First Excited State ofHe5

Abstract

The reaction Li 7 (d,a)He 5 was studied with the use of coincidence circuitry and solid-state chargedparticle detectors. Targets of natural and isotopic lithium were bombarded with 150-200 keV deuterons, and a particles emitted at laboratory angles of 90 and 82 deg were detected in coincidence. The (d,a) reaction proceeding to the ground state of He 5 was observed, its differential cross section at 90 deg was measured relative to that for Li 6 (d,a)ce, and a value of 2.4_i,o +1 -5 was assigned to the parameter A in the function /(0) = 1-K4 sin30 which describes the center-of-mass ce-particle distribution resulting from the disintegration of He 5 . The first excited state of He 5 was found to have an excitation energy of 2.6±0.4 MeV and a width of 4.0±1.0 MeV. The intensity of the excited state alpha group was greater than that of the ground-state group by a factor of about 1.5. There was no evidence for any other excited state up to at least 7 MeV. The ratio of the differential cross sections at 90 deg for Li 6 (d,p)Li 7 and Li 6 (d,a)a was determined for several values of Ed and found to agree with reported cross-section data. 9 F.

Evidence for a New Low-Lying Resonance State inH7e

“…Low-lying resonance states in 7 He͑ 6 He 1 n͒, formed after fragmentation reactions of a 227 MeV͞ nucleon 8 He beam on a carbon target, have been studied. Coincidences between 6 He nuclei and neutrons, corresponding to the one-neutron knockout channel in 8 He, were selected.…”

“…Coincidences between 6 He nuclei and neutrons, corresponding to the one-neutron knockout channel in 8 He, were selected. The relative energy spectrum in the 6 He 1 n system shows a structure, which is interpreted as the 7 He (I p 3͞2 2 ) ground state, unbound with 0.43(2) MeV relative to the 6 He 1 n system and a width of G 0.15͑8͒ MeV overlapping with an excited (I p 1͞2 2 ) state observed at 1.0(1) MeV with a width of G 0.75͑8͒ MeV.…”

“…The position of the excited 1͞2 2 state has generally been considered to lie approximately 4 MeV above the ground state [7], but several experiments rather indicate an excitation energy of 2.0 to 2.6 MeV [8,9]. Recent calculations [10,11] predict an energy difference of 1.2 to 1.4 MeV between the p 3͞2 and p 1͞2 states.…”

States of5He and8Be from the reaction7Li+d

“…The most recent paper by Gil, Marquez, Qu6bert and Sztark [2] ascribes to the first excited state of 5He the excitation energy E*= 2.6 MeV and the width F= 7 MeV. Fessenden and Maxson [4] evaluated such spectra as well and found E*=2.6 MeV, F=4.0 MeV. Strauss and Friedland [3] also measured a-a-coincidences and reported an excited state at E*=2.9 MeV and another one at 4.8 MeV.…”