Abstract
The forward-emitted low energy tail of the neutron spectrum generated by the $^{7}\mathrm{Li}(p,n)^{7}\mathrm{Be}$ reaction on a thick target at a proton energy of 1893.6 keV was measured by time-of-flight spectroscopy. The measurement was performed at BELINA (Beam Line for Nuclear Astrophysics) of the Laboratori Nazionali di Legnaro. Using the reaction kinematics and the proton on lithium stopping power the shape of the excitation function is calculated from the measured neutron spectrum. Good agreement with two reported measurements was found. Our data, along with the previous measurements, are well reproduced by the Breit-Wigner single-resonance formula for $s$-wave particles. The differential yield of the reaction is calculated and the widely used neutron spectrum at a proton energy of 1912 keV was reproduced. Possible causes regarding part of the 6.5% discrepancy between the $^{197}\mathrm{Au}(n,\ensuremath{\gamma})$ cross section measured at this energy by Ratynski and Kappeler [Phys. Rev. C 37, 595 (1988)] and the one obtained using the Evaluated Nuclear Data File version B-VII.1 are given.
Highlights
The accelerator-based proton-on-lithium reaction is one of the most frequently used sources for producing neutrons in the keV energy range and is used for various applications and cross section measurements
Renewed attention is paid to this reaction and the neutron spectrum was remeasured by two different groups in different facilities [7,8]
Modelbased spectrum determination considerably differs depending on the cross section used or contradictory results are found when measured neutron spectra are used to derive cross section parameters [11]. In addition to this we have found that the shape of the calculated neutron spectrum is somehow sensitive to the mathematical complications in the solution of the reaction yield
Summary
The accelerator-based proton-on-lithium reaction is one of the most frequently used sources for producing neutrons in the keV energy range and is used for various applications and cross section measurements. High quality Maxwell-Boltzmann neutron spectra for thermal energies of the distribution ranging from 30 to 50 keV are predicted [9] This calculation are carried out by computing the differential yield of the reaction for thick targets which is reigned by the reaction kinematics, the stopping power of protons on Li, and the 7Li(p,n)7Be reaction cross section. In this range the total cross section in the laboratory system is 4π times the zero degree center-of-mass cross section, confirming the isotropic behavior.
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