(1) A peak due to the recoiled 4 He nuclei with recoil angle ylab ¼ 01, when all of their energy is deposited within the sensitive volume of the detector. These nuclei produce the peaks appearing in Fig. 4a. The maximum energy, Emax, transferred to the recoiling 4He nucleus traveling in the direction of the incoming neutron, is En(4mM)/(m+M)2 ¼ 0.64En where En is neutron energy, M and m are the masses of 4He and neutron, respectively. A fitting procedure was applied to these peaks in order to calculate the centroid channel and the FWHM value.
(2) 4He recoil nuclei that deposit part of their energies within the detector volume and the rest in the detector wall (the wall effect). These recoils can have a continuum of all possible energies up to Emax.
(3) Recoil nuclei of the other gases (C,O) present in the detector volume.