Problem 6.240

Evaluate the amount of heat produced during a day by a $\beta$ -active $\mathrm{Na}^{24}$ preparation of mass $m=1.0 \mathrm{mg} .$ The beta-particles are assumed to possess an average kinetic energy equal to $1 / 3$ of the highest possible energy of the given decay. The half-life of $\mathrm{Na}^{24}$ is $T=15$ hours.