Question
An explosion in a nuclear reactor spread the isotope caesium-137 across a large area.
Ninety years after the explosion, the quantity of caesium-137 present will be 12.55%of its original level.
What is the half-life of caesium-137?
A 11.25 years
B 22.5 years
C 30.0 years
D 45.0 years
Answer/Explanation
Ans: C
Question
A reading is taken every 10 minutes of the number of emissions per second from a radioactive source. The table shows the readings.
time / min | number of emissions per second |
0 | 800 |
10 | 560 |
20 | 400 |
30 | 280 |
40 | 200 |
50 | 140 |
60 | 100 |
What is the half-life of the source?
A 10 min
B 20 min
C 40 min
D 60 min
Answer/Explanation
Ans: B