Excitation function shape and neutron spectrum of theLi7(p,n)Be7reaction near threshold

Abstract

The forward-emitted low energy tail of the neutron spectrum generated by the 7 Li(p,n) 7 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 Au(n,γ ) 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.

Li7(p,n)Be7 cross section from threshold to 1960 keV and precise measurement of the Martín-Hernández1, Mastinu2, González3 et al. 2019Phys. Rev. CSelf Cite

“…The 7 Li(p, n) 7 Be reaction is one of the most used nuclear reaction for accelerator-based neutron sources. Low threshold energy and high neutron yield make this reaction favorable for such a purpose.…”

“…We have previously measured the shape of the reaction cross section from threshold up to 10 keV above it [7]. The aim of this work is to deduce the 7 Li(p, n) 7 Be reaction cross section from the measured thick target yield in the proton energy range from threshold up to 80 keV above it.…”

“…The first is related to the cosmological lithium problem. The 7 Be(n, p) 7 Li reaction is responsible for most of the 7 Be destruction in the early Universe. The 7 Li primordial abundance depends on the 7 Be surviving fraction since 7 Be decays to 7 Li by electron capture.…”

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Background: The 7 Li(p, n) 7 Be reaction is one of the most used nuclear reaction for accelerator-based neutron sources. There are few experimental cross section data in the double-value energy region and they are discrepant, as are the reaction yields.

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Passive low energy nuclear recoil detection with color centers -- PALEOCCENE

“…To achieve nuclear recoils below 1 keV, neutrons of around 20 keV are needed. Suitable low-energy neutron sources can be realized by exploiting low-lying anti-resonances in materials like iron [27] or scandium; another choice could be photo-neutron sources [28] or the use of the reaction Li 7 (p,n)Be 7 which results in ∼ 20 keV neutrons [29]. These types of neutron sources are also used in the study of quenching for dark matter experiments to characterize the detector response, see for instance Ref.…”