- The document discusses radioactivity and nuclear processes, providing answers to questions about alpha, beta, and gamma radiation; radioactive decay; nuclear fission and fusion; and nuclear issues. - Sample questions from sections on the discovery of the nucleus, changes in the nucleus, and nuclear fission and fusion are presented along with short answers summarizing key points. - The final section addresses nuclear issues and risks, outlining benefits and drawbacks of nuclear power as well as discussing radon exposure and effective versus counterproductive ways to reduce radiation exposure.

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P7 Radioactivity
Student Book answers
P7.1 Atoms and radiation
Question
number
Answer Marks Guidance
1 a radiation from U consists = particles, radiation from lamp =
electromagnetic waves,
radiation from U is ionising, radiation from lamp is non-ionising
1
1
1 b radioactive atoms have unstable nuclei whereas atoms in lamp filament
do not,
decay of radioactive atom cannot be stopped whereas atoms in lamp
filament stop emitting radiation when
filament current switched off
1
1
2 a i alpha 1
2 a ii beta or gamma 1
2 b gamma 1
3 atoms have unstable nuclei,
these nuclei become stable by emitting radiation
1
1
4 a substance emits (ionising) radiation
so radioactive
1
1
4 b paper stopped most radiation from substance reaching Geiger counter,
paper absorbed radiation,
so must be alpha radiation
1
1
1

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P7 Radioactivity
Student Book answers
P7.2 The discovery of the nucleus
Question
number
Answer Marks Guidance
1 nucleus much smaller than atom,
nucleus positively charged,
mass of atom concentrated in nucleus
all positive charge of atom concentrated in nucleus
1
1
1
1
2 a B 1
2 b A: attracted by nucleus
C: unaffected by nucleus
D: repelled in wrong direction by nucleus
1
1
1
3 a i atoms not indivisible,
atoms contain negatively charged electrons
1
1
3 a ii any two from:
 nuclear: all positive charge concentrated in nucleus much
smaller than atom, plum pudding: positive charge spread out
throughout atom,
 nuclear: most mass concentrated in nucleus, plum pudding:
mass spread out throughout atom
 nuclear: most atom empty space, plum pudding: no empty
space
2
3 b nuclear model explains why some alpha particles scattered through
large angles,
in plum pudding model such large-angle scattering should not be
observed
1
1
4 a similarity: proton and neutron have about same mass (or both found in
nucleus)
difference: proton is charged whereas neutron has no charge
1
1

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P7 Radioactivity
Student Book answers
Question
number
Answer Marks Guidance
4 b He nucleus contains 4 (neutrons + protons) whereas H nucleus only
contains one = a single proton,
2 protons particles in He nucleus because He nucleus has twice as
much charge as H nucleus,
∴other 2 particles in He nucleus are neutrons
1
1
1

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P7 Radioactivity
Student Book answers
P7.3 Changes in the nucleus
Question
number
Answer Marks Guidance
1 a 6 p + 6 n 1
1 b 27 p + 33 n 1
1 c 92 p + 143 n 1
1 d 4 p
10 n
1
1
2 a 92 p + 146 n 1
2 b 90 p + 144 n 2
2 c 91 p + 143 n 2
3 a 
4
2
235
92 
 Th
U 231
90
2
3 b 
0
64
30Zn
Cu 1
64
29 

 2
4 
0
210
84Po
Bi 1
210
83 

 3

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P7 Radioactivity
Student Book answers
P7.4 More about alpha, beta, and gamma radiation
Question
number
Answer Marks Guidance
1 a stops irradiation of nearby people or objects 1
1 b alpha 1
1 c α, β 1
2 a i gamma 1
2 a ii alpha 1
2 a iii beta 1
2 b i gamma 1
2 b ii alpha 1
3 a can knock electrons from atoms,
this ionisation damages cell (or kills cell or affects genes in cell which
can be passed on if
cell generates more cells)
1
1
3 b (place Geiger tube in a holder so it can be moved horizontally,) move
tube so end close to source and Geiger counter detects radiation from
source,
move tube gradually away from source until count rate decreases
significantly,
distance from end of tube to source is range of α radiation from source
1
1
1
4 very little γ radiation absorbed by foil, it would all pass straight through
so thickness of foil would not affect detector reading
1
1

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P7 Radioactivity
Student Book answers
P7.5 Activity and half-life
Question
number
Answer Marks Guidance
1 a average time for no. nuclei in sample of isotope to halve 1
1 b 190 cpm 1
2 a i
4 milligrams (=
8 mg
2 )
1
2 a ii
1 milligram (=
8 mg
23 )
1
2 b 5% of 8 mg = 0.4 mg
so mass < 0.5 mg (=
8 mg
24 ) after 4 half-lives,
time taken ∴ just over 4 half-lives → about 65 hours
1
1
1
3 a i 160 million atoms 1
3 a ii 1
32 (=
1
25 )
1
3 a iii
number remaining =
320 million
25
= 10 million atoms
1
1
3 b
after 4 half-lives, count rate = initial count rate of
320 cpm
24 = < 37.5 cpm
so time taken to drop to 40 cpm from start < 180 minutes (4 half-lives)
1
1
4 after 2 half-lives count rate due to wood = 25% of initial count rate,
∴ the wood is 11 200 years old (= 2 × 5 600 yrs)
1
1

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P7 Radioactivity
Student Book answers
P7.6 Nuclear radiation in medicine
Question
number
Answer Marks Guidance
1 a beta or gamma,
can be detected outside body
1
1
1 b gamma,
radioactive source injected into patient to enter organ to be imaged so
needs to do least damage whilst in body,
gamma radiation passes through body tissue and detected using
gamma camera
1
1
1
2 any two from:
 food,
 drink,
 radon
1
3 a small ‘seeds’ of radioactive isotope placed in tumour,
radiation from isotope destroys cancer cells,
use isotope with half-lives not long enough to damage normal cells
surrounding tumour,
half-life not too short or unstable nuclei decay before radiation destroys
tumour
1
1
1
1
3 b beta or gamma 1
4 a too short: radioactive isotope decays too much before scan completed,
too long: patient exposed to ionising radiation unnecessarily
1
1
4 b too long: after scan radioisotope needs to be stored for a long time until
radioactivity insignificant,
too short: radioactive isotope decays too much before scan completed
1
1

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P7 Radioactivity
Student Book answers
Question
number
Answer Marks Guidance
5 a any three from:
 emits radiation detectable outside body (e.g., gamma),
 non-toxic,
 short half-life (1–24 hours),
 decays into stable isotope
3
5 b stable isotope in body (or elsewhere) not dangerous
whereas unstable isotope harmful
as it emits ionising radiation harmful to body
1
1
1

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P7 Radioactivity
Student Book answers
P7.7 Nuclear fission
Question
number
Answer Marks Guidance
1 a nucleus splits into two fragments,
releases energy and several neutrons
1
1
1 b nucleus absorbs neutron without undergoing fission,
forms unstable nucleus which decays
1
1
2 (in order) B, A, C, D, B 1
3 a to absorb fission neutrons,
and keep chain reaction under control by maintaining even rate of
fission
1
1
3 b more fission neutrons absorbed so number of fission neutrons in reactor
core decreases,
rate of release of energy due to fission ∴ decreases
1
1
3 c thick steel withstands very high temperature and pressure in core,
thick concrete walls absorb ionising radiation
that escapes through steel walls
1
1
1
4 a A and D 1
4 b undergone fission and released neutrons and energy 1
4 c C and E 1

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P7 Radioactivity
Student Book answers
P7.8 Nuclear fusion
Question
number
Answer Marks Guidance
1 a formation of nucleus when two smaller nuclei collide and fuse together 1
1 b forms He
3
2 nucleus (with 2 protons and single neutron) 1
2 a so enough KE to overcome force of repulsion between nuclei so they
fuse
1
2 b energy output < energy input so does not produce any energy overall 1
3 advantages
any two from:
 nuclear fusion fuel easily available
 fusion products non-radioactive (or less radioactive than) fission
products
 fusion stops if plasma out of control,
disadvantages
any two from:
 very large current needed to heat plasma to start fusion
 plasma difficult to control,
 at present, fission reactors produce far more power than fusion
reactors
2
2
4 a 1 p and 1 n 1
4 b He
p
H 3
2
1
1 

2
1
1
4 c p
p
He
He
He 1
1
1
1
4
2
3
2
3
2 


 2

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P7 Radioactivity
Student Book answers
P7.9 Nuclear issues
Question
number
Answer Marks Guidance
1 a i hazardous and ∴ a danger to people and animals if it escapes 1
1 a ii contains radioactive isotopes with long half-lives 1
1 b absorbed by surrounding tissues
and could damage or kill cells in body or cause cancer
outside less dangerous as α radiation has no penetrating power
1
1
1
2 a may be more concentrated than outdoors and people could breathe it
in,
lungs then exposed to α radiation,
ionising effect of α particles in tissue damages cells (or kills cells or
causes cancer)
1
1
1
2 b install pipes under house and pump radon gas out of ground before it
seeps into house,
top of outlet pipe from pump needs to be high up outside house
1
1
3 benefits:
any two from:
 no greenhouse gas emissions,
 reliable and secure electricity supplies,
 large-scale generation from small sites compared with
renewable supplies that take up much larger areas (or other
valid points)
drawbacks:
any two from:
 long-term storage of nuclear waste,
 possible escape of radioactive substances into environment,
 impracticality of fusion reactors, (or other valid points)
2
2

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P7 Radioactivity
Student Book answers
Question
number
Answer Marks Guidance
4 any five from:
 total annual dose ≈2400 units/year so risk of death about 1 in
10 000 /year,
 some such as cosmic radiation unavoidable,
 measures reducing total dose by < 10 units/year (e.g. avoiding
air travel) have negligible effect,
 reducing food and drink unlikely to be effective,
 may be counterproductive due to adverse effects,
 e.g., cutting food intake by more than half only reduces annual
dose by about 3% (∼0.5 ×
140
2400
) so reduce radiation risk very
slightly but would harm human health in most cases,
 could reduce risk from medical X-rays where possible by
restricting use of X-rays and using MRI instead
5