S.N. Bunker

Differential cross sections and polarizations in elastic p-d scattering at medium energies

Abstract Differential cross sections for p-d elastic scattering have been measured at 22.0, 35.0 and 46.3 MeV using the energy-analysed external proton beam of the UCLA sector-focussed cyclotron. The angular distributions cover centre-of-mass angles between 9° and 168°. At forward angles both protons and deuterons were observed using a d E /d x - E telescope counter consisting of a fully depleted surface-barrier detector ( ΔE ) and a NaI(Tl) scintillation detector. ( E ). At larger angles, protons were observed using an array of four NaI(Tl) scintillation detectors. The differential cross sections have in general a relative uncertainty less than 2%, while the absolute scale of the measurements has an uncertainty of 1.7%. The proton polarization angular distributions at 35.0 and 40.0 MeV were also measured. In this part of the experiment, the polarized proton beam facility was used. The polarized proton beam was obtained by scattering the internal beam of the cyclotron from a carbon scatterer. At 35.0 MeV, the polarization angular distribution covers centre-of-mass angles between 20° and 164°. At 40.0 MeV, measurements were made for centre-of-mass angles greater than 130° only. Scattered particles were observed using six NaI(Tl) scintillation detectors placed in groups of three on either side of the incident beam. The target used when detecting elastically scattered protons was deuterium gas. The backward part of the angular distribution was measured by detecting recoil deuterons from a deuterated polythylene target. The available proton polarization data for p-d elastic scattering have been used to construct a polarization contour diagram for the energy range of 10–400 MeV.

A study of the 9Be(p, pα)5He reaction at 26.0, 35.0 and 46.8 MeV

Abstract The cross sections for the reaction 9 Be(p, pα) 5 5 He were measured at 26.0, 35.0 and 46.8 MeV incident energies. The resulting data were analyzed in the plane-wave impulse approximation and compared to the results of existing data taken at 55.0, 57.0, 155.0 and 160 MeV. These data appear to be consistent with an S-state of relative motion of the α-cluster.

A search for T = 12 resonances in p+4He elastic scattering

Abstract The excitation function of the differential cross section of the 4 He(p, p) 4 He reaction has been measured for the four laboratory angles 82.3°, 92.3°, 102.3°, and 112.3° at incident proton energies between 22 and 46 MeV. A complete angular distribution for the 4 He(p, p) 4 He reaction has been measured at 47 MeV incident energy. In addition excitation functions at laboratory angles of 23.5°and 70.0° were measured for the 4 He(p, d) 3 He reaction between bombarding energies of 38.5 to 44.6 MeV. The investigation was undertaken to see if any T = 1 2 resonance effects exist in the p+ 4 He compound system from possible “states” in 5 Li around 20, 22 and 25 MeV. No departure from a monotomic energy dependence can be discerned to within the accuracy of the individual experimental points.

A study of the 16O(p, pα)12C and the 20Ne(p, pα)16O reactions at 46.8 MeV

Abstract The cross sections for the reactions 16 O(p, pα) 12 C and 20 Ne(p, pα) 16 O were measured at 46.8 MeV incident energy. An attempt was made to observe quasi-elastic p-α scattering. Within the context of the impulse approximation no clear evidence for this reaction mechanism was observed. These reactions appear to be dominated by sequential processes.

Excitation functions of proton-induced reactions in 16O at medium energies

Abstract Protons elastically and inelastically scattered from 16O were observed at lab angles between 60° and 160° using NaI(Tl) detectors. The incident beam energy was varied in approximately 200 keV steps from 21.25 to 33.12 MeV and in 500 keV steps at higher energies up to 38.5 MeV. Angular distributions at the same energies were also measured for inelastic proton scattering leaving the 16O nucleus with excitation energies of Q = 6.05, 6.13 MeV and Q = −8;.88 MeV. The excitation functions for the (p, d) and (p, α) reactions were measured at 70° for the same energy range, and the (p, t) reaction was observed above 31 MeV. The elastic scattering angular distributions have been integrated over the angular range 100°–160° and anomalies are observed. An optical-model-with-resonance analysis of the data is presented which indicates states at Ep = 21.6, 22.6, 23.5, 24.7, 26.4, 28.3 and 30.1 MeV with Jπ assignments 9 2 + , 9 2 + , 7 2 + , 7 2 + , 7 2 − , 5 2 − and 5 2 + , respectively. A coupled-channels calculation has also been compared with the elastic and inelastic scattering (Q = −6.05, −6.13 MeV) angular distributions.