Information About the Neutron-Neutron Scattering Length from the ReactionH3(n,d)2n

Abstract

Recently the reactions H 2 (7r"~,y)2n and H 2 (w, p)2n were investigated with the aim of determining the neutron-neutron l S 0 scattering length, a nn . The preferred value for a nn extracted from the first reaction is 1 ' 2 -17 F, unfortunately with an uncertainty of about 5 F. Several investigations 3 " 5 of the second reaction gave values around -22 F. While the theoretical analysis of the reaction H 2 (7T~,y)2« can be performed with an accuracy of ±1 F, 8 the reactions with more than two nucleons in the final state are considerably more difficult for interpretation.In a reaction a+A-~b +n + n the spectrum of the particle b reflects the neutron-neutron final-state interaction. However, distortive effects arise from at least two sources 7 :(i) Interaction between b and the system 2w. It is reasonable to expect that this depends upon the type of the particle b and on the relative b-2n energy.(ii) The interference between the n-n and the n-b resonances 8 and the interference between resonant and nonresonant processes. 9 The study of the reaction H 3 (n,d)2n offers another possibility 4 to extract a nn . The comparison of the reaction E 2 (n f p)2n and E B (n,d)2n allows one also to investigate the influence of the various distortive effects.In order to determine kinematically such a reaction one has to measure five parameters. The measurement of the energy of the charged particle at 0° at a fixed incident energy is, thus, an incomplete measurement, and only that region of the spectrum which corresponds to the strong final-state interaction of the two neutrons is liable to meaningful interpretation.The deuteron spectra from the reaction H 3 (n, d)2n at E n = 14.4 MeV were measured with different detecting systems. The targets used were (1) a solid Cu-Ti-H 3 target containing 0.3 mg of H 3 and 10% of He 3 ; (2) two gas targets, one containing 0.1 mg and the other 1.3 mg of H 3 , with the He 3 content less than 0.4%. The charged particles were detected with a semiconductor counter telescope 10 in conjunction with multidimensional analyzers. 11 The telescope consisted of two thin AE counters and an E counter depleted to detect 11.5-MeV protons.Two pulses (from the A£ 2 and E counters) were analyzed by a lOOxlOO-channel analyzer. The resulting three-dimensional graphs gave proton, deuteron, and triton &E 2 -vs-E spectra simultaneously. 12 In a set of measurements three pulses (from the AE lf &E 29 and E counters) were analyzed by a lOOxlOOxlOO-channel analyzer. All those events for which AE X and AE 2 pulses did not satisfy specific criteria were rejected. 13

Few-Body Research - Summary

“…The number of m-body interactions in an n-body system is n!/m!(n-m)! and that is already for 6 Li larger than n!/2!(n-2)! and it grows with A [13].…”

“…Due to partial cancellations 3NF becomes noticeable, e.g. in BE of 3 H 0.5-1.0 MeV out of 8.5 MeV, of 6 Li 6 out of 32 MeV and in scattering processes, see V.2 and VII. The 3NF that appears in N2LO differs from UIX and IL 3NF, which consists of chiral terms of higher order.…”

“…Results of several calculations based on Faddeev theory, GFMC and NCSM are listed in Table 2 and a remarkable agreement is obvious. AV18+UIX still underbinds nuclei starting with 6 He and the discrepancy increases with A. Fitting energies of 17 states in A≤8 new 3NF were constructed: IL 1-5 which contains besides 2PE also 3PE and ∆s. 3NF potentials IL1-5 are CD.…”

“…A variety of RIB are available with very short lifetimes, e.g. 14 Be (T= 4.2ms), 8 He (T= 119ms), 6 He (T= 0.807s), 8 Li (T=0.838s) and long-lived 10 C (T=19.3s) and 18 Ne (T=17s). High beam intensities are achieved: up to billion particles per second.…”

“…Yet, in 1960 "scarcely physics owed so little to so many" [3]. Half a century ago the Los Alamos group [4] and then Zagreb group [5] did many few nucleon studies culminating in the first determination of the neutron-neutron 1 S 0 scattering length, a nn , from 2 H(n,p)nn and 3 H(n,d)nn yielding −21 ± 1 fm and −18 ± 3 fm [6], respectively, with no theoretical uncertainties included. FB studies yielded nuclear data necessary for nuclear energy, e.g.…”