Half-life and activity

Question 1

What can be noted about the decay of nuclei (timing)

Answer 1

• We cannot predict when a radioactive isotope would decay as it is completely random

Question 2

What is the activity of a radioactive substance

Answer 2

• The overall rate of decay of all of the isotopes in a sample
• The number of decays per second in a sample

Question 3

What is the half-life of a radioactive substance

Answer 3

• The amount of time taken or the number of radioactivve nuclei in a sample to halve

Question 4

What happens to the activity of a substance as the number of unstable nuclei decreases and why

Answer 4

• The activity of the substance will also decrease
• This is not because the nuclei are decaying more slowly
• This is because there are less overall nuclei to decay

Question 5

What is radioactive activity measured in

Answer 5

• Becquerels
• 1 becquerel = 1 decay per second

Question 6

What is radioactivity measured using

Answer 6

• Geiger counter
• Records decays per second

Question 7

What is the corrected count rate of a geiger counter

Answer 7

• Corrected count rate = count rate - background count
• Measure background count with no source present