physics radioactivity form5 2014

8/21/2019 Physics Radioactivity Form5 2014

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5. 1 THE NUCLEUS OF AN ATOM

5 .1.1 The composition of the nucleus

1. Atomic Model has a. which consists of (p) and

..(n) with ..( e) revolving around the nucleus

like the planet revolving around the Sun.

2. A proton has apositivecharge whereas an electron has a ..

chargeve.

5.1.2 Nuclide

1. A nuclide is.

2 An atom of an element is represented by its symbol as above.

A is for ..number is for ..number and ! is forelement

5.1. !sotopes

1. "hat it meant by the isotopes #

Isotopes are .. of the. element with the same

number of . but dierent number of .

2. $or e%ample&

a'arbon ) carbon *12 126 C , carbon *1+14

6 C,

b',ydrogen) deuterium 21

H , tritium 31

H ,..

XA

Z

CHAPTER 5: RADIOACTIVITY


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Physics Module Form 5

E"e#cise 5.1

1. A nucleus contains protons and neutrons. "hich of these particles

e%periences an electrostatic force # ..

2. -old (Au ' has / protons and 110 neutrons. "rite the symbol for

this nuclide

. An isotope of nitrogen can be represented by ( 157 '. ,ow many of the

following particles does it have #

a' protons ) 3 neutrons ). 3 electrons )

5.2 $A%!OACT!&E %ECA'

5.2.1 $(dio(cti)it*

1. "hat is meant by the radioactivity #

2. 4he process is said to be spontaneous because

-It is not inuenced b an phsical factors such as temperature, pressure,

time , etc. 4he emission of radioactive rays is random means that )

a) emission occurs at irre!ular intervals

b) emission does not occur at the same rate

+. %escribe what happens to an atom when it undergoes radioactive decay.

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"hen a radioactive nucleus decas, its nucleus brea#s up, emits an alpha

particle or beta particle and ener!, and form a new atoms of a dierent

element

5.2.2 Ch(#(cte#istics of the th#ee t*pes of $(dio(cti)e Emissions

5adioactive

emissions

Alpha particles 6eta particles -amma rays

Symbol

ature

7lectron

harge 82 electric charges

Speed Speed of light

7nergy $or a particularsource,

all particle are emitted

with the same %&

$or a particular source

- particle emitted

have various %&

il

9n an

electric

:eld

6ends to positive

plate

9n

magnetic

:eld

6ends a little showing

that it has a big mass.

;irection of the bend

indicates that it is

positively charges

'end a lot showin!

that it has a small

mass. irection of the

bend indicates that it

is positivel char!ed

oes not bend

showin! that it is

neutral.

9onising

power

"eakest


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airAL,HA %ECA'

1.

-ETA %ECA'

2.

7%ample)

-AMMA ;7A=

7%ample)

4

X R + HeA - 4

Z - 2

4

2

X R + e + eer!y A

Z + 1

"

-1

e# eleme$ % - &'r$icle

e# eleme$ ( - &'r$icle

X X + ) + eer!y A

Z

"

"

eleme$ eleme$

hi!h$ eer!y lo# eer!y ) - r'y

A

Z

Po P* + He2

4

2

21"

4

,r Y + e90

"

-1

"

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. 4he e>uation below represents a nuclear reaction. "hat is the value of


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5.2.+ $(dio(cti)e %etecto#s

o 5adioactive

emission

;etector 5eason

1. 6eta and gamma.


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E"(mple 3


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. 4he activity of a sample of radioactive isotope decrease to J of its initial

value in 2 s. ,ow much more time would be re>uired for the activity to

decrease to 1KH+ of its initial value #

+. A detector is used for monitoring an %G source and a reading of 2+I units

is observed. After a time e>ual to twice the half G life of the %G source3 the

reading has fallen to HH units. 9f a F mm thick lead sheet is inserted between

the %G source and the detector3 the reading would probably be

F. A counter is placed near a very weak radioactive source which has a half G

life of 2 hours. 4he counter registers /F countK min at noon and FF count K

min at 2 p.m . 4he e%pected count G rate3 in count K min 3 at H p. m m on the

same day is

4. Some pond water becomes contaminated by the release of radioactive

waste.

4he radioactivity of a sample of the contaminated water is tested every week

for F weeks.

4he results are shown in the table below.

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76 ;raw the best curve through your points.

c6 @se your graph to :nd the half*life of the radioactive material in the

sample. Show clearly

on the graph how you obtained your answer.

half*life of radioactive material L weeks

d6 Suggest two maor sources of background radiation.

i6 Cosmic ras from the sun and other star

ii6 radioactive minerals on the earth

. @sing the table below answer the following >uestion.

$(dio(cti)eisotope

H(lf8life

Strontium*/I 20 years5adium*22H 1HI2 years9odine*120 2 minutes

"hat is the time taken if the activity of iodine left is only 12.FcountKmin #

5. $A%!O!SOTO,ES


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(6 The (pplic(tion of #(dioisotope in indust#ies

1. 5adioisotopes are isotopes with radioactive properties.

Radioisotope source Use in Mechanism

Americium -241 Smoke detector Alpha particle emitted from the source

ionise air molecules. The ionized air

molecules conduct electricity and a small

current flo to the detector. Smoke

a!sor! alpha particles" the current flo

decrease and tri##er the alarm.

$eta - ray Thickness control A radioisotope sends radiation throu#h

the sheet material as it comes off the

production line. % and & radiation are

used for thin sheets. A radiation detector

on the other side of the sheet measures

the intensity of the radiation passin#

throu#h the sheet. The detector inform

the machinery to ad'ust the thickness of

the sheet automatically.

,8,

1. The thickness of paper can be checked by putting a radioactive source on one side ofthe paper and a detector on the other side.

(a) Explain why and , sources would not be suitable., 'd

is not suitable because :________________________________

is not suitable because :________________________________

(b) ow would the a!ount of radiation passing through the paper be changedif the thickness of the paper increased"

_____________________________________________________________

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(c) #n such an experi!ent it was found that the nu!ber of counts per !inutevaried even when the thickness of the paper was unchanged. Explain thisobservation.

_____________________________________________________________

_____________________________________________________________

$. #n a paper !ill, paper pulp is s%uee&ed between rollers to for! a paper strip.

The pressure of the rollers is controlled by a signal fro! a radiation detector asshown radiation in the diagra!. ' radioactive source is placed on the paperopposite side of the paper to the detector.uggest how this arrange!ent produces paper of unifor! thickness.

#f the radiation detector displays the sa!e reading that is the expected readingwhen the paper strip passes through the pulp, we conclude that the thickness ofpaper is

_________________.

#f the radiation detector displays higher than the expected reading when the paperstrip passes through the pulp, we conclude that the thickness of paper is

__________________.

#f the radiation detector displays lower than the expected reading when the paperstrip passes through the pulp, we conclude that the thickness of paper is

__________________.

76 The applications of radioisotopes in medical field

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Medical field Examples Reasons

Sterilizing medical

equipment

Radioactive tracer

Cancer treatment

Blood clot

Question

The following table shows the properties of five radioisotopes substances *, + , , -

and

/roperties

0adioactive

alf life 0ays 1 0adiation 2ucleon

nu!ber

0adioactivity

* 34$ years 'lpha 56 $7

+ 89$7 years 'lpha, beta ga!!a $$9 87

9 hours a!!a 55 67

- 6.$; years a!!a 97 $6

86 days


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Agriculture

"#$%&C'EAR E%ER()

"#$#* Atomic Mass &nit +a# m# u ,

8 'to!s are too =======.to be !easured in kilogra! or gra!

$. The !ass of an ato!, nucleus and proton are !easured in atomic mass unit ( a.m.u )

4. 8 a.!.u >

Therefore, 8 a.!.u >

"#$#* %uclear Energ%uclear !ission

8. ?eaning :

$. Exa!ple :235

-2& -1

" n -2

36 Kr +141

56 Ba + 31

" n- energ

Exercise

8. #n a nuclear reaction * $46 is bo!barded by a neutron giving @s A 838, 0b A 54 and $

neutrons and energy is released . Bro! table below , deter!ine the energy released when one

* A $46 ato! undergoes such a nuclear reaction.

0adioactive ele!ent 'to!ic !ass unit, u

* $46 $46.735$

0b A 54 54.5$86;

@s A 838 837.58594

2eutron 8.77C9;

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%uclear !usion

8. ?eaning :

$. Exa!ple :The following e%uation shown a fusion reaction

nHeHH 1

"

4

2

3

1

2

1 ++ - energy

$.78387 u 4.78976 u 3.77$97 u 8.77C9; u

D 8 u > 8.99 x 87 27 kg , c > 4.77 x 87 + ! s 1

hat is the energy produced "

Exercise

8. ydrogen nuclei fuse together in the un. The nucleus of one isotope of hydrogen

contains one proton and has the nuclide notation

1

1 . Fther isotopes of hydrogen have

the nuclide notations2

1 and

3

1.

(a)tate the nu!ber of protons and the nu!ber of neutrons in a nucleus of each of the

two other isotopes of hydrogen.

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(b, 2uclei !ay fuse when they co!e together.

(i)Explain why nuclei do not easily co!e together.

.

ii, Explain why nuclei are able to co!e together in the centre of the un.

.

Chain Reactions

8. ' chain reaction is =a self * sustainin# reaction in hich the products of a reaction

can initiate another similar reaction

$. #n a chain reaction uranium !om!ar!ed !y a neutron.three free neutros !arium and

krypton and a #reat amout of ener#y are produced.

4. The three neutron will bo!bard another three uranium atoms.

%uclear Reactor

8. The !ost co!!on type of nuclear reactor in a nuclear plant is called the pressuri&ed

water reactor ( /0 ).

$. Uranium -2+,is used as nuclear fuel.

4. A lot of heatwill be produced

3. uclear fission can be controlled!y moderators #raphite

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6. uclear reactioncan be controlled by the $oron and admiumas control rod, to

absorb secondary neutron

9. @arbon dioxide or wateris usedas a coolin# a#ent " remo/e the heat of reaction

to make steam for tur!ine #enerator

;. The lead and concrete keep the radiation inside the reactor

.M/0RTA%T 0! /R0/ER MA%A(EME%T 0! RA1.0ACT.2E S&BSTA%CE

i# %egative Effects of Radioactive Su3stances

8. Radioacti/ewastes are considered dan#erouswaste

$. The negative effects of radioactive waste depend on..

a) 0uantity of aste

b) the type of aste

c) the half- life of aste

d) the type of radioacti/e rays emitted

4 Gong half A lives threaten our health

3. 0adioactive waste !ust be kept in a special thick !arrel made of lead or concrete

6. The barrel containing the radioactive waste then !uried in unused mines or nonresidential areas.

ii# Safet /recautions

8.ead is used to block radioactive rays

$. Use distance controller or ton#sto !ove radioactive !aterials

4. The uniformworn by workers in a nuclear plant !ust be kept in special !a#s

3. orker in radioactive energy station !ust wear !ad#esto which the worker have

been eposed to radioacti/e rays can !e determined.

6. uclear reactorshould be build on islands or areas far aay from residents

9.


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Exercise

8.#n a research laboratory using radioactive !aterials, safety precautions have to be

observed.

o!e of the safety precautions adopted by the laboratory are listed below.

Fn the lines after each precaution, state reasons why it is a wise precaution

+a, 0adioactive !aterials should only be picked up using longhandled tools.

0E'F2 :=======================....................................

+3, Bood !ust not be taken where radioactive !aterials are being used.

0E'F2 : Radioacti/e ill threaten our health.

+c, The researchers !ust wash their hands after the source has been put away safely.

0E'F2 :========================......................

+d, 0adioactive !aterials !ust be stored in a locked drawer or cabinet.

0E'F2 :=========================.........................

$.Table 8 and $ shows nuclear fission and nuclear fusion

%uclear fission


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E%uation 2

1 I

3

1

4

2e I

1

" n I Energy

Total ato!ic !ass 6.74784 a.!.u6.78734 a.!.u

T'


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ii) _____________________________________________________________

b) Jisadvantage

i) ___________________________________________________________

ii) _________________________________________________________

1

physics radioactivity form5 2014

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