Radioactivity: Answers

What is an isotope?

Isotopes are atoms of the same elements with the same number of protons but different numbers of neutrons.

Which types of radiation can be deflected by a magnetic field?

Any type of radioactive particle which is charged will be deflected by a magnetic field. Therefore, alpha particles which are positive) and beta particles (which are negative) will be deflected by a magnetic field. Gamma radiation, which has no charge will not be deflected.

Which type of radiation can only be stopped by a thick sheet of concrete?

Gamma radiation, which is the most penetrating, can only be stopped by a thick sheet of lead or concrete.

A sample of uranium with an atomic number of 92 and a mass number of 238 undergoes alpha emission. What is its new atomic number and mass number?

Alpha decay involves the emission of a particle consisting of 2 protons and 2 neutrons. Therefore the atomic number decreases by 2 and the mass number decreases by 4. The new atomic number is 90 and the new mass number is 238. Since the identity of the element changes if its atomic number changes, this means that the uranium is converted into thorium through radioactive decay.

Give three natural and three artificial sources of background radiation.

Three natural sources include: radioactive rocks, plants which have absorbed radioactive nutrients and cosmic rays.

Three artificial sources include: X-rays, nuclear weapons and nuclear power stations.

Explain how you would use a Geiger-Muller tube to calculate the radioactivity of a sample of plutonium.

First you would use the Geiger counter to measure the count rate in the absence of the plutonium in order to identify the levels of background radiation. You would then place the plutonium near to the Geiger counter (following appropriate safety precautions) and measure the count rate. Repeat three times and calculate a mean.

Radioactive half-life: Answers

What does the ‘activity’ of a radioactive source tell us?

The activity of a radioactive source is the number of decays per unit time - in other words, how often it is releasing radioactive particles.

What is meant by the term ‘half life’.

The half life of a radioactive sample is the time taken for half of the nucleus to decay.

Explain how radiation is used in smoke detectors.

Alpha radiation is used in smoke detectors. An alpha emitter releases alpha particles which travel across a gap in and are detected by a detector, which converts the flow of alpha particles into an electric current. If smoke enters the detector, the smoke absorbs the alpha particles which results in a drop in current. As soon as the current is reduced, this triggers activation of the smoke alarm.

Describe the difference between contamination and irradiation.

If a radioactive substance physically touches another object and transfers radioactive material onto it, that object is contaminated. If the radioactive substance is placed near to an object without touching it, the object is irradiated.

Why is ionising radiation harmful to human health?

Radioactive particles can ionise molecules inside our cells (they knock electrons off molecules, forming ions). This causes damage to cells and tissues and can cause DNA to mutate, leading to cancer.