Carbon (Z = 6) with mass number 11 decays to boron (Z = 5).
(a) Is it is β+-decay or a β–-decay?
(b) The half-life of the decay scheme is 20.3 minutes. How much time will elapse before a mixture of 90% carbon-11 and 10% boron-11 (by the number of atoms) converts itself into a mixture of 10% carbon-11 and 90% boron-11?
Given, 6C decays to 5B.
(a) 116C → 115B + β+
So, it is β+ decay.
(b) t1/2 = 20.3 min.
λ = min-1
Ci = 0.9C˳, Cf = 0.1C˳
So,
⇒
Taking loge both sides, we get
⇒
∴
So,