PH-2112
Half-life
Physics · Secondary 4 · Hard · Half-life
A radioactive source has a count rate of 120 counts/min at 14:00. At 15:00 the count rate has fallen to 30 counts/min. Assuming a constant half-life, what is the half-life of the source? (Ignore background radiation.)
- 15 min
- 20 min
- 30 min
- 60 min
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