n−pDifferential Cross Section and Polarization at 199 MeV

The relative differential cross sections and polarization parameters for free $n-p$ scattering, and for the reaction $n+d\to p+2n$ in which only the proton is detected (bound $n-p$ scattering), have been measured at an incident energy of 199 MeV, at two-nucleon c.m. angles between 77° and 158°. The neutron beam used, created by charge-exchange scattering of a polarized proton beam on a deuterium target, had an energy spread of ±12 MeV, a polarization of 73%, and an intensity of 1000 n/sec. The beam polarization was determined by comparing the asymmetry measured in the reaction $n+d\to p+2n$ with the polarization of the (previously studied) charge-symmetric reaction $p+d\to n+2p$, in which only the neutron is detected. The differential cross section $\sigma$ and the polarization $P$, for free $n-p$ scattering, the ratio $R_M$ of the bound to the free cross section, and the difference $P-P_b$ between the free and bound polarization parameters are listed. A 10% systematic error in $P$, due to uncertainty in beam polarization, is not included in the listed error. The cross-section measurements agree with those of Kazarinov and Simonov and with the phase-shift solution ${(\mathrm{Y}-\mathrm{IV})}_{\mathrm{np}}$ of Breit et al. but disagree with the older measurements of Guernsey, Mott, and Nelson. The polarization measurements are in satisfactory agreement with the (less accurate) results of Tinlot and Warner, but in only fair agreement with the phase-shift solution ${(\mathrm{Y}-\mathrm{IV})}_{\mathrm{np}}$. The ratio $R_M$, typically 0.65 ±0.04, is significantly smaller than that given by an impulse-approximation calculation, typically 0.76. The difference between polarization parameters for free and bound scattering is consistent with an impulse-approximation calculation but also consistent with zero.