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Measurements have been made of the p + He elastic scattering angular distributions at T = 21.85, 23.90, 25.75, 28.10, 30.35, 32.15, 34.25, 36.90, 39.75, 42.45, 44.05, 44.95, and 47.65 MeV in the angular range 10'& 6, 5 170. The data obtained have in genera1 relative errors smaller than 2/o, while the absolute scale of the measurements has an uncertainty of less than 2.5%. These data together with differential cross sections and analyzing power angular distributioris selected from the literature, as well as total reaction cross section information have been subjected to a phase shift analysis. Up to 45 MeV a single, continuous solution could be determined using phase shifts up through G-waves. As in an earlier phase shift analysis the phase shifts exhibit a smooth variation with energy except for the well-known resonance region around 23.4 MeU. Above 45 MeV some improvement was obtained with the inclusion of a small H-wave contribution. New total reaction cross section data were employed as a constraint on the imaginary parts of the phase shifts. The new analysis corroborates an early finding that the inelasticity is mainly associated with the even partial waves. NUCLEAR REACTIONS Measured do/dQ for He(p, p) He at T=21.85, 23.90, 25.75, 28.10, 30.35, 32.15, 34.25, 36.90, 39.75, 42.45, 44.05, 44.95, and 47.65 MeV for 10'6 9, 6 170; phase shift analysis using do /dQ and other selected do /d 0, A, and 0 R from the literature, 20 MeV & T~55 MeV. INTRODUCTION 'The elastic scattering of protons from 4He is one of the simpler systems amenable to a phase shift analysis aiding in the theoretical interpretation of the few-nucleon system 'Li. Over. the years there has been a continual improvement in the quality of the experimental data, be it differential cross sections, analyzing powers, or total reaction cross sections, in the precision with which the phenomenological analyses fit the experimental data, and in the theoretical representations of this five-nucleon system. There is reason to accept that once the phase shifts obtained in single energy analyses exhibit a continuous behavior as a function of energy starting at zero energy a unique solution has been obtained.Recently Plattner et al. ' presented a phase shift analysis of P+48e elastic scattering in the energy range 20-40 MeV. The data analyzed included both polarizations and differential cross sections.T he errors associated with the differential cross section data were significantly larger than those of the polar&ation data mainly as a result of the method of normalization adopted. In addition, there was a lack of reaction cross-section inform atiqn, thus precluding direct constraints on the inelastic parameters. In order to improve on the accuracy of the existing data set, the present measurements of P+4He elastic scattering differential cross sections angular distributions were made, where possible, at the same energies as the polarization angular distributions of Bacher et al. ' In a separate experiment measurements were also made of the p+'He total...

An attenuation technique has been used to measure the total reaction cross section cr" for the systems p+ 'He and p+'He at 10 and 16 incident proton energies, respectively, between 18 and 48 MeV. The attenuations were measured to about 2% and the elastic corrections are known to about 2%. This results in the cr"values being determined to about 8%, with smaller errors than this at the high energies and larger errors than this at the low energies. The data are compared with results from elastic scattering analyses using phase shifts, the optical model, and the resonating-group method.anticoincidence beam-attenuation technique. II. EXPERIMENT A. ApparatusThe University of Manitoba 50-MeV cyclotron was used to provide proton beams of the desired energies. The beam was momentum analyzed by a bending magnet and was tightly collimated before entering the total-reaction-cross-section appara.tus. The magnetic field of the bending magnet was measured with an NMR probe whose resonant frequency was calibrated in terms of proton energy by measuring a series of proton energies with a differential absorption technique. " The technique consists in degrading the proton energy with accurately lapped Si absorbers and determining the residual proton energy through comparison with the known energies of a particles emitted by '~'Am and ThC. The incident proton energies are then determined from Si range-energy tables. " By this method the beam energy was determined to +100 keV. The beam energy spread after momentum analysis and collimation was about 150 keV full width at half maximum (FWHM}.A schematic diagram of the total-reactioncross-section apparatus is shown in Fig. 1. 451

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