The Kent State ‘‘2π’’ neutron polarimeter

Abstract

We report here the performance of a medium-energy neutron polarimeter of a new design. Over the past decade, the Kent State group has undertaken a series of at IUCF of spin-obervables for the (p,n) reaction with the neutron polarimeter described in Ref. 5. The observables we measured were the analyzing power Ay (6), the induced polarization P(6), and the transverse polarization transfer coefficient D N N , (O), which are the only spin observables that can be measured with a beam polarized normal to the reaction plane. IUCF now has the capability of delivering proton beams of all three polarization states, and we developed our new polarimeter to utilize this capability. As with the design of our earlier polarimeter,5 this new polarimeter utilizes the analyzing power of n-p elastic scattering from the H nuclei of organic scintillators. Figure 1 shows the laboratory differential cross section a(6), the analyzing power Ay(6), and the product A; (6) x a(6) (which is the standard "figure of merit" for polarization analyzing reactions) for n-p elastic scattering at 130 MeV. The desired features that motivated the design of our new polarimeter were: (1) that it should be capable of measuring both normal and sideways components of polarization simultaneously for obtaining full sets of polarization transfer obersvables from (p,n) reactions, (2) that the scatterers present a compact face to the neutron production target, so that neutron spin-rotation magnets of modest aperture could be placed between the target and the polarimeter, and (3) that the photomultiplier tubes should be gain-stabilized to reduce instrumental asymmetries.In Fig. 2