Experimental studies of neutron-induced reactions in light nuclei

University dissertation from Uppsala : Acta Universitatis Upsaliensis

Abstract: Nuclear reactions induced by neutrons in light nuclei at around 100 MeV are studied in this thesis using two detection facilities, MEDLEY and LISA.The measurements were performed at the unique neutron beam line of the The Svedberg Laboratory in Uppsala.The MEDLEY facility has been developed to conduct experiments within, e.g., medical and radiation protection applications, and has been used to measure neutron-induced double-differential light-ion production cross sections. The facility consists of eight three-detector telescopes. The use of δE - δE - E techniques allow good particle identification for p, d, t, 3He and alpha particles over an energy range from a few MeV up to 150 MeV. The facility has been used to measure double differential cross sections of inclusive proton, deuteron and triton production induced by 95 MeV neutrons on carbon. Integrated production cross sections, as well as partial kerma coefficients, have been determined. It is found that the proton kerma coefficient is 35% higher than that of a recent evaluation, leading to a total kerma coefficient that is 25% higher. This supports a trend observed for similar data below 73 MeV. The LISA magnetic spectrometer has been used to perform a measurement of the double-differential cross section for the 9Be(n,p)9Li reaction at 96 MeV in the angular range 0o - 27o and up to about 20 MeV excitation energy. Cross sections for reactions leading to the ground state and the first excited state (2.69 MeV) of 9Li have been analysed and compared with thoseobtained from calculations within the distorted wave Born approximation. A Gamow-Teller (GT) unit cross section for the ground state transition of 7.4 +/- 1.2 mb/sr was determined from the identified GT strength. Discrepancies in the GT unit cross sections for the different (n,p) and (p,n) transitions from the 9Be ground state have been found, resembling the situation for the 13C reaction.The LISA spectrometer has also been used to measure the differential npscattering cross section at 96 and 162 MeV at backward angles (75o - 180o). The angular distributions have been normalized to the experimental total np cross section. Between 150o and 180othe angular distributions are steeper than those of some previous measurements and nucleon-nucleon potential predictions. Values of the charged πNNcoupling constant have been extracted.

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