1. Radioactivity–Introduction
Allsubstancesaremadeofatoms.Thesehaveelectrons(e)aroundtheoutside,andanucleusin
themiddle.
The nucleus consists of protons(p)andneutrons (n),andisextremelysmall.(Atoms are
almostentirelymadeofemptyspace!)
Insometypesofatom,thenucleusisunstable,andwilldecayintoamorestableatom.This
radioactivedecayiscompletelyspontaneous.
Youcanheatthesubstanceup,orsubjectittohighpressureorstrongmagneticfields-infact,
dowhateveryouliketoit-andyouwon'taffecttherateofdecayintheslightest.
This form of Lithium is not radioactive- it's just an example of a simple atom.Most
radioactive substances havemany more particles in their nucleus.
Whenanunstablenucleusdecays,therearethreeways thatitcandoso.Itmaygiveout:-
•analphaparticle(weusethesymbol á)
•abetaparticle(symbolâ)
•agammaray(symbol )Manyradioactivesubstances emitáparticlesandâparticles aswell
asrays.Infact,youwon'tfindapuresource;anything thatgivesoffrayswillalsogiveoffá
and/orâtoo.

2. TypesofRadioactiveRays
Alpha
Alpharadiationisaheavy,veryshort-rangeparticleandisactuallyanejectedheliumnucleus.
Somecharacteristicsofalpharadiationare:
•Mostalpharadiationisnotabletopenetratehuman skin.
•Alpha-emitting materialscanbeharmfultohumansifthematerialsareinhaled,swallowed,or
absorbedthroughopenwounds.
•Avarietyofinstrumentshasbeendesignedtomeasurealpharadiation.Specialtraining inthe
useoftheseinstrumentsis essentialformaking accuratemeasurements.
•Athin-windowGeiger-Mueller(GM)probecandetectthepresenceofalpharadiation.
•Instruments cannotdetect alpharadiationthrough evenathinlayerofwater,dust,paper,or
othermaterial,becausealpharadiationisnotpenetrating.
•Alpharadiationtravelsonlyashortdistance(afewinches)inair,butisnotanexternalhazard.
•Alpharadiationisnotabletopenetrateclothing.
Examplesofsomealphaemitters:radium,radon,uranium,thorium.
Alpha Particles
Alphaparticlesaremadeof2protonsand2neutrons.
Thismeansthattheyhaveachargeof+2,andamassof4
(the mass is measured in "atomic mass units", where each proton & neutron=1)
Alphaparticlesarerelativelyslowandheavy.
Theyhavealowpenetratingpower-youcanstopthemwith justasheetofpaper.
Becausetheyhavealargecharge,alphaparticlesionise otheratomsstrongly.

4. Beta
Betaradiationisalight,short-rangeparticleandisactuallyanejectedelectron.Some
characteristicsofbetaradiation are:
•Betaradiationmaytravelseveralfeetinairandis moderatelypenetrating.
•Betaradiationcanpenetratehumanskintothe"germinallayer,"wherenewskin cellsare
produced.Ifhighlevelsofbeta-emittingcontaminantsareallowedtoremainontheskinfora
prolongedperiodoftime,theymaycauseskininjury.
•Beta-emitting contaminants maybeharmfulifdepositedinternally.
•Mostbetaemitterscanbedetectedwith asurveyinstrumentandathin-windowGMprobe
(e.g.,"pancake"type).Somebetaemitters,however,produceverylow-energy,poorly
penetratingradiationthatmay be difficult or impossible to detect. Examples of these
difficult-to-detectbetaemittersarehydrogen-3(tritium),carbon-14,andsulfur-35.
•Clothingprovidessomeprotection againstbetaradiation.
Examplesofsomepurebetaemitters:strontium-90,carbon-14,tritium,andsulfur-35.
Beta Particles
Betaparticleshaveachargeofminus1,andamassofabout1/2000thofaproton.This means
thatbetaparticlesarethesameasanelectron.
Theyarefast,andlight.
Betaparticleshaveamediumpenetratingpower-theyarestoppedbyasheetofaluminiumor
plasticssuchasPerspex.
Betaparticlesioniseatoms thattheypass,butnotasstronglyasAlphaparticlesdo.

6. Gamma
Gammaradiation andxrays arehighlypenetratingelectromagneticradiation.Some
characteristicsoftheseradiations are:
•Gammaradiationorxrays areabletotravelmanyfeetinairandmanyinchesinhumantissue.
Theyreadilypenetratemost materialsandaresometimes called"penetrating"radiation.
•Xraysarelikegammarays.Xrays,too,arepenetratingradiation.Sealedradioactivesources
and machinesthatemitgammaradiationandxraysrespectivelyconstitutemainlyanexternal
hazardtohumans.
•Gammaradiation andxraysareelectromagneticradiationlikevisiblelight,radio waves,and
ultravioletlight.Theseelectromagneticradiationsdifferonlyintheamountofenergytheyhave.
Gammaraysandx raysarethemostenergeticofthese.
•Densematerialsareneededforshielding fromgammaradiation.Clothingprovideslittle
shieldingfrompenetrating radiation,butwillprevent contaminationoftheskinbygamma-
emittingradioactivematerials.
•Gammaradiationiseasilydetectedbysurveymeters with asodiumiodidedetectorprobe.
•Gammaradiation and/orcharacteristicxraysfrequentlyaccompanytheemissionofalphaand
betaradiationduringradioactivedecay.Examplesofsomegammaemitters:iodine-131,
cesium-137,cobalt-60,radium-226,andtechnetium-99m.
Gamma Rays
Gammaraysarewaves,notparticles.This meansthattheyhavenomass andno charge.
Gammarayshaveahighpenetratingpower-ittakesathicksheetofmetalsuchaslead,or
concretetoreducethemsignificantly.
Gammaraysdonotdirectlyioniseotheratoms,althoughtheymaycauseatoms toemitother
particleswhichwillthencauseionisation.
We don't find pure gamma sources - gamma rays are emitted alongside alpha or
betaparticles. Strictly speaking, gamma emission isn't 'radioactive decay' because it
doesn'tchange the state of the nucleus, it just carries away some energy.

7. Radioactive decay
Radioactivedecayistheprocessinwhichanunstableatomicnucleusspontaneouslyloses
energybyemittingionizingparticlesandradiation.Thisdecay,orlossofenergy,resultsinan
atomofonetype,calledtheparentnuclidetransformingtoanatomofadifferenttype,calledthe
daughternuclide.Forexample: acarbon-14atom(the"parent")emits radiationand
transformstoanitrogen-14 atom(the"daughter").Thisisarandomprocessontheatomiclevel,
inthatitisimpossibletopredict whenagivenatomwilldecay,butgivenalargenumberof
similaratomsthedecayrate,onaverage,ispredictable.
AlphaDecay
In alpha decay, the nucleus emits an alpha particle; an alpha particle is essentially a
heliumnucleus, 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 usein smoke detectors, a common household item.

8. Beta decay
A beta particle is often an electron, but can also be a positron, a positively-charged
particle that isthe 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 thechart of the
nuclidesattheBrookhaven National Laboratory.