The half-life of a radioisotope is 10 h. Find the total number of disintegrations in the tenth hour measured from a time when the activity was 1 Ci.

We know that,



Where,


A= Activity of the substance


A0 = Initial activity


t = time


λ = decay constant


Given,


Half-life = 10h, A0=1 Ci


Activity after 9 hours


= 0.536 Ci


Number of atoms left after 9 hours




Activity after 10 hours = 0.5 Ci [As 10h is half-life]


Number of atoms left after 10 hours




Hence, net disintegrations at the 10th hour = (1.03×1015-9.60×1014)


= 6.92×1013 atoms


1