Alpha, Beta & Gamma Radiation (AQA A Level Physics)

An isotope of thorium which has a nucleon number of 230 and a proton number of 90 undergoes a series of radioactive decays.

Which row shows the nucleon number and proton number of the isotope after the emission of 4 alpha (α) particles and 2 beta-minus (β^–) particles?

	new nucleon number	new proton number
A B C D	214 222 222 214	84 84 82 82

In an experiment to investigate the structure of the atom, alpha particles accelerated to the same speed were fired at gold nuclei.

The diagrams below represent possible paths taken by two alpha particles at two different times and the maximum forces acting on the alpha particles as a result of the electrostatic forces between a gold nucleus, labelled Au, and the alpha particles.

Which diagram best represents the possible paths of the alpha particles and the forces acting on them?

A Geiger counter is placed near a radioactive source and different materials are placed between the source and the Geiger counter.

The results of the tests are shown in the table.

Material	Count rate of Geiger counter / s–1
None	500
Paper	350
Aluminium foil	350
Thick steel	150

What is the radiation emitted by the source?

A	α only
B	α and γ
C	α and β
D	β and γ

A detector and counter are used to measure the count rate from a gamma source.

Which graph shows how the corrected count rate will vary with distance, d, between the source and detector?

The diagram below shows an arrangement used to maintain a constant thickness of sheet paper or steel as it is being rolled. A radioactive source and detector are used to monitor the thickness.

Alpha, beta or gamma sources could be selected for use in such an arrangement.

Which source would be the most suitable in each case?

	Paper	Steel
A B C D	alpha beta alpha beta	beta alpha gamma gamma

Which type of radiation is the most suitable for the following purposes?

	In a smoke detector	As a medical tracer	Monitoring thickness of aluminium foil	Testing for cracks in pipes
A B C D	alpha beta alpha alpha	beta gamma beta gamma	gamma gamma beta beta	alpha gamma alpha gamma

In an α–particle scattering experiment, a student set up the apparatus, as shown in the diagram below, to determine the number n of α–particles incident per unit time on a detector held at various angles θ.

Which of the following graphs best represents the variation of n with θ?

A student detects the counts from a radioactive source using a G–M radiation detector as shown in the diagram. The student places the source at different distances, d, and measures the count rate.

When the detector is placed 0.50 m the source, it receives a mean count rate of 1750 counts per minute. The mean background radiation is measured as 70 counts per minute.

The count rate should not exceed 5000 counts per minute.

What is the smallest distance of d the source can be placed at to avoid exceeding the limit?

A γ ray detector with a cross–sectional area of 5.0 × 10^–3 m² is placed 0.20 m from a source.

A corrected count rate of 1.2 counts s^–1 is recorded. The γ ray detector detects 1 in 100 of the γ photons incident on the facing surface of the detector.

How many photons are produced by the source every second?

Assume the source emits γ rays uniformly in all directions.

Polythene film is made by extruding polythene and drawing it into a long sheet which is wound onto a roll, as shown in the diagram below.

The manufacturer has to carefully choose a radioactive isotope which will effectively remove any electrostatic charge that has built up on the film. The manufacturer also has to consider the point X, Y or Z at which the radioactive isotope should be placed along the assembly line.

Which point should the radioactive be placed at, and which type of radiation should the manufacturer choose to remove excess electrostatic charge?

	Point	Type of radiation
A B C D	X X Y Z	alpha gamma beta alpha

A scientist is working with a sample of potassium-42 which initially has an activity of 2.0 × 10⁷ decays per second. When potassium-42 decays it emits β^– particles and gamma rays.

To determine the dose received by a scientist working with the source the number of gamma ray photons incident on each cm² of the body has to be known.

One in every five of the decaying nuclei produces a gamma ray photon. The scientist is initially working 1.50 m from the source with no shielding.

The scientist returns 12 hours later to find the dose at the same distance has reduced to 7 gamma rays per cm² per second.

At what distance from the source could the scientist now work and receive the same dose of photons per second per cm² as 12 hours earlier?