Cobalt-60, which undergoes beta decay, has a half-life of 5.26 yr. How many beta particles are emitted in 190s by a 3.10mg sample of Co-60? What is the activity of the sample in Bq?

Answer 1

k = 0.693/t_1/2
k has units of yr^-1

Convert 3.10 mg sample to moles.
moles = grams/molar mass.

Convert moles to atoms.
# atoms = moles x 6.02E23

rate = k*Number atoms
This will give you the rate in a year (decays per year). Convert to 190 seconds for the number of decays in that time.

Divide by 190 seconds to obtain dps (decays per second). That will be the number of Bq.