Elastic Photoproduction ofπ0Mesons in Helium and (γ, n) Reaction on Helium at High Energies

Abstract

843 so that q i and, finally, 3 M z =(M/j)(M z ) nlJT . (32) the form described in Appendix I, with the quantum numbers describing the subshell suppressed. Since only diagonal terms of the expectation value of the moment operator survive, M 2 =EkM| 2 [(^M(l),M,i^M(l)) + (^-M (2 ) >M22^/ 2-M (2 ))]. (34) APPENDIX II Let an arbitrary number of nucleons in the nljr subshell couple to a state with angular momentum / and Using Eq. (10) and realizing that an arbitrary number of nucleons from the n'Vj'r 1 subshell couple to a state with angular momentum /', Z|#M| 2 M=(J Z I), Y,\<IM\ 2 (2-M) = (/^2), and let these two states couple together to angular M M momentum 2 with maximum projection: 3>2 2 =Y,a M <Pj M (l)<Pj> 2 -M (2), M (33) (34) yields, using the results of the previous Appendix: (35) where 1 and 2 refer to the coordinates of the nucleons in the respective subshells, and the CLM are the Clebsch-Gordon coefficients. The states <pj M and <pj> M are of If/=/ / , then (/ 2 i)=(/ 22 )=l, giving the result (16).The "elastic" photoproduction of ir° mesons in helium has been measured as a function of center-of-mass angle for gamma-ray energies from 170 Mev to 340 Mev. The total cross section shows a maximum around 270-Mev excitation energy and the angular distribution at 300-Mev peaks around 65° in the center-of-mass system. An attempt has been made to interpret the results in terms of the differential cross section for photoproduction of TT° mesons in hydrogen, and to obtain (from the amount of interference of the waves emitted by the four nucleons) a value for the "mean radius" of the alpha particle and the relative phase of ir° emission from proton and neutron.The photodisintegration reaction 7+He 4 ->He 3 +w has also been investigated. The angular distribution of the He 3 recoil nuclei is found to be proportional to sin 2 0 for excitation energies between 40 Mev and 120 Mev.

Photodisintegration of Helium

“…Experiments on the photodisintegration of alpha particles have been performed by Benedict and Woodward, 19 Halpern et al 20 Fuller, 6 de Saussure and Osborne, 21 and Smith and Barton. 22 Benedict and Woodward measured the cross sections for the production of protons of energies from 45 to 120 Mev produced from He 4 by a bremsstrahlung beam, and have expressed their results in terms of differential cross sections.…”

“…Halpern et al 20 20 ; the solid triangles, Fuller 6 ; the open circles, Osborne et al 21 ; the solid squares, Woodward et al 19 ; and the solid circle, Smith et al 22 The curve is used for the numerical calculation of ©• & and outgoing neutrons, and analyzed their yield curve by the photon difference method. We have read their cross sections also from their curve of photoneutron cross section for He 4 , de Saussure and Osborne 21 have investigated the photodisintegration reaction 7+He 4 -> He 3 +?£ by measuring the energy and angular distribution of the He 3 recoil nuclei for photon energies between 40 and 120 Mev.…”

Exchange Moment Contributions to a Modified Shell Model

“…[1][2][3][4] Other authors have also observed the elastic photoproduction of ir° mesons in deuterium 5,6 and helium. 7,8 The group at the * This work has been supported in part by the joint program of the U. S. Atomic Energy Commission and the Office of Naval…”