Neutron-Proton Bremsstrahlung at 208 MeV

Abstract

Nucleon-nucleon bremsstrahlung provides a means of investigating the off-mass-shell behavior of the nucleon-nucleon interaction. Potential models, for example, must account for this behavior. This is important not only because these potentials are used in calculations of nuclear structure and nuclear matter, but also because they provide tests of the more fundamental descriptions of the N-N interaction.Ashkin and Marshak 1 and others 2 ' 3 in 1949 suggested nucleon-nucleon bremsstrahlung as a way of studying off-mass-shell effects. In recent years/?-/) bremsstrahlung (ppy) has received considerable experimental 4 " 9 and theoretical 10 "* 15 attention. However, further refinement of both experiment and calculations appears necessary to allow determination of explicit off-mass-shell behavior of the p-p interaction.Work on n-p bremsstrahlung {npy) is yet at a primitive stage. Calculations 1 ' 16 " 18 indicate that the cross section should be several times larger than that of ppy. No measurements of the "free" npy cross section have been reported except for an upper limit 19 established at the University of California at Los Angeles with 14-MeV neutrons. The experimental work of Wilson 20 and Cohen et al. 21 on proton-nucleus bremsstrahlung has recently been extended by Edgington and Rose 22 at Harwell. However, extraction of the npy cross section from measurements on complex nuclei is rather uncertain. 23 Edgington and Rose 22 using 140-MeV protons and a Dj^O-HgO difference method and Koehler et al. 24 at Rochester using 197-MeV protons and a liquid-deuterium target have extracted the "quasifree" npy total cross section. The results even when corrected for energy D difference are apparently incompatible. 24 We report here npy measurements using a neutron beam produced by the Lawrence Radiation Laboratory 184-in. cyclotron. The overall setup is shown in Fig. 1. A circulating beam of deuterons strikes an internal Be target and produces at the liquid-hydrogen target a collimated neutron beam 1.5 in. high by 1.2 in. wide. The peak, which comprises 90% of the beam, has a mean energy of 208 MeV, a full width at half-maximum of about 45 MeV, and a flux of ^10 7 neutrons per second.Most of the data were taken in the coplanar or so-called Harvard geometry in which the proton and neutron are detected at equal angles to the beam. The proton energies Ep were measured to about 1% in a Nal crystal placed behind the three plastic scintillators of the proton telescope. Neutrons were detected in a NE102 plastic scintillator 5 in. diam by 12 in. long, and their flight times t n , relative to a proton in S l9 were measured. The efficiency of the plastic for a 4-MeV electron threshold is a nearly constant 30 % over the energy range of interest, 25 <E n <125 MeV. It was measured in a separate experiment. 25 A second and identical proton telescope (not shown in Fig. 1) was used for most runs. It was placed at the same polar angle to the beam as the primary one, but above the plane so as to be outside the npy kinematic range. It then ser...

Differential cross section for neutron-proton bremsstrahlung

“…Similar effects are also found in the recent relativistic soft-photon analysis of N N bremsstrahlung by Timmermans et al [9]. The previously measured [2,3] doublydifferential npγ cross sections d 2 σ/dΩ n dΩ p tend to exceed the calculations [7,8] for larger values of θ n and θ p . However, since no photon angular distributions were extracted from these data, no stringent tests of theory could be made.…”

“…Prior to this work, no kinematically complete measurements of npγ cross sections had been per-formed. A few doubly-differential cross section measurements, with large statistical and systematic uncertainties [2,3], and inclusive photon spectrum measurements [4,5] have been reported. In the recent experiment of Volkerts et al [6], protonneutron bremsstrahlung cross sections at incident energy 190 MeV were obtained from measurements on the quasi-free channel in proton-deuteron bremsstrahlung (pd → ppnγ).…”

High Energy Photon Production in Nuclear Reactions

“…Detailed for mulas can be found elsewhere (11). The n-p-y differential cross sections d2u/(dOndOp) for various neutron and proton exit angles, as obtained by Brady et al (34) and Edgington & Rose (32), were compiled by Remington & Blann (35) and Nakayama (36) and can be found in (11). In general, the experimental results agree better with quantal calculations including charged mesons exchange currents contributions (33,36,37) than with semiclassical calculations (20,35).…”

“…2.1 Experimental Data on the Neutron-Prolan-Gamma Process Very few data have been reported on the neutron-proton-gamma process. Measurements were carried out at neutron beam energies of 130 (34), 208 (28), 72 (29), and 180 (30) MeV. Genuine n-p-y measurements require neu tron beams of high intensities and well-defi ned energies.…”

Differential cross section for neutron-proton bremsstrahlung

“…A few doubly-differential cross section measurements, with large statistical and systematic uncertainties [2,3], and inclusive photon spectrum measurements [4,5] have been reported. In the recent experiment of Volkerts et al [6], protonneutron bremsstrahlung cross sections at incident energy 190 MeV were obtained from measurements on the quasi-free channel in proton-deuteron bremsstrahlung (pd → ppnγ).…”