Search Results (10 total)

Diffusion of muonic deuterium μd and muonic hydrogen μp atoms produced following the stopping of negative muons in D₂ or H₂ at 300 K was studied at pressures of 47–750 mbar (H₂) and 94–1520 mbar (D₂) in two distinct target geometries. Time intervals were recorded between entry of negative muons into the gas and arrival of each resulting μd or μp atom at one of 50 foils immersed in the gas, and spaced regularly along the muon beam axis. The results of such measurements were fitted to time distributions generated by Monte Carlo methods, using theoretical scattering predictions and empirically chosen forms for the initial energy distributions of the muonic atoms in the 1S state. Results indicate muonic atom energy distributions which (a) are different for μd and μp and (b) vary with pressure. The best-fit energy distributions have mean energies ranging from 1.5 eV for μd at 94 mbar to ≥9 eV for μp at 750 mbar. The data are also sensitive to scattering cross sections for μd and μp, and are consistent with current theoretical calculations for the μd+D₂ cross sections. In the case of μp+H₂ scattering, the experimental data suggest discrepancies with the theoretical predictions.

Measurements are reported for the np-elastic analyzing power from 30° to 128° c.m., at 485 and 788 MeV, with a typical precision of 0.005 and absolute accuracy of 2%. Results strengthen the isospin-0 phase-shift analysis, and clarify the absolute normalization of the polarized neutron beam and the isospin-0 inelasticity. © 1996 The American Physical Society.

We have measured the analyzing power A_NO and the spin transfer K_NN for np-elastic scattering from about 60° to 170° c.m. at 485, 635, and 788 MeV. The new data clarify previous discrepancies and complete the first-order determination of nucleon-nucleon elastic scattering at these energies.

We have measured the spin-transfer parameters K_LL, K_SL, K_LS, and K_SS at 635 MeV from 50° to 178° c.m. and at 485 MeV from 74° to 176° c.m. These new data have a significant impact on the phase-shift analyses. There are now sufficient data near these energies to overdetermine the elastic nucleon-nucleon amplitudes.

Measurements of the spin-transfer parameter K_LL for ²H(p,n)2p at 0° to calibrate the neutron-beam polarization clarify a normalization discrepancy affecting np data at LAMPF. The new data are in good agreement with theoretical predictions.

Diffusion of muonic deuterium (μd) atomd in D₂ at 300 K was studied at pressures of 0.1–10 bars by measuring the distributions of time intervals between entry of negative muons into the gas and detection of photons emitted upon the arrival of μd atoms at foils spaced along the muon beam axis. Results indicate an approximately Maxwellian velocity distribution with a mean energy of 1.8±0.1 eV for the μd atoms, and μd scattering cross sections in agreement with theory.

The polarization transfer parameter D_t(180°) for n-p scattering has been measured at 50 MeV for the first time. Polarized neutrons produced in the ²H(darrow,narrow) ³He reaction were scattered from the hydrogen in a polyethylene target and the polarization of the recoil protons emitted at 0° was measured in a carbon polarimeter. The result of this measurement tests the prediction of D_t from a phase shift analysis of the N-N data and that of a theoretical proposal concerning n-p charge exchange.

The vector analyzing power A_y(E_n) for the breakup reaction ²H(p→,n)2p at laboratory angle θ_n=18° has been measured for E_p=21.3 MeV as a function of neutron energy. The experimental A_y(E_n) values are compared with the predictions of various three-nucleon Faddeev calculations.

The transverse polarization transfer coefficient K_y^y′ has been measured for the reaction ¹H(d→, n→)pp at 0° for E_d=42.8 MeV as a function of breakup neutron energy. For the high-energy neutrons (E_n>28 MeV) the average value for K_y^y′ is close to 0.6, in conformity with the prediction of a simple stripping or spectator model for polarization transfer in deuteron stripping reactions. Good agreement is found with available Faddeev calculations.

NUCLEAR REACTIONS ¹H(d→, n→)pp, E_d=42.8 MeV; measured K_y^y′ for θ_lab=0°; stripping model; Faddeev calculations.

The analyzing power A_y(θ) for elastic scattering of neutrons by ⁴He has been measured for eight angles in the range 80°<θ_lab<150° at 50.4 MeV. A polarized neutron beam (p_n=0.50) was produced through bombardment of a high-pressure deuterium target by a 50 MeV polarized deuteron beam (p_d=0.55) and by collimation of the neutrons in the 0° direction. A liquid-helium polarimeter placed in the neutron beam was used to measure asymmetries for left and right elastic scattering, with cyclic beam polarization reversal. Multiparameter methods of data acquisition and analysis were used to discriminate against backgrounds from ⁴He breakup reactions and from interactions with the target-cell walls. The extracted A_y values exhibit the large positive maximum at backward angles and the smaller negative minimum at more forward angles typical of n-⁴He scattering at lower energies. The n-⁴He A_y values are compared with p-⁴He results at a nearby energy by means of a phase-shift analysis and are found to be in good agreement (except perhaps in the negative minimum) when Coulomb corrections to the phase shifts are taken into account.

NUCLEAR REACTIONS ⁴He(n→, n)⁴He, E_n=50.4 MeV; measured A_y vs θ for 80°<θ_lab<150°.