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6Be (1984AJ01)

(See Energy Level Diagrams for 6Be)

GENERAL: See also (1979AJ01) and Table 6.6 [Table of Energy Levels] (in PDF or PS).

Model calculations: (1979SHZV, 1981HO23, 1982DE42, 1982HO05, 1982KR1B, 1982NG01, 1982VO01, 1982DE16).

Other topics: (1979KO1D, 1983BA3A, 1983NA03).

1. (a) 3He(3He, γ)6Be Qm = 11.489
(b) 3He(3He, p)5Li Qm = 10.90 Eb = 11.489
(c) 3He(3He, 2p)4He Qm = 12.8596
(d) 3He(3He, 3He)3He
(e) 3He(3He, pd)3He Qm = -5.4936
(f) 3He(3He, 2p)2H2H Qm = -10.987
(g) 3He(3He, 3p)3H Qm = -6.9544

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 negligible astrophysical importance compared to reaction (c): see (1979AJ01). 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 [Ex = 23.0 ± 0.5 MeV], Γc.m. ≈ 5 MeV (1974VE01). This appears to be a 33F cluster resonance which decays by an E1 transition to 6Be*(1.7). The γ-ray angular distributions are consistent with Jπ = 3- (1974VE01).

The analyzing power angular distribution has been measured at E(pol. 3He) = 14 MeV for the p0 group (reaction (b)) (1981KO34). See also (1979AJ01) and 5Li.

Measurements of the total cross section for reaction (c) have been carried out for E(3He) = 60 keV to 2.2 MeV. The measurements of (1974DW01), down to Ec.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): θ2p ≈ 3 × 10-6 (1974DW01). The cross section factor S(Ec.m.) = [5.2 - 2.8Ec.m. + 1.4E2c.m.] MeV · b [error in S is ± 20% for Ec.m. > 40 keV] (1974DW01). For the earlier work see (1966LA04, 1974AJ01). For polarization measurements (reaction (c)), see (1979AJ01).

The elastic scattering (reaction (d)) has been studied for E(3He) = 3 to 32 MeV [see (1979AJ01)] and at 120 MeV (1980TA11; also inelastic processes). The excitation function shows a smooth monotonic behavior except for an anmaly at E(3He) = 25 MeV in the L = 3 partial wave corresponding to a broad state in 6Be at Ex ≈ 24 MeV. Polarization measurements have been carried out at E(pol. 3He) = 17.9 to 32.9 MeV (1978VL01). A two level R-matrix analysis of the phase shifts (L ≤ 5) suggests three broad F-wave states at Ex ≈ 23.4(4-), 26.2(2-) and 26.7 MeV(3-) (1978VL01), in disagreement with the capture γ-ray results described above. See also (1979AJ01).

A kinematically complete experiment (reaction (e)) has been performed at E(3He) = 120 MeV: large peaks were observed which appear to correspond to 3He - d quasi-free scattering followed by p - d FSI. No evidence was seen for excited states of 3He (1978FU08). See also (1980TA11). At E(3He) = 50, 65 and 78 MeV (1978AL21, 1979LA14) have examined reactions (c), (e), (f), (g) and have compared the results with PWIA: deviations are observed. See also (1979PI11), (1979AJ01, 1982SL1A), (1980PE1N, 1982BA80, 1983TR1F; astrophysics) and (1978FE07, 1979FU1F, 1981BA25, 1981HO23; theor.).

2. 4He(3He, n)6Be Qm = -9.089

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 (1974AJ01) for the parameters of the first excited state. There is no evidence for other states of 6Be with Ex ≲ 5 MeV, not for a state near the 3He threshold at 11.5 MeV: see (1979AJ01).

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. The parameters of 6Be*(1.7) are displayed in Table 6.8 (in PDF or PS) of (1974AJ01). Angular distributions have been reported at Ep = 8.3 to 49.4 MeV [see (1979AJ01)] and at Ep = 144 MeV (1980MO10; n0). See also (1982KI1F; Ep = 800 MeV). In reaction (b) (1977WA05) report, at Ep = 47 MeV, some evidence for sequential decay via 6Be*(15.5 ± 2, 24 ± 2). See also (1979RAZI, 1980GO1J), (1982PE06) and (1980BA2H, 1980DU16, 1983GU1G; theor.).

4. 6Li(3He, t)6Be Qm = -4.307

Triton groups have been observed to 6Be*(0, 1.7). The width of the ground state is 89 ± 6 keV. The parameters of the excited state are displayed in Table 6.8 (in PDF or PS) of (1974AJ01). No other excited states have been seen with Ex < 13 MeV. There is no evidence for a state near 11.5 MeV; see (1979AJ01). The angular distribution of t0 has been studied by (1981BA37: E(3He) = 33.3 MeV). The α-spectrum following the α + p + p decay of 6Beg.s. has been measured by (1977GE02): the yield of low-energy α-particles appears to be enhanced compared with calculations based on the available phase space. The continuum has also been studied by (1983DE14). See also (1981DE1X), (1979BA1H; theor.) and 9B.

5. 6Li(6Li, 6He)6Be Qm = -7.795

See reactions 10 in 6He and 20 in 6Li.

6. 9Be(3He, 6He)6Be Qm = -9.687

Discrete states are not observed: see (1981DE1X, 1983DE14) [see also for a study of the continuum].