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Project

OnRADIOACTIVITY

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RadioactivityRadioactivity is the decay or disintegration of the nucleus of a radioactive element.

The radiation emitted is the alpha-particles, the beta-particles and the gamma rays

and a lot of heat. This phenomenon was rst discovered by a French Physicist, Henriec!uerel in "#$%. &ther famous people parts of this radioactive era are' (ord

Rutherford, and the )urie couple, *arie and Pierre. Radioactive decay is

a stochastic +i.e., random process at the level of single atoms, in that, according

to !uantum theory, it is impossible to predict when a particular atom will

decay. However, the chance that a given atom will decay is constant over time.

diagram showing an alpha particle + being eected

from the nucleus of an atom. Protons are red and

neutrons are blue.

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BECQUERELS DISCOVERY

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6n *arch of "#$%, during a time of overcast weather, ec!uerel found he couldnAt

use the sun as an initiating energy source for his eBperiments. He put his wrapped

photographic plates away in a darCened drawer, along with some crystalscontaining uranium. *uch to his ec!uerelAs surprise, the plates were eBposed

during storage by invisible emanations from the uranium. The emanations did not

re!uire the presence of an initiating energy source--the crystals emitted rays on

their ownD lthough ec!uerel did not pursue his discovery of radioactivity, others

did and, in so doing, changed the face of both modern medicine and modern

science. He was a member of a scientic family eBtending through several

generations, the most notable being his grandfather ntoine-)Esar ec!uerel

+">##"#>#, his father, leBandre-0dmond ec!uerel +"#9@$", and his son Gean

ec!uerel. +"#>#"$

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=orCing in the ec!uerel lab, *arie )urie and her husband, Pierre, began what

became a life long study of radioactivity. 6t tooC fresh and open minds, along with

much dedicated worC, for these scientists to establish the properties of radioactive

matter. *arie )urie wrote, The subect seemed to us very attractive and all the

more so because the !uestion was entirely new and nothing yet had been written

upon it. &n February ">, "#$#, the )uries tested an ore of uranium, pitchblende,for its ability to turn air into a conductor of electricity. The )uries found that the

pitchblende produced a current :@@ times stronger than that produced by pure

uranium. They tested and recalibrated their instruments, and yet they still found the

same puIIling results. The )uries reasoned that a very active unCnown substance in

addition to the uranium must eBist within the pitchblende. 6n the title of a paper

describing this hypothesiIed element +which they named polonium after *arieAs

native Poland, they introduced the new termJ radio-active.

fter much grueling worC, the )uries were able to eBtract enough polonium and

another radioactive element, radium, to establish the chemical properties of these

elements. *arie )urie, with her husband and continuing after his death, established

the rst !uantitative standards by which the rate of radioactive emission of charged

particles from elements could be measured and compared. 6n addition, she found

that there was a decrease in the rate of radioactive emissions over time and that

this decrease could be calculated and predicted. ut perhaps *arie )urieAs greatest

and most uni!ue achievement was her realiIation that radiation is an atomic

property of matter rather than a separate independent emanation. Polish-born

French physicist, famous for her worC on radioactivity and twice a winner of the

/obel PriIe. =ith Henri ec!uerel and her husband, Pierre )urie, she was awarded

the "$@: /obel PriIe for Physics. 1he was the sole winner of the "$"" /obel PriIe

for )hemistry. 1he was the rst woman to win a /obel PriIe, and she is the onlywoman to win the award in two diKerent elds.

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6n "$"", Rutherford conducted a series of eBperiments in which he bombarded a

piece of gold foil with positively charged +alpha particles emitted by radioactive

material. *ost of the particles passed through the foil undisturbed, suggesting thatthe foil was made up mostly of empty space rather than of a sheet of solid atoms.

1ome alpha particles, however, bounced bacC, indicating the presence of solid

matter. tomic particles, RutherfordAs worC showed, consisted primarily of empty

space surrounding a well-dened central core called a nucleus.

6n a long and distinguished career, Rutherford laid the groundworC for the

determination of atomic structure. 6n addition to dening the planetary model of the

atom, he showed that radioactive elements undergo a process of decay over time.

nd, in eBperiments which involved what newspapers of his day called splitting the

atom, Rutherford was the rst to articially transmute one element into another--

unleashing the incredible power of the atom which would eventually be harnessed

for both benecial and destructive purposes.

Taken together, the work of Becqere!, the Cr"e#, Rtherfor$ an$ other#,

%a$e %o$ern %e$"ca! an$ #c"ent"&c re#earch %ore than a $rea%' The(

%a$e "t a rea!"t( w"th %an( a))!"cat"on#' * !ook at the #e of "#oto)e#

re+ea!# #t #o%e of the wa(# "n wh"ch the )"oneer"ng work of the#e

#c"ent"#t# ha# -een t"!".e$'/

R*DI*TIO0S

". *!)ha1)art"c!e#2This type of radiation is positively charged. 6t is

relatively massive. 6t has a low penetrating power. 6t4s about "-9@thas

fast as light. 6t is eBactly liCe the helium atom.

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9. Beta1)art"c!e#2This type of radiation is negatively charged +but can

also be Lvely charged. 6t is relatively light. 6t is about as fast as light.

They are high energy electrons. 6t has a medium penetrating power.

:. 3a%%a Ra(#J This radiation is neutral in charge. Has a very high

penetrating power. 6t is at the speed of light. 6t is an electromagneticwave with very short wavelength. 6t is very light.

TY4ES O5 R*DIO*CTIVITY

I' 0*TUR*L R*DIOCTIVITY

This is the type of radioactivity which consists of a spontaneous

decay of the radioactive nucleus. The phenomenon is eBperienced

by naturally radioactive substances. The radiation might come out

individually or combined and, as always, with a lot of energy.

1ome radioactive substances areJ

*%er"c"% 167823sed in many smoCe detectors for homes and business.

To measure levels of toBic lead in dried paint samples. To ensure uniform

thicCness in rolling processes liCe steel and paper production and to help

determine where oil wells should be drilled.

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Ca$%"% 189:23sed to analyIe metal alloys for checCing stocC, sorting

scrap.

Ca!c"% 1 7;26mportant aid to biomedical researchers studying the cell

functions and bone formation of mammals.

Ca!"forn"% 1 6

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Io$"ne 1 8=823sed to diagnose and treat thyroid disorders. +Former

President Neorge ush and *rs. ush were both successfully treated for

NraveAs disease, a thyroid disease, with radioactive iodine.

Ir"$"% 1 8:623sed to test the integrity of pipeline welds, boilers and

aircraft parts.

Iron 1 2*aCes lightning rods more eKective.

Se!en"% 1 ;

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Tha!!"% 1 6972*easures the dust and pollutant levels on lter paper...and

gauges the thicCness of plastics, sheet metal, rubber, teBtiles and paper.

Thor"ate$ tng#ten23sed in electric are welding rods in the construction,

aircraft, petrochemical and food processing e!uipment industries. 6t produces

easier starting, greater arc stability and less metal contamination.

Thor"% 1 66:2Helps Muorescent lights to last longer.

Thor"% 1 6=92Provides coloring and Muorescence in colored glaIes and

glassware.

Tr"t"%23sed for life science and drug metabolism studies to ensure the

safety of potential new drugs. For self-luminous aircraft and commercial eBit

signs. For luminous dials, gauges and wrist watches and to produce luminous

paint.

Uran"% 1 6=723sed in dental Btures liCe crowns and dentures to provide

a natural color and brightness.

Uran"% 1 6=

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neutrons disintegrate within minutes outside of an atomic nucleus, neutron

radiation can be obtained only from nuclear disintegrations, nuclear reactions, and

high-energy reactions +such as in cosmic radiation showers or particle

accelerator collisions. /eutrons that have been slowed down through a neutron

moderator +thermal neutrons are more liCely to be captured by nuclei than fast

neutrons.

less common form involves removing a neutron via photodisintegration. 6n this

reaction, a high energy photon +gamma ray striCes a nucleus with energy greater

than the binding energy of the atom, releasing a neutron. This reaction has a

minimum cutoK of 9 *e7 +for deuterium and around "@ *e7 for most heavy nuclei.

*any radionuclides do not produce gamma rays with energy high enough to induce

this reaction. The isotopes used in food irradiation +cobalt-%@, caesium-":> both

have energy peaCs below this cutoK and thus cannot induce radioactivity in the

food.

1ome induced radioactivity is produced by bacCground radiation, which is mostly

natural. However, since natural radiation is not very intense in most places

on 0arth, the amount of induced radioactivity in a single location is usually very

small.

The conditions inside certain types of nuclear reactors with high neutron MuB can

cause induced radioactivity. The components in those reactors may become highly

radioactive from the radiation to which they are eBposed. 6nduced radioactivity

increases the amount of nuclear waste that must eventually be disposed, but it is

not referred to as radioactive contamination unless it is uncontrolled.

Un"+er#a! !aw of ra$"oact"+e $eca(

Radioactivity is one very fre!uent eBample of eBponential decay. The law describes

the statistical behavior of a large number of nuclides, rather than individual ones. 6nthe following formalism, the number of nuclides or nuclide population N, is of course

a discrete variable +a natural numberQbut for any physical sample Nis so large

+amounts of L "@9:, vogadroAs constant that t can be treated as a continuous

variable. 5iKerential calculus is needed to set up diKerential e!uations for modeling

the behavior of the nuclear decay.

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&ne-decay process

)onsider the case of a nuclideAdecaying into another Bby some processA

B+emission of other particles, liCe electron neutrinos S

e and electrons e

in beta decay, are irrelevant in what follows. The decay of anunstable nucleus is entirely random and it is impossible to predict when a particular

atom will decay. However, it is e!ually liCely to decay at any time. Therefore, given

a sample of a particular radioisotope, the number of decay events dNeBpected to

occur in a small interval of time dtis proportional to the number of atoms present N,

that is

Particular radionuclides decay at diKerent rates, so each has its own decay

constant . The eBpected decay dNUNis proportional to an increment of

time, dtJ

The negative sign indicates that Ndecreases as time increases, as each

decay event follows one after another. The solution to this rst-

order diKerential e!uation is the functionJ

=here N@is the value of Nat time t @.

=e have for all time tJ

=here Ntotalis the constant number of particles throughout the decay

process, clearly e!ual to the initial number ofAnuclides since this is

the initial substance.

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6f the number of non-decayedAnuclei isJ

Then the number of nuclei of B, i.e. number of decayedAnuclei, is

H(F-(6F0

Niven a sample of a particular radionuclide, the half-life is the time taCen for half the

radionuclideAs atoms to decay. For the case of one-decay nuclear reactionsJ

The half-life is related to the decay constant as followsJ set N = N0/2and t T"U9to

obtain

This relationship between the half-life and the decay constant shows that highly

radioactive substances are !uicCly spent, while those that radiate weaCly endure

longer. Half-lives of Cnown radionuclides vary widely, from more than "@ years, suchas for the very nearly stable nuclide 9@$i, to "@9:seconds for highly unstable ones.

The factor of ln +9 in the above relations results from the fact that concept of half-

life is merely a way of selecting a diKerent base other than the natural base e for

the lifetime eBpression. The time constant is the e-" -life, the time until only

"Ueremains, about :%.#V, rather than the

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for convenience, and from convention. They reMect a fundamental principle only in

so much as they show that the same roort!onof a given radioactive substance

will decay, during any time-period that one chooses.

*athematically, the nth

life for the above situation would be found in the same wayas aboveQby setting N = N0/n, WWW"XXX and substituting into the decay solution to

obtain

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ccording to the ig ang theory, stable isotopes of the lightest ve elements

+H, He, and traces of (i, e, and were produced very shortly after the emergence

of the universe, in a process called ig ang nucleosynthesis. These lightest stable

nuclides +including deuterium survive to today, but any radioactive isotopes of the

light elements produced in the ig ang +such as tritium have long since decayed.

6sotopes of elements heavier than boron were not produced at all in the ig ang,

and these rst ve 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 eBample, carbon-";, a radioactive nuclide with

a half-life of only :@ years, is constantly produced in 0arthAs upper atmosphere

due to interactions between cosmic rays and nitrogen.

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/uclides that are produced by radioactive decay are called radiogenic nuclides,

whether they themselves are stable or not. There eBist stable radiogenic nuclides

that were formed from short-lived eBtinct radionuclides in the early solar

system. The eBtra presence of these stable radiogenic nuclides +such as Ye-"9$

from primordial 6-"9$ against the bacCground of primordial stable nuclides can be

inferred by various means.Radioactive primordial nuclides found in the 0arth are

residues from ancient supernova eBplosions which occurred before the formation of

the solar system. They are the long-lived fraction of radionuclides surviving in the

primordial solar nebula through planet accretion until the present. The naturally

occurring short-lived radiogenic radionuclides found in rocCs are the daughters of

these radioactive primordial nuclides. nother minor source of naturally occurring

radioactive nuclides are cosmogenic nuclides, formed by cosmic ray bombardment

of material in the 0arthAs atmosphere or crust. The radioactive decay of theseradionuclides in rocCs within 0arthAs mantle and crust contribute signicantly

to 0arthAs internal heat budget.

DETECTIO0 O5

R*DI*TIO0S8' USI03 * DOSIETER OR * 5IL B*D3E2 dosimeter is a device worn by

radioactive worCers. 6t

is basically a lm which

darCens on incidence

of radiation. 6t is used to

Cnow the level of radiation

the worCer has been

eBposed to.

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6' * 3EI3ER COU0TER2This consists of a Neiger-*uller tube +which consists of

a wire, a scaleUrate meter, and often a loudspeaCer. The walls of the container

acts as the cathode while the central wire acts as the anode. The radiation

enters through a thin window. 0ach particle or ray ioniIes several gas atoms.

6ons attracted to the cathode, electrons to the anode. &ther atoms are hit on the

way creating an avalanche of more ions and electrons. The loudspeaCeramplies a clicC sound for each pulse showing the randomness of the decay.

=' 4!#e !f E!ectro#co)e

7' C!o$ Cha%-er

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7' 3a%%a1Ra$"ogra)h(J This is the production of a special type of photograph,

a radiograph. 6t is used for !uality control in industries. The maCing of a

radiograph re!uires some type of recording mechanism. The most common

device is lm. ra$"ogra)his actually a photographic recording produced by

the passage of radiation through a subect onto a lm, producing what is called

a latent image of the subect.

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;' Other #e# of ra$"oact"+"t(J 1teriliIation of medical instruments and

food is another common application of radiation. y subecting the

instruments and food to concentrated beams of radiation, we can Cill

microorganisms that cause contamination and disease. ecause this is

done with high energy radiation sources using electromagnetic energy,

there is no fear of residual radiation. lso, the instruments and food may

be handled without fear of radiation poisoning.

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;' 0c!ear reactor#aredevices that control ssion

reactions producing new

substances from the ssion

product and energy. /uclear

power stations use uranium in

ssion reactions as a fuel to

produce energy. 1team is

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The dangers of radioactivity and radiation were not immediately recogniIed. The

discovery of Y-rays in "#$< led to wide spread eBperimentation by scientists,

physicians, and inventors. *any people began recounting stories of burns, hair loss

and worse in technical ournals as early as "#$%. 6n February of that year, Professor

5aniel and 5r. 5udley of 7anderbilt 3niversity performed an eBperiment involving B-

raying 5udleyAs head that resulted in him losing hair under where the tube was

placed +reported in the T"e #$ra%s &c!encenews supplement. report by 5r. H.5.

HawCs, a graduate of )olumbia )ollege, of his suKering severe hand and chest

burns in an B-ray demonstration, was the rst of many other reports in'(ectr!ca(

Re)!e*. *any eBperimenters including 0lihu Thomson at Thomas 0disonAs

lab, =illiam G. *orton, and /iCola Tesla also reported burns. 0lihu Thomson

deliberately eBposed a nger to an B-ray tube over a period of time and suKered

pain, swelling, and blistering. &ther eKects were sometime blamed for the damage

including ultraviolet rays and +according to Tesla oIone. *any physicians claimed

there were no eKects form B-ray eBposure at all.

The genetic eKects of radiation, including the eKect of cancer risC, were recogniIed

much later. 6n "$9>, Hermann Goseph *uller published research showing genetic

eKects, and in "$;% was awarded the /obel PriIe for his ndings.

efore the biological eKects of radiation were Cnown, many physicians and

corporations began marCeting radioactive substances as patent medicine in the

form of glow-in-the-darC pigments. 0Bamples were radium enema treatments, and

radium-containing waters to be drunC as tonics. *arie )urie protested this sort of

treatment, warning that the eKects of radiation on the human body were not well

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understood. )urie later died from aplastic anemia, liCely caused by eBposure to

ioniIing radiation. y the "$:@s, after a number of cases of bone necrosis and death

of enthusiasts, radium-containing medicinal products had been largely removed

from the marCet +radioactive !uacCery.