N.E. Davison

Measurements of NN → dπ very near threshold: (I). The np → dπ0 cross section

Abstract We have measured cross sections for the reaction np→d π 0 at beam energies very near the pion-production threshold. The yield near threshold is 23% lower than the previously accepted value based on π + d→pp data. P-wave pion production was observed at energies as low as 1.5 MeV (c.m.) above threshold. There was no evidence of narrow πNN resonances in the energy range surveyed - 275 to 291 MeV, corresponding to pion c.m. momenta between 2 and 43 MeV/ c .

The neutron beam facility at triumf

Abstract The polarized neutron beam facility at TRIUMF has been upgraded for use in high precision neutron scattering experiments. Polarized neutrons are produced via transverse polarization transfer in the D(p,n)2p reaction at 9° in the lab. Proton beam position on the LD2 production target is stabilized to better than ±0.2 mm using a feedback system controlling beam line elements. The region of uniform neutron beam intensity at the experimental target location is a rectangular area 56 mm wide and 40 mm high. In that area the neutron beam intensity is 9 × 103 (100 nA cm2 s) and the neutron polarization is 50%. The facility is being used to determine charge symmetry breaking in n−p elastic scattering, to study neutron radiative capture by hydrogen, and a measurement of the spin correlation parameter Ann.

Radiative capture of polarized neutrons above pion production threshold

Abstract We have measured angular distributions of cross sections and analyzing powers for the radiative capture of polarized neutrons by hydrogen at E n = 370 and 478 MeV. The results are compared with a nucleon-delta coupled channels calculation. The predicted analyzing powers reproduce our 370 MeV data, but do not agree in detail with our results at 478 MeV.

Detection equipment for a test of charge symmetry in n−p elastic scattering☆

Detection equipment has been developed to allow precision measurements of n−p elastic scattering of 150 to 500 MeV polarized neutron beams at TRIUMF. The apparatus permits a determination of the difference in angle, ‡θ, at which the neutron and proton analyzing powers An and Ap cross zero with a precision of ±0.04° lab at 500 MeV. From this difference in ‡θ the difference between An and Ap can be obtained to a precision of ±0.001.

PROTON LOSS BY NUCLEAR INELASTIC INTERACTIONS IN GERMANIUM

Abstract The probability of protons undergoing nuclear inelastic interactions while stopping in germanium has been measured in a direct counting experiment using protons with energies between 25 and 49 MeV incident on a germanium detector. These values have been determined to an accuracy of approximately ±2%. Calculations of the proton reaction probability over the incident energy range 20–150 MeV have also been made, using previously reported proton total reaction cross sections. The experimental and calculated results agree to within ±1.8%.

T = 12and32 negative-parity states in 11B with the 14C(p, α)11B reaction

Abstract The 14 C(p, α) 11 B pickup reaction has been studied at a proton energy of 41.9 MeV. Differential cross sections to the ground state and 13 excited states (including members of the isospin T = 3 2 multiplet) were measured from 10° to 155° (lab). The experimental results show that only negative-parity states are strongly excited. This suggests that pickup strongly dominates over knockout as the primary reaction mechanism. A finite-range DWBA analysis of the data was carried out using cluster form factors, and the deduced spectroscopic factors compared with the shell-model calculations of Kurath.

Measurement of the proton total reaction cross section for 159Tb, 181Ta and 197Au between 20 and 48 MeV

Abstract Proton total reaction cross sections have been measured for the nuclei 159 Tb, 181 Ta and 197 Au at seven proton energies between 20 and 48 MeV using an attenuation technique. The experimentally determined energy dependence of the total reaction cross sections is compared with results obtained for black nucleus and optical model calculations.

Exchange terms in the optical model

Abstract A number of existing proton elastic scattering differential cross section and polarisation angular distributions for 16 O, 28 Si, 40 Ca, 58 Ni, 66, 68 Zn, 120 Sn and 208 Pb at several incident energies have been analyzed using an optical-model potential in which the real central and absorptive potentials are multiplied by “exchange terms” of the form [1+ C r ,(−1) l ] and [1+ C i (−1) l ] respectively. Since the major effect of these terms is to be found at backward angles, a number of differential cross section angular distributions for 16 O, 66,68 Zn and 208 Pb have been extended to θ lab = 175°. Small improvements in the quality of the fits to experimental data were obtained with C r , C i ≠ 0. The behaviour of the coefficients C r and C i as functions of incident proton energy is discussed.

Proton-helium total reaction cross sections between 18 and 48 MeV

Abstract Proton total reaction cross sections for 3 He and 4 He have been measured in the energy range 18 to 48 MeV at ten and sixteen energies respectively. Comparison is made with other experimental nucleon-induced reaction information. Comparing the p- 4 He measurements with phase shift analyses, resonating-group calculations, and optical model predictions, points to improvement for the model-dependent theoretical work.

A beam intensity profile monitor based on secondary electron emission

Two dual function intensity profile monitors have been designed for a measurement of parity violation in p-p scattering at about 230 MeV using longitudinally polarized protons. Each device contains a set of split secondary electron emission (SEM) foils to determine the median of the beam current distribution (in x and y). The split foils, coupled through servoamplifiers and operational amplifiers to upstream aircore steering magnets, have demonstrated the ability to hold the beam position stable to ±5 μm for beam position fluctuations up to 1000 Hz. These monitors also contain a set of foil strip planes giving information on the intensity distribution projected onto the two orthogonal axes, x and y. Data were acquired using 0.008 mm thick, 0.90 mm wide aluminum foil strips at 1.00 mm centers. The foil strip planes were able to determine the beam centroid to within ±3 μm after one hour of data taking with a 100 nA, 15 mm FWHM Gaussian beam.