Atoms and Nuclear Radiation - Paper 1

Question 1

Define radioactive decay

Answer 1

Radioactive decay is when an unstable atomic nucleus gives out radiation as it changes to become more stable.

Question 2

Define activity

Answer 2

Activity is the rate at which a source of unstable nuclei decays, measured in becquerels (Bq).

Question 3

Define count-rate

Answer 3

Count-rate is the number of decays measured each second by a detector (e.g. Geiger-Muller tube).

Question 4

List the possible nuclear radiation emitted in radioactive decay.

Answer 4

• Alpha particle - identical to helium nucleus.
• Beta particle - high speed electron ejected from the nucleus as a neutron turns into a proton.
• Gamma ray - electromagnetic radiation from the nucleus.
• Neutron

Question 5

Compare the penetration through materials, range in air and ionising power of alpha, beta and gamma radiation.

Answer 5

• Alpha - stopped by skin/paper - less than 5cm range in air - high ionising power
• Beta - stopped by 3mm aluminium foil - about a metre range in air - low ionising power
• Gamma - stopped by lead/concrete - more than a kilometre range in air - very low ionising power

Question 6

Define half-life

Answer 6

The half-life of a radioactive isotope is the time it takes for the number of nuclei of the isotope in a sample to halve, or the time it takes for the count-rate (or activity) from a sample containing the isotope to fall to half its initial level.

Question 7

Define radioactive contamination

Answer 7

Radioactive contamination is the unwanted presence of materials containing radioactive atoms on other materials.

Question 8

Define irradiation

Answer 8

Irradiation is the process of exposing an object to nuclear radiation - it does not become radioactive.