Search for States in the Three-Neutron and Triton Systems

Abstract

The original estimate 5 was set at the 90% confidence level. To conform with the prevailing custom of quoting a standard deviation, we have reduced our original estimate of error by a factor of 1.65. Figure 4 shows the coplanar cross sections (integrated over 7-ray angle) for (30°, 30°) as a function of bombarding energy. The curves are theoretical predictions, identified in the caption, while the plotted points show the corrected experimental results listed in Table III. It is evident from Fig. 4 that our five measurements (solid points) are lower than the others at similar energies. It is possible that the type of prompt background eliminated in our work by the baffles B have could caused an excess of counts in the other work.Our results at 47 MeV fall significantly below the calculation by Nyman 12 of the model-independent leading terms of the integrated cross section. The reason for this is not understood at present.Of the calculations based on various potential models of the nucleon-nucleon interaction, our data agree best with the calculation of Ref. 9 based on the Tabakin potential (dash-dot curve), although more refined calculations with this potential give larger cross sections. 13 Our points are generally consistent with a prediction based on the Bryan-Scott potential (solid curve). The Hamada-Johnston predictions (dashed curve) tend to be above our results. Recent estimates by Marker and Signell 14 show that Coulomb effects reduce the Hamada-Johnston predictions by about 5% at 62 MeV and 6% at 47 MeV. Although one cannot at this time make any firm statements about the best choice of nucleon-nucleon potential, it does appear from the present results that a momentum-dependent potential is preferable to a hard-core potential.3 He spectra from the bombardment of tritium and of 3 He targets with 22.25-MeV tritons are presented. No clear evidence for new states in either residual nucleus is obtained; however, the 3 H(2, 3 He)3w spectra provide weak evidence for the existence of a "trineutron" unbound by 1 to 1.5 MeV.

Detection of neutron clusters

“…4,7. In addition, it is not kinematically consistent with the breakup of 14 Be into 10 Be+ 3,4 n, as a low energy multineutron (11)(12)(13)(14)(15)(16)(17)(18) MeV/N) should be associated with a high energy 10 Be. In the following the discussion is therefore limited to the 6 remaining events.…”

“…These searches have relied on the very low cross-section (typically ∼ 1 nb) double-pion charge exchange (DπCX) [14,15,16] and heavy-ion multinucleon-transfer reactions [17,18,19,20]. Again no conclusive evidence for a bound A n or resonant states has been found in these studies.…”

“…We have subsequently considered the analysis of the energies assuming that 10 Be+ 4 n breakup took place. As the tetraneutron energy has been restricted to [11][12][13][14][15][16][17][18] MeV/N and the 14 Be beam energy is around 30 MeV/N, 10 Be fragments in coincidence with 4 n should have energies per nucleon higher than the beam. The resulting total kinetic energy ( Fig.…”

“…[9]) therefore does not exclude the possible existence of a very weakly bound 4 n. Experimentally, no limit has yet been placed on the binding energy of 4 n (or any other A n). Rather only limits on the production cross-sections could be estimated from twostep [10,11,12,13] or direct reactions [14,15,16,17,18,19,20]. In this paper, a new technique to produce and detect neutron clusters is presented.…”

The extremes of neutron richness

“…One year later, Thornton et al repeated the same experiment with better resolution [40], and found no evidence for a bound trineutron. Two years later Ohlsen et al used a triton beam and searched already for a more complex transfer reaction, 3 H(t, 3 He)3n [41]. The missing mass reconstructed from 3 He lead to a deviation from fourbody phase space, only at forward angles, that could be consistent with a low-energy trineutron resonance.…”