A=6Li (1966LA04)

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⁶Li (1966LA04)

(See Energy Level Diagrams for ⁶Li)

GENERAL: See Table 6.4 [Table of Energy Levels] (in PDF or PS).

Ground state:

μ = +0.82201 nm (1965FU1G: see also (1962SC15)).

Q = (-)0.5 mb (1958TO34);

Q = -(0.80 ± 0.08) mb (1964WH01).

1. (a) ³He(³H, γ)⁶Li	Q_m = 15.793	E_b = 15.793
(b) ³He(³H, p)⁵He	Q_m = 11.138
(c) ³He(³H, p)⁴He + n	Q_m = 12.096
(d) ³He(³H, n)⁵Li	Q_m = 10.131
(e) ³He(³H, d)⁴He	Q_m = 14.321
(f) ³He(³H, ³H)³He

Capture γ-rays (reaction (a)) to the first three states of ⁶Li have been observed for E(³He) = 1 to 3 MeV: the differential cross section for the ground state transition (90°) varies from 1.4 μb/sr at E(³He) = 1.1 MeV to 8 μb/sr at 3.0 MeV. At E(³He) = 1.1 MeV the transitions to the 2.18 and 3.56 MeV states each have intensities ≈ 15% that of the ground-state transition (1963KO04).

Angular distributions and total cross sections for reactions (b), (c) and (e) are given by (1963KU18) for E_t = 0.46 to 1.09 MeV. The total cross section has also been determined for E(³He) = 0.1 to 0.8 MeV (1953MO61), E_t = 0.15 to 0.97 MeV (1960YO06), and at E_t = 1.9 MeV (1963SM03). In the range E_t = 0.46 to 1.09 MeV, the cross section increases from 27 to 53 mb (1963KU18). At E_t = 1.9 MeV, it is 53 mb (1963SM03). The zero-energy cross section factor S₀ ≈ 1000 keV · b (1964BA2B, 1964PA1A). See also (1961BA40).

The angular distribution of deuterons is isotropic at E_t = 360 keV (1953MO61), but from 0.5 to 1 MeV it shows an increasingly strong maximum at 90°. It is suggested that the reaction proceeds via compound nucleus formation and that l = 1 is required (1963KU18).

For reaction (d), see (1963SM03). For reaction (f), see (1965LE02). See also (1963IN1A, 1963KU1H).

2. ⁴He(d, γ)⁶Li Q_m = 1.472

An upper limit for capture radiation at E_d = 1.06 MeV (⁶Li* = 2.18 MeV) is 0.1 mb (1954SI07). A search for resonant capture radiation at E_d = 3.1 MeV (⁶Li* = 3.56 MeV) yields Γ_dα < 0.2 eV. It is concluded that the intensity of parity non-conserving parts of the wave functions, F² ≲ 10^-7 (1958WI15).

3. (a) ⁴He(d, n)⁵Li Q_m = -4.190 E_b = 1.472
(b) ⁴He(d, p)⁵He Q_m = -3.182
(c) ⁴He(d, pn)⁴He Q_m = -2.225

Neutron spectra have been measured at 0° for E_d = 7.9, 8.9 and 9.9 MeV, and at several angles at the higher energy. The neutrons show forward peaking, indicative of stripping via reaction (a). The differential cross section (0°) plotted for E_d = 4.5 to 18.6 MeV shows a monotonic rise from 0.5 to 150 mb/sr (1962LE12: see also (1964RO1D)). Neutron spectra at E_d = 18.6 MeV (θ = 0° and 180°) indicate participation of reactions (a) (0°) and (b) (180°) (1961RY01). The proton spectra are also forward peaked at E_d = 20.2 MeV (1960AR1A) and 24 and 27 MeV (1963ER02). The proton yield over the range from 6.5 to 8.7 MeV excitation in ⁶Li gives no evidence of a 7.4 MeV, T = 0 state (see Table 6.8 (in PDF or PS)) (1964OH01).

At E_d = 20.2 MeV, the (d, pn) cross section is nearly as large as that for the elastic scattering at θ ≈ 45° (1960AR1A). Reaction (c) is presumably forbidden by isospin selection rules near threshold (1955HE90). See also (1965TO01).

4. ⁴He(d, d)⁴He E_b = 1.472

Elastic scattering studies have been carried out by (1949BL66: 0.9 to 3.5 MeV), (1953LA28: 1.0 to 1.2 MeV), (1955GA26: 0.3 to 4.6 MeV), (1947GU1A: 6.5 MeV), (1951BU1C: 7.9 MeV), (1964SE07, 1964SE1G: 2.9 to 11.5 MeV), (1964OH02: 3.5 to 10 MeV), (1962ST19: 6.0 to 13.7 MeV), (1963RO23, 1964RO1D: 5.7 to 14.3 MeV), (1951AL26: 10.3 MeV), (1954FR22: 13.7 and 19.0 MeV), (1960AR1A: 20.2 MeV), (1964BR43: 21 MeV), (1963VA14: 24.9 MeV), (1963ER02: 21.3 to 27.3 MeV).

Phase shift analyses have been carried out for the range E_d = 0.3 to 4.2 MeV by (1955GA74) and for 3 to 10 MeV by (1964SE07); see also (1964MC1F). Extrapolated phase shifts based on an optical model have been calculated by (1960GA08). The experimental s-wave phase shift decreases monotonically from E_d = 0.3 to 10 MeV: in the range 0 to 4 MeV it can be accounted for by hard-sphere scattering with r = 5 fm; if a radius of 3.5 fm is chosen, a contribution from the ground state is required, with θ²_α(g.s.) = 0.51 (1955GA74, 1960GA08). The d-wave phase shifts are split and exhibit resonance at E_x = 2.18 (³D₃), 4.87 (³D₂) and 6.24 MeV (³D₁): see Table 6.5 (in PDF or PS) (1955GA74, 1964SE07). Single level analysis of the p-wave phase shifts indicate the possible presence of 2^-, 1^- and 0^- levels at 6.8, 7.8 and 9 MeV (1964SE07: see, however, (1964MC1F)). Preliminary analysis of data in the range E_d = 5.6 to 12.5 MeV shows no effect from the presumptive T = 1 levels at E_x = 5.35, 6.63 and 8.37 MeV (1963RO23), nor from the suggested T = 0 state at 7.4 MeV (1964MC1F). At E_d = 21 to 27 MeV, increasing complexity of the angular distributions suggest l = 3 wave contributions (1963ER02). See also (1964MC1F).

A (d + α) model has been constructed by (1960GA08) to reproduce the phase shifts of (1955GA74); with this model, phase shifts and polarization parameters have been extrapolated to 14 MeV. Polarization parameters have also been calculated for E_d = 1.07 MeV (1959GO1H, 1959PO1C), at 2 and 3.5 MeV by (1959PH1B). A measurement at E_d = 1.07 MeV is consistent with expectation (1961PO01). Tensor polarization parameters for E_d = 4 to 7.5 MeV, measured by (1964MC1E, 1964SE1F), are in fair agreement with calculations of (1960GA08, 1964SE07). See also (1960DU1C, 1965GR1Q, 1965SE1E).

5. ⁴He(³He, p)⁶Li Q_m = -4.021

Differential cross sections for formation of the ground and 2.18 MeV states of ⁶Li have been measured for E_α = 27.5 to 41 MeV. Protons to the 3.56 MeV state were not observed: intensity < 1/5 of ground state group (1961CH09).

6. ⁶He(β^-)⁶Li Q_m = 3.510

See ⁶He.

7. ⁶Li(γ, γ)⁶Li

The width, Γ_γ, of the 3.56 MeV state is in good agreement with that expected from the intermediate coupling shell model (8.7 eV): see Table 6.6 (in PDF or PS) (1959CO67, 1963SK02). See also (1961VA1G, 1962BO17, 1962SE02).

8. (a) ⁶Li(γ, n)⁵Li Q_m = -5.662
(b) ⁶Li(γ, p)⁵He Q_m = -4.655
(c) ⁶Li(γ, d)⁴He Q_m = -1.472
(d) ⁶Li(γ, t)³He Q_m = -15.793

The total cross section for photoneutrons, measured with E(brems) = 5 to 20 MeV exhibits a peak at E_γ = 12.5 MeV, σ = 2.8 ± 0.53 mb (1959RO62). Measurements with monochromatic γ-rays have been made for E_γ = 5.4 to 9.0 MeV by (1964GR40) and from 10 to 32 MeV by (1965BE42). The former work shows a smooth rise, with a possible peak at 6.75 MeV, while the latter yields a maximum at ≈ 12 MeV, σ ≈ 1.6 mb and a gentle decrease to 0.6 mb at 32 MeV. See also (1951TI06, 1956ED15, 1964SH27). Another peak, at E_γ ≈ 26 MeV is reported by (1963CO15): it is suggested that this peak corresponds to giant resonance excitation of the α-particle core (see also (1963BI10, 1963CO1D)); however, (1965BE42) find no evidence for this peak. At E(brems) = 17.3 MeV, 58% of the neutrons are ascribed to reaction (a), 31% to (b). A search for n - p correlations expected on the quasi-deuteron model for (γ, np) yielded a negative result (1960PR06). The integrated cross section (total neutrons) to 40 MeV is about 40 MeV · mb (1963CO15). See also (1964ER1B).

Photoprotons have been observed with E_γ up to 90 MeV: see (1959AJ76) and (1960BA45, 1962CH26, 1962VO1C). A peak in the proton spectrum corresponding to E_x = 6.63 or E_x = 7.94 MeV is reported by (1965SH1F). See also (1960KO14, 1961MA29, 1964BA2C, 1964ER1B, 1964MA1X).

The cross section for reaction (c) is ≲ 5 μb in the range E_γ = 2.6 to 17 MeV (see (1959AJ76)) consistent with the expected inhibition of dipole absorption by isospin selection rules. In common with other (γ, d) reactions in light nuclei, an effective threshold first appears when sufficient energy is available to release at least one particle in addition to the deuteron (1962CH26, 1962VO1C, 1962VO1D). Resonant capture at the 2.18 MeV state is observed by (1959DA04): a value Γ_γ = 30 μeV is obtained. See also (1964KO1F).

For reaction (d), see (1962VO1C, 1964KO1F, 1965SH1F).

9. (a) ⁶Li(e, e)⁶Li
(b) ⁶Li(e, p)⁵He Q_m = -4.655
(c) ⁶Li(e, d)⁴He Q_m = -1.472

Elastic scattering has been studied at E_e = 187 (1955ST85, 1956HO93) and 426 MeV (1958BU17). Several different charge distributions provide acceptable fits to the observed form factors. The maximum charge density is 0.064 protons · fm^-3, R_rms = 2.70 ± 0.15 fm (1958BU17, 1959ME24, 1960JA1G: see also (1958CA1B, 1963BO1K, 1963SC1J)). Magnetic elastic scattering at E_e = 41.5 MeV, θ = 180°, has been studied by (1963GO04).

Inelastic spectra have been reported by (1960BA47: E_e = 40 MeV; θ = 132°, 160°), (1963BA19: E_e = 41.5 MeV; θ = 180°), (1964GO15: 75 MeV), (1963BI10: 101.4 MeV; θ = 60°) and (1963BE25: 180 MeV). Table 6.6 (in PDF or PS) summarizes the results. [For a review of the inelastic work to 1962, see (1962BA1D).] The inelastic spectrum of (1963BI10) shows two major absorption regions, from 9 to 17.5 MeV and from 17.5 to 32 MeV. Analysis of form factors on the assumption of E1 transitions leads to quite different values of < r² > for the two regions, supporting an α + d model. Fine structure is observed in both regions, possibly corresponding to discrete ⁶Li levels (1963BE25, 1963BI10, 1964BI04). Form factors for ⁶Li*(2.2) and (3.6) have been studied as a function of momentum transfer by (1963BE25, 1963BE53, 1964GO15). Interpretation in terms of nuclear models is discussed by (1963BE53, 1964KU1G, 1965DA1H). See also (1959ME1D, 1959UB1A, 1961PA1A, 1962JA06, 1965LO1J, 1965RA1D).

For reactions (b) and (c), see (1957KE1A).

10. ⁶Li(n, n')⁶Li*

Inelastic neutron groups have been observed corresponding to the 2.18 MeV state with incident neutron energies up to 14 MeV. Differential cross sections are reported from E_n = 3.4 to 7.5 MeV (1963BA1V, 1963BA50), and at 14 MeV (1962WO07, 1964AR25, 1965ME05). Angular distributions up to E_n = 7.5 MeV show no obvious indication of direct interaction; at E_n = 14 MeV, both elastic and inelastic neutrons (n₀ and n₁) show sharp forward peaking. At both energies, the excitation of ⁶Li*(3.56) is weak (1962WO07, 1963BA50). See also (1960KO1C, 1962EL1D, 1962JA1B, 1963EL1C, 1964PE1C, 1965WE1E).

11. ⁶Li(n, t)⁴He Q_m = 4.785

(1956LI37) calculates θ²_d = 0.5 for ⁶Li_g.s. from the data of (1954FR03). See also ⁷Li.

12. (a) ⁶Li(p, p)⁶Li
(b) ⁶Li(p, 2p)⁵He Q_m = -4.655
(c) ⁶Li(p, pd)⁴He Q_m = -1.472
(d) ⁶Li(p, ³He)⁴He Q_m = 4.021

Elastic scattering has been studied at E_p = 31 MeV by (1963DE01), at 40 MeV by (1960CH1B), and at 155 MeV by (1964TA02). At the latter energy, the polarization at high momentum transfers, q > 1.7 fm^-1 is strikingly different for ⁶Li and ⁷Li (1964TA02). Optical model analysis is discussed by (1963DE01, 1963JA1C). See also (1960SA28). Polarization of the scattered protons has been studied by (1962RO20, 1963HW01, 1964MA1Y).

Inelastic groups corresponding to several ⁶Li states are observed: see Table 6.7 (in PDF or PS). Angular distributions have been determined for E_p = 4 to 9 MeV (1963HA49), 31 MeV (1963DE01), 39.8 MeV (1959CH1B: see also (1963JA1C)), 155 MeV (1964JA03) and 185 MeV (1965HA17). The distributions at E_p = 155 to 185 MeV indicate dominant E2 transitions to ⁶Li*(2.2, 4.6, 5.4) and M1 to ⁶Li*(3.6) (1964JA03) and 185 MeV (1965HA17). At E_p = 149 MeV, a 3.56 MeV γ-ray is observed with a cross section of 0.7 ± 0.3 mb (1961CL09). See also (1957LE1E, 1959SY1A).

Reaction (b) has been studied at E_p = 155 MeV (1961GA09, 1962GA09, 1962GA23), 185 MeV (1962TI01, 1964TI02) and 460 MeV (1965TY1A). The spectra of summed proton energies (E_p1 + E_p2) show two peaks, with Q = -4.8 and Q = -22.4 MeV. As a function of angle of emission θ₁ = -θ₂, the higher energy peak exhibits a maximum at the angle corresponding to zero momentum of the target proton (θ₁ + θ₂ ≈ 90°), while the lower has a minimum at this point. The higher peak is thus interpreted as a quasi-free scattering from an l = 1 proton ⁶Li → ⁵He_g.s. + p and the lower corresponding to a l = 0 proton, leaving ⁵He* in a positive parity configuration with an excitation of about 16 - 17 MeV (see ⁵He* = 16.70 MeV).

Calculations of expected momentum distributions with various wave functions are discussed by (1962BE1J, 1962BE1K, 1962DI1A, 1962IN1A, 1962IN1C, 1962SA1F, 1963BE42, 1963EL1C, 1963JO07, 1963RI1B, 1964LI1D, 1965JA04, 1965JA1J, 1965JA1M, 1965MC1F, 1965RI1A, 1965WI1G). As compared with the analogous case of ⁷Li, there appears to be a difficulty here in accounting for the small width of the observed angular distribution.

At E_p = 155 MeV, the angular correlation of outgoing protons and deuterons (reaction (c)) give evidence for a substructure ⁶Li = ⁴He + d in a relative l = 0 state with a probability of 20 to 31% (1963RU05). See also (1962RU04, 1963RI1B, 1963SA1F, 1963TA1D, 1964BA1P, 1964DE1F, 1964SA1H, 1965DE1Q, 1965JA1L).

For reaction (d) see (1963RU05, 1963TE1B) and ⁷Be. (1956LI37) gives θ²_d for the ground state of ⁶Li = 0.30 (E_p = 15 MeV), 0.45 (18.5 MeV).

13. ⁶Li(d, d')⁶Li*

Deuteron groups have been observed corresponding to the ground state and the 2.18 MeV level (1957BR12: E_d = 7.0 and 7.5 MeV): see Table 6.7 (in PDF or PS). The 3.56 MeV state is not observed at E_d = 7.5 MeV, θ = 60°, consistent with its T = 1 character. The shape of the angular distribution of the deuterons to the 2.18 MeV state (E_d = 14.7 MeV) does not fit simple direct interaction theory (1960HA14: see also (1956HA90, 1964HA05, 1965JO09)). See also (1956SO21, 1956SO33, 1960EL09).

14. ⁶Li(α, α)⁶Li

Angular distributions of elastic and inelastic scattering (to the 2.18 MeV state) have been studied at E_α = 10.0 and 12.5 MeV (1963BL20), at 24 MeV (1964GR39) and at 31.5 MeV (1956WA29). At E_α = 31.5 MeV, a group is also observed to the 4.57 MeV state but not to the T = 1, 3.56 MeV level (1956WA29: see also (1964GR39)). See also (1962TE1D, 1963TE1B).

15. ⁶Li(⁶Li, ⁶Li')⁶Li*

Angular distributions (θ_c.m. = 12° to 40°) to the ground and 2.18 MeV states have been measured at E(⁶Li) = 63 MeV: they show diffraction-type structure. No evidence of the excitation of the 3.56 MeV T = 1 state is seen (1964GA01).

16. ⁷Li(γ, n)⁶Li Q_m = -7.253

See ⁷Li.

17. ⁷Li(p, d)⁶Li Q_m = -5.028

At E_p = 17.5 MeV, angular distributions of deuteron groups corresponding to ⁶Li*(0, 2.18, 3.56), analyzed by Butler theory give l_n = 1 for all these states. The ratios of observed reduced widths (see ⁷Li) are consistent with predictions of the shell model with pure, or nearly pure, LS coupling (1956RE04, 1959BE84, 1960MA32). See also (1961CL09). The bearing of this reaction and its inverse on tests of invariance under time reversal is discussed by (1959HE1C). See also (1964SH07).

18. ⁷Li(d, t)⁶Li Q_m = -0.995

At E_d ≈ 15 MeV, the angular distributions of the tritons indicate l_n = 1 (even parity) for the first three states of ⁶Li (1955LE24, 1957FR1B, 1959HA29, 1960HA14): reported reduced widths are listed in Table 7.7 (in PDF or PS). (1960HA14) report a board asymmetric bump at E_x ≈ 5.4 MeV, Γ ≈ 600 keV; no sharp states are reported for 4.4 < E_x < 8.5 MeV with σ > 0.3 mb/sr (E_d = 14.9 MeV, θ = 14°, 25°). See also (1956SO21, 1956SO33, 1959KU1C, 1959VL24, 1961OG1A, 1961SL06, 1962SL04, 1963OG1A, 1964BL1C).

19. ⁷Li(³He, α)⁶Li Q_m = 13.325

Alpha particle groups have been observed with E(³He) = 0.6 to 0.9 MeV (1960AL10), 1.5 MeV (1963CA02), 0.8 to 3 MeV (1965PA03), 4 MeV (1961WO05, 1963KN1C), 0.8 to 5.1 MeV (1963LI16) and 1.3 to 5.5 MeV (1965FO07). (1963LI16) find no evidence for reported levels at 4.3 or 6.6 MeV; (1965CO1F) confirms the levels at 4.3 and 5.35 MeV but finds no evidence for the higher states reported by (1960AL10). The results are summarized in Table 6.8 (in PDF or PS).

20. ⁹Be(γ, t)⁶Li Q_m = -17.688

See (1955AJ61).

21. ⁹Be(p, α)⁶Li Q_m = 2.126
Q₀ = 2.1254 ± 0.0018 (1965BR28).

Alpha particle groups have been observed with E_p = 7.2 to 7.5 MeV (1957BR12), 10 MeV (1963GR29), 3.50 to 12.50 MeV (1963BL20), 15.6 and 18.6 MeV (1962MA40). The results are summarized in Table 6.7 (in PDF or PS). Angular distributions of the α₀ and α₁ groups are reported for E_p = 6 to 11.5 MeV (1963BL20, 1963TE1B), 5.9 and 7 MeV (1964YA1A) and 15.6 and 18.6 MeV (1962MA40). See also ⁹Be. The 3.56 MeV state is observed to decay by γ-radiation: E_γ = 3.572 ± 0.012 MeV; the internal pair spectrum is consistent with an M1 transition (1954MA26: see also (1960GO13)).

The γ-ray angular distribution and the (α - γ) correlation are isotropic at E_p = 2.56 MeV, consistent with J = 0 for ⁶Li*(3.56) (1956ST93). See also (1959LE1B, 1962HA23, 1963ED1A, 1964BA1C) and ¹⁰B.

22. ⁹Be(d, ⁵He)⁶Li Q_m = -1.056

Not reported: see (1964BL1C).

23. (a) ¹⁰B(γ, α)⁶Li Q_m = -4.461
(b) ¹⁰B(p, pα)⁶Li Q_m = -4.461
(c) ¹⁰B(α, 2α)⁶Li Q_m = -4.461
(d) ¹⁰B(n, dn2α) Q_m = -5.933
(e) ¹⁰B(d, ⁶Li)⁶Li Q_m = -2.989

For reaction (a) see ¹⁰B; for (b) see (1964BA1C); for (c) see (1963ME01); for (d) see (1956FR18); for (e) see (1964GE10).

24. (a) ¹¹B(d, ⁷Li)⁶Li Q_m = -7.192
(b) ¹¹B(³He, ⁸Be)⁶Li Q_m = 4.566

Reaction (a) has not been reported: see (1964BL1C). For reaction (b), see (1964YO06).