Radioactive decay & nuclear radiation

Two students, A and B, used a cobalt‑60 source to investigate the inverse square law for a gamma radiation source. Cobalt‑60 is a pure gamma emitter.

The cobalt‑60 source was placed in a source holder. A Geiger‑Müller (GM) tube was connected to a counter and placed a short distance d away.

Student A set up the apparatus as shown.

Student B used the same distance d but rotated the GM tube by 90°, as shown below.

Both students recorded the count for 2 minutes.

Deduce which set‑up will lead to a smaller percentage uncertainty in the count rate.

Explain two modifications to the experimental method which would improve the accuracy of the data.

Student A suggests that the investigation into the inverse square law for a gamma radiation source could be carried out successfully using a radium‑226 source.

Radium‑226 emits alpha and beta radiation as well as gamma radiation.

Explain one modification that would be necessary if a radium‑226 source were to be used.

Nuclear decay is described as being spontaneous and random.

State what is meant by spontaneous and random in this context.

Explain why the decay constant of an isotope can be determined even though nuclear decay is random.

A radioactive source used in a school laboratory emits alpha and beta radiation.

Describe how the percentage of the activity due to beta radiation may be determined using a Geiger–Müller tube and ratemeter.

Americium‑241 is used in schools as a source of alpha radiation. A pure americium‑241 source was bought 34 years ago by a school.

Determine the percentage of the initial activity that would be expected today for the americium‑241 source.

half-life of americium-241 = 432 years

The decay products of americium are unstable and undergo a series of further decays.

The table shows the first three decays in this sequence.

A student states, “Protactinium‑233 emits beta particles when it decays, so by now the americium‑241 source bought 34 years ago will be emitting a significant amount of beta radiation.”

Discuss the student’s statement.

Radon is a radioactive gas. One isotope of radon,²²⁰₈₆Rn, decays to polonium, Po, by emitting an alpha particle.

Complete the nuclear equation for the decay of radon.

Radon is produced in the ground and escapes into the atmosphere.

Explain why this is a safety hazard.

The diagram shows apparatus for monitoring the decay of radon in the laboratory. Radon gas is produced in the plastic bottle from the decay of radium. A small amount of radon is then inserted into the decay chamber by squeezing the plastic bottle. A current is produced between two electrodes inside the chamber. This current is amplified and recorded by the ammeter.

Explain why a current is produced in the decay chamber.

A teacher is demonstrating the operation of the decay chamber to her class. She squeezes the bottle to introduce radon into the chamber.

She claims that within 450 s the activity of the radon in the chamber will be less than 1% of its initial value.

Assess whether her claim is correct.

half-life of radon = 55.6 s

A radioactivity monitoring badge is worn by people who might be exposed to radiation. The badge is made from photographic film wrapped in thin paper and then held in a plastic holder that has an open window and a lead window, as shown.

The film gets darker when exposed to ionising radiation.

Which of the following represents the film after the badge is exposed to beta radiation?

A student used a Geiger-Müller (GM) tube to determine a value for the background count. He recorded the count for 2 minutes, every 15 minutes, as shown in the table.

The counts are not the same.

Which of the following is the reason for this?

A teacher demonstrated the decay of protactinium using a Geiger-Müller (GM) tube connected to a data logger.

A sealed plastic bottle contains a solvent floating above a liquid containing a uranium salt. Protactinium is produced from the decay of uranium and is present in the solvent as shown.

Deduce whether alpha radiation or beta radiation from the inside of the bottle is detected by the GM tube.

The data logger output is shown below.

Determine the half-life of the protactinium.

Explain why the count rate doesn’t reach zero.

The photograph shows a vase made of uranium glass. Uranium glass is radioactive.

Uranium glass usually contains a maximum of 2% uranium. Uranium glass made in the early part of the 20th century can contain up to 25% uranium.

A student carried out an investigation to determine the percentage of uranium in the glass.

The student measured the count rate by placing a Geiger Muller (GM) tube against the vase at a single position. This value was used to calculate the decay rate for the whole vase.

Show that the decay constant for uranium is about 5 10⁻¹⁸s⁻¹

half-life of uranium = 1.41 10¹⁷s

Calculate the percentage of uranium, by mass, in the glass.

area of GM tube window = 6.36 10⁻⁵m² surface area of vase = 0.0177 m² background count rate = 525 counts in 10 minutes count rate when GM tube next to vase = 3623 counts in 5 minutes mass of vase = 149 g mass of uranium atom = 238 u

The uranium decays by emitting alpha particles.

Criticise the method used to determine the percentage of uranium in the vase.

A uranium nucleus decays to thorium by emission of an alpha particle.

It can be assumed that all the energy of the decay is transferred to kinetic energy of the alpha particle.

Calculate the speed of the emitted alpha particle.

mass of uranium nucleus = 238.0003 u mass of thorium nucleus = 233.9942 u mass of alpha particle = 4.0015 u

A student used a Geiger-Müller (GM) tube to determine the activity of a radium source. Radium emits α, β, and γ radiation.

He positioned the source 20 cm from the GM tube, as shown, and recorded the count for 1 minute. He repeated the measurement and calculated a mean count.

The student recorded the following results.

Criticise the student’s method for determining the count at this position.

From his results the student determined that the activity of the source was 3.0 Bq.

Comment on his value for the activity of the source.

Radioactive decay is often described in textbooks as a spontaneous, random process.

State what is meant by spontaneous decay.

*(b) Explain why there is an exponential decrease in the rate of decay for a sample containing a large number of unstable nuclei.

*4 Radium is a radioactive element. The most common isotope of radium has a half-life of almost two thousand years. A sample of radium can remain at a higher temperature than its surroundings for a long period of time.

Explain how a sample of radium is able to release significant amounts of energy over a long period of time.

*4 Radium is a radioactive element. The most common isotope of radium has a half-life of almost two thousand years. A sample of radium can remain at a higher temperature than its surroundings for a long period of time.

Explain how a sample of radium is able to release significant amounts of energy over a long period of time.

A student investigated the way in which gamma radiation spreads out from a source. He placed a cobalt-60 source in a source holder and set up a Geiger-Müller (GM) tube a short distance d away. He connected the GM tube to a counter as shown.

The student recorded the count for 2 minutes.

Describe how to determine the corrected count rate from the source.

His teacher turned the GM tube through 90° so that the side of the tube faced the source as shown below.

Explain why this arrangement could lead to more accurate data.

Explain another modification to the experimental method which would improve the accuracy of the data.

The variation in the intensity of gamma radiation with distance from a point source should obey an inverse square law. If this is the case, then the count rate C should vary with d according to the equation

where K is a constant. The student plotted against d and obtained the following graph.

Draw a line of best fit on the graph.

The student concluded that the graph was consistent with the gamma radiation intensity obeying an inverse square law.

Discuss the extent to which the data obtained supports the student’s conclusion.

It is suggested that the investigation into the way in which gamma radiation spreads out from a source, using the apparatus as shown in (b), could be carried out successfully using a radium-226 source.

Radium-226 emits α, β and γ radiation.

Justify this suggestion.