Question

10. Find the activity in Ci of 1g of Si 27 14 . What is the activity after 10 min?

Answer Should be : 9.94x10^10 Ci, and 10^-32 Ci according to prof.

Answer 1

Half-life of Si-24 is 140ms

so, the decay constant will be:

and 1 molecule of Si-24 weighs 24 x 1.67 x 10^-27 kg

so, the number of molecules in 1g of Si-24 will be:

Activity in Bq is then:

convert this into Ci to get the final answer.

For the 2nd part, use:

where t = 10 mins = 600 s and N_o = 2.495 x 10²².

substitute the decay constant to get new N and then obtain the new activity.