Question

A certain source gives 1500 counts/s at time t = 0. Its half-life is 1.5 min.

(a) How many counts per second will it give after 3.0 min?
Bq

(b) How many counts per second will it give after 4.5 min?
Bq

(c) How many counts per second will it give after 6.0 min?
Bq

Answer 1

a)

A_o = initial activity = 1500

A = final activity = ?

t = time taken = 3 min

T = half life period = 1.5 min

Using the equation

A = A_o 2^-t/T_1/2

A = 1500 2^-3/1.5

A = 375 counts/s

B)

A_o = initial activity = 1500

A = final activity = ?

t = time taken = 4.5 min

T = half life period = 1.5 min

Using the equation

A = A_o 2^-t/T_1/2

A = 1500 2^-4.5/1.5

A = 187.5 counts/s

C)

A_o = initial activity = 1500

A = final activity = ?

t = time taken = 6 min

T = half life period = 1.5 min

Using the equation

A = A_o 2^-t/T_1/2

A = 1500 2^-6/1.5

A = 93.75 counts/s