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8Li (1959AJ76)
(See the Energy Level Diagram for 8Li)
GENERAL: See also Table 8.1 [Table of Energy Levels] (in PDF or PS).
Theory: See (1955LA1D, 1956KU1A, 1957FR1B, 1957KU1B).
| 1. 8Li(β-)8Be | Qm = 16.001 |
The weighted mean of half-lives reported in (1955AJ61) is 0.848 ± 0.004 sec. A value of 0.873 ± 0.013 sec is given by (1958VE20). See also (1958IM1A). The decay is complex: see 8Be.
| 2. 6Li(t, p)8Li | Qm = 0.803 |
| Q0 = 0.790 ± 0.011 (1954AL35). |
The ground state reaction has been observed by (1952MO19, 1952PE02, 1954AL35, 1955CU17). (1955CU17) also reports one event corresponding to the transition to an excited state at 0.7 ± 0.2 MeV.
| 3. 7Li(n, γ)8Li | Qm = 2.035 |
The thermal capture cross section is 33 ± 5 mb (1947HU06), 42 ± 10 mb (1956KO1C). At En = 275 keV, neutron capture is not observed: σ < 0.25 mb (1956KO1C). Polarization of 8Li produced by polarized thermal neutrons has been detected by (1957BU44). See also (1957KU1B, 1958IM1A, 1958SH1A).
| 4. 7Li(n, n)7Li | Eb = 2.035 |
Cross sections for Li metal and for 7Li are reported in (1958HU18: see also (1956GO62, 1957KA1B, 1958BR16)). The thermal cross section is 1.07 ± 0.04 b (C. Hibdon: see (1955HU1B, 1956TH06)).
A pronounced resonance occurs at En = 258 keV (see Table 8.2 (in PDF or PS)). Total cross sections and angular distributions establish that the state has J = 3+, formed by p-waves (1956WI04). A further, broad peak centering at En ≈ 5 MeV may indicate a broad level of 8Li at ≈ 6.5 MeV (1958HU18: see also (1956GO62)).
Data on coherent scattering and total cross section for zero-energy neutrons permit two solutions for the two s-wave scattering lengths corresponding to anti-parallel (J = 1-) and parallel (J = 2-) interactions; for the first solution, the interaction is essentially pure J = 1-, for the other, pure J = 2-. Measurement of the interference between the s-wave background and the p-wave (channel spin 2) resonance indicate that the second solution is the correct one, and it is concluded that the splitting between parallel and anti-parallel interactions is about 1.5 MeV (1956TH06). (1956WI04) find, on the other hand, that the observed asymmetries in the angular distributions indicate a nearly statistical (5/3) mixture of J = 1- and 2- background. Use of scattering in 7Li as a polarization analyzer is discussed by (1956WI1E).
See also (1956BE98, 1957KH1A).
| 5. 7Li(n, n')7Li* | Eb = 2.035 |
The excitation function for 0.48-MeV γ-rays shows an abrupt rise from threshold (indicating s-wave formation and emission) and a broad maximum (Γ ≈ 1 MeV) at En = 1.35 MeV. The rise above threshold indicates the existence of a J = 1- level, which may be identified with the 1.35-MeV resonance (if a strong d-wave contribution is included). On the other hand, the latter resonance appears to be better described as a J = 1+ level, formed by p-waves. Under this assumption, Er(lab) = 1.45 MeV, Γ = 1.14 MeV, with the sum of reduced widths θ2in + θ2out ≈ 0.5 × (3ℏ2/2MR2). The ratio θ2in/θ2out = 0.1 to 0.4 or 1.0 to 3.0 (1955FR10).
| 6. 7Li(n, p)7He | Qm = -14 | Eb = 2.035 |
Not observed: see 7He.
| 7. 7Li(n, d)6He | Qm = -7.779 | Eb = 2.035 |
At En = 14 MeV, the cross section is 9.8 ± 1.1 mb (1953BA04). See also (1954FR03).
| 8. (a) 7Li(n, t)5He | Qm = -3.423 | Eb = 2.035 |
| (b) 7Li(n, t)4He + n | Qm = -2.466 |
The cross section for reaction (a) is 55 ± 8 mb at En = 14 MeV (1954FR03). See also (1954MA1E) and (1954BA1B).
| 9. 7Li(d, p)8Li | Qm = -0.192 |
| Q0 = -0.183 ± 0.02 (1955KH31). |
Three proton groups are observed, corresponding to the ground state and to levels at 0.974 ± 0.015 (1955LE24), 0.977 ± 0.02 MeV (1955KH31, 1955KH35) and 2.28 MeV (1955LE24). A search for further levels in the range Ex = 2.28 to 8 MeV revealed no levels with Γ < 80 keV (1958HA10, 1958HA1G). At Ed = 14 MeV, the angular distributions of the protons, analyzed by stripping theory, indicate ln = 1 and therefore even parity, J ≤ 3, for the ground state and the 0.98-MeV level (1955LE24). On the assumption that J = 2+ and 1+ for the ground state and 0.98-MeV level, respectively, (1957FR1B) calculate θ2 = 0.054 and 0.028 from the data of (1955LE24). These two levels are presumed to arise from a 33P term, with a third component of J = 0+ expected at higher energy (1957FR1B). See also (1955GI1A).
| 10. 7Li(t, d)8Li | Qm = -4.224 |
Not observed.
| 11. 7Li(α, 3He)8Li | Qm = -18.543 |
Not observed.
| 12. 9Be(γ, p)8Li | Qm = -16.885 |
| 13. 9Be(n, d)8Li | Qm = -14.658 |
Not observed.
| 14. 9Be(p, 2p)8Li | Qm = -16.885 |
Production of 8Li at Ep = 20 MeV is reported by (1956LE46). At Ep = 185 MeV, the summed proton spectrum shows two peaks, corresponding to pickup of protons with binding energies of ≈ 18 and ≈ 26 MeV, respectively. There is some indication of α-particle structure (1958MA1B, 1958TY49).
| 15. 9Be(d, 3He)8Li | Qm = -11.409 |
See (1954WI25).
| 16. 9Be(t, α)8Li | Qm = 2.928 |
Not observed.
| 17. 10B(n, 3He)8Li | Qm = -15.771 |
Not observed.
| 18. 11B(n, α)8Li | Qm = -6.636 |
See 12B.