Evidence for an Anomaly in the Excitation Function of the ReactionH2(p,γ)3

Abstract

The excitation function of the capture reaction 2 U(p, y) 3 He has been measured in the range 1^ = 10-17.5 MeV. An anomaly was observed and is interpreted as a broad resonance in 3 He at an excitation energy of 14.5 ±0.5 MeV with a width of about 2 MeV.The study of possible excited states in the three-nucleon system was initiated both experimentally and theoretically when Ajdacic et al. 1 reported evidence for the existence of a bound trineutron in the reaction 3 H(w, p)nnn. In the inelastic reaction 3 He(/>, />') 3 He, Kim et al. 2 also reported evidence for three excited states in 3 He at excitation energies of 8.2, 10.2, and 12.6 MeV. Both reactions were subsequently repeated and the results were not confirmed. Thereafter, many searches have been made by means of a variety of nuclear reactions. 3 Most of them gave no indication of the existence of excited states in the three-nucleon system.A theoretical investigation of the resonance behavior in the three-nucleon system has been performed by Benohr. 4 With a simple soft-core twonucleon potential and a variational technique, he found three broad resonances with quantum numbers (L, S, T) = (1, i !), (1,1, |), and (1, i £). In the phase-shift analysis of nucleon-deuteron scattering, 5 the quartet />-wave shift shows a positive excursion of about 40° for £^ = 2-5 MeV, and the doublet p-wave phase shift has a small positive rise at high energy. These preliminary results could indicate the existence of negative-parity resonances in the three-nucleon system. Theoretical Argand plots 6 for 2 s + i.2r-u Ti [ T = (^)-i x(rje 2i6 -1), where q is the nucleon momentum and 7} the absorption coefficient] indicate a broad 42 p (^s+i.ar+i^ resonance at E + feT^14~ U MeV and another broad 22 P resonance at E + ^iT -18 -Si MeV. It is unlikely that these />-wave resonances would stand out in the excitation curves of the nucleon-deuteron elastic scattering when superimposed on a nonresonant background.

Photonuclear reactions of three-nucleon systems

“…1 we show our theoretical results for the total cross section of 3 He photodisintegration compared to most of the available experimental data [2][3][4][8][9][10][11][12][13] up to E γ = 40 MeV. Not shown are the data by van der Woude et al [15] and Chang et al [17] who found evidence for an excited state in their measurements. This resonance behavior has never been confirmed by any other group.…”