A=5He (1988AJ01)

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⁵He (1988AJ01)

(See Energy Level Diagrams for ⁵He)

GENERAL: See also (1984AJ01) and Table 5.1 [Table of Energy Levels] (in PDF or PS) here.

Model discussions: (1983JA09, 1984VA06, 1984ZW1A, 1985FI1E, 1985GE06, 1985KW02, 1986KR12, 1988WO04).

Special states: (1982PO12, 1983VO02, 1984BE1B, 1984FI20, 1984GL1C, 1984VA06, 1984VAZS, 1984ZW1A, 1985BA68, 1985FI1E, 1987SV1A, 1988BA75, 1988KW02, 1988US1B).

Electromagnetic transitions: (1985FI1E).

Astrophysical questions: (1984SU1A, 1985BO1E).

Complex reactions involving ⁵He: (1985BO1J, 1985DE17, 1985PO11, 1986CS1A, 1986PO06, 1987BL1K, 1987BO40, 1987KI16, 1987PE1C).

Reactions involving pions: (1984DE52, 1985BE1C, 1985GE06, 1986CE04).

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).

Other topics: (1983BE55, 1984BE1B, 1984PO11, 1985AN28, 1985GI1E, 1986BL1D, 1987SV1A, 1988KW02, 1988US1B).

Ground state of ⁵He: (1983ANZQ, 1984FR13, 1985AN28, 1985FI1E, 1985TA1F, 1985FA01, 1987SV1A, 1988WA08, 1988WO04).

1. ³H(d, γ)⁵He Q_m = 16.70

At low energies the reaction is dominated by a resonance at E_d = 107 keV; the mirror reaction shows resonance at E_d = 430 keV. The branching ratio Γ_γ₀/Γ_n 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 E_d = 45 to 146 keV (1984CE08). Assuming Γ_n of ⁵He*(16.7) is 37 ± 5 keV (see reaction 6), then Γ_γ₀ = 2.1 ± 0.4 eV. (1986MO05) also report branching ratios up to E_d = 0.72 MeV and summarize the earlier work to 5 MeV. For measurements of TAP and VAP at E_{pol. d} = 0.4 and 8.6 MeV, see (1987RIZZ; prelim.). See also (1985RIZZ), (1979AJ01) and (1984NE1B, 1986LA1F, 1988KI1C; applications).

2. (a) ³H(d, n)⁴He Q_m = 17.5894 E_b = 16.70
(b) ³H(d, 2n)³He Q_m = -2.9883
(c) ³H(d, pn)³H Q_m = -2.2259

The cross section has been measured in the range E_t = 12.5 to 117 keV (1984JA08) [0.525(± 4.8%) mb to 3.739(± 1.4%) b] and in the range E_d = 79.913 to 115.901 keV (± 0.015 keV) (1987BR10) [3.849 to 4.734 b (± 1.6%)]. See also (1985FI1G; E_d = 13.8 to 114.3 keV). A strong resonance, σ (peak) = 4.88 b, appears at E_d = 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 E_d = 10 to 500 keV, the cross section is well fitted with the assumption of s-wave formation of a J^π = 3/2⁺ state. Measurements of cross sections and angular distributions for reaction (a) have been reported to E_d = 21 MeV and E_t = 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 E_d = 0.2 to 1.0 MeV indicates intervention of the s-wave, J^π = 1/2⁺ channel, as well as possible p-waves above E_d = 0.3 MeV. The polarization increases monotonically from 0.03 at E_d = 3 MeV to ≈ 0.5 at E_d = 6.5 MeV and then with a lower slope to 0.69 at E_d = 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 E_d = 6 MeV, but then the proton polarization becomes ≈ 15% higher, converging back to the neutron values at E_d ≈ 12 - 13 MeV. This may be due to experimental factors. Vector polarization transfer coefficients, K^y'_y (0^°) have been measured for E_{pol. d} = 5 to 11 MeV (1985HOZU, 1986HO1E; prelim.). For other polarization work see (1984AJ01).

(1987BR10) have derived astrophysical S-factors in the range E_d = 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 E_d = 10.9 to 83 MeV. A study of reaction (c) leads to the suggestion of a resonance at E_c.m. = 2.9 ± 0.3 MeV [E_x = 19.6 MeV], Γ_c.m. = 1.9 ± 0.2 MeV, consistent with J^π = 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.).

3. ³H(d, d)³H E_b = 16.70

The elastic scattering has been studied for E_d = 2.6 to 11.0 MeV: see (1984AJ01). The excitation curves show an interference at E_x ≈ 19 MeV and a broad (Γ > 1 MeV) resonance corresponding to E_x = 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 D_3/2 or D_5/2 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 E_d = 3.2 to 12.3 MeV show resonance-like behavior in the vector analyzing power near E_d = 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 E_x ≈ 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.).

4. ³H(t, n)⁵He Q_m = 10.44

At E_t = 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 E_x ≈ 2 MeV, Γ ≈ 2.4 MeV: see (1979AJ01). See also ⁶He and (1986BA73; theor.).

5. ³He(t, p)⁵He Q_m = 11.20

Some evidence is reported at E_t = 22.25 MeV for a broad state of ⁵He at E_x ≈ 20 MeV, in addition to a sharp peak corresponding to ⁵He*(16.7): see (1979AJ01). See also ⁶Li.

6. ⁴He(n, n)⁴He E_b = -0.89

The coherent scattering length (thermal, bound) is 3.07 ± 0.02 fm, pol. σ_s = 0.76 ± 0.01 b. Total cross sections have been measured for E_n = 4 × 10^-4 eV to 150.9 MeV and at 10 GeV/c [see (1984AJ01)] and at E_n = 1.5 to 40 MeV (1983HA20).

The total cross section has a peak of 7.6 b at E_n = 1.15 ± 0.05 MeV, E_c.m. = 0.92 ± 0.04 MeV, with a width of about 1.2 MeV: see (1966LA04). A second resonance is observed at E_n = 22.133 ± 0.010 MeV [σ_peak = 0.9 b] with a total width of 76 ± 12 keV and Γ_n = 37 ± 15 keV (1983HA20). Attempts to detect additional resonances in the total cross section have been unsuccessful: see (1966LA04).

The P_3/2 phase shift shows strong resonance behavior near 1 MeV, while the P_1/2 phase shift changes more slowly, indicating a broad P_1/2 level at several MeV excitation. (1966HO07) have constructed a set of phase shifts for E_n = 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 E_res = 17.669 MeV ± 10 keV, γ²_d = 2.0 MeV ± 25%, γ²_n = 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 P_1/2 and P_3/2 resonances are, respectively, E_c.m. = 1.97 and 0.77 MeV, Γ_c.m. = 5.22 and 0.64 MeV: see (1984AJ01). Angular distributions of A_y have been studied by (1984KL05, 1984KR23, 1986KL04) for E_{pol. 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 J^π = 1/2⁺ is found to lie at E_x ≈ 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.).

7. ⁴He(p, π⁺)⁵He Q_m = -141.24

Differential cross sections have recently been reported at E_p = 201 MeV (1985LE19) and at E_{pol. p} = 800 MeV (1984HO01; also A_y). See also (1987SO1C) and (1985GE06; theor.).

8. (a) ⁴He(d, p)⁵He Q_m = -3.12
(b) ⁴He(d, pn)⁴He Q_m = -2.22459

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 E_x = 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 E_α = 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; E_pol.
d = 2.1 GeV) and (1985DO03, 1985NEZW, 1986KO1J, 1987FU10, 1987KA1M, 1987KUZI; theor.).

9. ⁴He(⁷Li, ⁶Li)⁵He Q_m = -8.14

(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 E_x ≈ 5 MeV (1/2⁺) and 12 MeV (3/2⁺, 5/2⁺) in ⁵He - ⁵Li (1988WO10).

10. (a) ⁶Li(γ, p)⁵He Q_m = -4.59
(b) ⁶Li(e, ep)⁵He Q_m = -4.59
(c) ⁶Li(π⁺, π⁺p)⁵He Q_m = -4.59

At E_γ = 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 E_γ = 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 E_x = 5 - 15 MeV (1986LAZH; prelim.). See also ⁶Li. At E_π⁺ = 130 and 150 MeV, ⁵He*(0, 16.7) are populated (1987HU02).

11. ⁶Li(n, d)⁵He Q_m = -2.37

Angular distributions of d₀ have been studied at E_n = 6.6 to 56.3 MeV. At E_n = 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).

12. ⁶Li(p, 2p)⁵He Q_m = -4.59

At E_p =100 MeV the population of ⁵He*(0, 16.7) and possibly of a broad structure at E_x ≈ 19 MeV is observed: momentum distributions for ⁵He*(0, 16.7) and angular correlation measurements are also reported. Recent work is reported at E_p = 47 and 70 MeV (1983VD03), 70 MeV (1983GO06) and 1 GeV (1985BE30, 1985DO16). See also (1984AJ01).

13. ⁶Li(d, ³He)⁵He Q_m = 0.90

⁵He_g.s. has been observed at E_d = 14.5 MeV: see (1979AJ01).

14. ⁶Li(α, αp)⁵He Q_m = -4.59

At E_α = 140 MeV ⁵He*(0, 20.0) are populated: see (1984AJ01).

15. ⁶Li(⁶Li, ⁷Be)⁵He Q_m = 1.01

Angular distributions have been obtained at E(⁶Li) = 156 MeV to ⁵He_g.s.. Unresolved states at E_x = 16 - 20 MeV are also populated (1987MI34).

16. ⁶Li(¹²C, ¹³N)⁵He Q_m = -2.65

See reaction 9 (1988WO10).

17. ⁷Li(γ, d)⁵He Q_m = -9.62

See ⁷Li.

18. (a) ⁷Li(π⁺, 2p)⁵He Q_m = 128.51
(b) ⁷Li(π^-, 2n)⁵He Q_m = 126.94

Reaction (a) at E_π⁺ = 59.4 MeV involves ⁵He*(0, 4.) and a broad peak centered at E_x ≈ 21 MeV with Γ ≈ 4 MeV. It is not clear whether ⁵He*(16.7) is populated (1986RI01). See also (1979AJ01, 1984AJ01).

19. ⁷Li(n, t)⁵He Q_m = -3.36

The angular distribution of t₀ has been measured at E_n = 14.4 MeV: see (1979AJ01) and ⁸Li. See also (1986BOZG).

20. (a) ⁷Li(p, ³He)⁵He Q_m = -4.13
(b) ⁷Li(p, pd)⁵He Q_m = -9.62

At E_p = 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 ⁴D_3/2 or ⁴D_5/2 [compare ³H(d, d)]. Particle-particle coincidence data have been obtained at E_p = 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 E_p = 670 MeV (1981ER10) while at 200 MeV some structure at E_x ≈ 20 MeV is reported in addition to the ground state (1986WA11).

21. (a) ⁷Li(d, α)⁵He Q_m = 14.23
(b) ⁷Li(d, n)⁴He⁴He Q_m = 15.1216

At E_d = 24 MeV, the α-particle spectrum from reaction (a) shows structures corresponding to the ground and 16.7 MeV states and to states at E_x ≈ 20.2 and 23.8 MeV with Γ ≈ 2 MeV and ≈ 1 MeV, respectively. Reaction (b) proceeds mainly via excited states of ⁸Be and ⁵He_g.s. and possibly as well ⁵He*(4.): see (1979AJ01). See also (1987WA21) and ⁸Be.

22. (a) ⁷Li(³He, pα)⁵He Q_m = 8.73
(b) ⁷Li(³He, ³He d)⁵He Q_m = -9.62

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).

23. (a) ⁹Be(p, pα)⁵He Q_m = -2.47
(b) ⁹Be(p, d³He)⁵He Q_m = -20.82

Both reactions have been studied at E_p = 26.0 to 101.5 MeV [see (1984AJ01)] and at E_p = 150.5 MeV (1985WA13) [reaction (a)]. See also (1985VD03; theor.).

24. ⁹Be(d, ⁶Li)⁵He Q_m = -9.92

The angular distribution to ⁵He_g.s. has been measured at E_d = 13.6 MeV (1984SH1F; prelim.).

25. (a) ⁹Be(³He, ⁷Be)⁵He Q_m = -0.88
(b) ⁹Be(³He, α)⁴He⁴He Q_m = 19.0043

See (1984AJ01). For reaction (b) see ⁸Be and (1987WA25).

26. ⁹Be(α, 2α)⁵He Q_m = -2.47

See (1984AJ01).

27. ¹⁰B(n, ⁵He)⁶Li Q_m = -5.35

See ⁶Li.

28. ¹⁰B(d, ⁷Be)⁵He Q_m = -1.97

An angular distribution has been measured at E_d = 13.6 MeV involving ⁵He_g.s. and ⁷Be*(0.43) (1983DO10).

29. ¹¹B(⁷Li, ¹³C)⁵He Q_m = 9.06

At E(¹¹B) = 88 MeV a broad structure is observed at E_x = 5.2 ± 0.3 MeV, Γ = 2.0 ± 0.5 MeV (1987BEYI). See also (1988BEYJ).