A=6He (1988AJ01)

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⁶He (1988AJ01)

(See Energy Level Diagrams for ⁶He)

GENERAL: See also (1984AJ01) and Table 6.1 [Table of Energy Levels] (PDF or PS) here.

Model calculations: (1983GA12, 1983LE14, 1984FI14, 1984PA08, 1984VA06, 1985EM01, 1985FI1E, 1986EM02, 1986FI07, 1986KU08, 1986KU1F, 1986VA13, 1986VO09, 1987DA1H, 1988KA1J).

Special states: (1984FI14, 1984FIZW, 1984VA06, 1985EM01, 1985FI1E, 1986EM02, 1986FI07, 1986KU08, 1986VA13, 1986VO09, 1986WI04, 1987BL18, 1987DA1G, 1987DA1H, 1987KO39, 1987KUZI, 1988DA1E).

Electromagnetic transitions: (1984VA1B, 1985FI1E, 1986FI07).

Complex reactions involving ⁶He: (1982AL33, 1983AN13, 1983KU1B, 1983OL1A, 1984BA1H, 1984GL06, 1984KO1A, 1984LA27, 1984WE03, 1985BA1C, 1985BO1J, 1985JA18, 1985MA02, 1985MA13, 1985WO11, 1986AV1B, 1986CS1A, 1986EN1B, 1986MA1V, 1986SA30, 1986SIZS, 1986WE1C, 1987BA1I, 1987BA38, 1987BA39, 1987BO40, 1987GR11, 1987GU1L, 1987KO1Z, 1987PE1C, 1987TAZU, 1987WI09, 1987YA16, 1988AL1G, 1988LI1A, 1988ST06, 1988TA1A, 1988WO10).

Applications: (1985TA1D).

Muon and neutrino capture and reactions: (1983JU01, 1984WA1J).

Reactions involving pions, other mesons and baryon states (see also reactions 4 and 5): (1982BE1D, 1984KO16, 1984RE1C, 1984ZA1A, 1985ER06, 1985RE1B, 1986AK1A, 1986HA1L, 1987FA1H, 1987JA1C).

Hypernuclei: (1982KA1D, 1982MO1B, 1982WA1A, 1983BA1D, 1983MO1C, 1983SH1E, 1984BO1D, 1984BO1G, 1984BO1H, 1984CH1G, 1984DZ1A, 1984KE1C, 1984MI1E, 1984MO1H, 1984ZH1B, 1985BA1E, 1985GU1J, 1985IK1A, 1985MO1F, 1986BO1E, 1986DA1B, 1986PO1G, 1986PO1H, 1986WA1J, 1986ZH1B, 1987BO1L, 1987BO1O, 1987CO1S, 1987DZ1B, 1987JI1A, 1987PO1H, 1987SU1K, 1987WA36, 1987YA1M, 1988GI1B, 1988JI1A, 1988PO1H, 1988TA29).

Other topics: (1983BA1L, 1984FI14, 1985AN28, 1986KO1N, 1986KU1F, 1987AJ1A, 1988DA1E).

Ground state of ⁶He: (1983ANZQ, 1983GR26, 1983LE14, 1984FR13, 1984PA08, 1985AN28, 1985FI1E, 1985SA32, 1986KU08, 1986VO09, 1987BL18, 1987HA30, 1987HA34, 1987SA15, 1988DAZW, 1988JO1C).

The interaction nuclear radius of ⁶He is 2.18 ± 0.02 fm (1985TA18, 1985TA13) [see also for derived nuclear matter, charge and neutron matter rms radii].

1. ⁶He(β^-)⁶Li Q_m = 3.507

The decay proceeds to the ground state of ⁶Li [J^π = 1⁺] via a super-allowed Gamow-Teller transition. The half-life is 806.7 ± 1.5 msec; log ft = 2.910 ± 0.002: see (1984AJ01). See also (1986RO27), (1985GR1A) and (1983LE14, 1984BO03, 1984PA08, 1988SA2J; theor.).

2. (a) ³H(t, n)⁵He Q_m = 10.44 E_b = 12.307
(b) ³H(t, 2n)⁴He Q_m = 11.33216
(c) ³H(t, t)³H

The cross section for reaction (b) has recently been measured for E_t = 30 to 115 keV by (1986BR20, 1985JA16) who have also calculated the astrophysical S-factors [the extrapolated S(0) ≈ 180 keV · b] and discussed the earlier measurements. See also (1974AJ01, 1979AJ01) and (1986JA1E; applied). For muon-catalyzed fusion see (1985ZI1C, 1987BR1V, 1987PO1M). See also (1984BY1A, 1984BY1B, 1984FI1F, 1985BU1B, 1985GU1G, 1985KA1M, 1985VA1B, 1986BA73, 1986BY1A, 1987PR08, 1987WY1A, 1988RYZW; theor.).

3. ⁴He(t, p)⁶He Q_m = 7.507

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. ⁶Li(e, π⁺)⁶He Q_m = 143.075

(1986SH14) report breaks in (e, π⁺) spectra at E_e = 202 MeV corresponding to E_x = 7, 9, 12, 13.6, 17.7 and 24.0 MeV. Using the shape of the virtual photon spectrum results in groups whose angular distributions suggest that the states at 13.6, 17.7 and 24.0 MeV are spin-dipole isovector states [J^π = 1^-, 2^-]. For the earlier work see (1984AJ01). [Note: The states reported here at 7, 9 and 12 MeV are inconsistent with the work reported in reactions 7, 8, 14 and 15, and with the work on the analog region in ⁶Be].

5. (a) ⁶Li(π^-, γ)⁶He Q_m = 136.062
(b) ⁶Li(π^-, π⁰)⁶He Q_m = 1.097

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 has been reported: see (1979AJ01). (1986PE05) have recently studied the capture branching ratios to ⁶He*(0, 1.8). For reaction (b) see (1984AJ01).

6. ⁶Li(n, p)⁶He Q_m = 2.725

Angular distributions of the p₀ group have been reported at E_n = 4.7 to 6.8 MeV, at 14 MeV and at 59.6 MeV [see (1979AJ01, 1984AJ01)] and at 118 MeV (1987PO18; prelim.). At E_n = 59.6 MeV broad structures in the spectra are ascribed to states at E_x = 15.5 ± 0.5 and 25 ± 1 MeV with Γ = 4 ± 1.5 and 8 ± 2 MeV (1983BR32, 1984BR03) [see for discussions of the GDR strength]. The ground state reaction has also been studied at E_n = 198 MeV (1988JA01). See also (1986ALZJ, 1986POZX, 1988MIZX), (1986AU1D, 1987BR32, 1987HE22, 1988HA12) and (1983GM1A, 1985ER06, 1986ER1A; theor.).

7. ⁶Li(d, 2p)⁶He Q_m = -4.949

At E_d = 55 MeV, ⁶He*(0, 1.8) [the latter weak] are populated: no other states are observed with E_x ≤ 25 MeV [see (1984AJ01)].

8. 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 for E_x ≤ 8.5 MeV: see (1979AJ01). Differential cross sections for the transition to ⁶He*(1.8) are reported at E(⁶Li) = 65 MeV (1987AL23).

9. ⁶Li(⁶Li, ⁶Be)⁶He Q_m = -7.795

Angular distributions have been studied for E(⁶Li) = 32 and 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).

10. (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). Reactions (a) and (b) have been studied by (1985SE17). See also ⁷Li, (1984AJ01) and (1986BA2G; theor.).

11. 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 an 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): see (1979AJ01).

12. ⁷Li(p, 2p)⁶He Q_m = -9.975

At E_p = 1 GeV the separation energy between 6 - 7 MeV broad 1p_3/2 and 1s_1/2 peaks is reported to be 14.1 ± 0.7 MeV (1985BE30, 1985DO16). See also (1983GO06) and (1979AJ01).

13. 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 an 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). (1987BO39) [E_d = 30.7 MeV] deduce that the branching ratio of ⁶He*(1.8) into a dineutron [n²: T = 1, S = 0] and an α-particle is 0.75 ± 0.10. See also (1985BO55) and (1987DA31; theor.).

14. 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). Angular distributions have been recently reported at E_t = 0.151 and 0.272 MeV (1987AB09; α₀, α₁) and at E(⁷Li) = 31 MeV. (1987AL23; to ⁶He*(0, 1.8, 13.6)).

15. ⁷Li(³He, p³He)⁶He Q_m = -9.975

At E(³He) = 120 MeV the missing mass spectra show ⁶He*(0, 1.8) and a strong, broad peak corresponding to ⁶He*(16) [possibly due to unresolved states]. There is no indication of a state near 23.7 MeV but there is some evidence of structures at E_x = 32.0 and 35.7 MeV, with Γ ≤ 2 MeV (1985FR01).

16. (a) ⁷Li(⁶Li, ⁷Be)⁶He Q_m = -4.369
(b) ⁷Li(⁷Li, ⁸Be)⁶He Q_m = 7.280

In reaction (a) at E(⁶Li) = 93 MeV a broad peak (Γ = 5.5 MeV) is reported at E_x = 14 MeV. A second structure may also be present at 15.5 MeV (1987GLZW, 1988BUZH; prelim.). ⁶He*(0, 1.8) are also populated (1988BUZH). For reaction (b) see ⁸Be. See also ⁷Be, (1984AJ01), (1988BU1Q) and (1984BA53; theor.).

17. 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). For a study of possible dineutron breakup of ⁶He*(1.8) see (1983OT02). See also ¹⁰Be and (1983SH1J).

18. ⁹Be(⁶Li, ⁹Be)⁶He Q_m = -4.575

See ⁹B.

19. ¹⁰B(n, pα)⁶He Q_m = -7.184

Not observed: see (1984TU02).

20. ¹¹B(⁷Li, ¹²C)⁶He Q_m = 5.983

At E(¹¹B) = 88 MeV the population of the ground state and the first-excited state at E_x = 1.8 ± 0.3 MeV (Γ ≤ 0.2 MeV) is reported (1987BEYI). See also (1988BEYJ).