Neutron-Helium Interaction. I. Scattering of Polarized Neutrons at 1.01 and 2.44 MeV

J. R. Sawers, Jr., G. L. Morgan, L. A. Schaller, and R. L. Walter
Phys. Rev. 168, 1102 – Published 20 April 1968
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Abstract

Precision angular distributions of the asymmetry in the scattering of 1.015- and 2.44-MeV polarized neutrons from helium were determined. The reactions Li7(p, n)Be7 and C12(d, n)N13 served as neutron sources, and target thicknesses of 46 and 175 keV, respectively, were used. Analyzing angles ranged from 30° to 140°, in 10° increments. A spin-precession solenoid was employed and the helium was contained in a high-pressure scintillation cell. It is demonstrated that asymmetry data alone are sufficient to accurately determine the scattering phase shifts at 2.44 MeV. Here the phase-shift values were found to be 142.1°, 21.2°, and 121.6° for the δ0, δ11, and δ13 phase shifts, respectively. d waves were not found to be necessary. Assuming hard-sphere scattering, the s-wave phase shift gives a radius of 2.42 F, which is consistent with the values recently obtained by others from both n-He and p-He scattering data. Since at 1.015 MeV, equally good fits to the present data could be obtained with vaules of δ0 differing by as much as 15°, the hard-sphere formula was used in conjunction with the scattering radius determined at 2.44 MeV to fix the s-wave phase shift at 155.5°. The fit to the data then required that δ11=4.4° and δ13=61.2°. The presently determined s-wave phase shifts are larger than the commonly accepted ones due to Dodder, Gammel, and Seagrave (DGS). At both energies the δ13 was in excellent agreement with DGS, although δ11 is about 1.6° below DGS at 1.015 MeV, and 2.8° above at 2.44 MeV.

  • Received 31 August 1967

DOI:https://doi.org/10.1103/PhysRev.168.1102

©1968 American Physical Society

Authors & Affiliations

J. R. Sawers, Jr.*, G. L. Morgan, L. A. Schaller, and R. L. Walter

  • Duke University, Durham, North Carolina

  • *NSF Graduate Fellow. Present address: Experimental Station, E. I. du Pont de Nemours, Wilmington, Del.
  • NASA Graduate Fellow. Present address: University of Basel, Basel, Switzerland.
  • Present address: University of Fribourg, Fribourg, Switzerland.

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Issue

Vol. 168, Iss. 4 — April 1968

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