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Atomic physics
CORE questions
Core 1
State one safety reason why
(a) radioactive sources should not be touched with bare hands,
..........................................................................................................................................[1]
(b) radioactive sources emitting γ-rays should be stored in lead boxes with thick sides,
..........................................................................................................................................[1]
(c) the radiation symbol should be displayed on the cupboard or drawer in which radioactive materials are kept.
..........................................................................................................................................[1]
Core 2
(a) One nuclide is written as 21084 Po.
(i) Which figure is the proton number (atomic number)? ..................................................
(ii) Which figure is the nucleon number (mass number)? .................................................
(iii) Which figure gives the number of protons in the nucleus? ..........................................
(iv) How can you find the number of neutrons in the nucleus?
[4]
(b) An α-particle can be written as^42 α.
Polonium 21084 Podecays into lead (Pb) by emitting an α-particle.
Complete the nuclear equation below, by writing the correct numbers in the boxes.
21084 Po → Pb + 42 α
[2]
Core 3
This question deals with the decay of a radioactive source. The radioactive source has a count rate of 640 counts / minute at the start of an experiment. This value has been plotted on Fig. 1
Fig. 1
The source has a half-life of 20 minutes.
(a) (i) What would you expect the count rate to be after 20 minutes?
................................ counts / minute
(ii) Plot this value on the graph. [2]
(b) (i) What would you expect the count rate to be after a further 20 minutes (i.e. 40 minutes after the start of the experiment)?
................................ counts / minute
(ii) Plot this value on the graph. [2]
(c) Plot two further points which might be expected if the decay curve were perfect. [1]
(d) Draw a smooth curve through all five points on your graph. [1]
EXTENSION questions
Extension 1
(a) A radioactive source contains an isotope of thorium.
Thorium ( 22890 Th) decays by α-particle emission to radium (Ra). Write an equation to show this decay.
[2]
(b) The radium produced is also radioactive. Fig. 2 shows a laboratory experiment to test for the presence of the radioactive emissions from the thorium source, using a radiation detector. In the laboratory there is a background count of 20 counts / minute.
Fig. 2
The readings are given in the table.
position reading in counts / minute
P 2372
Q 361
State and explain
(i) which radiation could be causing the count at a,
(ii) which radiations could be causing the count at P.
[4]
Extension 1
(c) All three types of radioactive emission cause some ionisation of gases.
(i) Explain what is meant by the term ionisation of gases.
(ii) Suggest a reason why γ-radiation produces very little ionisation.
[3]
Extension 2
(c) Fig. 4 shows a beam of β-particles entering a magnetic field, the direction of which is into the paper.
Fig. 4
On Fig. 4 continue the path of the beam of β-particles as they pass through the magnetic field [2]
Extension 3
Lengths of steel may be joined by welding them together, as illustrated in Fig. 5
Fig. 5
A liquid radioactive source is to be used to test that the welds joining lengths of steel pipe are of equal thickness.
The diameter of the pipes is 120 mm and the pipe wall thickness is 5 mm.
The liquid runs through the pipes whilst a suitable detector moves around the outside of the joints.
(a) With the aid of a labelled diagram, explain how this method detects places where the welds are thinner than 5 mm.
..........................................................................................................................................[3]
Atomic physics – answers
Core 1
(a) to avoid contamination
(b) to prevent radiation getting out
(c) to warn of the presence of radioactive material
Core 2
(a) (i) 84 or bottom one
(ii) 210 or top one
(iii) 84 or bottom one
(iv) 210 – 84 or take bottom from top or take proton number from nucleon number
(b) 206 82
Core 3
(a) (i) 320
(ii) plot must be to within ± ½ small square
(b) (i) 160
(iii) plot must be to within ± ½ small square
(c) points plotted at (60, 80) and (80, 40) ± ½ small square
(d) smooth curve through points by eye
(e) either of last two boxes ticked
(f) randomness or background
Extension 1
(a)^22890 Th → 42 He + 22488 Ra
(b) (i) must be γ because α and β are absorbed by aluminium
(ii) α or β or γ
(c) (i) atoms of gas gain or lose electrons by colliding with particles
(ii) any three from they are photons not particles they have no mass they have no charge they do not have enough energy
Extension 2
(a) AZ X → (^) -^01 e + (^) Z+A 1 Y
(b) (i) some beta absorbed by paper thicker paper, less pass through / lower reading
(ii) no gamma would be absorbed by the paper gamma are less safe
(c) diagram should show a smooth curve towards the bottom of the page
Extension 3
(a) the diagram should show the radioactive liquid on pipe, weld and detector in correct places where the weld is thin the reading rises radiation passes more easily through / is less absorbed by thinner metal
(b) (i) alpha – none passes through steel beta – some passes through steel gamma – most / all passes through steel
(ii) either beta or gamma with a clear reason (alpha absorbed completely)
(c) general shielding / absorbing distance monitoring radiation received
