Question

For a 90 mg Ra-226 sample (T12 = 1,600 years) with an activity of 3.29 x 10 Bq, compute the following. (a) 1 in Bq) Bg (b) the number of atoms in the sample, based on mass considerations atoms (c) the number of atoms in the sample based on its activity atoms

Answer 1

(a) half-life, T_1/2 =1600 years

0.693 0.693 1 = "= (1600 x 8760 X 3600) = 1.3734 = 1.3734 x 10-11 Bq (ans) X=

(b) the atomic weight of Ra = 226

1 mole i.e 226g of Ra has Avogadro's number of atoms i.e No. of atmos in 226 g Ra = 6.023X10²³

No. of atoms in 90mg of Ra-226, N = (6.023X10²³) X ( 90X10^-3 / 226) = 2.3985 X10²⁰ (ans)

(c) activity of 90 mg Ra-226,

dN d = 3.29 x 10°Bq → IN = 3.29 X 10 Bq →1.3734 x 10-11 N = 3.29 x 10°Bq N = 2.3955 x 1020 atoms (ans) 29