FIG. 3. Kurie plot for Lis.just below the end point of 1.202 ±0.005 Mev to about 0.2-Mev kinetic energy, comparing well with the recent work of Cook, Langer, Price and Sampson. 4 No electrons were observed above the end point except for a slight tailing due to the instrument resolution of 2.6 percent.The momentum distributions obtained for B 12 and Li 8 are shown in Fig. 1. The possibility of scattering from the copper foil was checked by evaporating a thin lithium metal deposit on a 0.2-mg/cm 2 beryllium foil and running the low momentum end of the Li 8 spectrum again. No noticeable difference was found down to the lowest momentum plotted in Fig. 1. Figure 2 shows the Kurie plot for the B 12 spectrum. A straight line fits the higher energy end of the spectrum quite well from a total electron energy of 12moc 2 nearly to the end point of 27.30moc 2 (13.43±0.06-Mev kinetic energy). This determination of the end point is in good agreement with the value 13.3±0.5 Mev obtained by Hereford 5 using an absorption method. The slight tail just at the high energy end of the spectrum can almost entirely be accounted for by the instrument resolution. The deviation of the plot from a straight line below a total energy of I2mac 2 is very marked.The Kurie plot for the spectrum of Li 8 is shown in Fig. 3. It will be seen that there is difficulty in passing a straight line through even a small portion of the spectrum. The deviation from linearity at the high energy end is much more pronounced than for the B 12 spectrum and cannot be ascribed to the instrumental resolution. The extrapolation of the best straight line fit to the spectrum gives an end point of «25.8mo£ 2 («12.7-Mev kinetic energy). Since the available energy in the decay of Li 8 is 15.98 Mev, this result is consistent with the alpha-particle data and indicates that few, if any, transitions occur to the ground state. A more detailed analysis is necessary to determine more accurately the location and width of the excited state in Be 8 and in particular a matching of the /3-decay spectrum with the spectrum of the alpha-particles should now be possible. Work on these points is now in progress. W ITH the experimental equipment already described in a previous letter, 1 other measurements of the positive excess of the penetrating component have been taken. Five flights were made at 5000 m and eight at 7300 m. During the latter, both in the climbing and in the descending flights, a control count was taken at 5000 m. The duration of the flights covered 7| hours at 5000 m and the same for the flights at 7300 m. The coincidence resolving time during the flights at 5000 m was 20 /usee.
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