Topic 5.3: Radioactive Decay Questions

A radioactive isotope has a half-life of 4.0 days.

A sample starts with an activity of 2.4 × 10⁸ Bq.

Determine the activity of the sample after 16 days.

Radium-224 (${}_{88}^{224}$Ra) decays by alpha emission to radon.

Identify the proton number and the nucleon number of the radon daughter nuclide.

State the two quantities that are conserved when a nuclear decay equation is balanced.

A radiation is found to travel at almost the speed of light and is deflected by a magnetic field in the direction expected for a negative charge.

Identify the type of radiation and state one further property that distinguishes it from gamma radiation.

State what an alpha particle is in terms of its constituent particles, and give its charge.

State what is meant by the activity of a radioactive source, and state its SI unit.

State what is meant by the *mass defect* of a nuclear decay.

A sample of magnesium-27 (${}_{12}^{27}$Mg) is a beta-minus emitter.

A stationary nucleus emits an alpha particle (mass 4 u) and recoils as a daughter nucleus (mass 234 u).

The total energy released is 4.80 MeV.

Estimate the kinetic energy of the alpha particle, in MeV.

Outline how a beam containing alpha, beta-minus and gamma radiation could be separated, and describe how each radiation behaves, when the beam is passed through a uniform magnetic field directed into the page.

A nucleus at rest undergoes alpha decay.

The atomic masses are: parent = 238.050790 u, daughter = 234.043600 u, alpha = 4.002600 u.

Show that the energy released in the decay is about 4 MeV.

(1 u = 931.5 MeV c⁻².)

A decay has a mass defect of 0.004500 u.

Determine the energy released, in joules.

(1 u = 1.661 × 10⁻²⁷ kg, c = 3.00 × 10⁸ m s⁻¹.)

Two sources M and N have the same half-life.

The activity of M is presently 6 times the activity of N.

Deduce the ratio of the activity of M to the activity of N after four half-lives have passed.

Thorium-234 (${}_{90}^{234}$Th) emits a beta-minus particle, and the nuclide formed then emits a second beta-minus particle.

Determine the proton number and the neutron number of the FINAL nuclide.

Explain why, when a stationary nucleus decays into two products, the lighter product carries the larger share of the released energy.

A worker handling a sealed radioactive source is told that, of the three types of radiation, gamma poses the greatest hazard from outside the body but alpha poses the greatest hazard if the source material is inhaled.

Explain this apparent contradiction.

A Geiger counter placed next to a fresh radioactive source records a count rate of 410 counts per second.

When the source is removed, the counter still records 10 counts per second from background radiation.

The source has a half-life of 15 minutes.

A nucleus of radium-226, ²²⁶₈₈Ra, first emits an alpha particle.

The nuclide produced then emits a beta-minus (β⁻) particle.

What are the numbers of protons and neutrons in the final nuclide?

A research lab compares a gamma (γ) source with a beta-minus (β⁻) source. A technician writes three statements comparing the γ radiation with the β⁻ radiation:

I. The γ radiation travels faster than the β⁻ radiation in a vacuum.
II. The γ radiation is more penetrating than the β⁻ radiation.
III. The γ radiation is more strongly ionizing than the β⁻ radiation.

Which of the statements are correct?

A student tests an unknown radioactive source.

A sheet of paper placed in front of it does not change the count rate, but a 3 mm aluminium plate reduces the count rate almost to the background level.

When the radiation passes between two charged plates, it is deflected.

Identify the type of radiation and justify your answer using all three observations.