
^{8}Li (2004TI06)(See Energy Level Diagrams for ^{8}Li) GENERAL: References to articles on general properties of ^{8}Li published since the previous review (1988AJ01) are grouped into categories and listed, along with brief descriptions of each item, in the General Tables for ^{8}Li located on our website at (www.tunl.duke.edu/nucldata/General_Tables/8li.shtml). See also 2 in (1988AJ01) [Electromagnetic Transitions in A = 510] (in PDF or PS), 8.2 [Table of Energy Levels] (in PDF or PS) and 8.3 [Electromagnetic transitions in ^{8}Li] (in PDF or PS). Ground State Properties:
The interaction nuclear radius of ^{8}Li is 2.36 ± 0.02 fm (1985TA18) [see (1985TA18) also for derived nuclear matter, charge and neutron matter r.m.s. radii]. ^{8}Li atomic transitions: Atomic excitations in the lithium isotopes were analyzed in (2000YA05) where a theoretical framework was developed that correlates the atomic decay energies in neutral Li ions with the nuclear sizes.
The β^{} decay is mainly to the broad 2^{+} firstexcited state of ^{8}Be, which then breaks up into 2α [see reaction 24 in ^{8}Be]. The weighted average of the ^{8}Li halflife is 839.9 ± 0.9 ms based on measured values of 838 ± 6 ms (1971WI05), 836 ± 3 ms (1979MI1E) and 840.3 ± 0.9 ms (1990SA16). The log ft ≥ 5.6, using τ_{1/2} = 839.9 ms, Q = 16.0052 MeV and branching ratio ≤ 100%; other values in the literature that account for the decay to the broad Γ ≈ 1.5 MeV ^{8}Be*(3.0) state are log ft = 5.37 (1986WA01) and log ft = 5.72 (1989BA31). The quadrupole moment of ^{8}Li was deduced by measuring the asymmetry in βNMR spectra. We adopt Q(^{8}Li) = +32.7 ± 0.6 mb, which results from a new method, modified βNMR (NNQR), that is 100 times more sensitive than previous methods (1993MI34). This value is larger than 28.7 ± 0.7 mb (1988AR17) and the previous adopted value 24 ± 2 mb (1988AJ01). The sign of the ^{8}Li quadrupole moment was measured and is positive (1994JA05). The tilted foil technique was used to polarize atomic ^{8}Li, and the hyperfine interaction led to a nuclear polarization of 1.2 ± 0.3% which was deduced from the measured βdecay asymmetry (1987NO04). The polarization quantum beat in the hyperfine interaction was measured by varying the foil separation distances (1993MO33, 1996NO11). See also (1987AR22) for discussion of hyperfine structure splitting in lithium isotopes. The pure GamowTeller (ΔT = 1) βdecay of ^{8}Li to the ^{8}Be*(3.0) level has been measured in a search for timereversal violation (1990SR03, 1992AL01, 1996SR02, 2003HU06); the present constraint for the time violating parameter is R = (0.9 ± 2.2) × 10^{3}. See also (1992DE07, 1995YI01, 1998KA51). Searches for secondclass currents in ^{8}Li βdecay have yielded negative results: see (1988HA21, 1989TE04, 2003SM02). For an analysis of the antineutrino energy distribution shape in ^{8}Li βdecay, see (1987LY05, 2002BH03). For a comment on the usefulness of βdecay asymmetries to reveal information on spin dynamics in nuclear reactions involving polarized projectiles see (2001DZ02). A suggestion to use ^{8}Li βdecay for calibration of the SNO detector is described in (1998JO09, 2002TA22). βNMR is used to measure the ^{8}Li quadrupolecoupling constants in Mg and Zn (1993OH11). For condensed matter applications of ^{8}Li βdecay see (1993BU29, 1993NO08, 1994HO23, 1996EB01).See also (1993CH06, 1993MO28, 2003SU04).
Small angle scattering in the ^{1}H(^{8}Li, ^{8}Li) reaction was measured at E(^{8}Li) = 698 MeV/A (2002EG02, 2003EG03).
Angular distributions have been obtained at E_{t} = 23 MeV for the proton groups to ^{8}Li*(0, 0.98, 2.26, 6.54 ± 0.03); Γ_{cm} for ^{8}Li*(2.26, 6.54) are 35 ± 10 and 35 ± 15 keV, respectively. J for the latter is ≥ 4: see (1979AJ01). A multicluster model is used to calculate excitation function and γray flux from ^{6}Li(t, p_{1})^{8}Li*(0.981), which is proposed as a diagnostic tool for fusion reactions (2000VO22, 2001VO02).
At E_{n} = 1.5  1340 eV agreement was found with the expected 1/v (velocity) energy dependence, and a thermal cross section of 40 ± 2(stat.) ± 4(syst.) mb was measured (1996BL10). (1998HE35) measured σ_{ave.} = 101.9 mb for an energy bin for E_{n} = 1.7  20 meV, and σ_{ave.} = 36.6 μb for E_{n} = 5  150 keV. A reanalysis of the ion chamber efficiencies used by (1989WI16) led to a revised cross section σ(E_{n} = 25 keV) = 57 ± 9 μb and Γ_{γ} = 0.18 eV (1998HE35). Measurements by (1991LY01), who analyzed σ(E) from E_{thermal} to 3.0 MeV, determined σ_{thermal} = 45.4 ± 3.0 mb and the γray branching ratios at E_{n} = thermal (see 8.4 (in PDF or PS)). At E_{n} = 30 keV, (1991NA16, 1991NA19) measured σ_{γ0} = 35.4 ± 6.0 μb and σ_{γ1} < 9.1 μb. The excitation function shows the resonance corresponding to ^{8}Li*(2.26): E_{res} = 254 ± 3 keV, Γ_{n} = 31 ± 7 keV, Γ_{γ} = 0.07 ± 0.03 eV: see 8.5 (in PDF or PS) and (1974AJ01). Theoretical models are discussed in (1988DE38, 1993KR18, 1994DE03, 1996SH02, 1997BA04, 1999BE25, 2000BE21, 2000CS01, 2001KO54). The decay of ^{8}Li*(2.26) → ^{7}Li_{g.s.} + n in the interaction of 35 MeV/A ^{14}N ions on Ag is reported by (1987BL13).
The thermal cross section is 0.97 ± 0.04 b [see (1981MUZQ)], σ_{free} = 1.07 ± 0.03 b (1983KO17). The real coherent scattering length is 2.22 ± 0.01 fm. The complex scattering lengths are b_{+} = 4.15 ± 0.06 fm and b_{} = 1.00 ± 0.08 fm (1983KO17); see also (1979GL12). See (1984AJ01) for earlier references. Total and elastic cross sections have been reported for E_{n} = 5 eV to 49.6 MeV: see (1979AJ01, 1984AJ01, 1988AJ01). Cross sections have also been reported for n_{0}, n_{0+1} and n_{2} at E_{n} = 6.82, 8.90 and 9.80 MeV. (1987SC08; n_{2} at the two higher energies). A pronounced resonance is observed at E_{n} = 254 keV with J^{π} = 3^{+}, formed by pwaves: see 8.5 (in PDF or PS). A good account of the polarization is given by the assumption of levels at E_{n} = 0.25 and 3.4 MeV, with J^{π} = 3^{+} and 2^{}, together with a broad J^{π} = 3^{} level at higher energy. Broad peaks are reported at E_{n} = 4.6 and 5.8 MeV (± 0.1 MeV) [^{8}Li*(6.1, 7.1)] with Γ ≈ 1.0 and 0.4 MeV, respectively, and there is indication of a narrow peak at E_{n} = 5.1 MeV [^{8}Li*(6.5)] with Γ ≪ 80 keV and of a weak, broad peak at E_{n} = 3.7 MeV: see (1974AJ01, 1984AJ01, 1988AJ01). A multilevel, multichannel Rmatrix calculation is reported by (1987KN04). This analysis leads to predictions for the cross section for elastic scattering, for (n, n') to ^{7}Li*(0.48, 4.68, 6.68) and for triton production. A number of additional (broad) states of ^{8}Li, unobserved directly in this and in other reactions, derive from this analysis (1987KN04). See (1989FU03) for a resonating group study of ^{8}Li*(6.53) [J^{π} = 4^{+}; T = 1]; see also (2002GR25). See also references cited in (1988AJ01).
The excitation function for 0.48 MeV γrays shows an abrupt rise from threshold (indicating swave formation and emission) and a broad maximum (Γ ≈ 1 MeV) at E_{n} = 1.35 MeV. A good fit is obtained with either J^{π} = 1^{} or 1^{+} (2^{+} not excluded), Γ_{lab} = 1.14 MeV. A prominent peak is observed at E_{n} = 3.8 MeV (Γ_{lab} = 0.75 MeV) and there is some indication of a broad resonance (Γ_{lab} = 1.30 MeV) at E_{n} = 5.0 MeV. At higher energies there is evidence for structure at E_{n} = 6.8 and 8 MeV followed by a decrease in the cross section to 20 MeV: see (1979AJ01, 1984AJ01). The total cross section for (n_{0} + n_{1}) and n_{2} have been reported at E_{n} = 8.9 MeV (1984FE1A). For Rmatrix analyses see (1987KN04) in reaction 5 and (1984AJ01). The cross section for reaction (b) rises from threshold to ≈ 360 mb at E_{n} ≈ 6 MeV and then decreases slowly to ≈ 250 mb at E_{n} ≈ 16 MeV: see (1985SW01, 1987QA01). Cross sections for tritium production have been reported from threshold to E_{n} = 16 MeV (1983LI1C), 4.57 to 14.1 MeV (1985SW01), 7.9 to 10.5 MeV (1987QA01), 14.74 MeV (1984SMZX) and at 14.94 MeV (1985GO18: 302 ± 18 mb). At E_{n} = 14.95 MeV the total α production cross section [which includes the (n, 2n d) process] is 336 ± 16 mb (1986KN06). Spectra at 14.6 MeV may indicate the involvement of states of ^{4}H (1986MI11). See also references cited in (1988AJ01).
See (1985CH37, 1986CH24). See also (1988AJ01).
Angular distributions and analyzing powers for the transitions to ^{8}Li*(0, 0.98, 2.26) have been studied at E_{p} = 200.4 MeV. [The (p, π^{}) reaction to the analog states in ^{8}B is discussed: see reaction 4 in ^{8}B.] The (p, π^{+}) cross sections are an order of magnitude greater than the (p, π^{}) cross sections and show a much stronger angular dependence (1987CA06). Angular distributions of cross section and A_{y} have also been measured at E_{p} = 250, 354 and 489 MeV to the first three states of ^{8}Li. Those to ^{8}Li*(0, 2.26) have differential cross sections which exhibit a maximum near the invariant mass of the Δ(1232) and A_{y} which are similar to each other and to those of the pbar p → dπ^{+} reaction. ^{8}Li*(6.53) is populated (1987HU12, 1988HU11).
Measurements in the vicinity of the E_{cm} = 0.61 MeV ^{9}Be*(17.3) resonance found σ[^{7}Li(d, p)] = 143.6 ± 8.9 mb (1996ST18), σ[^{7}Li(d, ^{8}Li)p: ^{8}Li β^{} / → ^{8}Be → 2α] = 151 ± 20 mb (1996ST18), and σ[^{7}Li(d, p)] = 155 ± 8 mb (1998WE05). An extensive review in (1998AD12) presented the results found in 8.6 (in PDF or PS). However, (1998WE05) suggest that systematic errors may persist in the (1998AD12) evaluation. Angular distributions of the p_{0} and p_{1} groups [l_{n} = 1] at E_{d} = 12 MeV have been analyzed using DWBA: S_{expt.} = 0.87 and 0.48 respectively for ^{8}Li*(0, 0.98). Angular distributions have also been measured at several energies in the range of E_{d} = 0.49 to 3.44 MeV (p_{0}) and 0.95 to 2.94 MeV (p_{1}). The lifetime of ^{8}Li*(0.98), determined from ^{2}H(^{7}Li, p)^{8}Li via the Dopplershift attenuation method, is 10.1 ± 4.5 fsec: see (1979AJ01). See also references cited in (1988AJ01). The ^{7}Li(d, p)^{8}Li β^{} / → ^{8}Be → 2α reaction was studied in the range of 0.4  1.8 MeV to investigate a mechanism where the ^{8}Li reaction products are backscattered out of the target which introduces up to a 20% systematic error in measurements of the reaction yield (1998ST20). They determined that ^{8}Li reaction products are increasingly backscattered out of the target with: (i) increasing the Z of the backing material, (ii) decreasing the thickness of the deposited Li/Be target, and (iii) decreasing the incident projectile energy.
See (1984KO25).
See reaction 1 in ^{8}He. The triton spectrum observed in ^{8}He βdecay was analyzed in a singlelevel Rmatrix model that indicated the triton emission branching ratio is (8.0 ± 0.5) × 10^{3} (1991BO31, 1993BO24). The Rmatrix fit indicates a level at ^{8}Li*(9.3 ± 1.0 MeV, J^{π} = 1^{+}) with a reduced width γ_{reduced} = 0.978 ± 0.012 MeV^{1/2} that decays primarily by triton emission; this corresponds to B(GT) = 5.18 and log ft = 2.87 [B(GT) = 8.29, using the definition given in the introduction]. A subsequent analysis of the (1993BO24) data used a multilevel, multichannel Rmatrix model that included lowlying 1^{+} states in ^{8}Li that participate in ^{8}He βdecay (see 8.7 (in PDF or PS)) and suggests E_{x} = 9.67 MeV, B(GT) = 4.75 and log ft = 2.91 (1996BA66) [B(GT) = 7.56, using the definition given in the introduction]. Branching ratios for ^{8}Li states are given in (1988BA67). See also Fig. 2.
The ^{9}Be(γ, p_{0}) reaction was measured in the range from E_{γ} = 22  25.5 MeV and was evaluated in a simple cluster model (1999SH05). The analysis indicated that mainly E1 and E2 multipolarities contribute to the breakup cross section. The photodisintegration of ^{9}Be was measured at E_{γ} = 180  240 MeV, and the (γ + nucleon) reaction dynamics were studied by measuring ^{9}Be(γ, p) at E_{γ} = 187  427 MeV in the Δ(1232) resonance region (1988TE04).
The total cross section for ^{9}Be(γ, pπ^{0}) was measured with bremsstrahlung γrays in the range of E_{γ} = 200  850 MeV (1987AN14).
For reaction (a) see (1984AJ01) and (1985KI1A). The summed proton spectrum (reaction (b)) at E_{p} = 156 MeV shows peaks corresponding to ^{8}Li_{g.s.} and ^{8}Li*(0.98 + 2.26) [unresolved]. In addition, sstates [J^{π} = 1^{}, 2^{}] are suggested at E_{x} = 9 and 16 MeV, with Γ_{cm} ≈ 6 and 8 MeV; the latter may actually be due to continuum protons: see (1974AJ01). At E_{p} = 1 GeV the separation energy between 5 and 8 MeV broad 1p_{3/2} and 1s_{1/2} groups is reported to be 10.7 ± 0.5 MeV (1985BE30, 1985DO16). See also (1987GAZM). For reaction (b) angular distributions were measured at 70 MeV. The data were evaluated using the distorted wave Tmatrix approximation (DWTA) where it was determined that the 1s and 1p shells dominate in the nucleusnucleon singleparticleknockout reaction mechanism (2000SH01).
Angular distributions have been reported for the ^{3}He ions to ^{8}Li*(0, 0.98, 2.26, 6.53) at E_{d} = 28 MeV [C^{2}S (abs.) = 1.63, 0.61, 0.48, 0.092] and 52 MeV. The distributions to ^{8}Li*(6.53)[Γ < 100 keV] are featureless: see (1979AJ01).
At E_{t} = 12.98 MeV, angular distributions of the αparticles to ^{8}Li*(0, 0.98, 2.26, 6.53 ± 0.02 [Γ_{cm} < 40 keV]) have been measured: see (1974AJ01). Angular dependent differential cross sections for ^{9}Be(t, α) at E_{t} = 15 MeV were compared with DWBA and coupledchannel Born approximation calculations to extract the relative and absolute C^{2}S factors for ^{8}Li + p: see 8.8 (in PDF or PS) (1988LI27). At E_{t} = 17 MeV, σ(θ) and A_{y} measurements, analyzed by CCBA, lead to J^{π} = 4^{+} for ^{8}Li*(6.53): see (1984AJ01). For ^{8}Li*(0.98), τ_{m} = 14 ± 5 fsec, E_{x} = 980.80 ± 0.10 keV: see (1974AJ01).
At E(^{7}Li) = 52 MeV, numerous ^{12}B states are observed with E_{x} between 10  18 MeV; ^{8}Li*(0, 0.98, 2.25) participate (2003SO22). See also (1984KO25).
See (1986BE1Q).
At E_{p} = 45 MeV, ^{3}He ions are observed to a state at E_{x} = 10.8222 ± 0.0055 MeV (Γ_{cm} < 12 keV): the angular distributions for the transition to this state, and to its analog (^{8}Be*(27.49)), measured in the analog reaction [^{10}Be(p, t)^{8}Be] are very similar. They are both consistent with L = 0 using a DWBA (LZR) analysis: see (1979AJ01).
The ^{11}B(π^{+}, 3p) reaction was studied at 50, 100, 140 and 180 MeV using a large solid angle detector to measure the missing energy spectra (1992RA11).
The excitation function for ^{11}B(n, α)^{8}Li was measured at E_{n} = 7.6  12.6 MeV to determine, via detailed balance, the astrophysical rate for the ^{8}Li(α, n) reaction in the vicinity of the ^{12}B*(10.58) level (1990PA22). Angular distributions of the α_{0} and α_{1} groups have been measured at E_{n} = 14.1 and 14.4 MeV: see (1974AJ01, 1984AJ01, 1988AJ01). Energy dependent ^{8}Li(α, α) elastic scattering phase shifts, which are important for calculating the ^{11}B(n, α)^{8}Li reaction rate, were calculated in the range of E_{cm} < 4 MeV (1996DE02).
At E(^{7}Li) = 34 MeV angular distributions have been studied involving ^{8}Li*(0, 0.98) and ^{10}B_{g.s.} (1987CO16).
Differential and total cross sections for ^{12}C(π^{}, 2d) were measured at 165 MeV (1990PA03). See (1987GA11) for a theoretical treatment of the reaction mechanism.
The π^{+} absorption reaction mechanism was studied by measuring protons produced in ^{12}C + π^{+} reactions at 30  135 MeV (2000GI07).
Nuclear effects in the spallation reaction mechanism (i.e., evenodd and oddodd nucleon pairing) were studied via ^{12,13}C(p, ^{6,7,8,9}Li) reactions at 1 GeV (1992BE65).
See (1984NE1A).
Angular distributions were measured at E(^{7}Li) = 9 MeV/A, and a DWBA analysis was used to determine the ratio of p_{1/2}/p_{3/2} contributions, and the Asymptotic Normalization Constant (ANC) for ^{7}Li + n → ^{8}Li (2003TR04). Then, using charge symmetry, the ^{7}Be + p → ^{8}B ANC was deduced, which corresponds to S_{17}(0) = 17.6 ± 1.7 eV · b.
Elastic and inelastic scattering of ^{8}Li on ^{nat}C were measured at E(^{8}Li) = 13.8  14 MeV (1991SM02). Optical model parameters were deduced for the 2^{+} ground state and the first 1^{+} excited state at ≈ 1 MeV and B(E2)(↑) = 30 ± 15 e^{2} · fm^{4} was deduced. In addition ^{nat}Au(^{8}Li, ^{8}Li) was measured for comparison with Rutherford scattering. The ^{8}Li first 1^{+} excited state at 1.0 ± 0.1 MeV was observed in Coulomb excitation on ^{nat}Ni at E(^{8}Li) = 14.6 MeV (1991BR14) and B(E2)(↑) = 55 ± 15 e^{2} · fm^{4} was determined for this excitation. See (2003BE38) for elastic and inelastic scattering on Pb at E(^{8}Li) = 20  36 MeV.
A measurement to determine muon induced background rates in largevolume scintillation solar neutrino detectors found σ = 2.93 ± 0.80 μb and 4.02 ± 1.46 μb for ^{nat}C(μ, ^{8}Li) at E_{μ} = 100 and 190 GeV, respectively (2000HA33).
Total cross sections and chargechanging cross sections for the lithium isotopes on C and Pb were measured at 80 MeV/A (1992BL10); it was deduced that postabrasion evaporation plays a minor role in these reactions. For reaction (b) the energydependent total reaction cross sections at 20  60 MeV/A were measured (1996WA27) and compared with microscopic and shell model predictions. A review of nuclear radii deduced from interaction cross sections is given in (2001OZ04).
Population of the ^{8}Li ground state and 2.255 MeV neutron unbound state was reported in reactions (a) and (b) at 35 MeV/A. The reaction nuclear temperature was estimated (1987BL13). In a similar study of 35 MeV/A ^{14}N on ^{165}Ho, (1987KI05) deduced that the ^{8}Li*(2.255) state has Γ = 33 keV from the ^{7}Li + n relative energy spectrum.
