Effect of Angular Localization on Direct Nuclear Reactions

Phys. Rev. 129, 1355 – Published 1 February 1963
Paul A. Benioff

Abstract

Some interesting effects of the angular localization of reaction sites caused by the damping of the incident and exit particle waves by the nuclear optical potential are described. Using the reactions Li7(p,2p)He6 and Be9(p,2p)Li8, as examples, we show that, due to the angular localization, the total reaction cross section is different for aligned than for unaligned target nuclei. For the Li7 target in j-j or L-S coupling the fractional change, f, in the cross section for an incident energy of 6 BeV was given by f=0.165(2x-1), where x is the fractional population of Li7 in the M=|32| substates. At 140 MeV the value of the constant in the above expression was slightly but not significantly smaller. For the reaction Be9(p,2p)Li8 the fractional change in the cross section is one half of and of the opposite sign of the Li7 value for the same amount of target alignment. Another result of angular localization of reaction sites in the nucleus is that J0 product nuclear states will be oriented with respect to the incident beam. Using (p,pn) and (p,2p) reactions on O16 and Ni58 as examples, the amount of product nuclear state alignment was computed for the 1p32 and 1f72 excited hole states of O15, N15, and Ni57. The population ratios obtained for the substates in O15 or N15 were |32|:|12|=0.58:0.42 and for Ni57, |72|:|52|:|32|:|12|=0.34:0.25:0.21:0.20. The angular anisotropies, [W(π2)-W(0)]W(π2)], expected from gamma decay of these states were computed to be -0.125 assuming an M1 transition for the O15 or N15 32-states and 0.162 assuming an E2 transition for the Ni57 72-state.

DOI: http://dx.doi.org/10.1103/PhysRev.129.1355

  • Received 4 September 1962
  • Published in the issue dated February 1963

© 1963 The American Physical Society

Authors & Affiliations

Paul A. Benioff

  • Argonne National Laboratory, Argonne, Illinois

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