Half life

Question 1

Similarities between all radioactive decay?

Answer 1

• All radioactive substances decay in the same way
• Follows the same pattern
• Constant probability of decay

Question 2

What does a high probability of decay mean?

Answer 2

Decays very quickly

Question 3

What does a low probability of decay mean?

Answer 3

Decays much slower, remains radioactive for longer

Question 4

What is the unit for radioactive decay?

Answer 4

Becquerel, Bq (1Bq is equal to 1 radioactive decay per second)

Question 5

What is meant by half life?

Answer 5

Half-life is the time it takes for half of the unstable nuclei in a sample to decay or for the activity of the sample to halve or for the count rate to halve.

Question 6

What is the same across all half life graphs?

Answer 6

The shape of the curve will always stay the same.

Question 7

Question
An iridium-192 source had a half life of 74 days and an initial activity of 1200Bq. What will the activity of the iridium source be after 222 days?

Answer 7

Answer
No. of half lives in 222 days - 222/74= 3 half lives
1 half life the activity will be 1200bq/2= 600Bq
2nd half life the activity will be 600/2 = 300Bq
3rd half life activity will be 300/2= 150Bq

Question 8

What properties help with determining uses?

Answer 8

• Half-life
• Penetrating power
• Ionising power

Question 9

2 main uses of radioactivity in medicine?

Answer 9

Radio therapy and radio imaging

Question 10

What can the isotope carbon-14 do?

Answer 10

Date the age of very old dead cells.

Question 11

What is radio-imaging?

Answer 11

The radio active material is injected into the body
Makes its way to investigating area
Emits gamma rays that can be detected outside of the body
Gamma rays cause few issues as they pass straight through and are very weak ionisers.

Question 12

What is radiotherapy?

Answer 12

Radioactive materials used to kill cells (cancerous)
Beta may be used, short ranged and damaging.
Half life is typically a few days, depends on dose required - longer half lives will deliver higher doses.

Question 13

How does carbon dating work?

Answer 13

Carbon 14 is a naturally occurring radioactive isotope of carbon. It emits beta particles with a half life of 5370 years. By measuring the proportion of carbon 14 to the usual isotope carbon 12, organic objects up to 60000 years old can be dated.