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of positrons to conversion electrons is 17/1. The L photoelectron spectrum has been observed with a thorium converter.The Compton spectrum produced in a copper radiator has inflection points corresponding to gamma-rays of 3.30=1=0.14 Mev and 2.13±0.12 Mev.It seems plausible to assume that CI 34 decays to S 34 alternatively by three beta-gamma transitions. This is summarized in the following table. The figures involving the low energy gamma-ray are in parentheses because its position in the disintegration scheme is uncertain.T HE first measurements of the coherent scattering cross section for neutrons on deuterium were made by studying the powder diffraction pattern of NaD. 1 These measurements showed the coherent scattering amplitude to have a positive sign and although the accuracy of the cross-section measurements suffered from uncertainty in the sample purity, they definitely indicated that the coherent scattering cross section is smaller than the total scattering cross section and hence that the scattering is spin dependent.Since the time of these early experiments a number of other measurements involving the deuterium scattering amplitudes have been made. Powder diffraction patterns have been obtained at this Laboratory on several deuterium containing compounds; Fermi and Marshall 2 have studied the transmission of neutrons by deuterium gas, and Hurst and Alcock 3 have measured the angular dependence of the scattering by the gas.Compounds studied by the powder technique include heavy ice, 4 TI1D2 and UD 3 , 5 and more recent measurements on NaD and LiD, and in addition, a study by 1 Shull, Wollan, Morton, and Davidson, Phys. Rev. 73, 842 (1948). . 6 Unpublished data by R, E. Rundle and the present authors. Branching Beta-energy ratio ft Gamma-energy Total energy 4.45±0.11 Mev 0.46 1.2X10 7 (0.145±0.003 Mev) (4.6±0.11 Mev) 2.58±0.26Mev 0.28 1.7X10« 2.13±0.12Mev 4.7±0.3Mev 1.3 ±0.2 Mev 0.26 8.9X10* 3.30±0.14 Mev 4.6±0.2 MevThe portion of the Kurie plot due exclusively to the high energy positron component has been examined more extensively in this laboratory. 9 However, using the allowed Fermi function, no evidence of any divergence from linearity was found in the resulting plot. 9 David Green (private communication).Levy and Peterson 6 has been made on ND 4 Br. Most of these compounds have been studied for the primary purpose of determining the hydrogen positions in the respective crystal lattices. Pure compounds have, however, been used in every case and each experiment can be considered as a separate determination of the coherent scattering cross section of deuterium. The recent measurements with NaD and LiD* have, however, been made for this express purpose and these compounds have the advantage over the more complex compounds in that the determination of the cross section is not tied in with a simultaneous crystallographic study of the hydrogen atom locations. Only the recent measurements on NaD will be discussed in detail; the large absorption by Li makes the LiD results less significant. Samples were...

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