(See Energy Level Diagrams for 6He)
Electromagnetic transitions: (1982AW02).
The decay proceeds to the ground state of 6Li [Jπ = 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, τ1/2 = 806.7 ± 1.5 msec; log ft = 2.910 ± 0.002. See also (1979AJ01, 1979DO1A) and (1977SA1A, 1978SE1B, 1979DE15, 1981PAZZ; theor.).
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 Et = 34 to 160 keV. (1981JA1F) suggests that the (t, 2n) cross sections below Et = 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.).
Angular distributions of the protons to 6He*(0, 1.80) have been measured at Et = 22 and 23 MeV. [No L-values were assigned.] No other states are observed with Ex ≲ 4.2 MeV: see (1979AJ01).
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. See also (1979AJ01). The charge-exchange process with stopped pions (reaction (b)) has been studied by (1981BA16).
Angular distributions of the p0 group are reported at En = 4.7 to 6.8 MeV and at 14 MeV [see (1979AJ01)] and at En = 59.6 MeV (1982BR04). There is no evidence for the excitation of 6He*(1.8) (1982BR04). See also (1980MI02) and 7Li.
At Ed = 55 MeV the population of 6He*(0, 1.8) [the latter weak] is observed: no other states are observed with Ex ≲ 25 MeV (1979ST15).
The ground-state angular distribution has been studied at Et = 17 MeV. At Et = 22 MeV only 6He*(0, 1.8) are populated with Ex ≲ 8.5 MeV. See (1979AJ01) for additional discussion and for references. See also (1983AB1A).
Angular distributions have been studied at E(6Li) = 32 amd 36 MeV for the transitions to 6Heg.s., 6Beg.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).
At E(7Li) = 78 MeV, 6He*(0, 1.8) are populated (1982AL1G).
At En = 60 MeV, the deuteron spectrum shows two prominent peaks attributed to states centered at Ex = 13.6, 15.4 and 17.7 MeV (± 0.5 MeV) and a possible state or states (populated with a lp transfer ≥ 2) at Ex = 23.7 MeV. DWBA analyses of the d0 and d1 groups are consistent with lp = 1 and S(1p3/2) = 0.62 for 6Heg.s. and to S(1p3/2) = 0.37, S(1p1/2) = 0.32 for 6He*(1.8) (1977BR17). See (1974AJ01) for earlier measurements.
The summed proton spectrum at Ep = 100 MeV shows 6He*(0, 1.8) and a broad group centered at Ex ≈ 14 MeV: the angular correlation for 6Heg.s. is in quite good agreement with DWIA: see (1979AJ01).
Angular distributions of the 3He ions to 6He*(0, 1.8) have been measured at Ed = 14.4 and 22 MeV: they have a lp = 1 character and therefore these two states have Jπ = (0 - 3)+. There is no evidence for any other states of 6He with Ex < 10.7 MeV: see (1979AJ01).
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 Γγ/Γα ≤ 2 × 10-6: for Γc.m. = 113 ± 20 keV, Γγ ≤ 0.23 eV. Angular distributions of the α0 and α1 groups have been measured at Et = 13 and 22 MeV. No other α-groups are reported corresponding to 6He states with Ex < 24 MeV (region between Ex ≈ 13 and 16 MeV was obscured by the presence of breakup α-particles): see (1979AJ01). See also 10Be.
At E(3He) = 120 MeV a kinematically complete experiment has been carried out by (1980VO1B): in addition to 6Heg.s. a structure corresponding to Ex = 17 MeV, Γ < 5 MeV is reported.