1. Half life Topic – Physics 2a Prior learning Half life- [t ½ ]
Key words
Half life, ionising, dose, absorb, quality factor

2. Intro: half life – [t ½] Topic – Physics 2a
The rate of decay of a radioisotope is measured by its half-life.
The half-life, t 1/2, of a radioisotope is the time that it takes for half of the nuclei in a sample of the radioisotope to decay.
The activity of a sample indicates the number of radioactive decays that are occurring in the sample each second.
Radioactive activity measured in becquerels (Bq) = 1 degradation per second

3. Task 1: Notes -Decay of radioactive isotope
Topic – Physics 2a
Task 1: Notes -Decay of radioactive isotope
Decay follows the mathematical relationship:
Generalised formula = A=Ao(½)(t/t½)
Or A=Ao(½)(n)
Ao = initial numbers of isotopes in a sample or mass of isotope in sample (at start 0)
A = decaying quantity remaining
T= time transpired
T ½ = half life
N – number of half lives gone

4. Task 2:Examples Topic – Physics 2a N= t/t½ N= number of half lives
t= time transpired
Sample X has a half life of 2 hrs, how many half lives will it have in 8 hours?
8/2 = 4 half lives
Sample X has a half life of 12 hrs, how many half lives will it have in 5 days?
120/12 = 10 half lives

5. Tasks Read page 174/175 Heinemann Notes on physics file pg 175
Make a note of some of the applications of radio-isotopes and there half life
Worked example 5.4A and B
How is Carbon 14 used for dating? Pg 177