Proton Angular Distribution for 90 Mev Neutron-proton Scattering

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The angular distribution of the recoil protons in neutron-proton scattering at 90 Mev has been measured for angles between 5{sup o} and 65{sup o} from the direction of the neutron beam. The neutrons were produced by stripping 190 Mev deuterons in a 1/2 inch Be target in the 184-inch F.M. cyclotron. R. Serber has calculated the neutron energy distribution; it has a peak at 90 Mev and a half width of 27 Mev. This distributiQn has been checked experimentally for the neutrons by Wilson Powell and by W.Chupp, E.Gardner, and T.B.Taylor for the protons also produced by stripping. The neutrons ... continued below

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Hadley, James; Leith, Cecil E. & York, Herbert F. November 3, 1947.

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The angular distribution of the recoil protons in neutron-proton scattering at 90 Mev has been measured for angles between 5{sup o} and 65{sup o} from the direction of the neutron beam. The neutrons were produced by stripping 190 Mev deuterons in a 1/2 inch Be target in the 184-inch F.M. cyclotron. R. Serber has calculated the neutron energy distribution; it has a peak at 90 Mev and a half width of 27 Mev. This distributiQn has been checked experimentally for the neutrons by Wilson Powell and by W.Chupp, E.Gardner, and T.B.Taylor for the protons also produced by stripping. The neutrons were collimated by a two-inch hole through 8 feet of concrete. Thin paraffin scatters of known hydrogen and carbon content were used; the number of protons arising from neutron-carbon and neutron-air reactions was determined by using pure carbon scatters and by making blank runs. The scatters were placed in the beam outside of the concrete shielding at a point approximately 52 feet from the cyclotron target. The scattered protons were detected by a telescope of four proportional counters used in coincidence, and set at a constant distance from the scatterer but at a varying angle from the neutron beam. A copper absorber was placed between the scatterer and the counters. The thickness of the absorber was adjusted for each angle so that only protons scattered by incident neutrons of energy greater than 66 Mev could be counted. It was found that the results did not depend on whether the absorber was placed in front of all four counters, or between the first two. The beam was monitored by placing a second one inch piece of paraffin in the neutron beam and measuring the protons scattered from it by means of two additional proportional counters. Fig. 1 is a plot of our results transposed into the center of mass system. Relative proton intensity per unit solid ang1e is plotted against cos {theta}, where {theta} is the scattering angle in this system. The proton peak in the forward direction is expected on the basis of exchange force theory. The apparent symmetry about 90{sup o} would indicate that there are equal amounts of exchange and non-exchange scattering. The experiments are limited at present to {theta} {le} 130{sup o} because of the miniumum energy a proton must have in order to be detected by our counting system. The data shown are in agreement within statistical error with points determined from some 200 cloud chamber pictures of knock-on protons taken by Wilson Powell's group. The errors indicated are twice the probably errors calculated on the basis of the counting statistics. The additional error is a somewhat arbitrary estimate of the possible size of systematic experimental errors. The possible sources of the latter are geometrical inaccuracies, changing coincidence efficiency with proton energy and counting rate, and effects due to stray neutrons. All of these errors would be functions of angle. Thus far, investigations of these factors has indicated that each is smaller than the statistical errors. A detailed report of this work will be made later after more data have been taken, and the sources of experimental error more thoroughly investigated.

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  • Report No.: UCRL-5
  • Grant Number: DE-AC02-05CH11231
  • DOI: 10.2172/970323 | External Link
  • Office of Scientific & Technical Information Report Number: 970323
  • Archival Resource Key: ark:/67531/metadc929097

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  • November 3, 1947

Added to The UNT Digital Library

  • Nov. 13, 2016, 7:26 p.m.

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  • Nov. 18, 2016, 4:13 p.m.

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Hadley, James; Leith, Cecil E. & York, Herbert F. Proton Angular Distribution for 90 Mev Neutron-proton Scattering, report, November 3, 1947; Berkeley, California. (digital.library.unt.edu/ark:/67531/metadc929097/: accessed November 18, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.