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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: (1965WH1A, 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, 1972CA37, 1972GH1A, 1972PN1A, 1972ST1C, 1973JU2A).

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

1. 6He(β-)6Li Qm = 3.510

The decay proceeds to the ground state of 6Li [Jπ = 1+] and is a super-allowed Gamow-Teller transition. The half-life is 808.1 ± 2.0 msec. Using this τ1/2 and Eβ-(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 τ1/2 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 Qm = 10.44 Eb = 12.303
(b) 3H(t, 2n)4He Qm = 11.3324
(c) 3H(t, d)4H Qm = -9.2
(d) 3H(t, 3n)3He Qm = -9.2460

The cross section for neutron production (reactions (a) and (b)) rises monotonically from 40 keV to 2.2 MeV (1951AG30, 1957JA37, 1958JA06, 1971ST1M). The zero-energy cross-section factor S0 ≈ 300 keV · b (1964PA1A). At Et = 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 ann = -15.0 ± 1.0 fm for the 1S0 scattering length (1972KU08): see this paper for a review of other ann 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 Eb = 12.303

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

4. 4He(t, p)6He Qm = -7.511

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

5. 6Li(π-, γ)6He Qm = 136.059

The excitation of 6He*(0, 1.8) and possibly of (broad) states at Ex = 15.6 ± 0.5, 23.2 ± 0.7 and 29.7 ± 1.3 MeV is reported by (1973BA62) from Eγ 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 Qm = -2.727

At En = 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)6Beg.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 Qm = -3.491

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

8. 6Li(3He, 3p)6He Qm = -10.446

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

9. 6Li(6Li, 6Be)6He Qm = -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 Qm = -9.978

At Eγ = 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 Qm = -9.978

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

12. 7Li(n, d)6He Qm = -7.753

At En = 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 Qm = -9.978

The summed proton spectrum at Ep = 156 MeV shows peaks corresponding to 6He*(0, 1.80) [partially resolved] and Ex = (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 Ex = 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 Qm = -4.488

Angular distributions of the 3He groups to 6He*(0, 1.80) have been measured at Ed = 14.4 MeV (1955LE24) and 22 MeV (1971ST05): they are consistent with l = 1 and therefore with Jπ = 0+, 2+ for these two states. The cross sections for formation of these two states at Ed = 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 Ex < 10.7 MeV (1971ST05). See also (1970BA1V).

15. 7Li(t, α)6He Qm = 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 Γγ/ Γn is < 4 × 10-4 (1964HU1A), Γγα ≤ 2 × 10-6 (1966LI1A). Angular distributions of the α0 and α1 groups have been measured at Et = 13 MeV (1965AJ01) and 22 MeV (1971ST05): they are consistent with l = 1 pickup and therefore with Jπ = 0+, 2+ for 6He*(0, 1.80). No other α-groups are reported corresponding to 6He states with Ex < 12 MeV (1965AJ01), Ex < 24 MeV (1971ST05: Et = 16 → 22 MeV; region between Ex ≈ 13 and 16 MeV was obscured by presence of breakup α-particles). See also (1966SE1D, 1970AB12) and (1966LA04).

16. 7Li(3He, 4Li)6He Qm = -12.9

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

17. 7Li(7Li, 8Be)6He Qm = 7.278

See (1968ST12).

18. 9Be(n, α)6He Qm = -0.602

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

19. 9Be(p, 4Li)6He Qm = -24.1

This reaction has been studied at Ep = 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 Qm = -5.386

At Et = 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 Qm = -1.287
(b) 11B(7Li, 6He)12C Qm = 5.979

See (1968ST12).

22. 11B(d, 7Be)6He Qm = -11.563

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