Performance of the neutron polarimeter NPOL2 for (p,n) polarization transfer measurements

A high performance neutron polarimeter NPOL2 has been constructed to measure polarization transfer observables Dij for neutron kinetic energies of Tn = 150–400 MeV. The NPOL2 system consists of 6 planes of two-dimensional position-sensitive neutron detectors with a size of 1 × 1 × 0.1 m3. Neutron polarization is determined from the azimuthal distribution of the elastic n + p scattering in the scintillator material. The effective analyzing powers (Ay;eff) of NPOL2 have been calibrated by using the polarized neutrons from the 0° 2H(p,n)pp reaction at Tp = 146, 228, 296, 346 and 392 MeV as well as by using the polarized neutrons from the 0° 6Li(p,n)6Be(g.s.) reaction at Tp = 228 MeV. The Ay;eff values of NPOL2 have reasonable values, typically 0.223 ± 0.012 and 0.132 ± 0.004 for (n,n) and (n,p) channels, respectively, at Tn = 291 MeV. The figure-of-merit value defined as εD.S.(Ay;eff)2 is over 4 × 10−4 for the wide neutron kinetic energy region of Tn = 200–400 MeV, where εD.S. is the double scattering efficiency.