
^{6}Li (1966LA04)(See Energy Level Diagrams for ^{6}Li) GENERAL: See Table 6.4 [Table of Energy Levels] (in PDF or PS). See also (1955AU1A, 1955LA1C, 1956ME1A, 1957FR1B, 1957HU1C, 1957LE1E, 1958PI1A, 1959BA1M, 1959BR1E, 1959FE1B, 1959SK1A, 1959UB1A, 1960AN1B, 1960JA1G, 1960KO1D, 1960PH1A, 1960TA1C, 1960WA1F, 1961BA1E, 1961KO1G, 1961SH1B, 1961TA05, 1961VA1G, 1962CO1D, 1962CR09, 1962DI1B, 1962FO08, 1962GA09, 1962IN02, 1962IN1C, 1962IN1A, 1962JA06, 1962ME1C, 1962NA1B, 1962SA1F, 1962ST1E, 1962WA1E, 1963BO1K, 1963BU1C, 1963DA04, 1963EL1D, 1963HA1H, 1963JA1C, 1963JO07, 1963KL1A, 1963KU03, 1963KU1B, 1963MO1F, 1963OL1B, 1963SA1F, 1963SC1J, 1963SC30, 1963VL1A, 1963WA1H, 1964GR1J, 1964JI1A, 1964MA1G, 1964MI16, 1964NE1E, 1964OL1A, 1964SA1F, 1964SH05, 1964ST1B, 1964WA1E, 1965BE1R, 1965BE1H, 1965BO1C, 1965DA1H, 1965EL1B, 1965GO1L, 1965HA1L, 1965JA04, 1965JA1L, 1965LO1G, 1965LO1H, 1965MA1N, 1965MU1A, 1965NE1C, 1965RA1E, 1965SA1J). Ground state: Q = ()0.5 mb (1958TO34); Q = (0.80 ± 0.08) mb (1964WH01).
Capture γrays (reaction (a)) to the first three states of ^{6}Li have been observed for E(^{3}He) = 1 to 3 MeV: the differential cross section for the ground state transition (90°) varies from 1.4 μb/sr at E(^{3}He) = 1.1 MeV to 8 μb/sr at 3.0 MeV. At E(^{3}He) = 1.1 MeV the transitions to the 2.18 and 3.56 MeV states each have intensities ≈ 15% that of the groundstate 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(^{3}He) = 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 zeroenergy cross section factor S_{0} ≈ 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).
An upper limit for capture radiation at E_{d} = 1.06 MeV (^{6}Li* = 2.18 MeV) is 0.1 mb (1954SI07). A search for resonant capture radiation at E_{d} = 3.1 MeV (^{6}Li* = 3.56 MeV) yields Γ_{dα} < 0.2 eV. It is concluded that the intensity of parity nonconserving parts of the wave functions, F^{2} ≲ 10^{7} (1958WI15).
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 ^{6}Li 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).
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 swave 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 hardsphere scattering with r = 5 fm; if a radius of 3.5 fm is chosen, a contribution from the ground state is required, with θ^{2}_{α}(g.s.) = 0.51 (1955GA74, 1960GA08). The dwave phase shifts are split and exhibit resonance at E_{x} = 2.18 (^{3}D_{3}), 4.87 (^{3}D_{2}) and 6.24 MeV (^{3}D_{1}): see Table 6.5 (in PDF or PS) (1955GA74, 1964SE07). Single level analysis of the pwave 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).
Differential cross sections for formation of the ground and 2.18 MeV states of ^{6}Li 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).
See ^{6}He.
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).
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 γrays 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 αparticle 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 quasideuteron 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).
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 < r^{2} > for the two regions, supporting an α + d model. Fine structure is observed in both regions, possibly corresponding to discrete ^{6}Li levels (1963BE25, 1963BI10, 1964BI04). Form factors for ^{6}Li*(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).
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 (n_{0} and n_{1}) show sharp forward peaking. At both energies, the excitation of ^{6}Li*(3.56) is weak (1962WO07, 1963BA50). See also (1960KO1C, 1962EL1D, 1962JA1B, 1963EL1C, 1964PE1C, 1965WE1E).
(1956LI37) calculates θ^{2}_{d} = 0.5 for ^{6}Li_{g.s.} from the data of (1954FR03). See also ^{7}Li.
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 ^{6}Li and ^{7}Li (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 ^{6}Li 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 ^{6}Li*(2.2, 4.6, 5.4) and M1 to ^{6}Li*(3.6) (1964JA03) and 185 MeV (1965HA17). At E_{p} = 149 MeV, a 3.56 MeV γray 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 θ_{1} = θ_{2}, the higher energy peak exhibits a maximum at the angle corresponding to zero momentum of the target proton (θ_{1} + θ_{2} ≈ 90°), while the lower has a minimum at this point. The higher peak is thus interpreted as a quasifree scattering from an l = 1 proton ^{6}Li → ^{5}He_{g.s.} + p and the lower corresponding to a l = 0 proton, leaving ^{5}He* in a positive parity configuration with an excitation of about 16  17 MeV (see ^{5}He* = 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 ^{7}Li, 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 ^{6}Li = ^{4}He + 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 ^{7}Be. (1956LI37) gives θ^{2}_{d} for the ground state of ^{6}Li = 0.30 (E_{p} = 15 MeV), 0.45 (18.5 MeV).
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).
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).
Angular distributions (θ_{c.m.} = 12° to 40°) to the ground and 2.18 MeV states have been measured at E(^{6}Li) = 63 MeV: they show diffractiontype structure. No evidence of the excitation of the 3.56 MeV T = 1 state is seen (1964GA01).
See ^{7}Li.
At E_{p} = 17.5 MeV, angular distributions of deuteron groups corresponding to ^{6}Li*(0, 2.18, 3.56), analyzed by Butler theory give l_{n} = 1 for all these states. The ratios of observed reduced widths (see ^{7}Li) 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).
At E_{d} ≈ 15 MeV, the angular distributions of the tritons indicate l_{n} = 1 (even parity) for the first three states of ^{6}Li (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).
Alpha particle groups have been observed with E(^{3}He) = 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).
See (1955AJ61).
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 α_{0} and α_{1} 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 ^{9}Be. The 3.56 MeV state is observed to decay by γradiation: E_{γ} = 3.572 ± 0.012 MeV; the internal pair spectrum is consistent with an M1 transition (1954MA26: see also (1960GO13)). The γray angular distribution and the (α  γ) correlation are isotropic at E_{p} = 2.56 MeV, consistent with J = 0 for ^{6}Li*(3.56) (1956ST93). See also (1959LE1B, 1962HA23, 1963ED1A, 1964BA1C) and ^{10}B.
Not reported: see (1964BL1C).
For reaction (a) see ^{10}B; for (b) see (1964BA1C); for (c) see (1963ME01); for (d) see (1956FR18); for (e) see (1964GE10).
Reaction (a) has not been reported: see (1964BL1C). For reaction (b), see (1964YO06).
