Radioactivity Uitm

8/19/2019 Radioactivity Uitm

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Group Members:1. AIZAM AZLIM MOHD NOR (2011270912)2. HAZIZAN MOHD SHAFAI (20112077!)". SAIF#DDIN ISMAIL ( 2011!0!$!)!.ZAMRI % MOHAM&D NOR (2011'9'0)$. MOHAMAD M#ZAIDI %INLAINI(2011'10')

Radioactivity


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Definition of radioactivity

• Radioactivity defined as the spontaneous

emission of particles (alpha, beta, neutron)

or radiation (gamma, K capture), or both atthe same time, from the decay of certain

nuclides that these particles are, due to an

adjustment of their internal structure.


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• Radioactivity can be natural or artificial. Innatural radioactivity, the substance already

has radioactivity in the natural state. In

artificial radioactivity, the radioactivity has been induced by irradiation.


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• A radionuclide is all the radioactive cores of the

same ind. All radioactive cores forming a

radionuclide have a !ell"defined radioactivity,!hich is common to all of them and that identifies

them# the same !ay that a type of chemical

reaction identifies the elements involved.

http://nuclear-energy.net/media/definicion/radioactive-particles.PNG


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$rigin of radioactivity

• In %&'

• Antoine"enri *ec+uerel discovered

radioactivity. e observed that, in studies on

the phosphorescence of substances, a

mineral of uranium !as able to gloss

photographic plates, !hich !ere ept at his

side.


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hat is an Atom-

• Atoms are the basicunits of matter and

the defining structure

of elements.• Atoms are made up

of three particles

protons, neutrons and

electrons.


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Isotopes

hat1s an isotope-

/!o or more varieties of an element

having the same number of protons but

different number of neutrons. 2ertain

isotopes are 3unstable4 and decay to

lighter isotopes or elements.

5euterium and tritium are isotopes of

hydrogen. In addition to the % proton,

they have % and 6 additional neutrons inthe nucleus respectively7.

Another prime example is Uranium

238 or !ust 238U.


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Radioactivity

By the end of the 1800s, it was known that certainisotopes emit penetrating rays. Three types of radiationwere known:

1) Alpha particles (α)

2) Beta particles (β)

) !amma"rays (γ)

By the end of the 1800s, it was known that certainisotopes emit penetrating rays. Three types of radiationwere known:

1) Alpha particles (α)

2) Beta particles (β)

) !amma"rays (γ)


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#here do these particles comefrom $

These particles generally comefrom the n%clei of atomic isotopes

which are not sta&le.

The decay chain of 'rani%mprod%ces all three of these formsof radiation.

(ets look at them in more detail*


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Alpha 8articles (α)

+adi%m

+22

88 protons18 ne%trons

+adon

+n222

-ote: This is theatomic weight, whichis the n%m&er of

protons pl%s ne%trons

8 protons1 ne%trons

n np

p

α (4/e)

2 protons2 ne%trons

The alpha-particle (α) is a Helium nucleus.

ts the same as the element /eli%m, with the

electrons stripped off


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:amma particles (γ )n m%ch the same way that electrons in atoms can &e in an

e:cited state , so can a n%cle%s.

-eon-e20


5in ecited state)


5lowest energy state)

gamma

-eon-e20

A gamma is a high energy light particle .

t is -;T 7isi&le &y yo%r naked eye &eca%se it is not in

the 7isi&le part of the


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o! do these particles differ -

8article >ass7(>e?


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Rate of 5ecay*eyond no!ing the types of particles !hich are emitted

!hen an isotope decays, !e also are interested in how frequentlyone of the atoms emits this radiation.

A very important point here is that !e cannot predict when a

particular entity will decay.

e do no! though, that if !e had a large sample of a radioactive

substance, some number !ill decay after a given amount of time.

Gome radioactive substances have a very high 3rate of decay4,

!hile others have a very lo! decay rate.

/o differentiate different radioactive substances, !e loo to

"uantify this idea of 3decay rate4


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alf"Hife /he #half$life% &h' is the time it taes for half the atoms of a

radioactive substance to decay.

or eJample, suppose !e had 6@,@@@ atoms of a radioactive

substance. If the half"life is % hour, ho! many atoms of that

substance !ould be left after

()))) &*)+'

*))) &2*+'

2*)) &(2.*+'

( hour &one lifetime' ,

2 hours &two lifetimes' ,

3 hours &three lifetimes' ,

/imeatoms

remaining

L of atoms

remaining


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Hifetime (τ) /he #lifetime% of a particle is an alternate definition of

the rate of decay, one !hich !e prefer.

It is just another !ay of eJpressing ho! fast the substance

decays..

It is simply (.-- x h and one often associates the

letter #τ% to it.

he lifetime of a #free% neutron is (-. minutes0τ neutron)1(-. min.

et4s use this a 5it to 5ecome comforta5le with it6

/he #lifetime% of a particle is an alternate definition of

the rate of decay, one !hich !e prefer.

It is just another !ay of eJpressing ho! fast the substance

decays..

It is simply (.-- x h and one often associates the

letter #τ% to it.

he lifetime of a #free% neutron is (-. minutes

0τ neutron)1(-. min.

et4s use this a 5it to 5ecome comforta5le with it6


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Hifetime (I)

The lifetime of a free ne%tron is 13.4 min%tes.

f had 1000 free ne%trons in a &o, after 13.4min%tes some n%m&er of them will ha7e decayed.

The number remaining after some time is gi7en &y theradioacti7e decay law

<

@

t N N e

τ −

= <

@

t N N e

τ −

=

N 0 = starting number of

particles

= particle’s lifetime

/his is the 3eJponential4. It1s

value is 6.D%&, and is a very useful

number. 2an you find it on your

calculator-


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Hifetime (II)<

@

t N N e

τ −

=-ote &y slight rearrangement of this form%la:

>raction of particles which did not decay N / N 0 = e-t/ τ

lifetimes

/ime

(min)

raction ofremainingneutrons

@τ @ %.@

%τ %M.D @.C&

6τ 6'.M @.%CBCτ MM.% @.@B@

Mτ B&.& @.@%&

Bτ DC.B @.@@D

0.00

0.20

0.40

0.60

0.80

1.00

1.20

0 2 4 6 8 10

Lifetimes

F r a c t i o n S

u r v i v e d

0.00

0.20

0.40

0.60

0.80

1.00

1.20

0 2 4 6 8 10

Lifetimes

F r a c t i o n S

u r v i v e d

After 3"? lifetimes, almost all of the

%nsta&le particles ha7e decayed awayAfter 3"? lifetimes, almost all of the%nsta&le particles ha7e decayed away


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Hifetime (I?)

!i7en a &atch of 1 species of particles, some will decay

within 1 lifetime (%τ), some within 2τ, some within τ, andso on*

#e A--;T say 6Carticle 33 will decay att

D22 min .Eo% 9%st cant

All we can say is that:

After 1 lifetime, there will &e 54F) remaining After 2 lifetimes, there will &e 513F) remaining After lifetimes, there will &e 5?F) remaining After 3 lifetimes, there will &e 52F) remaining, etc


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Hifetime (?)

f the particles lifetime is 7ery short, the particlesdecay away 7ery G%ickly.

#hen we get to s%&atomic particles, the lifetimesare typically only a small fraction of a second

f the lifetime is long 5like 28') it will hang aro%ndfor a 7ery long time

f the particles lifetime is 7ery short, the particlesdecay away 7ery G%ickly.

#hen we get to s%&atomic particles, the lifetimesare typically only a small fraction of a second

f the lifetime is long 5like 28') it will hang aro%ndfor a 7ery long time

if i ( )


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Hifetime (I?)#hat if we only ha7e 1 particle &efore %s$ #hat can we saya&o%t it$

Gurvival 8robability F N / N 0 = e-t/

Decay 7ro5a5ility 1 (.) &9urvival 7ro5a5ility'

lifetimes 9urvival 7ro5a5ility

(percent)

Decay 7ro5a5ility F%.@ N Gurvival 8robability

(8ercent)

% CDL CL6 %ML &L

C BL 'BL

M 6L '&L

B @.DL ''.CL


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Gummary 2ertain particles are radioactive and undergo decay.

Radiation in nuclear decay consists of α, β, and γ particles

/he rate of decay is give by the radioactive decay la!

Gurvival 8robability F (O

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Radioactivity Uitm