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GENERAL: See also (74AJ01) and Table 6.6 [Table of Energy Levels] (in PDF or PS) here.

Model calculations:(IR74A, CE76B, HE76C, IR76C).

Other topics:(WE73R, DA74F, MC74A, BE75Q, FE75, SI77D).

1. (a) 3He(3He, γ)6Be	Qm = 11.488	Eb = 11.488
(b) 3He(3He, p)5Li	Qm = 10.89
(c) 3He(3He, 2p)4He	Qm = 12.8596
(d) 3He(3He, 3p)3H	Qm = -6.9544
(e) 3He(3He, 3He)3He
(f) 3He(3He, d)4Li	Qm = -8.4
(g) 3He(3He, 2p)2H2H	Qm = -10.987

The yield of γ-rays to ⁶Be*(1.7) (reaction (a)) increases smoothly from 0.4 to 9.3 μb (assuming isotropy) for 0.86 < E(³He) < 11.8 MeV (90°). No transitions were observed to ⁶Be(0) [σ < 0.01 μb at E(³He) = 1.4 MeV]. This is understood in terms of a direct capture of ³He by ³He in the singlet spin state and with zero angular momentum: the 0⁺ --> 0⁺ γ-transition is forbidden. Reaction (a) is thus of negligable astrophysical importance compared to reaction (c) (HA67M) [see below]. The capture cross section from E(³He) = 12 MeV to 27 MeV continues to increase smoothly with energy at first and then shows a broad structure centered at E(³He) = 23 ± 1 MeV [E_x = 23.0 ± 0.5 MeV], Γ_c.m. ~ 5 MeV (VE74A, VE73F). This appears to be a ³³F cluster resonance which decays by an E1 transition to ⁶Be*(1.7). The γ-ray angular distributions are coinsistent with J^π = 3^- (VE74A).

For reaction (b) see ⁵Li and (IR76A; polarization measurements at E(³He) = 13.6 MeV).

Measurements of the total cross section section for reaction (c) have been carried out for E(³He) = 60 to 300 keV (DW74) and 0.16 to 2.2 MeV (DW71, DW69). The measurements of (DW74), down to E_c.m. = 30 keV, eliminate the possibility of a resonance [which might help explain the observed absence of solar neutrinos], unless it is extremely narrow (Γ < / ~ 100 eV): θ²_p ~ 3 x 10^-6 (DW74). (BA72JJ) has commented that such a high ³He + ³He cluster for a ⁶Be state at ~ 11.5 MeV is not expected. The cross section factor S(E_c.m.) = [5.2 - 2.8 E_c.m. + 1.4 E²_c.m.] MeV · b [error in S is ± 20% for E_c.m. > 40 keV] (DW74). For the earlier work see (66LA04, 74AJ01). For polarization measurements (reaction (c)), see (SL76C). The cross section of reaction (c) has been compared with that for ³H(³He, α)d [see reaction 1 in ⁶Li] at the same c.m. energy (16 MeV). At E(³He) = 13 MeV a deviation from the ratio of 2 is observed, which is qualitatively accounted for by a distorted wave zero-range calculation (RO74).

The elastic scattering (reaction (e)) has been studied for E(³He) = 3 to 32 MeV [see (74AJ01)], at 32 MeV (RO74) and at 120 MeV (TA77G; also inelastic processes). The optical model fit at 120 MeV appears to be poor (TA77G). The excitation function shows a smooth monotonic behavior except for an anomaly at E(³He) = 25 MeV in the l = 3 partial wave corresponding to a broad state in ⁶Be at E_x ~ 24 MeV (JE70). Polarization measurements have been reported at E(³He) = 4.33 to 17.5 MeV: the polarization is consistent with zero at θ ~ 63°, consistent with a description of the scattering which leaves the P- and F-wave phase shifts unsplit (BO72U, HA72GG). Polarization measurements have also been carried out at E(³He) = 8.9 to 34.8 MeV on a polarized ³He target (BA74N, BI75G, BA76R; abstracts) and at eight energies in the range E(³He-bar) = 17.91 to 32.9 MeV (VL78). A two level R-matrix analysis of the phase shifts (L < / = 5) suggests three broad F-wave states at E_x ~ 23.4 (4^-), 26.2 (2^-) and 26.7 MeV (3^-) (VL78), in disagreement with the capture γ-ray results described above. Measurements of various of these reactions in order to obtain a total reaction cross section at E(³He) = 17.9 and 21.7 MeV have been carried out by (PO75C; abstract). For reaction (f) see also (74AJ01). Reaction (g) has been studied at 50 and 78 MeV to look at the quasi-free scattering of the two deuterons. The cross sections are an order of magnitude smaller than those predicted by PWIA (AL78H).

(DA77C) have searched at E(³He) = 15 and 25 MeV for the ³He + ³He --> d + α + e⁺ + ν reaction [which had been reported by (SL75, PI76A, SL77B) to occur with a cross section of 3.4 nb/MeV · sr at E(³He) = 13.6 MeV]. (DA77C) find no evidence for this process with a cross section twenty times lower than reported by (SL75); thus the cross section for the p + p process at solar energies is not in error and cannot account for the solar neutrino puzzle.

At 120 MeV (FU77F) have studied ³He + ³He --> p + d + ³He and have interpreted the results as possible evidence for a 3N resonance. See also (BA71VV, UL74A, FE75, BA76, MC76E, NE76, NO76L, RO78B; astrophysical considerations), (TO75D, MI76K, SL78), (MC77D; applied) and (LI74E, AS76C, HE76C; theor.).

2. 4He(3He, n)6Be

Qm = -9.090

Neutron groups to ⁶Be*(0, 1.7) have been observed at E(³He) = 19.4 to 38.61 MeV: see Table 6.8 (in PDF or PS) in (74AJ01) for the parameters of the first excited state. There is no evidence for other states of ⁶Be with E_x < / ~ 5 MeV (EC66), nor for a state near the ³He threshold at 11.5 MeV: for the latter the differential cross section is < / ~ 7 μb/sr at θ_lab = 7.3° (MC77J; E(³He) = 38.61 MeV), < / ~ 7.5 μb/sr at θ = 0° (VI75; 36.2 MeV).

3. (a) 6Li(p, n)6Be	Qm = -5.070
(b) 6Li(p, pn)5Li	Qm = -5.66

Neutron groups have been observed to ⁶Be*(0, 1.7) as has the ground state threshold. The width of the ground state is 95 ± 28 keV (HO67A). The parameters of ⁶Be*(1.7) are displayed in Table 6.8 (in PDF or PS) of (74AJ01). Angular distributions have been reported at E_p = 8.3 to 49.4 MeV [see (74AJ01)] and at 14.9 and 17.8 MeV (AR74D; n₀). For a study at E_p = 800 MeV see (RI77A). In reaction (b) (WA77F) report, at E_p = 47 MeV, some evidence for sequential decay via ⁶Be*(15.5 ± 2, 24 ± 2). See also (SL76A) and (FE75; theor.).

4. 6Li(3He, t)6Be

Qm = -4.306

Triton groups have been observed to ⁶Be*(0, 1.7). The width of the ground state is 89 ± 6 keV (WH66). The parameters of the excited state are displayed in Table 6.8 (in PDF or PS) of (74AJ01). No other excited states have been seen with E_x < 13 MeV (MA66H; E(³He) + 40 MeV), < 10 MeV (RO66D; E(³He) = 31 MeV). An attempt has been made at E(³He) = 25.5 MeV (PA73E) and at 46.3 MeV (HA73CC) to observe the possible ⁶Be state at E_x = 11.5 MeV, of astrophysical interest: dσ/dΩ < / = 0.19 μ/sr at θ_c.m. = 45° at the lower energy; dσ/dΩ < / = 1.6 μb/sr at 8.4° and at 46.3 MeV. Upper limits for the spectroscopic factor are S < / = 0.006 (PA73E) and < / = 0.001 (HA73CC). See also (CH75I). The ground state angular distribution shows a pronounced oscillatory character, consistent with l = 0; that for the 1.7 MeV state is relatively structureless (RO66D). Angular distributions are also reported by (GI72D; n₀; 27.0 MeV). The α-spectrum following the α + p + p decay of ⁶Be_g.s. has been measured by (GE77A): the yield of low energy α-particles appears to be enhanced compared with calculations based on the available phase space. See also (HA77L) and (FE75, HA78E; theor.).

5. 6Li(6Li, 6He)6Be

Qm = -7.795

See reactions 9 in ⁶He and 18 in ⁶Li (WH74, WH74A, WH74E, WH75).

6. 9Be(3He, 6He)6Be

Qm = -9.690

See (74AJ01).