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Title:Proton Compton effect for 300 MeV photons
Author(s):Gray, Edward Ray
Doctoral Committee Chair(s):Hanson, A.O.
Department / Program:Physics
Subject(s):proton comption effect
elastic photon scattering
spark chamber technique
prion-nucleon resonance
Abstract:Cross section measurements of the elastic scattering of photons by protons have been taken at the University of Illinois Betatron using a spark chamber technique. The betatron was run at 335 MeV using the newly installed radio frequency cavity. This allowed measurements to be taken at the maximum of the first pion-nucleon resonance. The bremsstrahlung beam was scattered from a liquid hydrogen target, and the scattered photons were converted and detected in a series of lead plates, spark chambers, and scintillation counters. These counters provided electronic triggering information, and the position of the showers produced by the scattered photons was observed in the spark champers and was used to determine the direction of the scattered photon relative to the photon beam. A spark chamber telescope, which consisted of two aluminum foil spark chambers, a bending magnet, two aluminum foil spark chambers, and two scintillation counters, was used to detect the recoil protons. Again the counters provided trigger information and were required to be in coincidence with the photon detection counters before the spark chambers Were triggered. Spark chambers in the proton telescope gave the direction of the proton recoil and the angle of deflection in the bending magnet. This deflection in the magnet was used to calculate the momentum of the proton, and with the direction of the recoil prot6n, the proton momentum was used to calculate the expected direction of an elastically scattered photon" A comparison of the expected direction of the photon from an elastic event to the observed direction of tpe scattered photon allowed a statistical separation of the elastic from the inelastic events to be made. The inelastic events corresponded to pi zero photoproduction and represented about 90 percent of the events.observed. After being divided into discreet photon energy bins, the number of elastic events observed were used to calculate the average Compton cross section for that bin. The number of inelastic events gave a measured value for the pi zero photoproductlon cross sections, and these Citl'OSS sections were compared to existing measurements and theory. Since this process had been well established by other measurements, the comparison of the values of the pi zero cross sections measured 'in this experiment to earlier va.lues established the correctness of the measurement procedure of this experiment. The Compton cross sections in micro barns per steradian obtained at the 900 CMS angle were .145 ± .016 for an energy bin of 285 to 335 MeV and .155 ± .031 for a bin of 260 to 285 MeV. For the 1350 angle the values were .213 ± .018 for a 285 to 335 MeV bin~ 0152 ± .016 f,or a 235 to 285 MeV bin, and 00442 ± .0076 for a 185 to 235 MeV bin. The pi zero photoproduction cross sections obtained at the 900 CMS angle were 26.4 ± 1.6 for 285 to 335 MeV, 18.5 ± .4 for 260 to 285 MeV, and 9.60 ± .5 for 235 to 260 MeV. For the 1350 angle the values are 18.7 ± .3 for 285 to 335 MeV, 10.1 ± .2 for 235 to 285 MeV, and 2.98 ± .13 for 185 to 235 MeV. At the 1350 angle the two lower energy Compton cross sections measured were in agreement with previously measured values taken by an Illinois group~ and the high energy cross section measurement provided new data at the 1350 angle essentially in agreement with theory. The 90° values were in agreement with previous Illinois measurements on the low energy side and with Cornell measurements on the high energy side at the middle of the first pion nucleon resonance. Both the present 900 measurement at about 310 MeV and the Cornell measurement with which it agrees are in disagreement with existing theories and remain unexplainably low.
Issue Date:1966
Genre:Dissertation / Thesis
Rights Information:1966 Edward Ray Gray
Date Available in IDEALS:2011-07-07
Identifier in Online Catalog:6163789

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