Evaluation Home Page |
| Information on mass chains and nuclides |
|
 |
8Li (1966LA04)
(See Energy Level Diagrams for 8Li)
GENERAL: See (1955LA1D, 1956KU1A, 1957FR1B, 1960TA1C, 1962IN02, 1963LO1E, 1963NA1E, 1964BE1N, 1964GR1J, 1964LO1F, 1964ST1B).
See also Table 8.1 [Table of Energy Levels] (in PDF or PS).
Ground state:
| 1. 8Li(β-)8Be | Qm = 16.002 |
The beta decay leads mainly to 8Be*(2.9): see 8Be. Reported half-lives are listed in Table 8.2 (in PDF or PS); taking τ1/2 = 0.849 sec and Q = 16.002 - 2.90, ft = 4.14 × 105 (1966BA1A). The distribution of recoil momenta indicates Jπ = 2+ (see 8Be).
The asymmetry of the β-decay has been exploited as an indicator of 8Li nuclear polarization: see 7Li(n, γ)8Li.
| 2. 6Li(t, p)8Li | Qm = 0.803 |
Ground-state protons have been observed with Et up to 3.3 MeV: see (1952MO19, 1952PE02, 1954AL35, 1955CU17).
At E(6Li) = 4.5 MeV, the 0.98 MeV γ-ray has been observed. Doppler shift measurements give τ < 0.2 psec for 8Li*(0.98). The transition is thus dipole in character, with a maximum E2 admixture of 2 × 10-3 in intensity (1965MO1P).
| 3. 7Li(n, γ)8Li | Qm = 2.033 |
The thermal capture cross section is 37 ± 4 mb (1964ST25); capture γ-rays of energy Eγ = 2.02, 1.06 and 0.96 MeV are reported with intensity ratios 0.8/0.2/0.3 (1961JA19; prelim. values). See also (1959BO1C).
The cross section for capture radiation has been measured for En = 40 to 1000 keV: it decreases from 50 μb at En = 40 keV to 5 μb at 1000 keV. A maximum in the cross section appears at En = 250 keV corresponding to the known resonance in 7Li(n, n); Γγ = 0.07 ± 0.03 eV (1959IM04).
Measurement of the asymmetry of β-decay of 8Li produced by capture of polarized neutrons indicate that the thermal capture takes place > 80% in the Jc = 2 channel (1959CO68, 1961WA03, 1962AB01). An NMR determination yields g = 0.8265 ± 0.0004 nm/ℏ, or with J = 2, μ = +1.653 ± 0.0008 nm (1959CO68, 1962CO08). Shell model calculations give this value with a/K = 2.1 (1959KU1E).
| 4. 7Li(n, n)7Li | Eb = 2.033 |
Total cross sections for Li and for 7Li are reported in (1960HU08, 1964ST25). Recent measurements of the total cross section have been reported for En = 1 to 390 keV (1964HI04), 10 to 155 keV (1959BI19), 0.2 to 2.2 MeV (1961LA1A, 1964LA19), 1.5 to 7.5 MeV (1963BA50), 14 MeV (1964AR25), and 18 to 28 MeV (1960PE25). Angular distribution information is summarized in (1963GO1M). See also (1964LA19). A measurement at En = 96 MeV (1960SA25) has been analyzed in terms of the optical model by (1960HO14). See also (1962BA1W, 1963LU10). The thermal cross section is 1.07 ± 0.04 b (1960HU08); the coherent scattering length (thermal, bound) is a = -2.1 fm (1964ST25). See also (1961ME02). A pronounced resonance is observed at En = 256 keV with J = 3+, formed by p-waves (Table 8.3 (in PDF or PS)). Polarization measurements confirm the assignment and indicate that the background s-wave scattering is contributed mainly by channel spin Jc = 2 (1961DA04, 1962EL01: see also (1961LA1A)) in agreement with earlier results of (1956TH06) but in conflict with (1956WI04). In this case, the coherent scattering length in the Jc = 1 channel is a1 = [+1.2], a2 = [-3.6] fm, suggesting an s-wave, Jπ = 2-, resonance at positive neutron energy (1956TH06, 1960LA1C). A good account of the polarization is given by the assumption of levels at En = 0.25 and 3.4 MeV, with Jπ = 3+ and 2-, together with a broad Jπ = 3- level at higher energy (1964LA19). It is noted that the polarization near the J = 3+ resonance is similar in shape to that of 7Li(p, n)7Be at the presumptive mirror level, but opposite in sign (1962EL01). A broad maximum centering at En ≈ 5 MeV may indicate a level at Ex ≈ 6.4 MeV (1956GO62, 1960HU08, 1963BA50, 1964ST25).
See also (1960PE02, 1962FO1E, 1962OT01, 1963AL1J, 1963GL1E, 1963HA1G, 1963WE20).
| 5. 7Li(n, n')7Li* | Eb = 2.033 |
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. Other odd parity assignments to this resonance lead to excessive reduced widths. A good fit is obtained with either J = 1- or 1+, Γlab = 1.14 MeV, Jπ = 2+ is not excluded (1955FR10). In the range En = 1.5 to 4 MeV, the cross section for emission of 0.48 MeV γ-rays remains constant at first and then increases to 280 mb at En = 4 MeV (1963BA50). The cross section for emission of 0.48 MeV γ-rays is ≈ 80 mb (± 12%) over the range En = 13.6 to 14.3 MeV (1962BE35). See also (1963GO1M, 1963MA61).
| 6. 7Li(n, 2n)6Li | Qm = -7.253 | Eb = 2.033 |
The cross section is 27 ± 15 mb at En = 10.2 MeV and 56 ± 5 mb at 14.1 MeV (1963AS01). See also (1964ST25).
| 7. 7Li(n, d)6He | Qm = -7.755 | Eb = 2.033 |
At En = 14 MeV, the cross section is 9.8 ± 1.1 mb (1953BA04), 14 ± 1.5 mb (1963BA56).
| 8. 7Li(n, t)4He + n | Qm = -2.467 | Eb = 2.033 |
The cross section rises to 450 mb at En ≈ 8 MeV and thereafter decreases slowly to 300 mb at 15 MeV (1964ST25). The large cross section, comparable to the geometric value, supports the hypothesis that 7Li may be described as an (α + t) cluster (1962RO12). See also (1963AL1J, 1963BA50, 1963BR28, 1964VA19).
| 9. 7Li(d, p)8Li | Qm = -0.192 |
Observed proton groups indicate levels at 974 ± 15 (1955LE24), 977 ± 20 keV (1955KH35) and at 2.28 MeV (1955LE24, 1960HA14). At Ed = 3.5 MeV, no excited states are observed below the 0.97 MeV level with an intensity > 1/160 of the ground-state group (1961ER01). At Ed = 15 MeV, no states observed in the region 2.28 < Ex < 8 MeV: a limit of 0.6 mb/sr is placed on groups with widths ≲ 100 keV (θ = 10°, 14° and 25°) (1960HA14). See also (1965WA12).
Angular distributions at Ed = 14 to 15 MeV have been analyzed by PWBA: see Table 8.4 (in PDF or PS). At low bombarding energies, Ed = 0.5 to 4 MeV, angular distributions show striking agreement with simple PWBA theory. The applicability of the theory in this range is ascribed to the proximity of a pole in the stripping cross section when Q and Ed are small (1960SE08, 1960WA1G, 1963SE1F). Analysis in both PWBA and DWBA is reported by (1961HA1G): the latter leads to nearly ten times larger θ2n.
The cross section for 7Li(d, p)8Li*(γ)8Li has been measured for Ed = 1.9 to 3.3 MeV: no resonances appear. The γ-ray angular distribution, very nearly isotropic for Ed > 2.3 MeV, indicates that stripping dominates. If the transition is M1 (see 6Li(t, p)8Li), the 0.97 MeV state has J = 1+ or 2+: Eγ = 980 ± 10 keV (1962CH14).
The polarization of recoil 8Li nuclei has been studied at Ed = 10 MeV (1963LE1K).
See also (1959BO1C, 1959HA29, 1959SE1A, 1960PR1D, 1960SE13, 1963AL19, 1963GL1C, 1963SE1G).
| 10. 7Li(t, d)8Li | Qm = -4.225 |
See (1965AJ01).
| 11. 7Li(α, 3He)8Li | Qm = -18.546 |
Not reported.
| 12. 9Be(γ, p)8Li | Qm = -16.885 |
At Ebrems. = 32 MeV, transitions are observed to the ground and first excited states of 8Li (1962CU05). See also (1958CH31, 1962NE14, 1963NE02, 1965AL02, 1965KO1B).
| 13. 9Be(n, d)8Li | Qm = -14.660 |
Not reported.
| 14. 9Be(p, 2p)8Li | Qm = -16.885 |
At Ep = 138 MeV, the cross section of production of 0.98 MeV γ-rays is 2.4 ± 0.4 mb (1961CL09). The summed proton spectrum shows two peaks, corresponding to pickup of protons with binding energies of ≈ 16.7 ± 0.3 MeV and 25.8 ± 0.4 MeV (1p3/2 and 1s1/2, respectively) (1958MA1B, 1958TY49, 1962GA23, 1964TI02, 1966TY01). See also 9Be.
| 15. 9Be(d, 3He)8Li | Qm = -11.391 |
See (1954WI25).
| 16. 9Be(t, α)8Li | Qm = 2.930 |
At Et = 12.98 MeV, α-particle groups are observed to the 8Li ground state, to the states at 0.98 and 2.26 MeV and to a state at 6.530 ± 0.020 MeV. The width of the 6.53 MeV state is < 40 keV (1965WA12).
| 17. 9Be(7Li, 8Be)8Li | Qm = 0.367 |
See 9Be.
| 18. 10B(n, 3He)8Li | Qm = -15.754 |
Not reported.
| 19. 10B(p, 3p)8Li | Qm = -23.472 |
See (1965BE1P).
| 20. 11B(γ, 3He)8Li | Qm = -27.210 |
See (1963NE07).
| 21. 11B(n, α)8Li | Qm = -6.632 |