The Specific Charge of Disintegration Electrons from Radium E

Rough preliminary measurements of the ratio $\frac{e}{m}$ for the pure primary beta-particles from radium E and of momentum about 2000 $H\ensuremath{\rho}$ were described in a recent Letter to the Editor. The present article includes a more detailed description of these results as well as of more accurate results obtained with an improved experimental arrangement. In order to ascertain the origin of the side-peaks observed by the former measurements, in the new apparatus the resolving power was increased by doubling the length of the electric condenser, and the scattering was reduced by the use of aluminum for the construction of the condenser. In addition several auxiliary defining slits were inserted at points along the electron path, and all calibrations were rechecked so that the central peak could be located with moderate accuracy. In the preliminary measurements no special attempt had been made toward great accuracy, since the apparatus was designed primarily to distinguish between ordinary Lorentz electrons and the widely differing special type of heavy electrons required by the speculation that the well-known beta-ray paradox might be explained by variations, with velocity, of the rest mass of the electrons created in the nucleus, rather than by the neutrino hypothesis. With the improved apparatus extremely sharp peaks were observed by means of the Geiger counter, showing that the method described in the preceding article offers the possibility of very accurate determinations of the ratio $\frac{e}{m}$. The side-peaks were greatly reduced in height and separation, as compared with those in the preliminary experiments; and with variations in the slits behaved in such a way as to indicate that they are due to scattering from the condenser plates, as previously suspected, or possibly to small nonuniformities in the magnetic field. In any case the latter variations in the side-peaks were found to have no appreciable influence on the position of the central peak, and the side-peaks are therefore of no serious consequence. Further, an analysis along the lines indicated in the preceding article was carried out for the detailed resolution characteristics in this particular case, and it was found that no side-peaks should be expected in the absence of scattering, although second degree equations do occur in the cut-off conditions for the source-condenser system. The central peak was found to be so sharp that it was possible to locate it without difficulty to within $\frac{1}{10}$ percent of the voltage at the peak. In fact, the accuracy in determining the peak voltage was limited, in the present arrangement, rather by fluctuations in the magnetic field and in the battery voltage. Similarly, the absolute determination of $\frac{e}{m}$ was limited rather by the accuracy of calibrations, both electromagnetic and geometrical. In the present arrangement no special aim was made toward accurate absolute results to better than one or two percent, but the method offers the possibility of considerably greater accuracy; and if one requires only relative values of $\frac{e}{m}$, the same accuracy could be obtained without special precautions as to the calibrations. In addition, one is here free from the grave uncertainties (to be discussed in a later article) associated with the possibility of scattering in the Bucherer-Neumann experiments. The final corrected value of $\frac{e}{m}$ was found to be in agreement with the theory of relativity to within 1\textonehalf{} percent, which is well within the limits of experimental error. The above-mentioned speculations as regards the special type of heavy electron are therefore untenable.