(See Energy Level Diagrams for 5He)
Electromagnetic transitions: (1985FI1E).
Hypernuclei: (1982KA1D, 1983BA1D, 1983BE1G, 1983MO1C, 1983SH1E, 1983SH38, 1984AS1D, 1984BO1A, 1984BO1H, 1984CH1G, 1984HU1B, 1984KO1F, 1984MI1E, 1984SH07, 1984SH1J, 1984ZH1B, 1985AH1A, 1985BA1F, 1985GI1E, 1985IK1A, 1985KO1G, 1985KU1A, 1985MO1F, 1985OS1C, 1985TA1E, 1985YA05, 1985YA1B, 1986AN1R, 1986BA1H, 1986BA1W, 1986BO1E, 1986CH1I, 1986DA1B, 1986DO1B, 1986LI1L, 1986MA1C, 1986SH1I, 1986SH1K, 1986SH1V, 1986SZ1A, 1986WA1J, 1986YA1F, 1987BO1L, 1987BO1O, 1987KA1Q, 1987MI38, 1987PO1H, 1987SH1H, 1987YA1C, 1987YA1M, 1988BA1G, 1988BO1E, 1988LA1B, 1988LI1C, 1988NO1A, 1988PO1H, 1988TA29).
At low energies the reaction is dominated by a resonance at Ed = 107 keV; the mirror reaction shows resonance at Ed = 430 keV. The branching ratio Γγ0/Γn integrated over the resonance from 0 to 275 keV is (5.6 ± 0.6) × 10-5 (1986MO05), in very good agreement with the earlier value of (5.4 ± 1.3) × 10-5 for Ed = 45 to 146 keV (1984CE08). Assuming Γn of 5He*(16.7) is 37 ± 5 keV (see reaction 6), then Γγ0 = 2.1 ± 0.4 eV. (1986MO05) also report branching ratios up to Ed = 0.72 MeV and summarize the earlier work to 5 MeV. For measurements of TAP and VAP at Epol. d = 0.4 and 8.6 MeV, see (1987RIZZ; prelim.). See also (1985RIZZ), (1979AJ01) and (1984NE1B, 1986LA1F, 1988KI1C; applications).
The cross section has been measured in the range Et = 12.5 to 117 keV (1984JA08) [0.525(± 4.8%) mb to 3.739(± 1.4%) b] and in the range Ed = 79.913 to 115.901 keV (± 0.015 keV) (1987BR10) [3.849 to 4.734 b (± 1.6%)]. See also (1985FI1G; Ed = 13.8 to 114.3 keV). A strong resonance, σ (peak) = 4.88 b, appears at Ed = 105 keV: see Table 5.2 (in PDF or PS) in (1979AJ01) and (1987BR10). For a discussion of R-matrix analysis and evidence for a "shadow" pole, see (1987BR10, 1987HA20). See also (1987HA44, 1987MO1K). From Ed = 10 to 500 keV, the cross section is well fitted with the assumption of s-wave formation of a Jπ = 3/2+ state. Measurements of cross sections and angular distributions for reaction (a) have been reported to Ed = 21 MeV and Et = 20.0 MeV [see (1974AJ01, 1979AJ01, 1984AJ01)] as well as at 1.0, 1.5 and 2.0 MeV (1987LI07).
A study of reaction (a) with polarized deuterons at Ed = 0.2 to 1.0 MeV indicates intervention of the s-wave, Jπ = 1/2+ channel, as well as possible p-waves above Ed = 0.3 MeV. The polarization increases monotonically from 0.03 at Ed = 3 MeV to ≈ 0.5 at Ed = 6.5 MeV and then with a lower slope to 0.69 at Ed = 13 MeV. The change in the slope may be caused by excited states of 5He near 20 MeV. Comparison with the 3He(d, p)4He mirror reaction at corresponding c.m. energies shows excellent agreement between the polarization values in the two reactions up to Ed = 6 MeV, but then the proton polarization becomes ≈ 15% higher, converging back to the neutron values at Ed ≈ 12 - 13 MeV. This may be due to experimental factors. Vector polarization transfer coefficients, Ky'y (0°) have been measured for Epol. d = 5 to 11 MeV (1985HOZU, 1986HO1E; prelim.). For other polarization work see (1984AJ01).
(1987BR10) have derived astrophysical S-factors in the range Ed = 79.9 to 115.9 keV [S(0) = 11.71 ± 0.08 MeV · b; multilevel fit], as well as reactivities. See (1984JA08) for the earlier work, and (1985CA41, 1987VA36).
Reaction (b) has been studied for Ed = 10.9 to 83 MeV. A study of reaction (c) leads to the suggestion of a resonance at Ec.m. = 2.9 ± 0.3 MeV [Ex = 19.6 MeV], Γc.m. = 1.9 ± 0.2 MeV, consistent with Jπ = 3/2- [see, however, Table 5.1 (in PDF or PS)]: see (1974AJ01, 1979AJ01). See also (1983BAZP, 1984SLZZ, 1987GOZF), (1986BR20, 1986RA21) and (1984SHZK, 1985FIZW, 1986CO1J, 1986ILZZ, 1986KO21, 1986VAZU; theor.). For applications see (1983GO1C, 1983HU1A, 1984BA1D, 1984HU04, 1984MA71, 1984VL1A, 1986AL1H, 1986CA1E, 1986EN1A, 1986GR1H, 1986HA1N, 1986HA1V, 1986KE1H, 1986KN1A, 1986KU1G, 1986LE1F, 1986LO1B, 1986OK1B, 1986PA1G, 1986PE1H, 1986SA1M, 1986TA1K, 1986WI1B, 1987BA2I, 1987BO1Q, 1987KA1O, 1987LE1G, 1987SO1A, 1987WU1C, 1987ZW1A, 1988KU1E).
For recent developments in muon-catalyzed fusion see (1986JO1B, 1987BA2P, 1987BR1G) and (1983JO1B, 1983TA1C, 1984AN1A, 1984BA1V, 1984BR1G, 1984CA1B, 1987AC1A, 1987BA2L, 1987BE1Y, 1987BR1T, 1987CA1O, 1987NA1K, 1987PE1D), (1983PO1E, 1984AJ01, 1984AN1C, 1984CH1F, 1984HA1J, 1984KR1B, 1984MO1G, 1984OT1A, 1986BR1H, 1986JO1C, 1986KA1K, 1987BR1W, 1987JO1A, 1987PO1M) and (1983SG1A, 1984BU1E, 1984BY1B, 1984FI1F, 1984ME1B, 1985BA1G, 1985CO1C, 1985FR1D, 1985GO1E, 1985GU1G, 1985HI1A, 1985KA1C, 1985KA1N, 1985ME1C, 1985ME1D, 1985RA1B, 1985VA1B, 1986BL15, 1986BO1F, 1986CO1K, 1986DA1D, 1986HU1C, 1986JO1C, 1986KH1B, 1986ME1D, 1986TA1J, 1986TA1L, 1987AK1B, 1987BE1W, 1987CO1N, 1987CO1P, 1987CO1W, 1987KA1Z, 1987KO1R, 1987ME1E, 1987RA1L, 1987TA1I, 1987WY1A, 1988JA1C, 1988RO1G; theor.).
The elastic scattering has been studied for Ed = 2.6 to 11.0 MeV: see (1984AJ01). The excitation curves show an interference at Ex ≈ 19 MeV and a broad (Γ > 1 MeV) resonance corresponding to Ex = 20.0 ± 0.5 MeV, similar to that seen in 3He(d, d) [see 5Li]. Together with data from 3H(d, n)4He, this work favors an assignment D3/2 or D5/2 with a mixture of doublet and quartet components (channel spin 1/2 and 3/2) if only one state is involved [any appreciable doublet component would, however, be in conflict with results from 7Li(p, 3He)5He]. Measurements of differential cross section and analyzing power using polarized deuterons with Ed = 3.2 to 12.3 MeV show resonance-like behavior in the vector analyzing power near Ed = 5 MeV. The anomaly appears in the odd Legendre coefficients and is interpreted in terms of a (1/2, 3/2)- excited state of 5He with Ex ≈ 19.6 MeV. Broad structure in the differential cross section near 6 MeV, principally in the even Legendre coefficients, corresponds to an even parity state 5He*(20.0). For other polarization measurements (and for references) see (1979AJ01). For d-t correlations see (1987PO03). See also "Complex reactions" in the 5He "GENERAL" section and (1981PL1A, 1983HAYX, 1986BO01; theor.).
At Et = 0.5 MeV, the reaction appears to proceed via three channels: (i) direct breakup into 4He + 2n, the three-body breakup shape being modified by the n-n interaction; (ii) sequential decay via 5He(0); (iii) sequential decay via a broad excited state of 5He. The width of 5He(0) is estimated to be 0.74 ± 0.18 MeV. Some evidence is also shown for 5He* at Ex ≈ 2 MeV, Γ ≈ 2.4 MeV: see (1979AJ01). See also 6He and (1986BA73; theor.).
The coherent scattering length (thermal, bound) is 3.07 ± 0.02 fm, pol. σs = 0.76 ± 0.01 b. Total cross sections have been measured for En = 4 × 10-4 eV to 150.9 MeV and at 10 GeV/c [see (1984AJ01)] and at En = 1.5 to 40 MeV (1983HA20).
The total cross section has a peak of 7.6 b at En = 1.15 ± 0.05 MeV, Ec.m. = 0.92 ± 0.04 MeV, with a width of about 1.2 MeV: see (1966LA04). A second resonance is observed at En = 22.133 ± 0.010 MeV [σpeak = 0.9 b] with a total width of 76 ± 12 keV and Γn = 37 ± 15 keV (1983HA20). Attempts to detect additional resonances in the total cross section have been unsuccessful: see (1966LA04).
The P3/2 phase shift shows strong resonance behavior near 1 MeV, while the P1/2 phase shift changes more slowly, indicating a broad P1/2 level at several MeV excitation. (1966HO07) have constructed a set of phase shifts for En = 0 to 31 MeV, l = 0, 1, 2, 3, using largely p-α phase shifts. At the 3/2+ state the best fit to all data is given by Eres = 17.669 MeV ± 10 keV, γ2d = 2.0 MeV ± 25%, γ2n = 50 keV ± 20% (see Table 5.2 ( in PDF or PS) in (1979AJ01)).
An R-function analysis of the 4He + n data below 21 MeV (including absolute neutron analyzing power measurement and accurate cross section measurements) has led to a set of phase shifts and analyzing powers which are based on the 4He + n data alone (rather than also including the 4He + p data). At r = 3.3 fm the values obtained for the P1/2 and P3/2 resonances are, respectively, Ec.m. = 1.97 and 0.77 MeV, Γc.m. = 5.22 and 0.64 MeV: see (1984AJ01). Angular distributions of Ay have been studied by (1984KL05, 1984KR23, 1986KL04) for Epol. n = 15 to 50 MeV: see also for phase-shift analysis and comparison with 4He(p, p).
The excitation energies and the spectroscopic factors for 5He states are obtained by (1985BA68) from 2-level R-matrix fits to the phase shifts, as functions of the channel radius. For a ≈ 5.1 fm a very broad state with Jπ = 1/2+ is found to lie at Ex ≈ 7 MeV in both 5He and 5Li, in agreement with the shell-model calculation by (1984VA06). Broad 3/2+ and 5/2+ states then lie at ≈ 14 MeV and the 1/2- state is at about 2.6 MeV. (1985BA68) suggest that the phase-shift analysis should be redone with values of a larger than those previously used (a ≈ 3 fm). See also (1984AJ01, 1984SI1A, 1985AL1D, 1985SI1B, 1985WI1B, 1986BA1Y), (1986BU1D, 1986DO1H; applications) and (1981PL1A, 1982AZ02, 1983DM01, 1983KU06, 1984BL21, 1984FI20, 1984SC1A, 1984SHZK, 1985HA04, 1985HO1B, 1985KI11, 1985MI1F, 1985NEZW, 1985SO06, 1985SO08, 1985SP05, 1985TI07, 1985TI08, 1986CA1K, 1986KO1J, 1986OK06, 1986WI04, 1987CA13, 1987DU1B, 1987HA44, 1987KR16, 1987MO1K, 1987PO1G, 1987QI01, 1987SH09, 1987SO04, 1987US1A, 1987VA36; theor.). For the breakup reaction see (1987MI1N; theor.).
A typical proton spectrum (reaction (a)) consists of a peak corresponding to the formation of the ground state of 5He, plus a continuum of protons ascribed to reaction (b). A study of the latter reaction shows evidence for sequential decay via 5He*(0, 16.7 ± 0.1 [Γ = 80 ± 30 keV]) and suggests some fine structure near Ex = 19 MeV [see also reactions 12 and 20]: see (1979AJ01). Differential cross sections and VAP have been measured for the ground state group at E pol. d = 5.4, 6.0, and 6.8 MeV (1985LU08; also TAP) and at 6 to 11 MeV (1985OS02). At Eα = 28.3 MeV tensor polarization measurements involving the ground state transitions to 5He (and 5Li) deviate from theoretical predictions which assume charge symmetry (1985WI15). See also 6Li (1988PUZZ; Epol. d = 2.1 GeV) and (1985DO03, 1985NEZW, 1986KO1J, 1987FU10, 1987KA1M, 1987KUZI; theor.).
(1988WO10) report a study of this reaction and of the 4He(7Li, 6He)5Li reaction at E(7Li) = 50 MeV, and of the 6Li(12C, 13N)5He and 6Li(13C, 14C)5Li reactions at E(C) = 90 MeV. Properties of the two lowest states of A = 5, from R-matrix parameters (a = 5.5 fm), are displayed in Table 5.2 (in PDF or PS). Positive-parity states are then predicted to lie at Ex ≈ 5 MeV (1/2+) and 12 MeV (3/2+, 5/2+) in 5He - 5Li (1988WO10).
At Eγ = 60 MeV, the proton spectrum shows two prominent peaks attributed to 5He*(0 + 4.0, 20 ± 2): see (1979AJ01). The (γ, p0+1) cross section has been reported for Eγ = 34.5 to 98.8 MeV. A broad secondary structure is also observed (1988CA11). In reaction (b) the missing energy spectrum show strong peaks due to 5He*(0, 16.7) and possibly some strength in the region Ex = 5 - 15 MeV (1986LAZH; prelim.). See also 6Li. At Eπ+ = 130 and 150 MeV, 5He*(0, 16.7) are populated (1987HU02).
Angular distributions of d0 have been studied at En = 6.6 to 56.3 MeV. At En = 56.3 MeV angular distributions have also been obtained to 5He*(16.7) and, possibly, to two higher states: see (1979AJ01, 1984AJ01). See also (1986BOZG).
At Ep =100 MeV the population of 5He*(0, 16.7) and possibly of a broad structure at Ex ≈ 19 MeV is observed: momentum distributions for 5He*(0, 16.7) and angular correlation measurements are also reported. Recent work is reported at Ep = 47 and 70 MeV (1983VD03), 70 MeV (1983GO06) and 1 GeV (1985BE30, 1985DO16). See also (1984AJ01).
5Heg.s. has been observed at Ed = 14.5 MeV: see (1979AJ01).
At Eα = 140 MeV 5He*(0, 20.0) are populated: see (1984AJ01).
Angular distributions have been obtained at E(6Li) = 156 MeV to 5Heg.s.. Unresolved states at Ex = 16 - 20 MeV are also populated (1987MI34).
At Ep = 43.7 MeV, angular distributions of the 3He groups to the ground state of 5He (Γ = 0.80 ± 0.04 MeV; L = 0 + 2) and to levels at 16.7 MeV (L = 1) and 19.9 ± 0.4 MeV (Γ = 2.7 MeV) have been studied. Since no transitions are observed in the 7Li(p, t)5Li reaction to the analog 20 MeV state in 5Li [see 5Li], the transition is presumably S-forbidden and the states in 5He - 5Li near 20 MeV are 4D3/2 or 4D5/2 [compare 3H(d, d)]. Particle-particle coincidence data have been obtained at Ep = 43.7 MeV. They suggest the existence of 5He*(20.0) with Γ = 3.0 ± 0.6 MeV and of a broad state at ≈ 25 MeV. No T = 3/2 states decaying via T = 1 states in 4He were observed: see (1979AJ01). In reaction (b) 5He*(0 + 4, 16.7, 25) appear to be involved at Ep = 670 MeV (1981ER10) while at 200 MeV some structure at Ex ≈ 20 MeV is reported in addition to the ground state (1986WA11).
At Ed = 24 MeV, the α-particle spectrum from reaction (a) shows structures corresponding to the ground and 16.7 MeV states and to states at Ex ≈ 20.2 and 23.8 MeV with Γ ≈ 2 MeV and ≈ 1 MeV, respectively. Reaction (b) proceeds mainly via excited states of 8Be and 5Heg.s. and possibly as well 5He*(4.): see (1979AJ01). See also (1987WA21) and 8Be.
A kinematically complete experiment is reported at E(3He) = 120 MeV. The cross section for reaction (b) is an order of magnitude greater than that for reaction (a). The missing mass spectrum for the composite of both reactions suggests the population of several states of 5He, in addition to 5He*(0, 16.7, 20.0), including a state at 35.7 ± 0.4 MeV with a width of ≈ 2 MeV (1985FR01).
The angular distribution to 5Heg.s. has been measured at Ed = 13.6 MeV (1984SH1F; prelim.).
An angular distribution has been measured at Ed = 13.6 MeV involving 5Heg.s. and 7Be*(0.43) (1983DO10).