A sample of pure cobalt-60 has an activity of 8 µCi.

Question

(t1/2 cobalt-60 = 5.26 a)

(a) How many atoms of cobalt-60 are present in the sample?
atoms

(b) What is the mass in grams of the sample?
g

The way I approached part a was to first convert the microCi into Bq (for a value of 296000 Bq). I then tried to find the decay constant, k, by converting 5.26a into seconds (for a value of 16.6E7 s) and using the equation ln2/((16.6E7) and ended up with 4.17E-9 (note: for the t I used more significant values then listed)....

After this I'm not so sure...but I tried using N=-dN/dT= (-2960000/(4.178E-9)= -7.083E12 atoms...which is of course wrong. Can someone redirect me in my way of thinking?

Thanks

Answer 1

I think your next step is Ro=kNo
The activity, Ro, = 296,000 dps
k = 4.178 x 10^-9 sec^-1, solve for No. Check my thinking.