Files in this item



application/pdf1969_staples.pdf (4MB)Restricted to U of Illinois


Title:Photoproduction of neutral pions in helium by 335 MEV Bremsstrahlung
Author(s):Staples, John William
Doctoral Committee Chair(s):Hanson, A.O.
Department / Program:Physics
Subject(s):neutral pions
recoil nucleus
semiconductor telescope
Abstract:The differential cross section was measured for the, coherent production of neutral pions from He4 by photons to an energy of 335 MeV. Bremsstrahlung from the University of Illinois 340 MeV betatron impinged upon a gaseous He4 target cooled to 20.4oK. The recoil nucleus was detected with a semiconductor telescope in coincidence with at least one gamma resulting from the decay of the neutral pion. The particle events were recorded on photographic film in both analogue and digital form. The resolution of the recoil telescope 4 was sufficient to permit separation of the He recoils from the background of He3 recoilS and a11owed'a better identification of the coherent He4 events that had been achieved in earlier experiments. The laboratory cross sections were found to vary from 40 ub/sr at 200 and 230 MeV photon energy decreasing with energy to 55 ub/sr for the single measurement at 500 for a photon energy of 320 MeV. These cross sections are, moderate1y smaller than those given by Palit and Bellamy and are much smaller than earlier measurements by DeSaussure and Osborne. The experimental cross sections are compared with those calculated by means of an impulse approximation, using the amplitudes for the photoproduction of neutral pions from nucleons. The laboratory energy and angle of the He4 recoil define the kinematic variables in the He4 system but do not explicitly define the variables in the nucleon system, which are required to evaluate the nucleon photoproduction amplitude. The correct evaluation of these variables is a difficult problem involving appropriate averages of the effects of nucleon motion within the nucleus. Three simplified ways of specifying the variables in the nucleon frame are presented and compared to each other with respect to their usefulness of representing the experimental results. Calculations done elsewhere show that corrections to the impulse approximation for interactions of the pion in the final state reduce the predicted cross section by about a factor of two in the resonance region. Using this correction and specifying the center of mass pion momentum and gamma energy, variables equal in the nucleon and helium frames gives reasonable agreement with the experimental cross sections.
Issue Date:1969
Genre:Dissertation / Thesis
Rights Information:1969 John William Staples
Date Available in IDEALS:2011-07-12
Identifier in Online Catalog:6074989

This item appears in the following Collection(s)

Item Statistics