The Number ofγ-rays Emitted per Second from Radium B and C in Equilibrium with a Gram of Radium and the Number Emitted per Atom Disintegrating

Number of $\gamma$ rays emitted by RaB and RaC per atom disintegrating.— $\gamma$-rays entering a metal produce $\beta$-ray emissions. By a $\beta$-ray emission is meant the simultaneous emission of one or more $\beta$-rays, initially in the general direction of the exciting $\gamma$-rays. Those $\beta$-ray emissions which passed through the metal window front of a counting chamber were counted, using an automatic registering device previously described. Different thicknesses of various metals were used as fronts. Corrections for scattered $\gamma$-rays and for $\beta$-rays from the walls of the chamber were determined experimentally. A standard 1.305 mg of radium was used, placed between the poles of an electromagnet. The coefficient of absorption of the $\gamma$-rays was determined from corrected counts with different thicknesses of absorbing metal placed between the source and the counting chamber but nearer the source, and the coefficient of absorption of the $\beta$-rays from a determination of the thickness of the metal cover which gave the maximum number of counts. From these coefficients and the geometrical constants, the total number of emissions which would have been produced if all the $\gamma$-rays from RaB and RaC had been absorbed in the metal was determined for Al, Cu, Sn, Pt, and Pb and found the same for all within a mean variation of ±3 per cent, viz. 7.28×${10}^{10}$ per gm Ra per sec. equal, within experimental error, to twice 3.57×${10}^{10}$ which is the number of atoms of each disintegrating per second. Evidently this proves that each radioactive transformation results in the emission of a $\gamma$-ray entity which sooner or later produces a $\beta$-ray emission from a single atom. For the hard $\gamma$-rays, capable of penetrating 1.55 cm of lead, the number of counts, corrected for absorption and scattering, came out 76 per cent of the total. Ionisation experiments, repeated by the author, give about 73 per cent, the smaller figure being due to the smaller relative ionising power of the fast $\beta$-rays. Since $\gamma$-rays are entities, the counts seem to be more significant.