The quasifree scattering process (QFS) has been studied in the reaction D(P, 2P)n at incident energies of 14, 17, 20, 28, 88, 38, 45, and 57 MeV at 0I =OR --43' (left and right) to the incident beam and PLR --180'. The QFS peak cross section remains almost constant from 20 to 100 MeV and begins to drop at lower energies. The magnitude of the cross section, as well as the shape of the QFS peak, is compared with predictions of a modified-simple-impulse-approximation calculation including a cutoff radius. The energy dependence of the QFS peak cross section is compared with the corresponding cross sections of the reaction D(P,Pn)P and to the free nucleon-nucleon elastic scattering cross sections.

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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

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