
^{6}He (1974AJ01)(See Energy Level Diagrams for ^{6}He) 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).
The decay proceeds to the ground state of ^{6}Li [J^{π} = 1^{+}] and is a superallowed GamowTeller transition. The halflife 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 electronneutrino 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).
The cross section for neutron production (reactions (a) and (b)) rises monotonically from 40 keV to 2.2 MeV (1951AG30, 1957JA37, 1958JA06, 1971ST13). The zeroenergy crosssection factor S_{0} ≈ 300 keV · b (1964PA1A). At E_{t} = 1.90 MeV, the total cross section for production of αparticles is 106 ± 5 mb (1958JA06). A kinematically complete study of reaction (b) gives a_{nn} = 15.0 ± 1.0 fm for the ^{1}S_{0} 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 ^{5}He. For reaction (c) see (1967JA07) and (1968ME03). For reaction (d) see (1968OH04). For a review of the earlier work see (1966LA04).
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.).
At E_{t} = 22 MeV, angular distributions of the protons to ^{6}He*(0, 1.80) have been measured. No other states are observed with E_{x} ≲ 4.2 MeV (1971ST05). See also (1970BA1V).
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 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 ^{6}He*(0, 1.8) are 0.31 ± 0.04% and 0.15 ± 0.03%, respectively (1973BA62).
At E_{n} = 14 MeV the p_{0} angular distribution is similar in shape to the angular distributions in ^{6}Li(p, p')^{6}Li*(3.56) and in ^{6}Li(p, n)^{6}Be_{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 ^{7}Li.
At E_{t} = 22 MeV, the only states which are observed with E_{x} ≲ 8.5 MeV are ^{6}He(0) and ^{6}He*(1.80) (1971ST05).
This reaction has been studied at E(^{3}He) = 53.2 MeV (1970BA41).
Differential cross sections have been measured at E(^{6}Li) = 32 and 36 MeV for the reaction going to the ground states of ^{6}He and ^{6}Be (1973WH02): see reaction 16 in ^{6}Li and ^{12}C in (1975AJ02). See also (1973WH1C).
At E_{γ} = 60 MeV, the proton spectrum shows two prominent peaks attributed to ^{6}He*(0 + 1.8, 18 ± 3) (1973GA16). See also (1970SA14) and ^{7}Li.
See (1966MU1A, 1969BA1F; theor.) and ^{7}Li.
At E_{n} = 14.4 MeV, the angular distribution of the deuterons to ^{6}He(0) has been measured and analyzed by DWBA (1970MI05, 1971MI12). See also (1966ME03, 1967ME11, 1973LI02) and ^{8}Li.
The summed proton spectrum at E_{p} = 156 MeV shows peaks corresponding to ^{6}He*(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 ^{6}He*(15.3) is consistent with that for a pure sstate. There is no indication of the expected ^{33}P 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.).
Angular distributions of the ^{3}He groups to ^{6}He*(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 ^{6}Li*(3.56, 5.37) in ^{7}Li(d, t)^{6}Li: see reaction 21 in ^{6}Li (1971DE08). There is no evidence for any other states of ^{6}He with E_{x} < 10.7 MeV (1971ST05). See also (1970BA1V).
The energy of the first excited state is 1.797 ± 0.025 MeV, Γ = 113 ± 20 keV (1965AJ01). ^{6}He*(1.80) decays into ^{4}He + 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 α_{0} and α_{1} 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 ^{6}He*(0, 1.80). No other αgroups are reported corresponding to ^{6}He 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 αparticles). See also (1966SE1D, 1970AB12) and (1966LA04).
This reaction has been studied at E(^{3}He) = 53.2 MeV (1970BA41).
See (1968ST12).
The α_{0} angular distribution has been measured at E_{n} = 14.4 MeV (1967PA03). See also (1969OG01, 1969VA1F), (1966LA04) and ^{10}Be.
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, α_{2}) reaction to the analog state in ^{6}Li, indicating different reaction mechanisms (1970DE17, 1971DE2B).
At E_{t} = 23.5 MeV angular distributions have been obtained for the transitions involving ^{6}He in the ground and 1.8 MeV states and ^{6}Li in the ground, 2.19 and 3.56 MeV states (1973VO08): see also reaction 26 in ^{6}Li.
See (1968ST12).
See reaction 20 in ^{7}Be and reaction 32 in ^{6}Li (1972GO1P).
