Physics Question?

Question

The counting rate from a radioactive source is
2600 counts/s at time t = 0, and 4 min later
the rate is 1300 counts/s. What is the half-life of the source? Answer in units of s.

-and-

What is the decay constant? Answer in units
of min^−1

-and-

What is the counting rate after 8 min? An-
swer in units of Bq.

Answer 1

Well, the count rate went down by half in four minutes, so the half-life is...four minutes.

The decay constant is ln ( 2 ) / half-life.

The count after eight minutes (a total of two half-lives from time zero) will be 650 counts per second.