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Description
A high-and-flat efficiency moderated neutron detection array has been recently developed for photoneutron cross section measurements at the future ELI-NP gamma-ray beam source. It is composed of three concentric rings of 4, 8 and 16 $^3$He proportional counters embedded in a high density polyethylene block and has a ~37% efficiency flat within 5% in the 10 keV to 5 MeV neutron energy interval. We performed a commissioning experiment using proton beams delivered by the 9 MV Tandem accelerator of IFIN-HH. We measured the neutron production cross sections for proton induced reactions on $^{nat}$Cu and $^{27}$Al. During irradiations, the proton beam current was continuously monitored using four charge integrator units coupled to the electrically insulated Faraday cup, collimator, reaction chamber and target. The charge collection was validated against separate activation measurements on $^{nat}$Cu.
The (p,xn) reactions on $^{nat}$Cu were investigated in the 4.5 MeV to 14 MeV proton energy range with 250 keV steps. The low energy measurements below 10 MeV served to validate the detection efficiency calibration against well-known $^{nat}$Cu(p,n) cross sections. The measurements above the $^{65}$Cu(p,2n) reaction threshold at 10 MeV were performed in both continuous and pulsed proton beam conditions. Neutron multiplicity sorting techniques were applied to the pulsed beam data in order to extract the $^{nat}$Cu(p,n) and $^{nat}$Cu(p,2n) components, where only the $^{65}$Cu isotope contributed to the (p,2n) channel. Using ring-ratio information, the average total kinetic energies of neutrons emitted in the $^{nat}$Cu(p,xn) reactions have also been determined for the entire investigated energy range.
The $^{27}$Al(p,n) reaction was investigated in the 5.8 MeV to 6.75 MeV energy range with 5 keV steps. Our measured cross sections reproduce the resonant structures previously observed also by Sekharan [1] and Bubb [2]. The new cross sections are in good agreement with the ones reported by Sekharan [1], which are systematically higher than the results of Bubb [2].
We here present the new experimental results for the $^{nat}$Cu(p,xn) and $^{27}$Al(p,n) measurements in comparison with preceding data. The $^{nat}$Cu(p,xn) reactions cross sections and average energies of the neutron emission spectra are compared to statistical model calculations.
[1] K.K.Sekharan et al., Nuclear Instruments and Methods 133, 253 – 257 (1976).
[2] I.F. Bubb et al., Nuclear Physics 65, 656 – 661 (1965).
