Neutron Spectra from 30-MeV Deuterons on a Thick Beryllium Target. [Cross Sections]. PDF Download

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The neutron spectra produced by bombarding a thick beryllium target with 30-MeV deuterons at the University of California, Davis, cyclotron was measured. These spectra are of interest in studying the effect of neutrons on materials to be used in future fusion reactors. The spectra were inferred from the activation of two sets of detector foils placed at an angle THETA = 0° to the deuteron beam, one immediately behind the beryllium target block, and one 40 mm to the rear. The SAND-II program was used to analyze the foil activation data to obtain the fluence in each of one hundred energy groups. The neutron spectrum (fluence/MeV) close to the target decreases continuously with energy in the range 2 to 30 MeV, while the spectrum 40 mm back has a minimum at about 8 MeV and a peak at about 14 MeV. The contribution from neutrons of energies less than 10 MeV is much greater than that found in previous spectral measurements made at large distances from the target. This difference is attributed to the neutrons which are emitted at large angles from the deuteron beam. These observations show the importance of evaluating the neutron spectrum near the target if samples of materials are to be irradiated in this location.