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USNDP

8Li (1974AJ01)


(See Energy Level Diagrams for 8Li)

GENERAL: See also (1966LA04) and Table 8.1 [Table of Energy Levels] (in PDF or PS).

Shell model: (1966BA26, 1973HA49).

Special levels: (1966BA26, 1970FR1C).

Electromagnetic transitions: (1966BA26, 1972EV03, 1973HA49).

Special reactions: (1965AF1A, 1966BA1R, 1966KL1C, 1967AU1B, 1967GO1F, 1968GR1E, 1970AZ1A, 1971AG01, 1971DH1A, 1971KA1K, 1972VO06, 1973KO1D, 1973WI15).

Pion and kaon reactions: (1967ZE1A, 1968BA1M, 1968BE1R, 1968BH1A, 1969BA1L, 1970AG1B, 1970BA44, 1971DH1A, 1971VA1E, 1971VA19, 1972WE20, 1972BA1C, 1973GE1K).

Astrophysical questions: (1967MI1C, 1970BA1M).

Other topics: (1966TO04, 1967DI1B, 1971BA2Y, 1972AN05, 1972GA1L, 1972PN1A, 1973JU2A).

Ground state properties: (1966BA26, 1969PE1D, 1972VA36, 1973EN1B, 1973MA1K, 1973SU1B).

J = 2 (1973NE10);

μ = +1.65335 ± 0.00035 nm (1973HA12);

μ = +1.6532 ± 0.0008 nm (1959CO68, 1962CO08);

μ = +1.6530 ± 0.0008 nm (1967GU14). See also (1967SH14, 1969FU11, 1971SH26).

1. 8Li(β-)8Be Qm = 16.006

The β-decay leads mainly to 8Be*(2.9): see 8Be. Measurements of the half-life of 8Li include τ1/2 = 841 ± 4 msec (1954KL36), 848 ± 5 msec (1960JA12), 844.0 ± 0.7 msec (1966CL02), 854 ± 8 msec (1968DA12), 838 ± 6 msec (1971WI05): τ1/2 = 842 ± 6 msec is adopted. [For other measurements see Table 8.2 (in PDF or PS) in (1966LA04)]. See also (1968BO32). Taking τ1/2 = 842 msec and Q = 16.006 - 2.94, log ft = 5.61 (B. Zimmerman, private communication). See also (1966BA1A, 1969BA43). The distribution of recoil momenta indicates Jπ = 2+ (see 8Be).

The coefficient for the angular correlation between β-, (ν-bar)e and α-particles, b = -0.88 ± 0.08 (1965GR25), -1.01 ± 0.07 (1966EI02), in substantial agreement with b = -1, expected from axial vector coupling.

See also (1970SC34) and 8Be.

2. 6Li(t, p)8Li Qm = 0.801

Transitions to 8Li*(0, 0.98) have been observed: see (1966LA04). See also (1968CO1H).

3. 7Li(n, γ)8Li Qm = 2.0327
Q0 = 2032.78 ± 0.15 keV (E.T. Jurney, private communication);
Q0 = 2032.8 ± 1 keV (1967RA24).

The thermal capture cross section is 45.4 ± 3 mb. Neutron capture γ-rays are observed with Eγ = 980.6 ± 0.2, 1052.0 ± 0.2 and 2032.5 ± 0.28 keV, with intensities of 10.6 ± 1, 10.6 ± 1 and 89.4 ± 1 γ/100 neutrons: Ex = 980.7 ± 0.2 keV for the first excited state (E.T. Jurney, private communication). The cross section for capture radiation has been measured for En = 40 to 1000 keV: it decreases from 50 μb to 5 μb over that interval. The cross section shows the resonance corresponding to 8Li*(2.26): Γγ = 0.07 ± 0.03 eV (1959IM04). See also (1967GU14), (1966LA04) and (1970AU1B; astrophys. calculations).

4. 7Li(n, n)7Li Eb = 2.0327

The thermal cross section is 1.07 ± 0.04 b (1960HU1A); the coherent scattering length (thermal, bound) is -2.1 ± 0.1 fm (1969BA1P, 1973MU14). Total cross-section measurements have recently been reported at En = 0.010 to 1.236 MeV (1968HI1E), 0.10 to 1.50 MeV (1970ME1C), 1.12 to 2.30 MeV (1968KN1B), 2.5 to 15.0 MeV (1971FO1A), 3.35, 4.83, 5.74 and 7.5 MeV (1968HO03: also σel), 10 MeV (1967CO01) and 0.6 to 30.0 MeV (C.A. Goulding, private communication, and (1973GO2B)). See also (1968EN1A, 1972PR03). Polarization measurements at En = 4.4 MeV are reported by (1966ST09; n0). For earlier references see (1966LA04). See also (1966DA1B, 1972LA1F) and (1966AG1A, 1966SE1E, 1967BE1F, 1967HO1F; theor.). For angular distribution measurements see 7Li and (1970GA1A).

A pronounced resonance is observed at En = 261 keV with Jπ = 3+, formed by p-waves (Table 8.2 (in PDF or PS)) (1970ME1C). 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). Broad peaks are reported at En = 4.6 and 5.8 MeV (± 0.1 MeV) [8Li*(6.1, 7.1)] with Γ ≈ 1.0 and 0.4 MeV, respectively, and there is indication of a narrow peak at En = 5.1 MeV [8Li*(6.5)] with Γ ≪ 80 keV and of a weak, broad peak at En = 3.7 MeV (1971FO1A: D.G. Foster and C.A. Goulding, private communications). See also reaction 5.

5. 7Li(n, n')7Li* Eb = 2.0327

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. A good fit is obtained with either Jπ = 1- or 1+ (2+ not excluded), Γlab = 1.14 MeV (1955FR10). At higher energies a prominent peak is observed at En = 3.8 MeV (Γlab = 0.75 MeV) and there is some indication of a broad resonance (Γlab = 1.30 MeV) at En = 5.0 MeV. Between En = 6.0 and 9.0 MeV, the cross section decreases monotonically. The two resonances are interpreted as being due to states with Jπ = 2+ or 3+ [8Li*(5.4)] and Jπ = 3+ or 3- [8Li*(6.4)] [(1972PR03: Γλ, γ2λ and θ2λ are listed for these two states under various assumptions)]. Cross-section measurements have also recently been reported for En = 3.35, 4.83, 5.74 and 7.5 MeV (1968HO03; n1, n2), 10 MeV (1967CO01; n2) and 19.0 to 21.0 MeV (1972PR03; γ1). See also (1965DE1G, 1972CO1K), and (1966LA04) for a listing of earlier references.

6. 7Li(n, 2n)6Li Qm = -7.251 Eb = 2.0327

See (1963AS01, 1964ST25).

7. (a) 7Li(n, p)7He Qm = -10.42 Eb = 2.0327
(b) 7Li(n, p)4He + 3n

At En = 19 MeV, the upper limit for reaction (b) is 10 mb (1971KO24). See also 7He and (1973LI02).

8. 7Li(n, d)6He Qm = -7.753 Eb = 2.0327

See (1967VA12, 1973LI02) and (1966LA04).

9. 7Li(n, t)4He + n Qm = 2.4668 Eb = 2.0327

The cross section rises to 450 mb at En ≈ 8 MeV and thereafter decreases slowly to 300 mb at En = 15 MeV (1964ST25). The large cross section, comparable to the geometric value, is understood in terms of the (α + t) cluster nature of 7Li (1962RO12). Cross sections for this reaction have recently been reported at En = 3.35, 4.83, 5.74 and 7.5 MeV (1968HO03) and at 10 MeV (1967CO01). See also (1967VA12, 1971AN1M, 1973LI02) and 5He, and (1966JE1B).

10. 7Li(d, p)8Li Qm = -0.1919
Q0 = -188 ± 7 keV (1967SP09).

Proton groups have been observed to 8Li*(0, 0.98, 2.26): see (1966LA04). At Ed = 15 MeV, no states are observed in the region 2.3 < Ex < 8 MeV: a limit of 0.6 mb/sr is placed on groups with widths ≲ 100 keV (θ = 10°, 14°, 25°) (1960HA14). Angular distributions of the p0 and p1 groups [ln = 1] at Ed = 12 MeV have been analyzed by DWBA: Sexp. = 0.87 and 0.48, respectively for 8Li*(0, 0.98) [Sexp./Stheor. = 0.84, 1.09] (1967SC29). For PWBA analyses, see (1966LA04).

The first excited state decays by emitting a 980 ± 10 keV γ-ray. The transition is M1 (1962CH14). The lifetime of 8Li*(0.98) is 10.1 ± 4.5 fsec (1971TH02). See also (1966TH1B, 1968FI1F).

11. 7Li(t, d)8Li Qm = -4.2249

See (1970CH1Q) and 10Be. See also (1970JA1J; theor.).

12. 7Li(α, 3He)8Li Qm = -18.546

Not reported.

13. 8He(β-)8Li Qm = 10.70

8He decays with τ1/2 = 122 ± 2 msec to 8Li*(0.98) with an 88% branch [log ft = 4.20; B. Zimmerman, private communication] and to neutron unstable states with a 12 ± 1% branch. The allowed decay supports the assignment Jπ = 1+ to 8Li*(0.98) (1965PO06).

14. 9Be(γ, p)8Li Qm = -16.888

See (1962CU05, 1966DE13, 1968AD09). See also (1966LA04).

15. 9Be(e, ep)8Li Qm = -16.888

See (1969BA1F; theor.). See also 9Be.

16. 9Be(n, d)8Li Qm = -14.664

See (1969SC05) in 10Be.

17. 9Be(p, 2p)8Li Qm = -16.888

The summed proton spectrum at Ep = 156 MeV shows peaks corresponding to 8Li(0) and 8Li*(0.98 + 2.26) [unresolved]. In addition s-states [Jπ = 1-, 2-] are suggested at Ex = 9 and 16 MeV, with Γc.m. ≈ 6 and 8 MeV: the latter may actually be due to continuum protons (1967RO06). See also 9Be and (1966LA04) [(1965TY1A) has now been published as (1966TY01)]. See also (1971GR1K), (1965CO1E) and (1967KO1B, 1968JA1D, 1973AS02; theor.).

18. 9Be(d, 3He)8Li Qm = -11.395

At Ed = 38 MeV, differential cross sections have been obtained for the 3He groups corresponding to 8Li*(0, 0.98, 2.26) (1966GA21: see 9Be(d, t)8Be).

19. 9Be(t, α)8Li Qm = 2.926

At Et = 12.98 MeV, α-particle groups are observed to 8Li*(0, 0.98, 2.26) and to a state at Ex = 6.530 ± 0.020 MeV with Γc.m. < 40 keV (1965WA12). For angular distributions to these four states, see (1968AJ01): the distribution of the α-particles to 8Li*(6.53) is rather featureless and does not involve a forward maximum, suggesting l > 1. A large l-transfer is consistent with the narrow width of this unbound state (1968AJ01). At Et = 20 MeV these four 8Li states were also observed. 8Li*(6.53) was found to have Γc.m. = 40 ± 10 keV. No other groups corresponding to sharp states of 8Li (Γ ≲ 100 keV) with Ex ≲ 16 MeV were observed at θ = 15°, 25° and 35° (F. Ajzenberg-Selove and O. Hansen, private communication). The α0 angular distribution has also been measured at Et = 2.10 MeV (1970CO04) and 0.52 to 1.31 MeV (1969NA04; also α1 at Et = 0.52 to 1.67 MeV).

The mean lifetime, τm = 14 ± 5 fsec for 8Li*(0.98): Ex = 980.80 ± 0.10 keV (1972CO09). See also 12B in (1975AJ02).

20. 9Be(7Li, 8Be)8Li Qm = 0.368

See (1966LE10) and (1968TO1C; theor.).

21. 10Be(d, α)8Li Qm = 2.372

This reaction has been observed for Ed = 0.7 to 3.0 MeV: see 12B (1970GO11, 1973GO09).

22. 10B(n, 3He)8Li Qm = -15.755

Not reported.

23. 11B(γ, 3He)8Li Qm = -27.211

See (1963NE07).

24. 11B(n, α)8Li Qm = -6.633

Angular distributions have been obtained at En = 14.1 MeV for the α0 and α1 groups (1973BO26). See also (1966JA1C) and 12B in (1975AJ02).

25. 12C(α, 8B)8Li Qm = -41.445

At Eα = 129 MeV, 8B groups are observed to 8Li*(0, 0.98, 2.26) (1968MC02).

26. 13C(7Li, 12C)8Li Qm = -2.914

At E(7Li) = 34 MeV angular distributions have been measured for the transitions to 8Lig.s. + 12Cg.s., 8Li*0.98 + 12Cg.s., 8Lig.s. + 12C*4.4 and 8Li*0.98 + 12C*4.4 (1973SC26).

27. 18O(7Li, 17O)8Li Qm = -6.014

See (1969NE1E).