Radioactive Decay Practice Questions

Complete the table to describe the nature of each type of radiation emitted from an unstable nucleus.

Some unstable nuclei emit a positron ($\beta^+$). State what a positron is.

Explain what is meant by background radiation.

Give one source of background radiation that originates from the Earth and one that originates from space.

Give one artificial (man-made) source that contributes to background radiation.

With no source present, the counter records a background count rate of $24$ counts per minute. When a radioactive source is placed near the GM tube, the counter records $186$ counts per minute.

Calculate the count rate due to the source alone.

State the unit of activity of a radioactive isotope.

State what is meant by the half-life of a radioactive isotope.

A sealed source of an isotope has an activity of $480\ \mathrm{Bq}$. The half-life of the isotope is $2$ days.

Calculate the activity of the source after $6$ days.

Explain why the student measured the count rate before putting the source in the holder.

Use the results in the table to deduce which types of radiation are emitted by this source. Explain your answer.

The student repeated each measurement three times and calculated a mean. Explain why this was necessary.

Americium-241 decays by alpha emission to neptunium (Np).

Complete the nuclear equation by giving the mass number and atomic number of the neptunium nuclide.

$$^{241}_{95}\mathrm{Am} \rightarrow \;\mathrm{Np} \;+\; ^{4}_{2}\mathrm{He}$$

Sodium-22 decays by $\beta^+$ emission to neon (Ne).

Complete the nuclear equation by giving the mass number and atomic number of the neon nuclide.

$$^{22}_{11}\mathrm{Na} \rightarrow \;\mathrm{Ne} \;+\; ^{0}_{+1}\mathrm{e}$$

Describe what happens inside the nucleus during $\beta^+$ decay.

After emitting the positron, the neon nucleus also emits a gamma ray.

State the effect of gamma emission on the mass number and the atomic number of a nucleus, and explain why gamma rays are often emitted after alpha or beta decay.

Use Figure 1 to determine the half-life of this isotope. Show clearly on your working how you obtained your answer.

Calculate the activity of the sample $18$ hours after the first measurement.

Give the net decline in the activity of the sample over these $18$ hours as a ratio.

Describe how photographic film is used to detect ionising radiation.

Describe how a GM tube and counter detect and measure radiation.

A GM tube placed close to a source records $1500$ counts in $5$ minutes.

Calculate the mean count rate in counts per second.

Complete the table to show the change in the mass number and the change in the atomic number of a nucleus for each type of emission. The first row has been completed for you.

Describe what happens inside the nucleus during $\beta^-$ decay.

Calculate the number of undecayed sodium-24 nuclei remaining in the sample after $60$ hours.

A student says, "After $15$ hours I can say exactly which nuclei in the sample will have decayed."

Explain why the student is wrong, and explain why the half-life is still useful for predicting how this sample behaves.

The sample can be disposed of as ordinary waste once its activity has fallen below $1\%$ of its original value.

Calculate the minimum time that must pass before the sample can be disposed of. Give your answer in hours.

Alpha radiation and beta-minus radiation are both emitted from unstable nuclei.

Compare alpha radiation and beta-minus radiation in terms of what they are, how strongly they ionise and how well they penetrate materials.