Answers to end-of-chapter questions
Chapter 23
1
Radiation
2
Symbol
Type of particle or
electromagnetic radiation
Mass
alpha
α
2 protons + 2 neutrons (He nucleus)
beta
β
electron
gamma
γ
electromagnetic radiation
Charge
1
+2
small
−1
0
0
radiation in the environment
background
detectors of ionising radiation
Geiger counter, photographic film
three types of ionising radiation from radioactive
substances
alpha, beta, gamma
3 a it has negative charge
b charged; Fleming’s left-hand rule
c it is uncharged
4
Radiation
Penetration
Absorption
Absorbed by
alpha
least penetrating
most easily absorbed
thin paper, a few cm of air
beta
in between
in between
thin metal foil
gamma
most penetrating
least easily absorbed
thick lead or concrete
5 a (average) time, half, decay
b See Figure 23.10a.
6
Use
… because …
Finding the age of an object
radioactive substances decay at a known rate.
Seeing through solid objects
radiation can penetrate matter.
Sterilising medical equipment
radiation can destroy living cells.
Tracing the movement of hazardous
substances
small amounts of radiation can be detected.
© Cambridge University Press 2014 IGCSE Physics
Answers to end-of-chapter questions: Chapter 23
1
7 β is more penetrating than α.
[1]
[1]
Detect using Geiger counter.
Place thin paper over sources − α does
not pass through.
Place thin aluminium foil over
sources − neither passes through.
[1]
[1]
8 a 15
[1]
[1]
counts per minute
b 65 − 15
= 50 counts per minute
c
[1]
[1]
Count rate /
counts per minute
65
40
11 a i background
or any of the following:
contaminated surfaces
other radioactive material nearby
radiation from rocks/soil
cosmic rays/radiation from space
radon gas from ground
ii count rate = 136
4
= 34 counts/min
b i alpha or α
ii 876
4
− 34
= 185 counts/min
12 a i proton
15
0 half- 2
4
6
Time / hours
life
8
correct graph drawn
After one half-life, the measured
count rate will be down to 25 + 15 = 40
Reading across from 40 on the graph,
and then down, half-life = 1.3 h
approximately.
9 a The formation of an ion
by the removal of one or more
electrons from an atom.
b X-rays
10 a (for example) A patient with cancer is
exposed to γ-radiation.
This damages the cancerous cells,
which then die.
b (for example) During the manufacture
of cardboard, β-radiation is passed
through the card.
If the card is too thick (too thin),
the amount of radiation detected will be
too low (too high).
The machinery is automatically
adjusted to give the correct thickness.
© Cambridge University Press 2014 IGCSE Physics
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ii proton and neutron
0
[1]
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b number of protons = 47
number of neutrons = 107 − 47 = 60
[1]
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c i 8 h ± 0.25 h
[1]
ii Choose two points on the graph; for
each, halve the value and add 8 h to
the time.
[2]
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Answers to end-of-chapter questions: Chapter 23
2