A=07Li (1966LA04)

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⁷Li (1966LA04)

(See Energy Level Diagrams for ⁷Li)

GENERAL: See (1957HU1C, 1959BA1M, 1959BA1D, 1959BR1E, 1959FE1B, 1959MA1F, 1959MA1G, 1960KU1B, 1960PE11, 1960PH1A, 1960SH1A, 1960TA1C, 1961BA1D, 1961BA1E, 1961BL1C, 1961CL10, 1961KH03, 1961TA05, 1961TO04, 1962CL1F, 1962CR09, 1962IN02, 1963CH08, 1963CL1B, 1963KL1A, 1963SC30, 1964BE1N, 1964GR1J, 1964MA1G, 1964NE1E, 1964OL1A, 1964SA1F, 1965BE1R, 1965FA1B, 1965JA1L, 1965NE1C, 1965PR1F).

See also Table 7.1 [Table of Energy Levels] (in PDF or PS).

Ground state:

Q = -45 ± 5 mb (1961KA29, 1963VA19, 1964WH01);

μ = +3.2564 nm (1965FU1G).

1. ⁴He(t, γ)⁷Li

Q_m = 2.467

Excitation functions and angular distributions have been studied in the range E_α = 0.5 to 1.9 MeV by (1961GR27), E_α = 0.5 to 1.3 MeV by (1959HO03). The cross section rises smoothly, as expected for a direct capture process; at E_α = 1.32 MeV, σ = 3.58 ± 0.06 μb, and the corresponding reduced cross section factor S = 0.064 ± 0.016 keV · b (1961GR27) in good agreement with the value 0.05 calculated by (1961CH1C). Cross sections of (1961GR27) are 2 to 2.5 times higher than those of (1959HO03).

The branching ratio of γ₀/γ₁ (to ⁷Li(0) and ⁷Li*(0.48)) is 1/(0.4 ± 0.05), essentially independent of energy and angle. At E_α = 0.56 MeV, the angular distribution of γ's is isotropic (± 6%), while some preference for forward emission appears at E_α = 1.6 MeV. Assuming θ²_α = 1.25 and 1.05 for the ground and 0.48 MeV states of ⁷Li, and taking into account only E1 capture from s- and d-waves, (1963TO06) have calculated the total cross section from 0 to 7 MeV and the γ-ray intensity ratios: the calculations are in excellent agreement with the data of (1961GR27). See also (1961TO04).

2. ⁴He(t, t)⁴He E_b = 2.467

Angular distributions have been measured for E_t = 1.2 to 2.2 MeV (1956HE16), 1.7 MeV (1958AL05), E_α = 11 to 28 MeV (1960BR1J). See also (1961TO04).

3. ⁴He(α, p)⁷Li Q_m = -17.347

At E_α = 38.5 MeV, two groups of protons are observed leading to the ground and 0.48 MeV states of ⁷Li (1958BU38).

4. ⁶Li(n, γ)⁷Li Q_m = 7.253

Two γ-rays with E_γ = 7.26 ± 0.03 and 6.78 ± 0.05 MeV, and relative intensities 10 and 7.5 ± 2.0, corresponding to transitions to the first two states of ⁷Li are observed (1957BA18). The total radiative capture cross section is 45 ± 10 mb (1964ST25). See also (1961JA19, 1961TO04).

5. ⁶Li(n, n)⁶Li E_b = 7.253

The total cross section has been measured for E_n = 4 eV to 29 MeV (1958HU18, 1960HU08, 1960PE25, 1963BA50, 1964AR25, 1964ST25). A pronounced resonance occurs at E_n = 262 keV with a peak cross section of 11.2 b (1960HU08). The elastic contribution is 7.2 b (1961LA1A). No other clearly defined resonance is observed, although the cross section exhibits a broad maximum at E_n ≈ 5 MeV (1954JO17, 1960HU08). The coherent scattering length (thermal, bound) is 1.8 fm (1964ST25).

Angular distributions are tabulated by (1963GO1M): see also (1961LA1A, 1962BA1W, 1963BA50). All observations near the 0.262 MeV resonance are consistent with p-wave formation of a J^π = 5/2^- level (⁷Li*(7.48)). Table 7.2 (in PDF or PS) gives the resonance parameters compared with those for ⁷Be*(7.18). These states are believed to have a ⁴P_5/2 character, in agreement with their large θ²_n and θ²_p (see ⁷Be and (1956ME1A, 1957MA57)).

The scattering of polarized neutrons on ⁶Li has been studied for E_n = 0.19 to 0.42 MeV (1961DA04), 0.14 to 0.66 MeV (1962EL01), and 0.2 to 2.0 MeV (1964LA19). The data agree reasonably well with polarizations calculated from the resonance parameters of Table 7.2 (in PDF or PS) with a background of s-wave potential scattering in which channel spin J_c = 1/2 dominates (1961DA04, 1962EL01, 1964LA19).

See also (1960KO1C, 1960LA1C, 1962MA1R, 1963AL1J, 1964PE1E).

6. (a) ⁶Li(n, p)⁶He Q_m = -2.727 E_b = 7.253
(b) ⁶Li(n, d)⁵He Q_m = -2.430

The cross section for reaction (a) at E_n = 14 MeV is 6.7 mb (1953BA04, 1954FR03). See also (1963BA56).

For reaction (b) see reaction 8 and (1954FR03, 1956RI34).

7. ⁶Li(n, 2n)⁵Li Q_m = -5.662

The cross section is 33 ± 15 mb at E_n = 10.2 MeV, 70 ± 6 mb at E_n = 14.1 MeV (1963AS01).

8. ⁶Li(n, α)³H Q_m = 4.785 E_b = 7.253

Excitation functions and angular distributions are summarized in (1958HU18, 1960HU08, 1963GO1M, 1964ST25). Recent measurements are reported for E_n < 30 keV (1961BE24) and for E_n = 0.19 MeV (1963BA2A), 1 to 600 keV (1965SC07), 0.1 to 0.3 MeV (1959PA02), 9 to 340 keV (1959BA46), 1.2 to 8 MeV (1959MU25), 2.0 to 2.65 MeV (1959PU75), 8 to 14 MeV (1963MA61), 14.4 MeV (1964VA19). See also (1960PE24, 1961BE24, 1962BE1P, 1962CA1F, 1963AL1J, 1963CH20, 1963WA1K).

The isotropic thermal cross section is 949 b: in the eV-keV range, the cross section falls off somewhat more slowly than 1/v (1958HU18); for E_n = 9 to 90 keV, σ = 3.96E^-0.367 b (E in keV) (1959BA46). The failure to follow the 1/v law may reflect a broad s-wave resonance (1959BA46, 1959GA08, 1960LA1C, 1961BE24). Results of (1965SC07) are consistent with strict 1/v dependence for E_n < 20 keV. (1956MA83) have analyzed cross section data for E_n = 20 to 565 keV and find no need for an s-wave resonance. The s-wave background contribution is mainly (75%) in the J_c = 1/2⁺ channel.

A resonance occurs at E_n = 258 keV, with σ_max = 2.75 b (1959BA46), 2.80 ± 0.22 b (1959GA08): see also (1965MA1Y). The resonance is formed by p-waves, J^π = 5/2^-, and has a large neutron width and a small α-width (Table 7.2 (in PDF or PS)) (1959GA08). Above the resonance the cross section decreases monotonically to E_n = 18 MeV, except for a slight bump near E_n = 1.6 to 2.1 MeV (1959GA08, 1959MU25). A careful search in the range E_n = 2.0 to 2.65 MeV (E_x = 9 to 9.55 MeV) revealed no evidence for a level reported in ⁶Li(γ, n) (1959PU75). See also (1964GI1F).

In the range E_n = 8 to 14 MeV, the reaction ⁶Li(n, dn)⁴He shows a large cross section, reaching 0.6 b at E_n ≈ 6 MeV (1962RO12).

9. ⁶Li(d, p)⁷Li Q_m = 5.028

Proton spectra and angular distributions have been studied at E_d = 1.5 MeV (1964RI1E), 1.6 MeV (1960AN02), 3.4 to 5.2 MeV (1963ME09), 7 to 7.5 MeV (1957BR97), 8.0 MeV (1953HO48), 14 to 15 MeV (1955LE24, 1959HA29, 1960HA14). Groups corresponding to the ground state and to the states at 0.48, 4.6 and 7.5 MeV have been identified: see Table 7.3 (in PDF or PS). The first two and the last show stripping patterns with l_n = 1, while the angular distribution of p₂ (E_x = 4.6 MeV) is isotropic. It is noted that stripping to this level is forbidden if it has the character ²²F. Ratio of observed θ²_n are consistent with assignments ²²P to the g.s. and 0.48 and ²⁴P to the 7.5 MeV state (1960HA14, 1960MA32).

The angular correlation between the protons and the 0.48 MeV γ-rays is isotropic (see (1955AJ61)) indicating J = 1/2 for ⁷Li*. The mean lifetime is reported to be (7.7 ± 0.8) × 10^-2 psec (1956BU83: see also ⁹Be(d, α)⁷Li) see Table 7.4 (in PDF or PS). See also (1959BO1C, 1959HE1C, 1960NE1C, 1961HA1F, 1963BI27). The polarization of p₀ and p₁ protons has been observed at E_d = 1.6 MeV by (1961VA03). The circular polarization of the 0.48 MeV γ-rays has been studied by (1964SC1J). See also (1964PA16, 1965HE1B).

10. ⁶Li(t, d)⁷Li Q_m = 0.995

The reaction has been observed to the ground and 0.48 MeV states at E_t = 0.24 MeV (1954AL35) and 1.5 and 1.9 MeV (1961HO21). See also (1955CU17, 1961HO1F, 1963BA2B).

11. ⁶Li(α, ³He)⁷Li Q_m = -13.325

Not reported.

12. (a) ⁶Li(⁶Li, p⁴He)⁷Li Q_m = 3.556
(b) ⁶Li(⁹Be, ⁸Be)⁷Li Q_m = 5.587
⁹Be(⁶Li, ⁸Be)⁷Li

See (1960MA1H, 1961LE1K, 1962BE16, 1962MC12, 1963BA1Q, 1963CO35, 1963NO02, 1965SA1L), ¹²C and ¹⁵N.

13. ⁷Li(γ, γ)⁷Li

Resonance scattering and absorption by ⁷Li*(0.48) has been studied by a number of observers: the derived mean lifetimes are listed in Table 7.4 (in PDF or PS). See also (1960VA1G).

14. (a) ⁷Li(γ, n)⁶Li Q_m = -7.253
(b) ⁷Li(γ, p)⁶He Q_m = -9.980
(c) ⁷Li(γ, d)⁵He Q_m = -9.683
(d) ⁷Li(γ, t)⁴He Q_m = -2.467

Reports on the structure of the (γ, n) cross section differ widely. According to (1954GO1A, 1958RY77: E_brems. = 24 MeV), a broad maximum appears at E_γ = 16.8 MeV, with σ_max = 2.3 mb and a width Γ = 9.3 MeV. Fine structure corresponding to levels at E_x = 9.66 ± 0.04, 10.8, 12.4, 14.0 and 17.5 MeV is also reported (1954GO39, 1958RY77). Up to E_brems. = 19 MeV, the work of (1964AL08) confirms the gross structure of (1958RY77): additional levels at E_x = 13.6, 15.3 and 16.5 MeV are found: see Table 7.5 (in PDF or PS). (1955HE51) and (1959RO62) find, on the other hand, a weak rise at 8 MeV, a pronounced narrow peak at 14 MeV, followed by a deep minimum at 17 MeV and a sharp rise thereafter. It is suggested by (1964AL08) that the discrepancies are to be traced to different spectral sensitivities in the neutron detectors. Evidence is found for enhanced emission of slow neutrons from a level near E_x = 17.25 MeV (1964AL08). With E_brems. = 57 MeV, (1960FA06) find a broad maximum near 19 MeV, σ = 3.2 ± 0.8 mb, and a slow tailing off to 57 MeV: see also (1963CO1D). Reported integral cross sections, ∫ σdE, are 0 - 24 MeV: 33 MeV · mb (1954GO1A), 18 MeV · mb (1958RY77); 0 - 25 MeV: 39 MeV · mb (1960FA06); 0 - 50 MeV: 93 MeV · mb (1960FA06). (1964GR40) report cross sections for E_γ = 7.4 to 10.8 MeV: a value Γ_γ = 0.9 ± 0.4 eV is obtained for ⁷Li*(7.48). See also (1960KU1C).

The (γ, p) cross section determined by ⁶He production shows a splitting of the giant resonance into 2 components, at 15.5 and 19.6 MeV: smaller resonances are reported at 12.7, 25.4, 32.0 and 38.0 MeV (1963CL03: see also (1954RU27)). Peaks at 12.5, 13.5 and 14.3 MeV are reported by (1962SH24), while (1963KU25) report 6 peaks in the range E_x = 11 to 24.5 MeV. According to (1954TI16, 1962GR08) only a single maximum occurs, at ≈ 15.6 MeV, with a width of ≈ 4 MeV. Polarization of photoprotons at E_γ = 335 MeV is small and consistent with zero (1962LI13). See also (1963FU1D, 1963KI1C).

The ratio σ_γp/σ_γd has been investigated by (1962BE1N, 1962CH26, 1962VO1C). See also (1963KU16).

Peaks reported in the (γ, t) cross section are listed in Table 7.5 (in PDF or PS). See also (1961KO1J, 1963WA07).

See also (1964BI03, 1964MA2B).

15. ⁷Li(e, e)⁷Li

Elastic scattering has been studied at E_e = 41.5 MeV (1963GO04: θ = 180°) and 187 MeV (1955ST85). At the lower energy the magnetic scattering is consistent with that expected from a point dipole (1963GO04). The higher energy results yield an r.m.s. charge radius of about 2.1 fm (1957HO1E).

In inelastic scattering studies at E_e = 41.5 MeV, θ = 180°, weak broad peaks, ascribed to M1 transfer, are reported at Q = -6.9, -10.5, -14.0 MeV (1963BA19: see Table 7.6 (in PDF or PS)). At E_e = 102 to 177 MeV, excitation of states at 0.48, 4.63 ± 0.05, (5.7 ± 0.1), 6.8 ± 0.1 and 7.5 ± 0.08 MeV is reported. Transitions to the E_x = 0.48 MeV state show both longitudinal and transverse E2 contributions (see (1963WI1B)), while the others are mainly longitudinal E2: reported B(E2) are listed in Table 7.6 (in PDF or PS) (1963BE26, 1963BE53, 1964BI03). See also (1959ME1D, 1962BA1D, 1964GU1B, 1964MA2C, 1965CH11).

16. ⁷Li(n, n)⁷Li

Elastic angular distributions have been measured for E_n = 1.5 to 7.5 MeV (1963BA1V, 1963BA50) and 14 MeV (1964AL1N) and compared with optical model scattering.

At E_n = 14 MeV, evidence is reported for states at E_x = 4.6 ± 0.25, ≈ 6.5, 7.5 ± 0.25, and (9.25) MeV (1954AL24). For E_n = 1.5 to 7.5 MeV, the excitation of the 4.6 MeV state shows no evidence of direct interaction (1963BA50). A DWBA analysis of the distribution of this group at E_n = 14 MeV has been carried out by (1960PE1A). See also (1960HE1F, 1962WO07).

A tabulation of various partial cross sections is given by (1963BA50) and (1964AL1N). See also (1963GL1F, 1963OP1A, 1964VA19).

17. ⁷Li(p, p)⁷Li

Elastic scattering and polarization has been studied at E_p = 40 MeV (1959CH1B, 1960CH1B), 150MeV (1962NE12), 155MeV (1964TA02), 156MeV (1964JA03) and 160 to 180MeV (1959JO43, 1960JO14, 1961JO18, 1962RO1F). Analysis in terms of optical parameters is reported by (1961JO18, 1964SA1L).

Inelastic proton groups have been observed corresponding to the excited states of ⁷Li at 0.48, 4.63, 6.56 and 7.48 MeV: see (1952AJ38). At E_p = 185 MeV, proton groups are observed to these states, as well as to states at 5.5 ± 0.3 MeV (Γ ≈ 0.4 MeV) and 9.6 ± 0.2 MeV. The width of the 6.5 MeV state is reported to be ≈ 1 MeV. Angular distributions have been measured for the 4.6 and 6.5 MeV states (1965HA17). A check of the isotropy of the 477 keV radiation (J = 1/2 → 3/2) yields an upper limit F² < 10^-4 for the intensity of a parity non-conserving part of the wave function (1958WI38). Relative intensities of the Q = -4.6, -6.6 and -7.5 MeV groups, observed at E_p = 17.5 MeV, are consistent with the assignments ²²F_7/2, ²²F_5/2, ²⁴P_5/2, respectively (1957LE1E, 1957MA04). At E_p = 150 MeV, the E_x = 4.6 MeV state is strongly excited compared to the E_x = 0.48 and 6.5 MeV states, consistent with the assumed rotational character of these levels (1962NE12, 1964JA03). See also (1960HA21, 1960HE1F, 1962RU04, 1963CH08, 1963RI1B, 1964ST15, 1965WE1E).

18. (a) ⁷Li(p, 2p)⁶He Q_m = -9.980
(b) ⁷Li(p, pd)⁵He Q_m = -9.683
(c) ⁷Li(p, α)⁴He Q_m = 17.347

The summed proton energy spectrum, observed at E_p = 155 to 450 MeV, shows two peaks, with Q ≈ -11.6 and Q ≈ -25.4 MeV, corresponding to formation of ⁶He(g.s. + 1.80) and an excited state near 15 MeV (see ⁶He). Angular distributions indicate that the higher energy peak corresponds to the removal of a p-proton while the lower results from removal of an s-proton (1958MA1B, 1959MA1F, 1960HI10, 1961GA09, 1962BE1J, 1962BE1K, 1962DI1A, 1962GA09, 1962GO1P, 1962IN02, 1962IN1A, 1962ST1E, 1962ST1F, 1962TI01, 1963BE1A, 1963BE42, 1963EL1C, 1963JO07, 1963RI1B, 1963TA1D, 1964BA1C, 1964LI1D, 1964TI02, 1965RI1A, 1966TY01).

For reaction (b), see (1962RU04, 1963SH1A, 1964SA1H, 1965JA1L). For reaction (c), see (1962MA40, 1965ZH1A) and ⁸Be.

19. (a) ⁷Li(p, d)⁶Li Q_m = -5.028
(b) ⁷Li(d, t)⁶Li Q_m = -0.995
(c) ⁷Li(d, ³He)⁶He Q_m = -4.486
(d) ⁷Li(t, α)⁶He Q_m = 9.834

Reduced widths derived from PWBA analysis of pickup reactions (a) and (b) are listed in Table 7.7 (in PDF or PS). For reaction (c), θ² = 0.025 and 0.008 for ⁶He(0) and ⁶He*(1.80) (1957FR1B, 1960MA32).

20. ⁷Li(d, d')⁷Li*

Inelastic deuteron groups are observed corresponding to the ground and 0.48, 4.6 and 7.5 MeV states. At E_d = 14.8 MeV, the Q = -7.46 MeV group is only weakly excited (1960HA14). At E_d = 28 MeV, the Q = -4.6 MeV group is strong: the angular distribution is strongly forward. A fit with PWBA requires l = 0 + 2 (1962SL02). See also (1952AJ38, 1959AJ76).

Elastic scattering at 28 MeV has been analyzed in the black disc approximation, yielding R = 4.1 fm (1962SL02). See also ⁹Be and (1958EL45, 1958RO49, 1959HA29, 1959SI1A, 1961SL06, 1965JU1A).

21. (a) ⁷Li(α, α')⁷Li*
(b) ⁷Li(⁷Li, ⁷Li')⁷Li*
(c) ⁷Li(²⁰Ne, ²⁰Ne')⁷Li*

Inelastic alpha groups are observed corresponding to the 0.48 and 4.6 MeV states: see (1955AJ61). At E_α = 13.2, 31.8 and 48 MeV, the angular distributions of the Q = -4.6 MeV group show a prominent peak in the forward hemisphere (1956CO61, 1957SI36, 1960MA15). Analysis by PWBA yields R = 5.6 fm, l = 2 (1960MA15). See also (1962MA59). For reaction (b), see (1960BL1B).

Coulomb excitation of ⁷Li*(0.48) in reaction (c) has been studied at E(²⁰Ne) = 9 to 11 (1960ST17), 15.4 (1962RI09) and 16 MeV (1961AN07). The observed intensity leads to a value of the reduced transition matrix element B(E2) = 7.6 e²fm⁴ (1962RI09), 7.3 e²fm⁴ (1960ST17) corresponding to a partial half life τ = 1.5 nsec. Comparison with the quoted τ_1/2 of the state, 0.08 psec, yields Γ(E2)/Γ(M1) = 5 × 10^-5 (1960ST17): see Tables 7.4 (in PDF or PS) and 7.6 (in PDF or PS). See also (1963BE1R).

22. ⁷Be(ε)⁷Li Q_m = 0.862

The decay proceeds to the ground and 0.48 MeV states. Reported branching ratios are listed in Table 7.8 (in PDF or PS). The γ-ray energy is 477.8 ± 0.3 keV (see (1955AJ61, 1957DU37)). The weighted mean value of the half life is 53.37 ± 0.11 days (1949SE20, 1953KR16, 1956BO36, 1957WR37); ft = 2.00 × 10³ for the ground state transition and 3.45 × 10³ for the excited state (1965BA2C). Both transitions are super-allowed (1954MA1D, 1956CH1B). The internal conversion coefficient of the 0.48 MeV γ is 5.8 - 16.6 × 10^-7 indicating an E2/M1 ratio between 0 and 0.8 (1959LE30). Calculations of electron capture and nuclear matrix elements support the conclusion that ⁷Li is close to LS coupling (1962BA1X). See also (1959BL1C, 1963CH08, 1963KI1D).

23. ⁷Be(n, p)⁷Li Q_m = 1.644

See ⁸Be.

24. (a) ⁹Be(γ, d)⁷Li Q_m = -16.693
(b) ⁹Be(γ, np)⁷Li Q_m = -18.917

See (1955AJ61) and ⁹Be.

25. ⁹Be(n, t)⁷Li Q_m = -10.435

See (1957SC12, 1957VA12) and ¹⁰Be.

26. ⁹Be(p, ³He)⁷Li Q_m = -11.199

At E_p = 43.7 MeV, ³He groups are observed corresponding to the ⁷Li levels at 0, 0.48, 4.6 and 7.5 MeV and to a new state at 11.13 ± 0.05 MeV, with Γ = 268 ± 30 keV. From the similarity of the angular distribution and cross section to that in the (p, t) mirror reaction, it is concluded that the level has J^π = 3/2^-; T = 3/2 (1965DE08).

27. (a) ⁹Be(p, pd)⁷Li Q_m = -16.693
(b) ¹⁰B(p, p³He)⁷Li Q_m = -17.786

See (1963SH1A, 1964BA1C, 1964BA1P, 1964SH1C).

28. ⁹Be(d, α)⁷Li Q_m = 7.154

A number of α-groups have been observed with deuteron energies up to 27.5 MeV. These correspond to levels at 480 ± 2 keV (1948BU31, 1953CO02, 1961JA23), 4.62 ± 0.02 MeV (1953GE01: see also (1964MA04)), and 7.5 MeV (1951GO47, 1964MA04). Angular distributions have been studied for the ground and E_x = 0.48 MeV states at E_d = 0.4 to 2.4 MeV (1962BI11), 10 MeV (1962WE04) and 13.6 MeV (1962IV1A); those to the 4.6 and 7.5 MeV states at E_d = 27.5 MeV (1964MA04). The widths of the 4.6 and 7.5 MeV states are, respectively, 93 ± 25 and 80 ± 20 keV (1966HA09). The upper limit to the intensity of an α-particle group to a state at E_x ≈ 5.5 MeV is 5% of the intensity of the group to ⁷Li*(7.48) (1966HA09: E_d = 11.1 MeV). See also (1964YA1A).

The (α, γ) angular correlation has been observed for E_d = 0.40 and 0.84 MeV, (1953UE01, 1954CO17). There is no significant departure from isotropy, in agreement with J = 1/2 for the 0.48 MeV level. The mean life of this state is reported to be (7.7 ± 0.8) × 10^-2 psec (1956BU83): see Table 7.4 (in PDF or PS).