Unit 2.8 - Half-life

Question 1

What is meant by the term half-life?

Answer 1

The time it takes for the number of radioactive nuclei in a radioactive sample to halve (or the time taken for the count rate of a sample containing a radioactive isotope to halve)

Question 2

How can the random nature of nuclear decay be modelled?

Answer 2

Using a constant probability of ‘decay’ (e.g. a large collection of coins, dice, or a suitably programmed spreadsheet)

Question 3

What is the most common use of knowledge of half lives (on our spec)?

Answer 3

Carbon dating - organisms take in carbon-14 while alive, but do not when dead, so the amount of carbon-14 in a fossil or bone can be used to determine its age

Question 4

What is the most common use of beta radiation?

Answer 4

Measuring paper thickness (by how much beta radiation is received at the detector) and using this measurement to control paper thickness as it is produced

Question 5

What is the most common use of alpha radiation?

Answer 5

Smoke alarms - alpha radiation ionises the air and allows a small current to flow between two electrodes; alpha radiation is blocked by smoke, current falls and alarm goes off

Question 6

Name some common uses of gamma radiation

Answer 6

Can be used to kill microbes and kill the bacteria on food to keep it fresh for longer; as a radioactive tracer in blood or other liquids to check they are flowing properly (Gamma source injected into blood; arterial blockage causes a radioactive build-up which can be detected from outside the body)