
^{7}Li (1966LA04)(See Energy Level Diagrams for ^{7}Li) 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: μ = +3.2564 nm (1965FU1G).
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 γ_{0}/γ_{1} (to ^{7}Li(0) and ^{7}Li*(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 θ^{2}_{α} = 1.25 and 1.05 for the ground and 0.48 MeV states of ^{7}Li, and taking into account only E1 capture from s and dwaves, (1963TO06) have calculated the total cross section from 0 to 7 MeV and the γray intensity ratios: the calculations are in excellent agreement with the data of (1961GR27). See also (1961TO04).
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).
At E_{α} = 38.5 MeV, two groups of protons are observed leading to the ground and 0.48 MeV states of ^{7}Li (1958BU38).
Two γrays 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 ^{7}Li are observed (1957BA18). The total radiative capture cross section is 45 ± 10 mb (1964ST25). See also (1961JA19, 1961TO04).
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 pwave formation of a J^{π} = 5/2^{} level (^{7}Li*(7.48)). Table 7.2 (in PDF or PS) gives the resonance parameters compared with those for ^{7}Be*(7.18). These states are believed to have a ^{4}P_{5/2} character, in agreement with their large θ^{2}_{n} and θ^{2}_{p} (see ^{7}Be and (1956ME1A, 1957MA57)). The scattering of polarized neutrons on ^{6}Li 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 swave potential scattering in which channel spin J_{c} = 1/2 dominates (1961DA04, 1962EL01, 1964LA19). See also (1960KO1C, 1960LA1C, 1962MA1R, 1963AL1J, 1964PE1E).
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).
The cross section is 33 ± 15 mb at E_{n} = 10.2 MeV, 70 ± 6 mb at E_{n} = 14.1 MeV (1963AS01).
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 eVkeV 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 swave 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 swave resonance. The swave 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 pwaves, J^{π} = 5/2^{}, and has a large neutron width and a small αwidth (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 ^{6}Li(γ, n) (1959PU75). See also (1964GI1F). In the range E_{n} = 8 to 14 MeV, the reaction ^{6}Li(n, dn)^{4}He shows a large cross section, reaching 0.6 b at E_{n} ≈ 6 MeV (1962RO12).
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 p_{2} (E_{x} = 4.6 MeV) is isotropic. It is noted that stripping to this level is forbidden if it has the character ^{22}F. Ratio of observed θ^{2}_{n} are consistent with assignments ^{22}P to the g.s. and 0.48 and ^{24}P to the 7.5 MeV state (1960HA14, 1960MA32). The angular correlation between the protons and the 0.48 MeV γrays is isotropic (see (1955AJ61)) indicating J = 1/2 for ^{7}Li*. The mean lifetime is reported to be (7.7 ± 0.8) × 10^{2} psec (1956BU83: see also ^{9}Be(d, α)^{7}Li) see Table 7.4 (in PDF or PS). See also (1959BO1C, 1959HE1C, 1960NE1C, 1961HA1F, 1963BI27). The polarization of p_{0} and p_{1} protons has been observed at E_{d} = 1.6 MeV by (1961VA03). The circular polarization of the 0.48 MeV γrays has been studied by (1964SC1J). See also (1964PA16, 1965HE1B).
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).
Not reported.
See (1960MA1H, 1961LE1K, 1962BE16, 1962MC12, 1963BA1Q, 1963CO35, 1963NO02, 1965SA1L), ^{12}C and ^{15}N.
Resonance scattering and absorption by ^{7}Li*(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).
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 ^{7}Li*(7.48). See also (1960KU1C). The (γ, p) cross section determined by ^{6}He 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).
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).
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).
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 ^{7}Li 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 F^{2} < 10^{4} for the intensity of a parity nonconserving 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 ^{22}F_{7/2}, ^{22}F_{5/2}, ^{24}P_{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).
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 ^{6}He(g.s. + 1.80) and an excited state near 15 MeV (see ^{6}He). Angular distributions indicate that the higher energy peak corresponds to the removal of a pproton while the lower results from removal of an sproton (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 ^{8}Be.
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), θ^{2} = 0.025 and 0.008 for ^{6}He(0) and ^{6}He*(1.80) (1957FR1B, 1960MA32).
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 ^{9}Be and (1958EL45, 1958RO49, 1959HA29, 1959SI1A, 1961SL06, 1965JU1A).
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 ^{7}Li*(0.48) in reaction (c) has been studied at E(^{20}Ne) = 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 e^{2}fm^{4} (1962RI09), 7.3 e^{2}fm^{4} (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).
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 γray 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 × 10^{3} for the ground state transition and 3.45 × 10^{3} for the excited state (1965BA2C). Both transitions are superallowed (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 ^{7}Li is close to LS coupling (1962BA1X). See also (1959BL1C, 1963CH08, 1963KI1D).
See ^{8}Be.
See (1957SC12, 1957VA12) and ^{10}Be.
At E_{p} = 43.7 MeV, ^{3}He groups are observed corresponding to the ^{7}Li 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).
See (1963SH1A, 1964BA1C, 1964BA1P, 1964SH1C).
A number of αgroups 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 αparticle group to a state at E_{x} ≈ 5.5 MeV is 5% of the intensity of the group to ^{7}Li*(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). See also (1959AJ76) and ^{11}B.
With thermal neutrons, two groups of αparticles are observed, corresponding to ^{7}Li*(0, 0.48); the fraction of transitions leading to the ground state is about 6%: see ^{11}B. The γray energy is 478.5 ± 1.5 keV (1948EL1A), 478 ± 4 keV (1956DA23); the mean life is (7.5 ± 2.5) × 10^{2} psec (1949EL07): see Table 7.4 (in PDF or PS). See also (1952AJ38, 1955AJ61, 1959AJ76, 1960AN14, 1962LA07, 1963DE1F).
For reaction (a) see (1963ME01). For reaction (b) see ^{11}B. For reaction (c) see (1964BA1C).
See (1963DR1B).
