
^{6}He (1988AJ01)(See Energy Level Diagrams for ^{6}He) 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 ^{6}He: (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 ^{6}He: (1983ANZQ, 1983GR26, 1983LE14, 1984FR13, 1984PA08, 1985AN28, 1985FI1E, 1985SA32, 1986KU08, 1986VO09, 1987BL18, 1987HA30, 1987HA34, 1987SA15, 1988DAZW, 1988JO1C). The interaction nuclear radius of ^{6}He is 2.18 ± 0.02 fm (1985TA18, 1985TA13) [see also for derived nuclear matter, charge and neutron matter rms radii].
The decay proceeds to the ground state of ^{6}Li [J^{π} = 1^{+}] via a superallowed GamowTeller transition. The halflife is 806.7 ± 1.5 msec; log ft = 2.910 ± 0.002: see (1984AJ01). See also (1986RO27), (1985GR1A) and (1983LE14, 1984BO03, 1984PA08, 1988SA2J; theor.).
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 Sfactors [the extrapolated S(0) ≈ 180 keV · b] and discussed the earlier measurements. See also (1974AJ01, 1979AJ01) and (1986JA1E; applied). For muoncatalyzed fusion see (1985ZI1C, 1987BR1V, 1987PO1M). See also (1984BY1A, 1984BY1B, 1984FI1F, 1985BU1B, 1985GU1G, 1985KA1M, 1985VA1B, 1986BA73, 1986BY1A, 1987PR08, 1987WY1A, 1988RYZW; theor.).
Angular distributions of the protons to ^{6}He*(0, 1.80) have been measured at E_{t} = 22 and 23 MeV. [No Lvalues were assigned.] No other states are observed with E_{x} ≤ 4.2 MeV: see (1979AJ01).
(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 spindipole 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 ^{6}Be].
The excitation of ^{6}He*(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 ^{6}He*(0, 1.8). For reaction (b) see (1984AJ01).
Angular distributions of the p_{0} 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.).
At E_{d} = 55 MeV, ^{6}He*(0, 1.8) [the latter weak] are populated: no other states are observed with E_{x} ≤ 25 MeV [see (1984AJ01)].
The groundstate angular distribution has been studied at E_{t} = 17 MeV. At E_{t} = 22 MeV only ^{6}He*(0, 1.8) are populated for E_{x} ≤ 8.5 MeV: see (1979AJ01). Differential cross sections for the transition to ^{6}He*(1.8) are reported at E(^{6}Li) = 65 MeV (1987AL23).
Angular distributions have been studied for E(^{6}Li) = 32 and 36 MeV for the transitions to ^{6}He_{g.s.}, ^{6}Be_{g.s.} and, in inelastic scattering of ^{6}Li [see ^{6}Li], to the analog state ^{6}Li*(3.56): for a discussion of these see the references quoted in (1979AJ01).
At E_{γ} = 60 MeV, the proton spectrum shows two prominent peaks attributed to ^{6}He*(0 + 1.8, 18 ± 3): see (1979AJ01). Reactions (a) and (b) have been studied by (1985SE17). See also ^{7}Li, (1984AJ01) and (1986BA2G; theor.).
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 d_{0} and d_{1} groups are consistent with l_{p} = 1 and S(1p_{3/2}) = 0.62 for ^{6}He_{g.s.} and to S(1p_{3/2}) = 0.37, S(1p_{1/2}) = 0.32 for ^{6}He*(1.8): see (1979AJ01).
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).
Angular distributions of the ^{3}He ions to ^{6}He*(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 ^{6}He with E_{x} < 10.7 MeV: see (1979AJ01). (1987BO39) [E_{d} = 30.7 MeV] deduce that the branching ratio of ^{6}He*(1.8) into a dineutron [n^{2}: T = 1, S = 0] and an αparticle is 0.75 ± 0.10. See also (1985BO55) and (1987DA31; theor.).
The energy of the firstexcited state is 1.797 ± 0.025 MeV, Γ = 113 ± 20 keV. ^{6}He*(1.80) decays into ^{4}He + 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 α_{0} and α_{1} groups have been measured at E_{t} = 13 and 22 MeV. No other αgroups are reported corresponding to ^{6}He states with E_{x} < 24 MeV (region between E_{x} ≈ 13 and 16 MeV was obscured by the presence of breakup αparticles): see (1979AJ01). Angular distributions have been recently reported at E_{t} = 0.151 and 0.272 MeV (1987AB09; α_{0}, α_{1}) and at E(^{7}Li) = 31 MeV. (1987AL23; to ^{6}He*(0, 1.8, 13.6)).
At E(^{3}He) = 120 MeV the missing mass spectra show ^{6}He*(0, 1.8) and a strong, broad peak corresponding to ^{6}He*(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).
In reaction (a) at E(^{6}Li) = 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.). ^{6}He*(0, 1.8) are also populated (1988BUZH). For reaction (b) see ^{8}Be. See also ^{7}Be, (1984AJ01), (1988BU1Q) and (1984BA53; theor.).
Angular distributions have been reported for E_{n} = 12.2 to 18.0 MeV (α_{0}, α_{1}). No other states are observed with E_{x} ≤ 7 MeV: see (1979AJ01). For a study of possible dineutron breakup of ^{6}He*(1.8) see (1983OT02). See also ^{10}Be and (1983SH1J).
See ^{9}B.
Not observed: see (1984TU02).
At E(^{11}B) = 88 MeV the population of the ground state and the firstexcited state at E_{x} = 1.8 ± 0.3 MeV (Γ ≤ 0.2 MeV) is reported (1987BEYI). See also (1988BEYJ).
