Radioactivity
Nucleus
Electrons
Particle
Relative mass
Relative charge
Proton
1
+1
Neutron
1
0
Electron
almost zero
-1
1)
a) Fill in the labels on the atom. (1 mark)
b) Fill in the table with the correct values. (3 marks)
Isotopes
2
3
1
1
c) Fill in the blanks for the Hydrogen isotopes. (2 marks)
Decay
2) What three types of radioactive decay are there? …Alpha
Beta and Gamma (accept symbols)… (1 mark)
3) Describe each type of decay.
1…Alpha – Helium Nucleus 2 protons and 2 neutrons
2…Beta – 1 electron (released when a neutron turns into a
proton and gives out an electron)
3…Gamma – Electromagnetic ray (releases when an atomic
particle moves down an energy level and gives off energy) (3
marks)
4) Uranium-230 nuclei emit alpha radiation and become nuclei
of thorium (Th).
a) Complete the equation. (2 marks)
U __Th __ He
230
92
__
226
4__
90
2
5) Potassium-40 decays, via Beta emission, to Calcium 40.
Write a balanced equation for this decay. (use the periodic
table on the next page to help.)
40
19
K  Ca  
40
20
0
1
Detecting radiation
The following readings were taken using an unknown source of radiation.
Counts in 300 seconds
Readings
No source present
Average
102
94
110
102
No lead present
3466
3420
3410
3432
Thick lead plate present
105
109
89
101
Aluminium sheet in place of thick lead sheet
1834
1787
1818
1813
Source present at fixed distance from tube
6)
a) Complete the table by calculating the average readings.
b) What equipment would you use to count the emitted
radiation? ………… geiger muller (GM) tube………(1 mark)
c) Why are the readings on each line not the same?
…………Radiation is a random process therefore in a given
time there will almost never be the same count……..(2
marks)
7) What can you say, from the table, about the effect on the
radiation of:
a) The lead plate? …The lead stops all the radiation from the
source and the only radiation that is left is the background
radiation. …..(2 marks)
b) The aluminium plate? ………The aluminium plate stops most
but not all of the radiation. It stops less than the lead plate.(2
marks)
8) Why is it possible to say from the readings that:
a) Gamma radiation is emitted by the source? ……Not all the
radiation from the source is stopped by the aluminium plate.
Both alpha and beta will be stopped by the aluminium plate do
the only radiation left from the source will be gamma...(2
marks)
b) Alpha and beta radiation might be emitted by the source?
…most of the radiation from the source is stopped by the
aluminium which could be both alpha and beta...(2 marks)
9) What further tests could you make to find out whether or not
the source emits alpha radiation? …Try using thinner
aluminium or paper or just increase the distance of the GM
tube from the source. If the count drops then alpha could be
present ………..(2 marks)
10) (a) Uranium-234 (234U) is a radioactive element. The graph
shows the number of protons and
neutrons in the nuclei of the elements formed when uranium-234
decays.
(i) How does the graph show that uranium-234 (234U) and
thorium-230 (230Th) emit alpha
particles?
........ both lose 2 protons and (2) neutrons................ (1 mark)
(ii) What makes uranium and thorium different elements?
............ different number of protons (in the nucleus)(1 mark)
(iii) Radioactive decay may also produce gamma radiation.
Why does the emission of gamma radiation not cause a new
element to be formed?
..... gamma involves no change in the number of protons (in the
nucleus) or
gamma is a wave (not a particle). (1 mark)
(b) The graph shows how the thickness of different materials
needed to absorb 90% of the gamma radiation emitted by a
source depends on the energy of the radiation. The energy of the
gamma radiation is given in units called electron-volts.
(i) Which of the materials shown is least effective at absorbing
gamma radiation? Use the information in the graph to give a
reason for your answer.
. water because for all energy values the thickness of water
needed to absorb (90% of) the radiation is more than the other
materials.. (1 mark)
(ii) For gamma radiation of energy 1.5 million electron-volts, how
many times more effective is steel than water at absorbing the
radiation? Show clearly how you obtain your answer.
.......water thickness = 72cm steel thickness = 12cm
Answer = 6 times (2 marks)
(c) Scientists in the early twentieth century thought that atoms
were made up of electrons scattered inside a ball of positive
charge. This was called the ‘plum-pudding’ model of the atom.
Rutherford and Marsden did an experiment, in which a beam of
alpha particles was aimed at a thin sheet of gold.
Explain how the results of this experiment led to a new model of
the atom. You may include one or more diagrams in your answer.
any three from:
• most (alpha) particles passed undeflected / straight through the
gold
• suggesting most of the atom is empty (space)
• a few (alpha) particles scattered / deflected through (very) large
angles
• suggesting a concentrated / small nucleus
• nucleus is positive because it repels the positive (alpha)
particles
may be scored on annotated diagram provided not negated
elsewhere
accept repelled do not accept reflected / rebound / bounce back
no reference to experiment, maximum 1 mark
....................................................................... (3 marks)
11) (a) When an unstable barium nucleus changes into a
lanthanum nucleus, a beta particle is emitted.
(i) What is a beta particle?
(high energy) electron (1 mark)
(ii) How is the nucleus of a lanthanum atom different from the
nucleus of a barium atom?
..... one less neutron
one more proton (both required for mark)....... (1 mark)
(iii) Describe how a neutral atom may be changed by a collision
with a beta particle.
................... becomes charged / ionised......(1 mark)
(b) The diagram shows how radiation can be used to kill the cells
of a brain tumour.
Why is a beta emitting radioactive source unsuitable for this
purpose?
...... will not pass through the skull / bone......................(1 mark)