A=6He (1974AJ01)

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⁶He (1974AJ01)

(See Energy Level Diagrams for ⁶He)

GENERAL: See also (1966LA04) and Table 6.1 [Table of Energy Levels] (in PDF or PS).

Model calculations: (1965VO1A, 1966BA26, 1967HE01, 1967TH02, 1968BA35, 1968FA1B, 1968GO24, 1968VA1H, 1969HE1G, 1969LA19, 1969SO08, 1969TH1C, 1970AH1C, 1971JA06).

Meson and muon interactions: (1970DE1M, 1970PA1E, 1972MU07, 1972TR1E, 1973BA2G, 1973BA62, 1973KA1D, 1973MU11, 1973VE1F, 1974VE02).

Special reactions: (1965WH10, 1967AU1B, 1969KR20, 1970KR1G, 1972VO06, 1973FO09, 1973KO1D).

Astrophysical questions: (1970BA1M).

Other topics: (1965RA1A, 1965VO1A, 1967AN1A, 1968EW1A, 1968LE02, 1969AL1D, 1969GI1A, 1969HO1M, 1969LA19, 1969IN1A, 1969SH1A, 1970AL14, 1970FO1B, 1970PA1D, 1970SU1B, 1971LO13, 1971ST40, 1972CA37, 1972GH1A, 1972PN1A, 1973JU2A).

Ground state properties: (1965VO1A, 1968LE02).

1. ⁶He(β^-)⁶Li Q_m = 3.510

The decay proceeds to the ground state of ⁶Li [J^π = 1⁺] and is a super-allowed Gamow-Teller transition. The half-life is 808.1 ± 2.0 msec. Using this τ_1/2 and E_β^-(max) = 3508.4 ± 3.8 keV (1963JO04), log ft = 2.911 ± 0.003 (D.E. Alburger and D.H. Wilkinson, private communication). See Table 6.2 (in PDF or PS) in (1966LA04) for a listing of earlier τ_1/2 determinations.

The internal bremsstrahlung spectrum has been measured by (1965BI09). The electron-neutrino correlation results are in good agreement with pure axial vector interaction. An upper limit to the possible admixture of tensor interaction is 0.4% (1963JO15). See also the discussion in (1970PA23).

See also (1964FO1A; astrophys. considerations), (1968DA1J), (1966BA1A, 1966BA26, 1968GO24, 1968LE02, 1968VA1H, 1969KA1B, 1969KU13, 1969LA1D, 1970DA21, 1972LA07, 1973HA49, 1974VE02, 1973WI11; theor.) and (1966LA04).

2. (a) ³H(t, n)⁵He Q_m = 10.44 E_b = 12.303
(b) ³H(t, 2n)⁴He Q_m = 11.3324
(c) ³H(t, d)⁴H Q_m = -9.2
(d) ³H(t, 3n)³He Q_m = -9.2460

The cross section for neutron production (reactions (a) and (b)) rises monotonically from 40 keV to 2.2 MeV (1951AG30, 1957JA37, 1958JA06, 1971ST13). The zero-energy cross-section factor S₀ ≈ 300 keV · b (1964PA1A). At E_t = 1.90 MeV, the total cross section for production of α-particles is 106 ± 5 mb (1958JA06).

A kinematically complete study of reaction (b) gives a_nn = -15.0 ± 1.0 fm for the ¹S₀ scattering length (1972KU08): see this paper for a review of other a_nn determinations. See also (1970GR17, 1970PO05, 1972KU1N), (1969LA1F) and (1970SL1B).

For reaction (a) see also ⁵He. For reaction (c) see (1967JA07) and (1968ME03). For reaction (d) see (1968OH04). For a review of the earlier work see (1966LA04).

3. ³H(t, t)³H E_b = 12.303

Differential cross sections have been measured for E_t = 1.58 to 2.01 MeV (1956HO12) and at 1.90 MeV (1958AL05). See also (1968TH01; theor.).

4. ⁴He(t, p)⁶He Q_m = -7.511

At E_t = 22 MeV, angular distributions of the protons to ⁶He*(0, 1.80) have been measured. No other states are observed with E_x ≲ 4.2 MeV (1971ST05). See also (1970BA1V).

5. ⁶Li(π^-, γ)⁶He Q_m = 136.059

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. 4.4 ± 0.6% of stopped pions were absorbed radiatively: the branching ratios of ⁶He*(0, 1.8) are 0.31 ± 0.04% and 0.15 ± 0.03%, respectively (1973BA62).

6. ⁶Li(n, p)⁶He Q_m = -2.727

At E_n = 14 MeV the p₀ angular distribution is similar in shape to the angular distributions in ⁶Li(p, p')⁶Li*(3.56) and in ⁶Li(p, n)⁶Be_g.s.. The ratios of the cross sections for these isobaric analog transitions are consistent with charge independence (1972ME05). See also (1967ME11, 1970ME1J, 1973BO1Y), (1969MA1L; theor.) and ⁷Li.

7. ⁶Li(t, ³He)⁶He Q_m = -3.491

At E_t = 22 MeV, the only states which are observed with E_x ≲ 8.5 MeV are ⁶He(0) and ⁶He*(1.80) (1971ST05).

8. ⁶Li(³He, 3p)⁶He Q_m = -10.446

This reaction has been studied at E(³He) = 53.2 MeV (1970BA41).

9. ⁶Li(⁶Li, ⁶Be)⁶He Q_m = -7.797

Differential cross sections have been measured at E(⁶Li) = 32 and 36 MeV for the reaction going to the ground states of ⁶He and ⁶Be (1973WH02): see reaction 16 in ⁶Li and ¹²C in (1975AJ02). See also (1973WH1C).

10. ⁷Li(γ, p)⁶He Q_m = -9.978

At E_γ = 60 MeV, the proton spectrum shows two prominent peaks attributed to ⁶He*(0 + 1.8, 18 ± 3) (1973GA16). See also (1970SA14) and ⁷Li.

11. ⁷Li(e, e'p)⁶He Q_m = -9.978

See (1966MU1A, 1969BA1F; theor.) and ⁷Li.

12. ⁷Li(n, d)⁶He Q_m = -7.753

At E_n = 14.4 MeV, the angular distribution of the deuterons to ⁶He(0) has been measured and analyzed by DWBA (1970MI05, 1971MI12). See also (1966ME03, 1967ME11, 1973LI02) and ⁸Li.

13. ⁷Li(p, 2p)⁶He Q_m = -9.978

The summed proton spectrum at E_p = 156 MeV shows peaks corresponding to ⁶He*(0, 1.80) [partially resolved] and E_x = (13.4 ± 0.5) MeV [Γ ≈ 1.2 MeV] and (15.3 ± 0.3) MeV [partially resolved]. The angular correlation for ⁶He*(15.3) is consistent with that for a pure s-state. There is no indication of the expected ³³P states in the interval E_x = 4 to 10 MeV (1967RO06). For a summary of the earlier work see Table 6.3 (in PDF or PS) in (1966LA04) [(1966TY01) has now been published: see (1966TY01)]. See also (1965RO15, 1969RU1A) and (1967KO1B; theor.).

14. ⁷Li(d, ³He)⁶He Q_m = -4.488

Angular distributions of the ³He groups to ⁶He*(0, 1.80) have been measured at E_d = 14.4 MeV (1955LE24) and 22 MeV (1971ST05): they are consistent with l = 1 and therefore with J^π = 0⁺, 2⁺ for these two states. The cross sections for formation of these two states at E_d = 23.6 MeV have been compared with those for formation of the analog states of ⁶Li*(3.56, 5.37) in ⁷Li(d, t)⁶Li: see reaction 21 in ⁶Li (1971DE08). There is no evidence for any other states of ⁶He with E_x < 10.7 MeV (1971ST05). See also (1970BA1V).

15. ⁷Li(t, α)⁶He Q_m = 9.837

The energy of the first excited state is 1.797 ± 0.025 MeV, Γ = 113 ± 20 keV (1965AJ01). ⁶He*(1.80) decays into ⁴He + 2n. The branching ratio Γ_γ/ Γ_n is < 4 × 10^-4 (1964HU1A), Γ_γ/Γ_α ≤ 2 × 10^-6 (1966LI1A). Angular distributions of the α₀ and α₁ groups have been measured at E_t = 13 MeV (1965AJ01) and 22 MeV (1971ST05): they are consistent with l = 1 pickup and therefore with J^π = 0⁺, 2⁺ for ⁶He*(0, 1.80). No other α-groups are reported corresponding to ⁶He states with E_x < 12 MeV (1965AJ01), E_x < 24 MeV (1971ST05: E_t = 16 → 22 MeV; region between E_x ≈ 13 and 16 MeV was obscured by presence of breakup α-particles). See also (1966SE1D, 1970AB12) and (1966LA04).

16. ⁷Li(³He, ⁴Li)⁶He Q_m = -12.9

This reaction has been studied at E(³He) = 53.2 MeV (1970BA41).

17. ⁷Li(⁷Li, ⁸Be)⁶He Q_m = 7.278

See (1968ST12).

18. ⁹Be(n, α)⁶He Q_m = -0.602

The α₀ angular distribution has been measured at E_n = 14.4 MeV (1967PA03). See also (1969OG01, 1969VA1F), (1966LA04) and ¹⁰Be.

19. ⁹Be(p, ⁴Li)⁶He Q_m = -24.1

This reaction has been studied at E_p = 45 MeV: the shape of the angular distribution to the ground state is very different from that for the (p, α₂) reaction to the analog state in ⁶Li, indicating different reaction mechanisms (1970DE17, 1971DE2B).

20. ⁹Be(t, ⁶Li)⁶He Q_m = -5.386

At E_t = 23.5 MeV angular distributions have been obtained for the transitions involving ⁶He in the ground and 1.8 MeV states and ⁶Li in the ground, 2.19 and 3.56 MeV states (1973VO08): see also reaction 26 in ⁶Li.

21. (a) ¹⁰B(⁷Li, ⁶He)¹¹C Q_m = -1.287
(b) ¹¹B(⁷Li, ⁶He)¹²C Q_m = 5.979

See (1968ST12).

22. ¹¹B(d, ⁷Be)⁶He Q_m = -11.563

See reaction 20 in ⁷Be and reaction 32 in ⁶Li (1972GO1P).