Neutron-Neutron Quasifree Scattering

Abstract

The reaction D (?i,2n)p has been measured at i£ inc =14.1 MeV, 9 n^ =0 n^ = 30°, <p = 180°, and the results are compared with the predictions of two separable-potential models. Neutron-proton and proton-proton quasifree scattering from nucleon+deuter-on reactions at 14 MeV are also compared with the predictions of the same models. The upper limit of 2 mb/sr 2 is determined for the reaction D(n s ny)d,The purpose of this study is to contribute to the understanding of nucleon-induced deuteron breakup processes and to investigate what can be learned about neutron-neutron effective-range parameters from quasifree scattering (QFS). Experimental data 1 " 14 indicate that the enhancement associated with the quasifree kinematic conditions is one of the salient features of multiparticle reactions even at E inc~1 0 MeV. 6 " 9 However, this does not imply that the pole graph represents a dominant contribution, nor that the cross section can be factored, one term being the half-off-the-energy-she 111 matrix. The importance of the pole-graph contribution can be tested 15 " 19 and the results of measurements 11 * 17 " 19 of the reactions 6 Li(p,pa)d and 6 Li(o!, 2a)d at ^inc~ 50-80 MeV indicate that the spectator model 1 (SM) gives a correct description of the data except for a normalization factor. The spectator model has been seccessfully applied to D(N, 2N) QFS at E inc >150 MeV, 1 " 3 ' 20 but it fails at E inc <100 MeV. 4 " 10 Various simple modifications have been proposed: (i) off-the-energy-shell effects, but they do not seem to be large enough to account for the discrepancy between the data and the theory 10 ' 20 * 21 ; (ii) final-state interaction (FSI) effects, which improve the fit to the data at E inc £150 MeV, 2 ' 3 * 20 but do not explain the 46-MeV data 5 ; (iii) modified simple impulse approximation (MSIA), 22 which explains the energy variation of the absolute cross section and the shape of the spectra. 6 These simple models are inadequate at low energies, 23 ' 24 and indeed they do not explain, e.g., the observed ratio D(p,pn)/D(p, 2£). 6 ' 9 ' 13 ' 14 ' 5 Neutron-neutron interaction remains a problem of considerable interest. 26 The latest analysis of the reaction D(ti~,nn)y gives a value of a nn = ~16.6 ±1.3 fm. 27 A comparison procedure 28 applied to the reactions D(p,n)2p, D(n,p)2n, 3 Re(d,t)2p, and 3 R(d, 3 He)2n gives a nn =-16.45± 1.0 fm and r m = 3.1 ±0.5 fm. This application has been criticized 10 ' 29 * 30 and these values are not reliable independent determinations of a nn and r nn .Neutron-neutron QFS was studied by bombarding a cylindrical 2-in.x2-in. C 6 D 6 target with the 14.1-MeV neutron beam defined by associated a particles. Two outgoing neutrons were detected at ^n(3) ==^M (4) = 30°> <p = 180°. The overall angular resolution was ±6°. The main experimental problem is the large background from y's and from direct and elastically scattered neutrons. The background was reduced by requiring the four detectors (a, target, neutron-right, and neutronleft) to be in coincidence and by kinematically...

Final-state interactions

“…(3.41) not inconsistent with the original result of Haddock et al (1965) in (3.37) but in disagreement with the results of Nygren (1968). Quite recently, Haddock (see Slaus 1971) has reanalysed the data once again and quoted a, = -16.6 2 1-3 fm.…”

“…However, the small fraction of the predicted cross section observed may correspond to the favourable momentum configurations of the deuteron, which are those with the two nucleons far apart and almost at rest. Slaus et al (1971) studied the mirror reaction measuring the n-n correlation. The analysis was effected with some simple modified versions of the spectator model, and with several interaction potentials.…”

Neutron-neutron quasifree scattering in neutron-deuteron breakup at 10 MeV

“…This cross section depends on the nn effective range parameter (r nn ) in the low-momentum expansion of the s-wave scattering amplitude [5]. However, early measurements did not determine r nn with high enough precision to examine the validity of charge symmetry in the NN interaction [6][7][8][9][10].…”

Measurement of the $^1S_0$ neutron-neutron effective range in neutron-deuteron breakup

“…For this reason, several early experiments determined r nn from measurements of nn QFS in nd breakup. These experiments were performed at incident neutron energies between 14 and 25 MeV [27][28][29][30][31]. Although these measurements agreed well with theory, they were limited by large statistical uncertainties and were compared to theory which implemented several simplifying assumptions and used phenomenological N N interactions.…”

“…The situation was complicated by three recent measurements of nn QFS in nd breakup at incident neutron energies of 10.3,26,[25][26][27][28][29][30][31][32][33][34]. Rigorous Faddeev calculations [35] using the CD Bonn potential [5] underpredicted the measured cross section by about 16% [26,33,34]; the theory predicted the shape of the data but not its magnitude.…”