide. For exampl e:a carbon- 14 atom (the"parent") emits radiation and


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transfo rms to a nitrogen- 14 atom (the "daughte r"). This is a random proce ss

on the atomic level, in that it is impossible topredict when a given atom will

decay, but given a large number of similar atoms the decay rate, on

ave rage, is predi ctable.

Alpha Dec ay

In alpha decay, the nucleus emits an alpha particle; an alpha particle is essentially a helium

nucleus, so it's a group of two protons and two neutrons. A helium nucleus is very stable.

An example of an alpha decay involves uranium-238:

The process of transforming one element to another is known as transmutation.

Alpha particles do not travel far in air before being absorbed; this makes them very safe for use

in smoke detectors, a common household item.

Beta decay

A beta particle is often an electron, but can also be a positron, a positively-charged particle that is

the anti-matter equivalent of the electron. If an electron is involved, the number of neutrons inthe nucleus decreases by one and the number of protons increases by one. An example of such a

process is:

In terms of safety, beta particles are much more penetrating than alpha particles, but much lessthan gamma particles.

Gamma decay

The third class of radioactive decay is gamma decay, in which the nucleus changes from ahigher-level energy state to a lower level. Similar to the energy levels for electrons in the atom,

the nucleus has energy levels. The concepts of shells, and more stable nuclei having filled shells,

apply to the nucleus as well.

When an electron changes levels, the energy involved is usually a few eV, so a visible or

ultraviolet photon is emitted. In the nucleus, energy differences between levels are much larger,

typically a few hundred keV, so the photon emitted is a gamma ray.

Gamma rays are very penetrating; they can be most efficiently absorbed by a relatively thick

layer of high-density material such as lead.

A list of known nuclei and their properties can be found in the chart of the nuclides at the

Brookhaven National Laboratory.
http://www.dne.bnl.gov/CoN/index.htmlhttp://www.dne.bnl.gov/CoN/index.htmlhttp://www.dne.bnl.gov/CoN/index.htmlhttp://www.dne.bnl.gov/CoN/index.html


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Rad ioacti ve Dec aySeir ies

A rad ioactive decay series is the chain of deca ysthat occ urstar ting with arad ioactive isotope. An example of this is the uranium -radium series:

Uraniu m-238 decays thorium- 234

Thorium -234 decays protactini um-23 4

Protactinium-234 decays to form uranium-2 34

Uraniu m-234 decays thorium- 230

Thorium deca ys radium-2 26

Radium-226 goesthrough five mo re deca ysand four mo re deca ysto

yield the non-radioactive isotope 206Pb, or lead. This seri esis also called the

4n+2 series, becau sethe mass numbers of each of the isotopes in the series

canbe represented by 4n+2, whe ren is an intege r. The thorium series is a

4n series; it starts at thorium-232 and the end result is 208>Pb. The actinium

series, or 4n+3 series, begins with uranium -235 and endsat Pb-20 7.

Half life of radioactive elements

The half-life of a radio active element is the time that it takes for one half of the

atoms of that subs tance to disin tegr ate into another nuclear form. These can range

from me refractions of asecond, to many billions of yea rs. In addition, the half-life of

a particular radio nuclide is uni que to that radionuc lide, mea ning that knowledge of

the hal f-life leads to the identity of the radionucl ide.

The Half-Life From A Decay Curve

256 128

T1/2

T1/2= radio activ edec ay


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T1/2 = 3 hour s

Define Isotope

Iso topes (Greek isos = "equal", tpos = "site, place") areany of the diffe rent

types of atoms (nuc lides) of the samechemical ele ment, each having a

different atomic mass (mas snumber). Isotopes of an element have nuclei

with the same number ofprotons (the same atomic number) but different

numbers of neut rons. Therefore, isotopes of the same element havediffe rent

mass numbers (number of nucleo ns).

Rad iois otop e

A radioactive form of an element. A rad ioisotope consis ts of unstable atoms

that unde rgorad ioactive decay emit ting alpha, be ta or gam maradiat ion.

Radioisot opes occur natura lly, as inthe cases of radium and uranium, or may

be created artificial ly.

Applications of Radioactivity and Radioisotopes

Radioisot opes find nume rous uses in different areas such as medicine,

chemistry, biology, archaeology, agricult ure, industry and engineering.

Tracer Techniques

Radioisotopes arefrequently used as tracers or tagged atoms in

various fields. In tracer technique, a radioactive iso tope is added to the

reactants and its movement is studied by measuring radioactivity in

different parts.

In medic ine

In orderto find ifblood is circulating to a wound or not, a radioactiveiso tope isinjected into the blood stream. Aftera time per iod, blood

from the wound is examines for its rad ioactivit y. If no radioactive

iso tope is detected, it means that passage ofblood is hind ered. The

rate of circulation can also be detected by this meth od.

Tracer technique is also used for the detection of thyroid diso rderand

brain tumours.


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Can certherapy

g - rays emitted by the radioiso topes can be used in the treatment of

cance r. These radiations tend to destroy cance rous cells and the way

can arrest the spreading of the cance rous cells. 60CO is used in the

treatment of tumours and cancers.

In Agricu lture

The upt ake ofphospho rous by plan ts is studied by mixing radioactive

phosp horous with phosphatic fer tilisers.

In Chem istry

Tracer technique is used

To find the solub ility of sparingly soluble salt like lead sulphate. A lead

salt containing known amount of radioactive lead is dissolved in wate r.

Sulphuric acid is added tothe aqueous soluti on to precipitate lead as

lead sulphate.

Tracer technique is also used to study the path or mechan ism of the

react ion.

Consider the reaction

The question is how does the elimination of water takepla ce - does the

oxygen atom in water come from the alcoh ol or acid. This is studied by

label ling or tagging the oxygen inthe alcoh ol molecule. In other words, the

alco hol is prepa red with O18. Results show that the esterformed has the

rad ioactive oxygen. This shows that the starred oxygen com esfrom the

alco hol. Thus the -OH group of the acid and the H atom of the alcoh ol are

eliminated in the form of wate r.

Dangers of Radi oactive Rays

The main danger from radioactivity is the damage it does to

the cells in your bod y.

Most of this damage is due to i oni s at i on when the radiation passes, although

iflevels ofradiation arehigh the recan be damage due to heating effects asyourbody absorbs the ene rgy from the radiation, rather like heating food in

a mic rowave oven. This is particula rly true of gamma rays.


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AlphaParticles ( )

Alpha particles areslow, have a short range in air, and can be stopped bya sheet ofpape r.

You might therefore assume that alp hapar ticles arethe least dang erous ofthe three typ esofradiation .

Whilst they cannot penetrate your skin, you could

easily eat or drink something contaminated with ansource. This would put a source of particles

inside yourbody, wreaking havoc by i onising ato ms

in nearby cells. Ifthis happens to part of the DNA in

one of your cells, then that cell's instruct ions abouthow to live and grow have been scramble d. The cell

is then likely to do somethi ng very diffe rent to what

it's supposed to do, for example, it may turn

cance rous and start multiplying uncont rollabl y.

Thus alpha par ticles, whilst they have a low

penetrating power, can be the most dange rous

because they ionise so strongly.

Beta Particles ( )

-particleshave a longer range t han 's, but ionisemuch less strongly,with the result that they do around 1/20th of the damage done by the same

dose of alpha particles.

However, they do have mo repenetrating power, which means that they canget through your skin and affect cells inside you.

Gamma Rays ( )

Gam ma rays hardly ionise atoms at all, so they do not cause damage directly

in this wa y.

However, gam marays arevery diffi cult to stop; you requ irelead or conc reteshieldi ng tokeep you safe from them. When they areabsorbed by an atom,those atom gains quite a bit of ene rgy, and may then emit other par ticles. If

that atom is in one of your cells, this is not good!

Nu clear Energy

Nuclear ene rgy is released by the splitti ng (fission) or merging togeth er

(fusion) of the nuclei of atom(s). The convers ion of nuclear mass to ene rgy is

consistent with the mass-ene rgy equivalence formula E = m.c, in which

E = ene rgy release, m = mass defect, and c =the speed of light in a


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vacuum (a physical cons tant). Nuclear energy was first discove red by French

physicist Hen ri Becqu erel in 1896, when he found that photographic plates

sto red in the darknear uranium werebla ckened like X-ray plates, which had

been just recently discove red at the time 1895.

Ato mic Ma ss

Uni t

The atomic mass unit it the unit of mass for atoms and subatomic

parti clessuch as the proton, neut ron an elect ron

1 atomic mass unit or 1 u is 121 of the mass of the carbon- 12 atom.

The mass of one carbon-12 atom is 1.99265 x 10-26 kg

1 u = 261099265.11 21 kg

1 u = 1.66 x 10-27 kg

Mass de fect

Definition: The distance between the oretical calculated mass and

experimentally measu red mass of nucleus is called mass defect. It is den oted

by m. It can be calculated as follows:

Mass defect = (Theo retical calculated mass) - (measured mass of nucleus)

i.e, (sum of masse s ofprotons and neu trons) - (me asured mass of nucleu s)

- In nucl earreactions, the ene rgy that must be radiated or otherwise

removed as binding ene rgy may be in the form of elect romagnetic waves,

such as gam maradiat ion, or as heat. Again, however, no mass defi cit can in

theory app earuntil this radiation hasbeen emitted and is no longer part of

the system.

- The ene rgy given offduring either nuclear fusion or nuclear fission is the

difference between the binding energies of the fuel and the fusion or fission

products. Inpractice, this ene rgy may also be calculated from the substantial

mass diff erences between the fuel and products, once evolved heat and

radiati onhave been removed.

- When the nucleons aregrouped togeth erto form a nucleus, they lose a

small amount ofmass i.e. There is mass defect. This mass defect is released

as (often radiant) ene rgy acco rding to the relation E = mc2; thus binding

ene rgy = mass defect * c2 . This energy hol ds the nucleons together and is

known as bind ing ene rgy. In fact, mass defect is a measure ofthe binding

ene rgy of the nucleus. The greater the mass defect, the greater is the


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binding ene rgy of the nucleus.

Nuclear Fussions

Nuclear fission is the splitti ng of a heavy nucleus into two lighter nuclei

Fission occurs when the nucleus of an atom isbomba rded with a neut ron.

The energy of the neut ron causes the target nucleus to split into two (or

more) nuclei that arelighter than the parent nucleus, releasing a large

amount of ene rgy during the proce ss.

Problem Solving Invol ving Nucl earFussion

The relationsh ipbetween the mass and the ene rgy:

E = mc2

Whe re E = ene rgy released, in joules, J

m =loss of mass or mass defect, in kg

c = speed oflight = 3.0 x 108 m/s


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Example of nuclear power plant

A nuclear reactor

- Itproduces tremendous amount of ene rgy through nuclear

fiss ion.

Uranium fuel rods

- The nuclei aresplit by neut rons in a cont rolled chain reaction,

releasing a large amount of ene rgy.The ene rgy releas edhea ts

up the cold gas that passes through the reactor core.

Graphite moderator

- Acts as a moderator to slow down the fast neut rons produced by

the fission. Slower neut rons aremo re readily capt ured by the

uranium nuclei.]

Boron or cadmium cont rol rod

- The boron con trol rods absorb neut rons. It can cont rol the rate of

fission reactio n.When rods arelowe red into the reactor coreto

absorb some of the neut rons, the rate of the fission reaction

reduced.

Conc rete shield

- Prevents lea kage of radiat ion from the reactor core.


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Coolant

- Takeaway the heat from the nuclear reacto r.Substances with

high specif ic heat capacity such as water and carbon dioxide are

used.

Heat exchanger

- Heat ene rgy from the very hot gas is used to boil the water into

ste am

Importance OfPrope rmanagment OfRadioactive

SubstanceThe negative effec ts of radioactive substance

Somatic effec ts Genetic effects

Radiation burns Cancer

Leukemia Birth defects

Organ failure Down Syn drome

Vomitting Turner Synd rome

Hair loss Klinefelter Synd rome

Fatigue

Skin burn

Safety precaut ions needed in hand ling of radioactive substances

- Radioactive material is sealed in special designed containers

- Radioactive contamination may exist on surfa ces or in volume of air

- Workers should workbehind shields

- Weakrad ioactive sou rces areto be handled with forceps

- Food and drinks areprohib ited in the laborat ory


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Themanagement of radi oactive waste

High-level radioactive waste

Spent fuel is highly radioactive and needs to be handled with great careand

forethought. However, spent nuclear fuel becom esless radioactive over the

course of thousands of years of time. Afterabout 5pe rcent of the rod has

reacted the rod is no longer able to be used. Today, scientis tsare

experimenti ng on how to recycle these rods to reduce waste. In the

meantime, after40 years, the radiation flux is 99.9% lower than it was the

moment the spent fuel was removed, although still dange rously rad ioactive.

Low- level rad ioactive wast

The nuclear industry also produces a huge volume of low-level radioactive

waste in the form of contaminated items like clot hing, hand tools, water

purifier resins, and (upon decommissioning) the materials of which the

react oritself is built. In the United States, the Nuclear Regulatory

Commission has repeatedly attempted to allow low-level materials tobe

handled as normal waste: landf illed, recycled into consumer items, et cetera.

[citation needed] Most low-level waste releasesvery low levels of

rad ioactivity and is only consid ered radioactive waste becaus e of its history.


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19216425 folio fizik radioactivity

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