Question

1. Cobalt 60 is commonly used as a source in industrial radiography (nondestructive testing of steel products by imaging with gamma radiation). A typical Co source is 100 Curies. Given a half-life of 5.27 years: (a) Calculate the mass of Co needed for a 100 Ci source (Atomic mass = 59.9338 g/mole). (b) If the source is abandoned in a warehouse for 22 years, how many half-lives have elapsed? (c) How much activity remains?

Answer 1

Given: Activity (A) = 100 G source t1/₂ = 5.27 years. solution: Disten This is first order Reaction, so i {dis integration const) = In 2 *1/2 - In2 5:27 - 01315 NA at t=0; a Nai No. of Atoms A=XNA 100 = 0.1315 NA INA = 760 ☺ Mass of cobalt needel = 760 59,9338 6.023 X 1023 - 20 = 7.5626 X10

② No. of half life elapsed after 22 years Mhe In = 4 hay life t & after t=22 years cet No. of remains is Ne Atoms x = 2.303 log Na and dog 10 11 12 1303 = NA Nt = NA Nit 182.303 Ny = 1760 011315X22 2.303 [N+ = 42 Activity after 22 years = Ant I Ata 011315 * 42 = 5.5231