Spectra of the w+He 3 reactions were obtained for monoenergetic neutron fluxes of 0. 95, 2.67, 5.00, 8.07, and 17.5 Mev using a He 3 -filled proportional counter. Analysis of these spectra yielded the ratios to the total cross section of the total elastic, the He 3 (w,^)H 3 , and the He 3 (w,d)D reaction cross sections. Absolute cross sections were obtained by normalization to the known total cross section. Differential elastic-scattering cross sections for neutrons on He 3 were obtained through the relationship between the scattering angle of the neutron and the observed energy of the He 3 recoil in the counter filling. These angular distributions are compared with the theoretical angular distributions as calculated by Bransden, Robertson, and Swan. The present experiment was intended to discriminate between their assumed two special cases for the potential interaction, the symmetrical exchange force and the Serber exchange force. The experimental results favor the Serber exchange force. This experiment also was intended to make possible the analysis of more complex neutron spectra by providing knowledge of w+He 3 reaction cross sections and the spectra obtained when only monoenergetic neutrons are present. A comparison is made of the results of this experiment with cross sections calculated from inverse reactions and direct measurements of other investigators, where such data are available.
A 3He filled proportional counter can be used for neutron detection in the range 100 keV to 8 MeV by using the 3He(n,p)T reaction. The major limitation as a neutron spectrometer is that the 3He recoil distribution, arising from the elastic scattering of the higher energy neutrons present, masks the 3He(n,p)T peaks due to lower energy neutron groups. Since a 3He recoil and a proton of equal energies have difference specific ionizations and, therefore, different ranges in the counter filling, one thus has a means to distinguish between pulses from the 3He(n,p)T and 3He(n,n)3He reactions. For appropriate operating conditions the risetime of the pulses for these two events will be different. By converting this risetime to a pulse height and only accepting pulses with long risetimes [which correspond to protons from the 3He(n,p)T reaction], one has a neutron spectrometer useful in an energy interval between the maximum neutron energy present and that energy for which the proton range equals the range of the maximum energy 3He recoil. Spectra of monoenergetic neutrons obtained with a 3He filled proportional counter and the pulse risetime discrimination are presented to illustrate the energy range over which this detector may be used as a neutron spectrometer. Under typical operating conditions, spectra of the 24Mg(d,n)25Al, 28Si(d,n)29P, 32S(d,n)33Cl reactions were obtained to illustrate the performance of the spectrometer.
A systematic investigation of the opt!mum conditions for the design and operation of a gas scintillation counter has been made. The. gases studied were xenon, krypton, argon, helium, and various gas mixtures.Both a 6~92 and a quartz wmdow K1306 phototube were used with and without quaterphenyl as a wavelength. shifter. Under optimum conditions an energy spread of less than 4o/c is obtainable for the PO.IO a pa~tlcles;o The aJ?flicati?n of the gas scintillation counter as a fast "slow ~eutron detector," using the reactIOn B (n,a)LI, and Its usefulness as a fast fission detector have been examined and discussed.
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