Q12 of 26 Page 1

Define the activity of a radioactive sample. Write its S.I. unit.

A radioactive sample has activity of 10,000 disintegrations per second (dps) after 20 hours. After next 10 hours its activity reduces to 5,000 dps. Find out its half-life and initial activity.


Activity of a radioactive sample refers to the number of disintegrations per second or the rate of radioactive decay is called activity.


The SI unit is called Becquerel(Bq) which is disintegrations per second.


It is given that after 10 hours, the activity becomes half of its initial activity. Hence, the half-life is 10 hours.


It is given that the activity after 20 hours is 10,000 disintegrations per second. This is the activity after two half-lives ().


Hence,



therefore, initial activity is 40,000 dps.


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