The heating effects of thorium and radium product

The heating effect of radium and its decay products has been studied by many experiments, and the observed heatings compared with those calculated from the energy of the alpha, beta and gamma radiations. The most important of these measurements, as far as the α-rays are concerned, are those of Meyer and Hess, Rutherford and Robinson, and Hess. (See Meyer and Schweilder, 'Radioactivität,' 2nd edn., 1927, p. 225.et seq., for a complete list of references.) From the measurements of these authors it appeared that practically the whole of the observed heating could be accounted for by the absorption of the α-, β, and γ-rays. Fresh determinations of the quantities involved in the theoretical heating have, however, thrown doubt upon this conclusion. The chief source of uncertainty to-day in this respect is the value of the number (Z) of alpha particles emitted per second by a gram of radium. The most recent determinations of this quantity are those of Hess and Lawson, § and Geiger and Werner,|| who obtained the values 3.72 X 1010 and 3.40 X 1010 respectively. The former value leads to a calculated heating which agrees within 1 or 2 per cent, with the observed emission, some uncertainty arising here through the difficulty of accurately estimating the fraction of the energy of the beta and gamma rays which is absorbed in any given experimental arrangement. If, on the other hand, Geiger and Werner’s value be correct, it follows that about 10 per cent, of the observed heating must arise through some activity other than that of the known α-, β, and γ-rays.