Question

Draw the decay scheme of 42 K (Z=19), labeling the energies and probabilities (percentages) for each transition, using the information o f the Table below. The mass difference Δ of 42 K is - 35.02 MeV; the mass difference Δ of 42 C a (Z=20) is - 38.54 MeV.

Type of decay Half-life Major radiations, Energies (MeV), and frequency per disintegration (%)

β- 12.4 hr

β-: 3.52 max (82%), 2.00 max (18%)

: 1.52(18%)

(b) [4 marks] Calculate the activity of a 30 mCi source of 42K after 2.5 days.

Answer 1

a) K 42 is characterised by the emission of several beta particles with different end point energies.

The decay scheme of a radio active subtance is a graphical represention of all the transitions occuring in a decay,and their relationships.where the co-ordinate axis is energy increasing from bottom to top,and the abscissa is the proton number increasing from left to right,the arrows indicates the emitted particles.

194 40 (12.4 hr) +35.02 3.52 (824) Mev - 38.54 Meu 2.00 (18 20 Ca 42 (stable) De cay scheme f De Cay scheme a 19k 42 and 422=20

b) Equation for calculating the activity of a radio active substance is

r= activity rate × 3.700×10^10 10atoms/s/ci

r=30mci × 3.700×10^10 10

=1.11×10^12 10

Therefore, r= 1.11×10^12 10 atoms/s/ci .