find the upper limit. From the discrepancy between the observed ranges and the true ranges for radium E and uranium Xi, we can estimate that the correct range for the potassium beta-rays is 0.55 g/cm 2 . This value, by the use of Feather's 5 range energy equation R = 0.543 X-E -.160, gives 1.3 X10 6 volts as the upper limit of the K 40 beta-ray spectrum.No claims of exactness can be made for this value, but it is clear from the curves that K 40 emits beta-particles of higher energy than does radium E, where the upper limit is known 9-11 to be 1.15X10 6 volts. Another estimate may be made from the absorption coefficients since the absorption curves are exponential over a large part of their length. The absorption coefficients of radium E and uranium X2, and data from other bodies where the upper limits and absorption coefficients are known give a rough ,M/P VS. upper limit curve. From this curve the j*/p-12.8 for potassium yields an upper limit of 1.4 X10 6 volts. The last estimate is valid only if the shape of the potassium spectrum is sensibly the same as that of the other bodies.That the K 40 spectrum is not highly complex is indicated by the low intensity of the gamma-rays emitted. It is felt that the value derived from the corrected range is more reliable and that the best value is 1.3 X10 6 volts with an estimated error of 0.15X10 6 volts.• The former lower values of about 700 kilovolts for the upper limit of K 40 , derived largely from absorption data, are due in part to the fact that corrections were not made for the low activity of the source. Libby and Lee 12 have investigated the K 40 spectrum with a concentric arrangement of source and counter, and an axial magnetic field, and give a value of 725 kilovolts, but state that no effort was made to obtain an accurate value. This type of measurement with a more elaborate system of counters, has been repeated recently by Dzelepow, Kopjave, and Vorobjov, 13 who find a value of 1.35 X10 6 volts. These measurements were done some years ago at Copper AbsorberQueen's University, Kingston, Canada, and I wish to thank Dr. J. A. Gray, F.R.S., for the use of the equipment, and radioactive sources used in the experiment.i E. Konopinski, Rev. Mod.A PRELIMINARY investigation has been made, with coincidence methods, of the radiations from the 14.0hour radioactive Ga 72 . A sample of gallium was activated by exposure to slow neutrons from the cyclotron. The short period activity (20 min.) of Ga 70 was allowed to die out and the longer period activity investigated. The radiation consists of both gamma-and beta-rays.The most energetic gamma-ray was found by measuring the energy of Compton recoil electrons ejected from an aluminum radiator. The recoil electrons were made to pass through two thin-walled counters connected in a coincidence circuit. Thin sheets of aluminum were placed between the counters until the number of coincidences dropped to a small, constant background. The range of the recoil electrons was found to be 1.22 g/cm 2 (including counter wall thickness). From...
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The radiations from Sb m (60 d.) have been measured with the help of coincidence counting methods. The beta-ray absorption curve was measured and analyzed by the method of Bleuler and Zunti. Two groups of electrons were found with end points at 2.24 and 0.51 Mev. Gamma-gamma and beta-gamma coincidences were measured. A plot of the number of betagamma coincidences per recorded beta-particle indicates that the spectrum is complex. Two low energy groups were found with end points at 0.75 and 0.47 Mev.
1049find that the photo-fission cross section of bismuth is at least 10 3 times smaller than the cross section of uranium.It would be interesting to investigate the resonance scattering of photons by the dipole vibration. The value of J*
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