A certain sample of a radioactive material decays at the rate of 500 per second at a certain time. The count rate falls to 200 per second after 50 minutes.
(a) What is the decay constant of the sample?
(b) What is its half-life?
Initial Activity = 500
Final activity = 200
a) We know that,
Where,
A= Activity of the substance
A0 = Initial activity
t = time=50 mins
λ = decay constant
so,
b) Half life 
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