half life Flashcards
What is radiation measured with
Geiger-Muller tube and counter which records the count rate
What is Count rate
The number of radiation counts reaching per second
What is half life
The time it takes for the amount of radiation emitted by the source to half
What can half life be used for
To make predictions about radioactive sources even though their decays are under
What is activity measured in
becquerels (Bq)
What does the radioactive source do overtime
It decreases
What happens when a radioactive nucleus decays
Each time a radioactive nucleus decays to become a stable nucleus that activity will decrease
How long does it take for some isotopes to decay
For some isotopes it takes just a few hours before all the unstable nuclei have decayed whilst others take millions of years
What is the problem with trying to measure the decay
The activity never reaches 0 which is why you have to use the idea of half life to measure how quickly the activity drops off
What can a half life also be described as
The time taken for activity to fall to half of its initial value
What are the steps to calculate half life
Find activity after each half life
Divide the final activity by the initial activity then multiplied by 100 to make a percentage
The initial activity of a sample is 640 Bq. Calculate the final activity as a percentage of the initial activity after 2 half lives
640/2=320
320/2=160
(160/640) x 100 = 0.25 x 100 = 25%
