12. Calculate the activity in mCi and MBq of In-113 produced by irradiation of 1 g of pure Cd-111 for 3 hr with 12 MeV protons having a beam intensity of 1x10 13 particles/(cm 2 -sec). The cross section for formation of In-111 (T = 2.8 d) is 200 millibarns ( 1 mb = 1x10 -27 cm 2 ). Recall 1 mCi = 37 MBq
12. Number of In-111 produced in 3 Hr is given by:
where, n is particles incedent per second per unit area, n = 1 x 1013 /cm2s
ns is number of source particles , ie. (1/111)x 6.022 x 1023 = 5.425 x 1021
sigma is crossection of formation = 200 x 10-3 x 10-24 cm2 (given incorrect in statement)
t is time of irradiation. t = 3 x 60 x 60 s = 10800 s
hence, number of In-2.8 atoms:
Half life of In-111 T1/2 = 2.8 days = 2.8 x 24 x 60 x 60 s
T1/2 = 241920 s
As radioactivity constant is given by:
/s
As initial activity is
Hence, we can write as:
and
as required
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