A=6He (1984AJ01)

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⁶He (1984AJ01)

(See Energy Level Diagrams for ⁶He)

GENERAL: See also (1979AJ01) and Table 6.1 [Table of Energy Levels] (in PDF or PS).

Model Calculations: (1979SHZV, 1980FI1D, 1981KU13, 1982FI13, 1982KR1B, 1982LE11, 1982VO01).

Special states: (1982FI13, 1983DE16, 1983KR05, 1983LE01).

Electromagnetic transitions: (1982AW02).

Complex reactions involving ⁶He: (1978DU1B, 1978VO1A, 1979BO22, 1979VI05, 1980BO31, 1980WI1L, 1981BO1X, 1981CU05, 1981VO10, 1982BO1Q, 1982BO35, 1982BO40, 1982GU1H, 1982HE1D, 1983JA1C).

Muon and neutrino capture and reactions: (1978SE1B, 1979DE1D, 1979WA1D, 1980BR1A, 1980MU1B).

Reactions involving pion and other mesons: (1978FU09, 1979BA16, 1979BA1M, 1979DO1C, 1979PE1C, 1979SH1D, 1979WI1A, 1980BE20, 1981BA1M, 1981DU1H, 1981NI03, 1981SH06, 1982BO11).

Hypernuclei: (1978PO1A, 1978SO1A, 1980VE2B, 1981BA2P, 1981WA1J, 1982BA1Y, 1982BA2N, 1982BA2R, 1982KO1L).

Other topics: (1978FI12, 1979SHZV, 1979VA1A, 1981PAZZ, 1982AW02, 1982MO1Q, 1982NG01, 1982ZO1B, 1983BA2F, 1983BA3A, 1983DE16, 1983NA03).

Ground state of ⁶He: (1978SM02, 1981AV02, 1981PAZZ, 1982FI13, 1982KR1B, 1982LE11, 1982NG01, 1982VO01, 1983LE01).

1. ⁶He(β^-)⁶Li Q_m = 3.507

The decay proceeds to the ground state of ⁶Li [J^π = 1⁺] and is a super-allowed Gamow-Teller transition. Recent half-life measurements are 808.1 ± 2.0 msec (1974WI14), 798.1 ± 1.0 msec (1981BA58), 805.4 ± 2.0 msec (1982AL17): see Table 6.2 (in PDF or PS) in (1966LA04) for a listing of earlier determinations. We adopt the mean of the (1974WI14, 1982AL17) values, τ_1/2 = 806.7 ± 1.5 msec; log ft = 2.910 ± 0.002. See also (1979AJ01, 1979DO1A) and (1977SA1A, 1978SE1B, 1979DE15, 1981PAZZ; theor.).

2. (a) ³H(t, n)⁵He Q_m = 10.44 E_b = 12.305
(b) ³H(t, 2n)⁴He Q_m = 11.3322
(c) ³H(t, d)⁴H Q_m = -8.9
(d) ³H(t, 3n)³He Q_m = -9.2456
(e) ³H(t, t)³H

The cross section for neutron production (reactions (a) and (b)) rises monotonically from 40 keV to 2.2 MeV. The zero-energy cross section factor S₀ ≈ 300 keV · b. The cross section for reaction (b) increases monotonically for E_t = 34 to 160 keV. (1981JA1F) suggests that the (t, 2n) cross sections below E_t = 300 keV are poorly known and may be subject to large systematic errors. For the earlier work on these reactions, and for references, see (1974AJ01, 1979AJ01). See also (1979OH1B, 1981HA1P), (1982SL1A) and (1979HA1C, 1980HA1Y, 1981GE1C; theor.).

3. ⁴He(t, p)⁶He Q_m = -7.506

Angular distributions of the protons to ⁶He*(0, 1.80) have been measured at E_t = 22 and 23 MeV. [No L-values were assigned.] No other states are observed with E_x ≲ 4.2 MeV: see (1979AJ01).

4. ⁴He(α, 2p)⁶He Q_m = -27.320

See (1978GL03, 1982GL01: E_α = 61.5 → 158.2 MeV). See also ⁸Be.

5. ⁶Li(e, π⁺)⁶He Q_m = -143.074

From measurements at E_e = 170, 180 and 195 MeV, angular distributions of (γ, π⁺) to ⁶He*(0, 1.80) are derived by (1979SH1D, 1981SH06).

6. (a) ⁶Li(π^-, γ)⁶He Q_m = 136.061
(b) ⁶Li(π^-, π⁰)⁶He Q_m = 1.098

The excitation of ⁶He*(0, 1.8) and possibly of (broad) states at E_x = 15.6 ± 0.5, 23.2 ± 0.7 and 29.7 ± 1.3 MeV is reported by (1973BA62) from E_γ measurements using a pair spectrometer. See also (1979AJ01). The charge-exchange process with stopped pions (reaction (b)) has been studied by (1981BA16).

7. ⁶Li(n, p)⁶He Q_m = -2.724

Angular distributions of the p₀ group are reported at E_n = 4.7 to 6.8 MeV and at 14 MeV [see (1979AJ01)] and at E_n = 59.6 MeV (1982BR04). There is no evidence for the excitation of ⁶He*(1.8) (1982BR04). See also (1980MI02) and ⁷Li.

8. ⁶Li(d, 2p)⁶He Q_m = -4.949

At E_d = 55 MeV the population of ⁶He*(0, 1.8) [the latter weak] is observed: no other states are observed with E_x ≲ 25 MeV (1979ST15).

9. ⁶Li(t, ³He)⁶He Q_m = -3.488

The ground-state angular distribution has been studied at E_t = 17 MeV. At E_t = 22 MeV only ⁶He*(0, 1.8) are populated with E_x ≲ 8.5 MeV. See (1979AJ01) for additional discussion and for references. See also (1983AB1A).

10. ⁶Li(⁶Li, ⁶Be)⁶He Q_m = -7.795

Angular distributions have been studied at E(⁶Li) = 32 amd 36 MeV for the transitions to ⁶He_g.s., ⁶Be_g.s. and, in inelastic scattering of ⁶Li [see ⁶Li], to the analog state ⁶Li*(3.56): for a discussion of these see the references quoted in (1979AJ01).

11. ⁶Li(⁷Li, ⁷Be)⁶He Q_m = -4.369

At E(⁷Li) = 78 MeV, ⁶He*(0, 1.8) are populated (1982AL1G).

12. (a) ⁷Li(γ, p)⁶He Q_m = -9.975
(b) ⁷Li(e, ep)⁶He Q_m = -9.975

At E_γ = 60 MeV, the proton spectrum shows two prominent peaks attributed to ⁶He*(0 + 1.8, 18 ± 3): see (1979AJ01). For reaction (b) see (1980AS02: E_e = 108, 163 and 198 MeV). See also ⁷Li.

13. ⁷Li(n, d)⁶He Q_m = -7.750

At E_n = 60 MeV, the deuteron spectrum shows two prominent peaks attributed to states centered at E_x = 13.6, 15.4 and 17.7 MeV (± 0.5 MeV) and a possible state or states (populated with a l_p transfer ≥ 2) at E_x = 23.7 MeV. DWBA analyses of the d₀ and d₁ groups are consistent with l_p = 1 and S(1p_3/2) = 0.62 for ⁶He_g.s. and to S(1p_3/2) = 0.37, S(1p_1/2) = 0.32 for ⁶He*(1.8) (1977BR17). See (1974AJ01) for earlier measurements.

14. ⁷Li(p, 2p)⁶He Q_m = -9.975

The summed proton spectrum at E_p = 100 MeV shows ⁶He*(0, 1.8) and a broad group centered at E_x ≈ 14 MeV: the angular correlation for ⁶He_g.s. is in quite good agreement with DWIA: see (1979AJ01).

15. ⁷Li(d, ³He)⁶He Q_m = -4.481

Angular distributions of the ³He ions to ⁶He*(0, 1.8) have been measured at E_d = 14.4 and 22 MeV: they have a l_p = 1 character and therefore these two states have J^π = (0 - 3)⁺. There is no evidence for any other states of ⁶He with E_x < 10.7 MeV: see (1979AJ01).

16. ⁷Li(t, α)⁶He Q_m = 9.839

The energy of the first excited state is 1.797 ± 0.025 MeV, Γ = 113 ± 20 keV. ⁶He*(1.80) decays into ⁴He + 2n. The branching ratio Γ_γ/Γ_α ≤ 2 × 10^-6: for Γ_c.m. = 113 ± 20 keV, Γ_γ ≤ 0.23 eV. Angular distributions of the α₀ and α₁ groups have been measured at E_t = 13 and 22 MeV. No other α-groups are reported corresponding to ⁶He states with E_x < 24 MeV (region between E_x ≈ 13 and 16 MeV was obscured by the presence of breakup α-particles): see (1979AJ01). See also ¹⁰Be.

17. ⁷Li(³He, p³He)⁶He Q_m = -9.975

At E(³He) = 120 MeV a kinematically complete experiment has been carried out by (1980VO1B): in addition to ⁶He_g.s. a structure corresponding to E_x = 17 MeV, Γ < 5 MeV is reported.

18. ⁷Li(⁷Li, ⁸Be)⁶He Q_m = 7.280

See (1981BA58).

19. ⁹Be(n, α)⁶He Q_m = -0.598

Angular distributions have been reported for E_n = 12.2 to 18.0 MeV (α₀, α₁). No other states are observed with E_x ≲ 7 MeV: see (1979AJ01). See also ¹⁰Be.

20. ⁹Be(t, ⁶Li)⁶He Q_m = -5.380

At E_t = 21.5 and 23.5 MeV, angular distributions have been studied for the transitions to ⁶He*(0, 1.8) and ⁶Li*(0, 2.19, 3.56): see (1979AJ01). See also reaction 38 in ⁶Li and (1983WE02; theor.).

21. ⁹Be(³He, ⁶Be)⁶He Q_m = -9.687

See (1981DE1X, 1983DE14).