
^{8}Be (2004TI06)(See Energy Level Diagrams for ^{8}Be) GENERAL: References to articles on general properties of ^{8}Be 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}Be located on our website at (nucldata.tunl.duke.edu/nucldata/General_Tables/8be.shtml). See also 2 in (1988AJ01) [Electromagnetic Transitions in A = 510] (in PDF or PS), 8.9 [Table of Energy Levels] (in PDF or PS) and 8.10 [Electromagnetic transitions in ^{8}Be] (in PDF or PS).
Γ_{cm} for ^{8}Be_{g.s.} = 5.57 ± 0.25 eV: see reaction 4. See also reaction 29 and references cited in (1974AJ01, 1988AJ01).
The yield of γ_{1} has been measured for E_{α} = 32 to 36 MeV. The yield of γ_{0} for E_{α} = 33 to 38 MeV is twenty times lower than for γ_{1} , consistent with E2 decay: see (1979AJ01). Angular distributions were measured in the ^{4}He(α, γ) reaction in the region around the 16 MeV isospin mixed doublet as a study of CVC in A = 8 nuclei and second class currents (1994DE30, 1995DE18). No evidence for CVC violation was observed. Mixing ratios were reported as ε = [Γ^{T=0}_{M1}/Γ^{T=1}_{M1}]^{1/2} = +0.04 ± 0.02, δ_{0} = [Γ^{T=0}_{E2}/Γ^{T=1}_{M1}]^{1/2} = +0.21 ± 0.04, δ_{1} = [Γ^{T=1}_{E2}/Γ^{T=1}_{M1}]^{1/2} = +0.01 ± 0.03 and Γ^{T=1}_{M1} = 2.80 ± 0.18 eV (1995DE18), and they note that earlier values (1978BO30) were troubled by a transformation error. The E_{x} of ^{8}Be*(3.0) is determined in this reaction to be 3.18 ± 0.05 MeV (1979AJ01) [see also 8.11 (in PDF or PS)]. The E2 bremsstrahlung cross section to ^{8}Be_{g.s.} has been calculated as a function of E_{x} over the 3 MeV state: the total Γ_{γ} for this transition is 8.3 meV, corresponding to 75 W.u. (1986LA05). A calculation of the Γ_{γ} from the decay of the 4^{+} 11.4 MeV state to the 2^{+} state yields 0.46 eV (19 W.u.). The maximum cross section for the intrastate γray transition within the 2^{+} resonance is calculated to be ≤ 2.5 nb at E_{x} ≈ 3.3 MeV (1986LA19). See also (2001CS04) for discussion of the impact of variation in the NN force on the nucleosynthesis rates of ^{8}Be and ^{12}C.
The cross sections for formation of ^{7}Li*(0, 0.48) [E_{α} = 39 to 49.5 MeV] and ^{7}Be*(0, 0.43) [39.4 to 47.4 MeV] both show structures at E_{α} ≈ 40.0 and ≈ 44.5 MeV: they are due predominantly to the 2^{+} states ^{8}Be*(20.1, 22.2): see (1979AJ01). The excitation functions for p_{0}, p_{2}, d_{0}, d_{1} for E_{α} = 54.96 to 55.54 MeV have been measured in order to study the decay of the first T = 2 state in ^{8}Be: see 8.5 (in PDF or PS) in (1984AJ01). Cross sections for p_{0+1} are also reported at E_{α} = 37.5 to 140.0 MeV: see (1979AJ01, 1984AJ01). The cross sections for reaction (c) has been measured at three energies in the range E_{α} = 46.7 to 49.5 MeV: see (1979AJ01) and below. The production of ^{6}Li, ^{7}Li and ^{7}Be [and ^{6}He] has been studied at E_{α} = 61.5 to 158.2 MeV by (1982GL01), at 198.4 MeV by (1985WO11), and at E_{α} = 160, 280 and 320 MeV by (2001ME13). The production of ^{7}Li (via reactions (a) and (b)) and of ^{6}Li is discussed. At energies beyond E_{α} ≈ 250 MeV the α + α reaction does not contribute to the natural abundance of lithium, reinforcing theories which produce ^{6}Li in cosmicray processes and the "missing" ^{7}Li in the Big Bang: thus the universe is open (1982GL01, 1985WO11). The measurements of (2001ME13) have observed smaller cross sections for ^{6}Li production than previous extrapolations, and reduce uncertainty in extrapolation to higher energies. The inclusive cross section for production of ^{3}He has been measured at E_{α} = 218 MeV (1984AL03). For a fragmentation study at 125 GeV see (1985BE1E). See also references cited in (1988AJ01).
The ^{8}Be_{g.s.} parameters are determined from α  α scattering across the resonance region. Evaluation of the parameters requires an analysis of the influence of various possible charge states in the lowenergy ^{4}He(α, α) scattering process (1992WU09). A measurement that detected α  α coincidences at θ(α_{1}, α_{2}) = (45°, 45°) and (30°, 60°) was performed using a gas jet target, which permitted an energy resolution of 26 eV; the resulting parameters for ^{8}Be_{g.s.} are E_{b} = 92.04 ± 0.05 keV and Γ = 5.57 ± 0.25 eV (1992WA09). Previous values that had been obtained in a configuration that yielded 95 eV energy resolution were E_{b} = 92.12 ± 0.05 keV and Γ = 6.8 ± 1.7 eV (1968BE02). For E_{α} = 30 to 70 MeV the l = 0 phase shift shows resonant behavior at E_{α} = 40.7 MeV, corresponding to a 0^{+} state at E_{x} = 20.2 MeV, Γ < 1 MeV, Γ_{α}/Γ < 0.5. No evidence for other 0^{+} states is seen above E_{α} = 43 MeV. The dwave phase shift becomes appreciable for E_{α} > 2.5 MeV and passes through a resonance at E_{α} = 6 MeV (E_{x} = 3.18 MeV, Γ = 1.5 MeV, J^{π} = 2^{+}): see 8.11 (in PDF or PS). Five 2^{+} levels are observed from l = 2 phase shifts measured from E_{α} = 30 to 70 MeV: ^{8}Be*(16.6, 16.9) with Γ_{α} = Γ [see 8.11 (in PDF or PS)], and states with E_{x} = 20.1, 22.2 and 25.2 MeV. The latter has a small Γ_{α}. The l = 2 α  α phase shifts have been analyzed by (1986WA01) up to E_{α} = 34 MeV: intruder states below E_{x} = 26 MeV need not be introduced. However, see discussion in reactions 24 and 27, and see (1988BA75, 1989BA31, 2000BA89) which introduces an intruder state at ≈ 9 MeV. The l = 4 phase shift rises from E_{α} ≈ 11 MeV and indicates a broad 4^{+} level at E_{x} = 11.5 ± 0.3 MeV [Γ = 4.0 ± 0.4 MeV]. A rapid rise of δ_{4} at E_{α} = 40 MeV corresponds to a 4^{+} state at 19.9 MeV with Γ_{α}/Γ ≈ 0.96; Γ < 1 MeV and therefore Γ_{α} < 1 MeV, which is < 5% of the Wigner limit. A broad 4^{+} state is also observed near E_{α} = 51.3 MeV (E_{x} = 25.5 MeV). Over the range E_{α} = 30 to 70 MeV a gradual increase in δ_{6} is observed. Some indications of a 6^{+} state at E_{x} ≈ 28 MeV and of an 8^{+} state at ≈ 57 MeV have been reported; Γ_{cm} ≈ 20 and ≈ 73 MeV, respectively. A resonance is not observed at the first T = 2 state, ^{8}Be*(27.49). See (1979AJ01) for references. The elastic scattering has also been studied at E_{α} = 56.3 to 95.5 MeV (1987NE1C), 158.2, 650 and 850 MeV, and at 4.32 and 5.07 GeV/c [see (1979AJ01, 1984AJ01)], as well as at 198.4 MeV (1985WO11). For αα correlations involving ^{8}Be*(0, 3.0) see (1987CH33, 1987PO03). Resonances in α  α scattering and the role of α clustering in ^{8}Be have been investigated in theoretical studies of ^{4}He(α, α) (1987PR01, 1987VI05, 1987WA07, 1995LI07, 1996KU08, 1996VO15, 2000MO07, 2002BH03). For inclusive cross sections see (1984AJ01) and (1984AL03; 218 MeV). For studies at very high energies see reaction 3 and references cited in (1988AJ01).
The yield of γrays to ^{8}Be*(17.64) [1^{+}; T = 1] has been measured for E_{d} = 6.85 to 7.10 MeV. A resonance is observed at E_{d} = 6965 keV [E_{x} = 27495.8 ± 2.4 keV, Γ_{cm} = 5.5 ± 2.0 keV]; Γ_{γ} = 23 ± 4 eV [1.14 ± 0.20 W.u.] for this M1 transition from the first 0^{+}; T = 2 state in ^{8}Be, in good agreement with the intermediate coupling model: see 8.5 (in PDF or PS) in (1984AJ01) ^{†}. Angular distributions of cross sections and polarization observables [A_{y}^{(θ)}, A_{yy}^{(θ)}, T_{20}^{(θ)}] were measured at E_{pol. d} = 9 MeV (1991WI19) and E_{pol. d} = 2 and 9 MeV (1994WI08). In addition, (1994WI08) measured the excitation function from E_{d} = 7  14 MeV; capture to the ^{8}Be ground state and 3.0 MeV state were observed. A transition matrix element analysis for ^{6}Li(pol. d, γ_{0}) at 9 MeV indicates a 13  21% E1 contribution in addition to the expected dominant E2 strength. This suggests ≈ 1.5% Dstate admixture in the ^{8}Be ground state. See also (1979AJ01).
^{†} However, please note that there is an error in 8.5 (in PDF or PS) from (1984AJ01). For the 27.5 MeV level, the parameter given as Γ_{γ0} should be listed as Γ_{γ}(27.5 to 17.6).
Yield curves and cross sections have been measured for E_{d} = 48 keV to 17 MeV: see (1979AJ01, 1984AJ01). At E_{cm} = 96.6 keV σ = 3.17 mb ± 3%(stat.) ± 7.5%(syst.) (2001HO23). Polarization measurements are reported at E_{d} = 0.27 to 3.7 MeV. Angular distributions were measured for ^{6}Li(d, n) at E_{d} = 0.7  2.3 and 5.6  12.1 MeV and excitation functions for neutrons corresponding to ^{7}Be*(0, 0.43, 4.57, 7.21) are reported (1996BO27). Comparisons of the populations of ^{7}Be*(0, 0.43) and of ^{7}Li*(0, 0.48) have been made at energies up to E_{d} = 7.2 MeV. The (d, n)/(d, p) ratios are closely equal for analog states, as expected from charge symmetry: see (1979AJ01). However, the n_{1}/p_{1} yield ratio decreases from 1.05 at E_{d} = 160 keV to 0.94 at 60 keV: it is suggested that this is due to charge polarization of the deuteron (1985CE12). See reaction 7 for additional comments about the (d, p)/(d, n) ratio. See also ^{7}Be in (2002TI10) and (1988AJ01).
Excitation functions have been measured for E_{d} = 30 keV to 5.4 MeV: see (1979AJ01, 1984AJ01). The thick target yield of 0.48 MeV γrays is reported from ≈ 50 to 170 keV (1985CE12). An anomaly is observed in the p_{1}/p_{0} intensity ratio at E_{d} = 6.945 MeV [see (1979AJ01)], corresponding to the first 0^{+}; T = 2 state, Γ = 10 ± 3 keV, Γ_{p0} << Γ_{p1}, Γ_{p0} < Γ_{d}. The (d, p_{0})/(d, n_{0}) ratio is measured in the astrophysical range from 65 keV < E_{d} < 200 keV (1993CZ01, 1997CZ04). In this region the subthreshold isospin mixed 2^{+} level at ^{8}Be*(22.2; Γ ≈ 800 keV) could influence the (d, p_{0})/(d, n_{0}) ratio, which is important in inhomogeneous Big Bang nucleosynthesis models. The observed ratio is Γ_{n0}/Γ_{p0} = 0.95 ± 0.03 which is consistent with the presently accepted isospin mixing parameter ε = 0.20. The ^{6}Li(d, p) and ^{6}Li(d, α) reactions were measured at E_{d} = 20  135 keV (1993CE02), and a nearly constant σ(d, p_{0} + p_{1})/σ(d, α) ratio of 0.55 was observed indicating that there is no anomalous behavior in the low energy ^{6}Li(d, p) cross section. Polarization measurements have been reported at E_{d} = 0.6 to 10.9 MeV: see (1979AJ01). See also ^{7}Li in (2002TI10) and (1984KU15; theor.).
The yield of elastically scattered deuterons has been measured for E_{d} = 2 to 7.14 MeV. No resonances are observed: see (1974AJ01). See also (1983HA1D, 1985LI1C; theor.). The cross section for tritium production rises rapidly to 190 mb at 1 MeV, then more slowly to 290 mb near 4 MeV: see (1974AJ01). For VAP and TAP measurements at E_{d} = 191 and 395 MeV see (1986GA18).
Cross sections and angular distributions (reaction (a)) have been measured at E_{d} = 10 keV to 31 MeV: see (1979AJ01, 1984AJ01), (1992EN01, 1992EN04) for E_{d} = 10  1450 keV, and (1997CZ01) for E_{d} = 50  180 keV. A DWBA analysis by (1997CZ01) of data up to 1 MeV evaluated the impact of the subthreshold resonance ^{8}Be*(22.2) on the measured cross sections. In the DWBA analysis, data was limited to energies above E_{d} = 60 keV in order to minimize the effect of screening; the analysis indicated an energy E_{res} = (50 ± 20) keV for the subthreshold resonance. The ^{6}Li(^{6}Li, 2α)^{4}He reaction was measured at E(^{6}Li) = 6 MeV and was evaluated in the "Trojan Horse" method to extract the ^{6}Li(d, α) reaction cross sections and Sfactors in the astrophysically relevant range from E_{cm} = 13 to 750 keV (2001SP04); a detailed analysis of these data, that accounted for the electron screening process, deduced S(0) = 16.9 ± 0.5 MeV · b (2001MU30). See also (1992EN01, 1992EN04) for detailed discussion of electron screening in direct measurements of ^{6}Li(d, α) and ^{2}H(^{6}Li, α) in the energy range of E_{cm} < 1500 keV. See also (2002BA77). Polarization measurements are reported in the range 0.4 to 11 MeV: see (1979AJ01, 1984AJ01) and see below. See also reaction 7 for comments about the astrophysical (d, p)/(d, α) ratio. See (1984AJ01) for a critical analysis of thermonuclear reaction rate parameters. Pronounced variations are observed in the cross sections and in the analyzing powers. Maxima are seen at E_{d} = 0.8 MeV, Γ_{lab} ≈ 0.8 MeV and E_{d} = 3.75 MeV, Γ_{lab} ≈ 1.4 MeV. The 4 MeV peak is also observed in the tensor component coefficients with L = 0, 4 and 8 and in the vector component coefficients: two overlapping resonances are suggested. At higher energies all coefficients show a fairly smooth behavior which suggests that only broad resonances can exist. The results are in agreement with those from reaction 4, that is with two 2^{+} states at E_{x} = 22.2 and 25.2 MeV and a 4^{+} state at 25.5 MeV. A strong resonance is seen in the α* channel [to ^{4}He(20.1), J^{π} = 0^{+}] presumably due to ^{8}Be*(25.2, 25.5). In addition the ratio of the α*/α differential cross sections at 30° shows a broad peak centered at E_{x} ≈ 26.5 MeV (which may be due to interference effects) and suggests a resonancelike anomaly at E_{x} ≈ 28 MeV. A_{yy} = 1 points are reported at E_{d} = 5.55 ± 0.12 (θ_{cm} = 29.7 ± 1.0°) and 8.80 ± 0.25 MeV (θ_{cm} = 90.0 ± 1.0°) [corresponding to E_{x} = 26.44 and 28.87 MeV]. For references see (1974AJ01, 1979AJ01). At E_{d} = 6.945 MeV, the α_{0} yield shows an anomaly corresponding to ^{8}Be*(27.49), the 0^{+}; T = 2 analog of ^{8}He_{g.s.}. This T = 2 state has recently been studied using both polarized deuterons and ^{6}Li ions. The ratio of the partial widths for decay into ^{6}Li + d states with channel spin 2 and 0, Γ_{2}/Γ_{0} = 0.322 ± 0.091 (1986SO07). A measurement of angular distributions and the excitation function for ^{6}Li(d, α) for E_{d} = 18.2  44.5 MeV (1994AR24) found evidence for possible states at ≈ 41 MeV, ≈ 43 MeV and ≈ 50 MeV. A kinematically complete study of reaction (b) has been reported at E_{d} = 1.2 to 8.0 MeV: the transition matrix element squared plotted as a function of E_{αα*} (the relative energy in the channel ^{4}He_{g.s.} + ^{4}He*(20.1) [0^{+}]) shows a broad maximum at E_{x} ≈ 25 MeV. Analysis of these results, and of a study of ^{7}Li(p, α)α* [see reaction 18] which shows a peak of different shape at E_{x} ≈ 24 MeV, indicate the formation and decay of overlapping states of high spatial symmetry, if the observed structures are interpreted in terms of ^{8}Be resonances: see (1984AJ01). For other work see (1984AJ01). See also ^{6}Li in (2002TI10) and references cited in (1988AJ01).
At E_{t} = 2 to 4.5 MeV ^{8}Be*(0, 3.0, 16.6, 16.9) are populated (1984LIZY). See also (1966LA04, 1974AJ01).
Angular distributions have been studied in the range E(^{3}He) = 0.46 to 17 MeV and at E(pol. ^{6}Li) = 21 MeV. ^{8}Be*(0, 3.0, 16.63, 16.92, 17.64, 18.15, 19.0, 19.4, 19.9) are populated in this reaction: see (1974AJ01, 1979AJ01, 1984AJ01). Angular distributions of cross sections and A_{y}(θ) were measured for ^{6}Li(pol. ^{3}He, p_{0} and p_{1}) at E_{pol. 3He} = 4.6 MeV (1995BA24). A DWBA analysis indicates that a direct reaction mechanism dominated for both states, in contradiction with previous results that suggested a dominant compound nucleus contribution. See also (2003VO02, 2003VO08) for an evaluation of the reaction rates below E(^{3}He) = 1 MeV. For reaction (b) see (1974AJ01) and (1987ZA07). See also ^{9}B.
Deuteron groups have been observed to ^{8}Be*(0, 3.0, 11.3 ± 0.4). Angular distributions have been measured at E_{α} = 15.8 to 48 MeV: see (1974AJ01, 1979AJ01). A study of reaction (b) shows that the peak due to ^{8}Be*(3.0) is best fitted by using Γ = 1.2 ± 0.3 MeV. At E_{α} = 42 MeV the α  α FSI is dominated by ^{8}Be*(0, 3.0). See also 8.11 (in PDF or PS) and (1983BE51; theor.).
At E_{max}(^{6}Li) = 13 MeV reaction (a) proceeds via ^{8}Be* (0, 3.0, 16.6, 16.9, 22.5). The involvement of a state at E_{x} = 19.9 MeV (Γ = 1.3 MeV) is suggested. Good agreement with the shapes of the peaks corresponding to ^{8}Be*(16.6, 16.9) is obtained by using a simple twolevel formula with interference, corrected for the effect of finalstate Coulomb interaction, assuming Γ(16.6) = 90 keV and Γ(16.9) = 70 keV: see also 8.11 (in PDF or PS). The ratio of the intensities of the groups corresponding to ^{8}Be*(16.6, 16.9) remains constant for E(^{6}Li) = 4.3 to 5.5 MeV: I(16.6)/I(16.9) = 1.22 ± 0.08. Partial angular distributions for the α_{0} group have been measured at fourteen energies for E(^{6}Li) = 4 to 24 MeV. See (1979AJ01) for the references. The reaction mechanism for ^{6}Li(^{6}Li, X) was studied by measuring charged particle angular distributions for E(^{6}Li) = 2  16 MeV (1990LE05). Analysis in a statistical model indicated that the ^{6}Li(^{6}Li, α) reaction proceeds dominantly via direct, cluster transfer rather than an intermediate compound nucleus. At E(^{6}Li) = 36 to 46 MeV sequential decay (reaction (b)) via ^{8}Be states at E_{x} = 3.0, 11.4, 16.9 and 19.65 MeV is reported: see (1984AJ01). (1987LA25) report the possible involvement of the 2^{+} state ^{8}Be*(22.2). At E(^{6}Li) = 6 MeV the "Trojan Horse" method was used to evaluate ^{6}Li(^{6}Li, 2α) data to extract the ^{6}Li(d, α) reaction cross sections and Sfactors (2001SP04, 2001MU30): see reaction 9 For reaction (c) see (1983WA09) and ^{12}C in (1985AJ01). See also (1983MI10) and (1982LA19, 1985NO1A; theor.).
For reaction (a) electron/positron pair decay from ^{8}Be*(17.6, 18.15) J^{π} = 1^{+} levels was measured in a search for M1 deexcitation via pair production that would indicate the involvement of a shortlived isoscalar axion 4  15 MeV/c^{2} in mass. While an anomaly is seen in the pair production, the overall results are not consistent with the involvement of a neutral boson (1996DE51, 1997DE46, 2001DE11). Limits of < 10^{3} (1990DE02) and 4.1 × 10^{4} (2001DE11) were obtained for the axion to γray ratio. For reaction (b) cross sections and angular distributions have been reported from E_{p} = 30 keV to 18 MeV. Gamma rays are observed to the ground (γ_{0}) and to the broad, 2^{+}, excited state at 3.0 MeV (γ_{1}) and to ^{8}Be*(16.6, 16.9) (γ_{3}, γ_{4}). An Rmatrix fit to the γray spectrum obtained at E_{p} = 7.5 and 8 MeV yielded E_{x} = 2.91 MeV and Γ = 1.23 MeV for the ^{8}Be first excited state (1990RI06). See also (1994DE09) for comments on model dependences for deduced widths. Resonances for both γ_{0} and γ_{1} occur at E_{p} = 0.44 and 1.03 MeV, and for γ_{1} alone at E_{p} = 2, 4.9, 6.0, 7.3, and possibly at 3.1 and 11.1 MeV. The excitation function was measured for γ_{0} and γ_{1} across the resonance at E_{p} = 441 keV; the peak cross section was σ_{γ0} + γ_{1} = 5.0 ± 0.7 mb (yielding an average of 5.9 ± 0.5 mb when weighted with previous measurements). The branching ratio was σ(γ_{0})/σ(γ_{0} + γ_{1}) = 0.72 ± 0.07 (1995ZA03). Broad resonances are reported at E_{p} ≈ 5 MeV (γ_{0}), Γ ≈ 4  5 MeV, and at E_{p} ≈ 7.3 MeV (γ_{1}), Γ ≈ 8 MeV: see 8.12 (in PDF or PS). The E_{p} ≈ 5 MeV resonance (E_{x} ≈ 22 MeV) represents the giant dipole resonance based on ^{8}Be_{g.s.} while the γ_{1} resonance, ≈ 2.2 MeV higher, is based on ^{8}Be*(3.0). The γ_{0} and γ_{1} giant resonance peaks each contain about 10% of the dipole sum strength. The main trend between E_{p} = 8 and 17.5 MeV is a decreasing cross section. At the E_{p} = 0.44 MeV resonance (E_{x} = 17.64 MeV) the radiation is nearly isotropic and has been interpreted as arising from pwave formation, J^{π} = 1^{+}, with channel spin ratio σ(J_{c} = 2)/σ(J_{c} = 1) = 3.2 ± 0.5. Radiative widths for the γ_{0} and γ_{1} decay are displayed in 8.10 (in PDF or PS). A careful study of the αbreakup of ^{8}Be*(16.63, 16.92) [both J^{π} = 2^{+}] for E_{p} = 0.44 to 2.45 MeV shows that the nonresonant part of the cross section for production of ^{8}Be*(16.63) is accounted for by an extranuclear directcapture process. The γray transitions to ^{8}Be*(16.63, 16.92) are observed at E_{p} = 0.44, 1.03 and 1.89 MeV [^{8}Be*(17.64, 18.15, 18.9)]. The results are consistent with the hypothesis of nearly maximal isospin mixing for ^{8}Be*(16.63, 16.92): decay to these states is not observed from the 3^{+} states at E_{x} = 19 MeV, but rather from the 2^{} state at E_{x} = 18.9 MeV. Squared T = 1 components calculated for ^{8}Be*(16.6, 16.9) are 40 and 60%, and for ^{8}Be*(17.6, 18.2) they are 95 and 5%, respectively. At E_{p} = 25 MeV, the capture cross section to the 16 MeV 2^{+} doublet was measured (σ_{θ(γ)=90°} < 0.04 μb/sr) via a triple coincidence γ + 2α method (1991BR11). The cross section for (γ_{3} + γ_{4}) has also been measured for E_{p} = 11.5 to 30 MeV (θ = 90°) by detecting the γrays and for E_{p} = 4 to 13 MeV (at five energies) by detecting the two αparticles from the decay of ^{8}Be*(16.6, 16.9): a broad bump is observed at E_{p} = 8 ± 2 MeV (1981MA33). The angle and energy integrated yield only exhausts 8.6% of the classical dipole sum for E_{p} = 4 to 30 MeV, suggesting that this structure does not represent the GDR built on ^{8}Be*(16.6, 16.9). A weak, very broad [Γ ≥ 20 MeV] peak may also be present at E_{x} = 20  30 MeV. A direct capture calculation adequately describes the observed cross section (1981MA33). For the earlier references see (1979AJ01). See also references cited in (1988AJ01). Low energy ^{7}Li(p, γ) angular distributions and cross sections, mainly for γ_{0} and γ_{1} capture, were measured at E_{p} = 40  180 keV (1992CE02), E_{pol. p} = 80 keV (1994CH23, 1996GO01, 1997GO13), E_{p} = 100  1500 keV (1995ZA03), E_{p} = 80, 402 and 450 keV (1996HA06), and E_{pol. p} = 40  100 keV (2000SP01). The angular dependent crosssection and analyzing power data indicate significant nearthreshold contributions from pwave capture. Estimates of the pwave strength have been deduced from Transition Matrix Element (TME) fits to the polarization data (1994CH23, 1996GO01, 1997GO13), Rmatrix fits to the data (1995BB21, 1996BB26, 2000BA89), and other directplusresonances capture calculations (1992CE02, 1994RO16, 1995WE11, 1996CS05, 1997BA04, 1997GO13, 2000SP01, 2001SA30). The estimates range from < 10% up to ≈ 95%. It was suggested that the origin of pwave strength was the result of interference in the extended tails of the two 1^{+} resonances at E_{p} = 441 keV and 1030 keV, while a more recent measurement (2000SP01) that observed a negative slope in the astrophysical Sfactor, as the energy approaches zero, indicates that the subthreshold ^{8}Be state at E_{x} = 16.92 MeV is involved in the capture. There appears to be some agreement on the issue that there is a need for new model calculations for lowenergy capture that include the subthreshold state and the two resonances at E_{p} = 441 and 1030 keV. Polarized proton capture to the ^{8}Be*(16.6) state was measured at E_{pol. p} = 80 keV (1996GO01). See (1995ZA03, 2000NE09) for thermonuclear reaction rates and (1994CH70) for applications. Thick target proton induced γray yields, useful for elemental analysis, were measured at E_{p} = 2.2  3.8 MeV (1988BO37) and E_{p} = 7  9 MeV (1987RA23).
Measurements of cross sections have been reported for E_{p} = 1.9 to 199.1 MeV [see (1974AJ01, 1979AJ01, 1984AJ01)] and in the range 60.1 to 480.0 MeV (1984DA22; activation σ). Polarization measurements have been reported at E_{p} = 2.05 to 5.5 MeV, 30 and 50 MeV [see (1974AJ01)] and at E_{p} = 52.8 MeV (1988HE08) [K_{z}^{z'} = 0.07 ± 0.02]. See also below. The yield of ground state neutrons (n_{0}) rises steeply from threshold and shows pronounced resonances at E_{p} = 2.25 and 4.9 MeV. The yield of n_{1} also rises steeply from threshold and exhibits a broad maximum near E_{p} = 3.2 MeV and a broad dip at E_{p} ≈ 5.5 MeV, also observed in the p_{1} yield. Multichannel scattering length approximation analysis of the 2^{} partial wave near the n_{0} threshold indicates that the 2^{} state at E_{x} = 18.9 MeV has a width Γ = 50 ± 20 keV. See, however, reaction 23 here. The ratio of the cross section for ^{7}Li(p, γ)^{8}Be*(18.9) → ^{8}Be*(16.6 + 16.9) + γ to the thermal neutron capture cross section ^{7}Be(n, γ)^{8}Be*(18.9) → ^{8}Be*(16.6 + 16.9) + γ, provides a rough estimate of the isospin impurity of ^{8}Be*(18.9): σ_{p,γ}/σ_{n,γ} ≈ 1.5 × 10^{5}. The T = 1 isospin impurity is ≤ 10% in intensity. See also reaction 23 here and (1979AJ01, 1984AJ01). The structure at E_{p} = 2.25 MeV is ascribed to a J^{π} = 3^{+}, T = (1), l = 1 resonance with Γ_{n} ≈ Γ_{p} and γ_{n}^{2}/γ_{p}^{2} = 3 to 10: see (1966LA04). At higher energies the broad peak in the n_{0} yield at E_{p} = 4.9 MeV can be fitted by J^{π} = 3^{(+)} with Γ = 1.1 MeV, γ_{n}^{2} ≈ γ_{p}^{2}. The behavior of the n_{1} cross section can be fitted by assuming a 1^{} state at E_{x} = 19.5 MeV and a J = 0, 1, 2, positiveparity state at 19.9 MeV [presumably the 20.1  20.2 MeV states reported in reaction 4]. In addition the broad dip at E_{p} ≈ 5.5 MeV may be accounted for by the interference of two 2^{+} states. See 8.8 (in PDF or PS) in (1979AJ01). The 0° differential cross section increases rapidly to ≈ 35 mb/sr at 30 MeV and then remains constant to 100 MeV: see references cited in (1988AJ01). The total reaction cross section [^{7}Be*(0, 0.43)] decreases inversely with E_{p} in the range 60.1 to 480.0 MeV (1984DA22) [note: the values of σ_{t} supersede those reported earlier in (1979AJ01)]. The transverse polarization transfer, D_{NN} (0°), for the groundstate transition has been measured at E_{pol. p} = 160 MeV (1984TA07). See also (1986MC09; E_{pol. p} = 800 MeV) and references cited in (1988AJ01).
Absolute differential cross sections for elastic scattering have been reported for E_{p} = 0.4 to 12 MeV and at 14.5, 20.0 and 31.5 MeV. The yields of inelastically scattered protons (to ^{7}Li*(0.48)) and of 0.48 MeV γrays have been measured for E_{p} = 0.8 to 12 MeV: see (1974AJ01). Polarization measurements have been reported at a number of energies in the range E_{p} = 0.67 MeV to 2.1 GeV/c [see (1974AJ01, 1979AJ01, 1984AJ01)], at E_{p} = 1.89 to 2.59 MeV (1986SA1P; p_{0}) and at 65 MeV (1987TO06; continuum). See also (1983GLZZ). Anomalies in the elastic scattering appear at E_{p} = 0.44, 1.03, 1.88, 2.1, 2.5, 4.2 and 5.6 MeV. Resonances at E_{p} = 1.03, 3 and 5.5 MeV and an anomaly at E_{p} = 1.88 MeV appear in the inelastic channel. A phaseshift analysis and a review of the crosssection data show that the 0.44 and 1.03 MeV resonances are due to 1^{+} states which are a mixture of ^{5}P_{1} and ^{3}P_{1} with a mixing parameter of +25°; that the 2^{} state at the neutron threshold (E_{p} = 1.88 MeV) has a width of about 50 keV [see also reaction 14]; and that the E_{p} = 2.05 MeV resonance corresponds to a 3^{+} state. The anomalous behavior of the ^{5}P_{3} phase around E_{p} = 2.2 MeV appears to result from the coupling of the two 3^{+} states [resonances at E_{p} = 2.05 and 2.25 MeV]. The ^{3}S_{1} phase begins to turn positive after 2.2 MeV suggesting a 1^{} state at E_{p} = 2.5 MeV: see 8.13 (in PDF or PS). The polarization data show structures at E_{p} = 1.9 and 2.3 MeV. A phaseshift analysis of the (p, p) data finds no indication of a possible 1^{} state with 17.4 < E_{x} < 18.5 MeV [see, however, reaction 15 in (1979AJ01)]. An attempt has been made to observe the T = 2 state [^{8}Be*(27.47)] in the p_{0}, p_{1} and p_{2} yields. None of these shows the effect of the T = 2 state. 8.5 (in PDF or PS) in (1984AJ01) displays the upper limit for Γ_{p0}/Γ. The proton total reaction cross section has been reported for E_{p} = 25.1 to 48.1 MeV by (1985CA36). (1987CH33, 1987PO03) have studied p  ^{7}Li correlations involving ^{8}Be*(17.64, 18.15, 18.9 + 19.1 + 19.2). Elastic proton scattering on ^{7}Li was measured near the (p, n) threshold, E_{cm} = 1.2  2.4 MeV (1988GU10). Parameters for observed nearthreshold resonances are in 8.13 (in PDF or PS). See also (1994DE09) for comments on model dependences for deduced widths. See also ^{7}Li in (2002TI10) and references cited in (1988AJ01).
Angular distributions were measured for ^{7}Li(p, d) at E_{p} = 18.6 MeV (1987GO27); neutron spectroscopic factors were deduced, via DWBA analysis, for deuterons corresponding to the ^{6}Li ground state and first excited state. The excitation function for d_{0} measured for E_{p} = 11.64 to 11.76 MeV does not show any effect from the T = 2 state [^{8}Be*(27.47)]: see (1979AJ01). See also (1984BA1T).
The cross section increases from (4.3 ± 0.9) × 10^{5} mb at E_{p} = 28.1 keV to 6.33 mb at 998 keV. Astrophysical Sfactors have been calculated over that range: S(0) = 52 ± 8 keV · b (1986RO13), S(0) = 0.59 keV · b (1992EN01, 1992EN04). An analysis of the ^{2}H(^{7}Li, α) reaction (see reaction 19) in the Trojan Horse Method (THM), which assumes that the deuteron acts as a participant proton plus an spectator neutron and is not sensitive to electron screening effects, indicates S(0) = 55 ± 3 keV · b (2001LA35, 2003PI13, 2003SP02). Earlier work on the THM by the same group published the value S(0) = 36 ± 7 keV · b (1997CA36, 1999SP09, 2000AL04). For comments on the S factor see (1990RA28, 1991SC12, 1991SC25, 1991SC32, 1992SC22, 1992SO25, 1993RA14, 1993SC06, 1994KA02, 1995IC02, 1995YA02, 1997KI02, 2000BA89). See additional comments on electron screening in (1992EN01, 1992EN04, 1997BA95, 1997BO12, 2002BA77, 2002HA51, 2003PI13). See comments on nucleosynthesis rates and primordial abundances in (1991RI03, 1998FI02, 2000BU10). For the earlier work see (1984AJ01). Excitation functions and angular distributions have been measured at E_{p} = 10 keV  62.5 MeV: see (1979AJ01, 1984AJ01), E_{p} = 20  250 keV (1989HA14), and E_{cm} = 10  1450 keV (1992EN01, 1992EN04). Polarization measurements have been carried out for E_{p} = 0.8 to 22 MeV: see (1974AJ01), E_{p} = 9  22 MeV (1992TA21). In the range E_{p} = 23 keV to 62.5 MeV: see (1979AJ01, 1984AJ01). Polarization measurements have been carried out for E_{p} = 0.8 to 10.6 MeV [see (1974AJ01)]: in the range E_{p} = 3 to 10 MeV the asymmetry has one broad peak in the angular distribution at all energies except near 5 MeV; the peak value is 0.98 ± 0.04 at 6 MeV and is essentially 1.0 for E_{p} = 8.5 to 10 MeV. Above 10 MeV the asymmetry begins to decrease slowly. Broad resonances are reported to occur at E_{p} = 3.0 MeV [Γ ≈ 1 MeV] and at ≈ 5.7 MeV [Γ ≈ 1 MeV]. Structures are also reported at E_{p} = 6.8 MeV and at E_{p} = 9.0 MeV: see (1979AJ01). The 9.0 MeV resonance is also reflected in the behavior of the A_{2} coefficient. The experimental data on yields and on polarizations appear to require including two 0^{+} states [at E_{x} ≈ 19.7 and 21.8 MeV] with very small αparticle widths, and four 2^{+} states [at E_{x} ≈ 15.9, 20.1, 22.2 and 25 MeV]. See, however, reaction 4. A 4^{+} state near 20 MeV was also introduced in the calculation but its contribution was negligible. The observed discrepancies are said to be probably due to the assumption of pure T = 0 for these states. At E_{p} = 11.64 to 11.76 MeV the excitation function does not show any effect due to the T = 2 state at E_{x} = 27.47 MeV. See (1979AJ01) for references. A study of the ^{7}Li(p, α)^{4}He* reaction to ^{4}He*(20.1) [0^{+}] at E_{p} = 4.5 to 12.0 MeV shows a broad maximum at E_{x} ≈ 24 MeV: see reaction 9 and (1984AJ01). See also references cited in (1988AJ01).
The population of ^{8}Be*(0, 3.0, 16.6, 16.9, 17.6, 18.2, 18.9, 19.1, 19.2) has been reported in reaction (a). For the parameters of ^{8}Be*(3.0) see (in PDF or PS) 8.4 in (1974AJ01). Angular distributions were measured for ^{7}Li(d, n) at E_{d} = 0.7  2.3 and 5.6  12.1 MeV and excitation functions were reported for neutrons corresponding to ^{8}Be*(0 + 3.0, 16.6 + 16.9, 17.6, 18.15) (1996BO27). The ^{8}Be*(11.4) level is not observed. Angular distributions of n_{0} and n_{1} have been reported at E_{d} = 0.7 to 3.0 MeV and at E_{d} = 15.25 MeV [see (1974AJ01, 1979AJ01)], at 0.19 MeV (1983DA32, 1987DA25) and at 0.40 and 0.46 MeV (1984GA07; n_{0} only). The angular distributions of the neutrons to ^{8}Be*(16.6, 17.6, 18.2) are fit by l_{p} = 1: see (1974AJ01). At E_{cm} = 50, 83 and 199 keV, the measured cross sections are σ = 0.125, 2.11 and 4.01 mb, respectively (± ≈ 5%(stat.), ± 7.5%(syst.)) (2001HO23). Reaction (b) at E_{d} = 2.85 to 14.97 MeV proceeds almost entirely through the excitation and sequential decay of ^{8}Be*(16.6, 16.9) (1987WA21). See also (1988AJ01). At E_{d} = 19.7 MeV, ^{8}Be*(11.4) was observed at E_{x} = 11.3 ± 0.2 MeV with Γ = 3.7 ± 0.2 MeV (1995AR25). At E_{d} = 7 MeV, population of the two T = 0 levels at 20.1, 2^{+} and 20.2, 0^{+} is reported with widths Γ_{20.1} = 0.85 ± 0.25 MeV and Γ_{20.2} = 0.75 ± 0.25 MeV (1991AR18), and Γ_{20.1} = 0.90 ± 0.20 MeV and Γ_{20.2} = 0.70 ± 0.20 MeV (1992DA22). A complete kinematics measurement of d^{3}σ/(dΩ_{θ}dΨdE_{12}) at E_{d} = 3  6 MeV reported population of the 2^{+} doublet at 16.6 MeV and 16.9 MeV; intense forward neutrons were observed corresponding to the 16.6 MeV state indicating the ^{7}Li + p configuration of that state (1999GO15). See (2001LA35, 2003PI13, 2003SP02), and reaction 18 for measurements at E_{p} = 19  21 MeV that are evaluated in the "Trojan Horse" method to obtain information on the astrophysical ^{7}Li(p, α) rate. See also (2000HA50) for fusion applications. See also ^{9}Be.
Deuteron groups are observed to ^{8}Be*(0, 3.0, 16.6, 16.9, 17.6, 18.2). For the J^{π} = 2^{+} isospin mixed states see 8.11 (in PDF or PS). Angular distributions have been measured for E(^{3}He) = 390  1130 keV (2003FR22), for E(^{3}He) = 0.9 to 24.3 MeV and at E(pol. ^{3}He) = 33.3 MeV: see (1974AJ01, 1979AJ01, 1984AJ01). Reaction (b) has been studied at E(^{3}He) = 5.0 MeV (1985DA29) and at 9, 11 and 12 MeV (1986ZA09). ^{8}Be*(0, 3.0) are reported to be involved (1985DA29). Implications of this reaction for destroying ^{7}Li and ^{7}Be in astrophysical environments is discussed in (2003FR22). See also ^{10}B.
Angular distributions have been measured to E_{α} = 50 MeV: see (1974AJ01, 1979AJ01, 1988AJ01). The ground state of ^{8}Be decays isotropically in the cm system: J^{π} = 0^{+}. Sequential decay (reaction (b)) is reported at E_{α} = 50 MeV via ^{8}Be*(0, 3.0, 11.4, 16.6, 16.9, 19.9): see (1974AJ01). See also (1992KO26).
^{8}Be*(0, 3.0) have been populated. For reaction (a) see (1987BO1M; E(^{7}Li) = 22 MeV), and for reaction (b) see (1996SO17; E(^{7}Li) = 8 MeV).
The total (n, p) cross section has been measured from 25 × 10^{3} eV to 13.5 MeV. For thermal neutrons the cross sections to ^{7}Li*(0, 0.48) are 38400 ± 800 and 420 ± 120 b, respectively. A departure from a 1/v shape in σ_{t} is observed for E_{n} > 100 eV. The astrophysical reaction rate is ≈ 1/3 lower than that previously used, which could lead to an increase in the calculated rate of production of ^{7}Li in the Big Bang by as much as 20% (1988AJ01): see also (1998FI02). Results from a Rmatrix analysis of reaction (a) over the range from E_{cm} = 10^{8}  9.0 MeV (2003AD05) are summarized in 8.14 (in PDF or PS). In their analysis, ^{8}Be*(19.07) and ^{8}Be*(19.24) are treated as a single resonance. A different Rmatrix analysis (1988KO03) found a T = 1 impurity of ≈ 24% and Γ = 122 keV for the 2^{} ^{8}Be*(18.9) state. The approach of (1988KO03) defines the resonance energy and width as a pole of the Smatrix on the socalled Riemann sheet, which yields total widths that are smaller than the sum of the partial widths (2003AD05). At thermal energies the (n, α) cross section is ≤ 0.1 mb and the (n, γα) cross section is 155 mb: see (1974AJ01). See also references cited in (1988AJ01).
^{8}Li decays mainly to the broad 3.0 MeV, 2^{+} level of ^{8}Be, which decays into two αparticles. Both the βspectrum and the resulting αspectrum have been extensively studied: see (1955AJ61, 1966LA04). See also ^{8}B(β^{+}). Studies of the distribution of recoil momenta and neutrino recoil correlations indicate that the decay is overwhelmingly GT, axial vector [see reaction 1 in ^{8}Li] and that the ground state of ^{8}Li has J^{π} = 2^{+}: see (1980MC07). Detailed calculations are necessary to obtain the log ft values for decay to ^{8}Be*(3.0); values in the literature are: log ft = 5.37 (1986WA01), log ft = 5.72 (1989BA31). The data of (1971WI05) for ^{8}Li and ^{8}B βdecay have been analyzed extensively (1986WA01, 1989BA31, 2002BH03). In (1986WA01) a manylevel onechannel approximation Rmatrix analysis of the βdelayed α particle spectra in the decay of both ^{8}Li and ^{8}B [as well as of the L = 2 α  α phase shifts] found that there was no need to introduce "intruder" states below E_{x} ≈ 26 MeV of ^{8}Be in order to explain the data [see, e.g. (1969BA43, 1974AJ01, 1976BA67, 1979AJ01)]. Warburton extracted the GT matrix elements, for the decay to ^{8}Be*(3.0) and the doublet near 16 MeV, and pointed out the difficulties in extracting meaningful E_{x}, Γ and log ft values from β^{±} decay to the broad ^{8}Be*(3.0) state. On the other hand, the Rmatrix analysis of Barker (1989BA31) requires a broad 2^{+} intruder state at ≈ 9 MeV. See (1998FA05, 2000BA89, 2001CA50) for further comments on intruder states in ^{8}Be. Betaα angular correlations have been measured for the decays of ^{8}Li and ^{8}B for the entire finalstate distribution: see 8.10 (in PDF or PS) in (1979AJ01). (1980MC07) have measured β  α correlations as a function of E_{x} in the decay of ^{8}Li and ^{8}B; by detecting the β and both α particles involved in the ^{8}Be decay, the β  ν  α correlations were determined. They find that the decay is GT for 2 < E_{x} < 8 MeV. The absence of Fermi decay strength is expected because the isovector contributions from the tails of ^{8}Be*(16.6, 16.9) interfere destructively in this energy region: see (1980MC07). The measurement of the βdecay asymmetry as a function of E_{β} is reported by (1985BIZZ, 1986BI1D. (1986NAZZ) have measured the βspectrum and compared it with the spectrum predicted from the αbreakup data. See also references cited in (1988AJ01).
Angular distributions of ^{8}Be from ^{1}H(^{8}Li, ^{8}Be) were measured at E_{cm} = 1.5 MeV (1993CA04). The ^{8}Be_{g.s.} was reconstructed by detecting the coincident α particles and the data were transformed to represent the inverse kinematics ^{8}Li(p, n) reaction. The observed cross section, σ_{tot} = 21 ± 2(stat.) ± 4.2(norm.) mb, was 2 times smaller than estimates based on a HauserFeshbach calculation and indicates that ^{8}Li(p, n) does not contribute significantly to ^{8}Li burning in nucleosynthesis. See also (2003IS12).
A dynamic semimicroscopic model study of ^{8}Be(γ, p) considered dipoledipole and quadrupolequadrupole forces on the properties of Giant Dipole Resonances built on the ground state and first excited state of ^{8}Be (1995GO21). See also reaction 14 here.
The decay [see reaction 1 in ^{8}B] proceeds mainly to ^{8}Be*(3.0). Detailed study of the highenergy portion of the αspectrum reveals a maximum near E_{α} = 8.3 MeV, corresponding to transitions to ^{8}Be*(16.63), for which parameters E_{x} = 16.67 MeV, Γ = 150 to 190 keV or E_{x} = 16.62 MeV, Γ = 95 keV are derived: see (1974AJ01). Analyses (1986WA01, 1989BA31) of the β^{±} delayed αspectra following ^{8}B and ^{8}Li decay are described in reaction 24. The analysis of (1989BA31) requires a 2^{+} intruder state in ^{8}Be at E_{x} ≈ 9 MeV, while the analysis of (1986WA01) excludes intruder states below E_{x} = 26 MeV. See also (1988WA1E) and (1988BA75, 1998FA05, 2000BA89, 2001CA50). The determination of log ft values requires detailed calculations; values in the literature are: for decay to ^{8}Be*(3.0) log ft = 5.6 (1974AJ01), log ft = 5.77 (1989BA31); for decay to ^{8}Be*(16.63) log ft = 3.3 (1969BA43, 1979AJ01). The β^{+} spectrum has been measured by (1987NA08) and by (2000OR04): see reaction 1 in ^{8}B. See (1988AJ01) for additional references and discussion. See also (2000GR03, 2000GR07) for theoretical discussion of the cluster structure of 16.6 and 16.9 MeV resonances and their role in ^{8}B βdecay. See also (1994DE30).
Neutron groups to ^{8}Be*(0, 3.0) have been studied for E_{γ} = 18 to 26 MeV: see (1974AJ01, 1979AJ01). For reactions (a) and (b) bremsstrahlung γ rays from 4  8 MeV electrons were used to measure the θ_{lab} = 90° photoneutron emission excitation function (1989VA18). ^{9}Be levels at E_{x} = 1.735 ± 0.003, 2.43 and 3.077 ± 0.09 MeV were excited using a technique that uses electrons in a storage ring to Compton backscatter laser photons to produce highquality nearly monoenergetic γrays (2001UT01, 2001UT03, 2002SU19, 2003UT02); B(E1) and B(M1) values are deduced in (2001UT01, 2002IT07, 2002SU19). A measurement from neutron threshold to E_{γ} ≈ 20 MeV indicated that ^{8}Be excited states are strongly populated following neutron emission (1992GO27). The α(αn, γ) reaction competes with the 3α reaction to bridge the A = 5 and A = 8 mass gaps. γrays with E_{γ} = 1.5 to 6 MeV were used to study the α(αn, γ) reaction rate in inverse kinematics (2001UT03), and the resulting cross sections favor the compilation by NACRE (1999AN35) rather than the evaluation by (1988CA28). A theoretical study of photodisintegration in the threshold region around the ^{9}Be*(1.684) J^{π} = 1/2^{+} resonance is presented in (2001ME11). A multiclustermodel study of ^{9}Be photodisintegration (1998EF05) and an Rmatrix analysis of the situation (2000BA21) address discrepancies in the lowenergy cross section measurements. See also (1994KA25; theor.) for ^{9}Be Coulomb dissociation. Neutrons from ^{9}Be(γ, n) were used to estimate the number of hard Xrays (with E_{γ} > 1.67 MeV) that are produced in the plasma that results from impinging a 5 × 10^{8} W/cm^{2} laser on a Ta foil (2001SC12). See (1974AJ01, 1979AJ01) and ^{9}Be. Reaction (c) appears to proceed largely via excited states of ^{9}Be with subsequent decay mainly to ^{8}Be*(3.0): see (1966LA04, 1974AJ01), and ^{9}Be and ^{10}Be here. Neutrons from ^{9}Be(n, 2n) for E_{n} < 10.3 MeV were analyzed to determine the neutronneutron scattering length a_{nn} = 16.5 ± 1.0 fm (1990BO43). Measurements of ^{9}Be(n, 2n) for E_{n} < 12 MeV were made to assess the possibility of using ^{9}Be as a neutron multiplier in fusion reactors (1994ME08). See also (1988BE04) for a theoretical evaluation in the range from 5.9  14.1 MeV. For reactions (d) and (e) see (1974AJ01) and ^{9}Be. For reaction (e) see (1979AJ01).
For reaction (a) angular distributions of deuteron groups have been reported at E_{p} = 0.11 to 185 MeV [see (1974AJ01, 1979AJ01, 1984AJ01)] and at 18.6 MeV (1986GO23, 1987GO27; d_{0} and d_{1}) and 50 and 72 MeV (1984ZA07; to ^{8}Be*(0, 3.0, 16.9, 19.2)). Angular distributions of cross sections and analyzing powers were measured for deuterons from ^{9}Be(pol. p, d) at E_{pol. p} = 60 MeV. Analyzing powers for deuterons corresponding to ^{8}Be*(3.04, 11.4, 16.92, 19.24) were presented while peaks corresponding to ^{8}Be states at (0, 11.04, 17.64, 18.25, 19.4, 22.05) were observed; evidence for very broad states at higher energies was also reported (1987KA25). The angular distributions to ^{8}Be*(0, 3.0, 16.9, 17.6, 18.2, 19.1) are consistent with l_{n} = 1: see (1974AJ01). Neutron spectroscopic factors for n + ^{8}Be_{g.s.} and n + ^{8}Be*(3.04) were extracted from a DWBA analysis of ^{9}Be(p, d) at E_{p} = 18.6 MeV (1987GO27), and spectroscopic factors for n + ^{8}Be*(0, 3.04, 16.626, 16.922, 17.640, 18.15, 19.07) were extracted from ^{9}Be(p, d) at 33.6 MeV (1991AB04): see ^{9}B. For other spectroscopic factor measurements see (1979AJ01, 1984ZA07). An anomalous group is reported in the deuteron spectra between the d_{0} and the d_{1} groups. At E_{p} = 26.2 MeV, E_{x} = 0.6 ± 0.1 MeV (constant with θ). Analyses of the spectral shape and transfer cross sections are consistent with this "ghost" feature being part of the BreitWigner tail of the J^{π} = 0^{+} ^{8}Be_{g.s.}: it contains < 10% of the groundstate transfer strength. An analysis of reported Γ_{cm} widths for ^{8}Be*(3.0) in this reaction shows that there is no E_{p} dependence. The average Γ_{cm} at E_{p} = 14.3 and 26.2 MeV is 1.47 ± 0.04 MeV. Γ_{cm} = 5.5 ± 1.3 eV for ^{8}Be_{g.s.} and 5.2 ± 0.1 MeV for ^{8}Be*(11.4). Spectroscopic factors for ^{8}Be_{g.s.} (including the "ghost" anomaly) and ^{8}Be*(3.0) are 1.23 and 0.22 respectively at E_{p} = 14.3 MeV, and 1.53 and 1.02 respectively at E_{p} = 26.2 MeV. The width of ^{8}Be*(3.0) is not appreciably (< 10%) reaction dependent but the nearness of the decay threshold indicates that care must be taken in comparing decay widths from reaction and from scattering data: E_{res} = 3130 ± 25 keV (resonance energy in the α + α cm system) [E_{x} = 3038 ± 25 keV] and Γ_{cm} = 1.50 ± 0.02 MeV for ^{8}Be*(3.0): the corresponding observed and formal reaction widths and channel radii are γ_{res}^{2} = 580 ± 50 keV, γ_{λ}^{2} = 680 ± 100 keV and r_{c} = 4.8 fm. A study of the continuum part of the inclusive deuteron spectra is reported at E_{pol. p} = 60 MeV (1987KA25). See (1979AJ01, 1984AJ01) for the earlier work. The effects of electron screening were studied at around E_{p} = 16  390 keV. A directplus resonance model fit to the data result in the values of E_{res} = 336 ± 3 keV and Γ_{lab} = 205 ± 6 keV for ^{10}B*(6.87) and Γ_{α} = 68 ± 2 keV and Γ_{d} = 90 ± 4 keV (1997ZA06). See also (2002BA77). At E_{p} = 77  321 keV, angular distributions and analyzing powers of deuterons were measured; an Rmatrix evaluation of the data indicated that a directreaction model can adequately account for the observations (1998BR10) indicating that the subthreshold state in ^{10}B at E_{x} = 6.57 MeV does not contribute. An Rmatrix analysis of ^{10}B levels populated for E_{p} < 700 keV is reported in (2001BA47). Reaction (b) has been studied at E_{p} = 45 and 47 MeV: the reaction primarily populates ^{8}Be*(0, 3.0). At E_{p} = 70 MeV data were evaluated using a DWTA (Tmatrix) approach to decompose the 1s and 1p shell contributions in the quasielastic knockout of neutrons (2000SH01). See (1979AJ01), and ^{9}Be, ^{9}B here. For work at E_{p} = 1 GeV see (1985BE30, 1985DO16). For reaction (c) [FSI through ^{8}Be*(0, 3.0)] see (1974AJ01, 1984AJ01). See also (1992KO26; theor.) and ^{10}B.
At astrophysicallyrelevant energies, E_{cm} = 57  139 keV, ^{9}Be(d, t_{0}) angular distributions and total cross sections were measured and are compared with DWBA calculations (1997YA02). At E_{d} = 8  50 MeV, angular distributions of t_{0} and t_{1} are evaluated in a DWBA analysis and vertex constants, G^{2}, and neutron spectroscopic factors are deduced (1995GU22). Angular distributions of t_{0} were measured at E_{d} = 7 MeV and were evaluated in a DWBA analysis that indicated transfer mechanisms dominated at forward angles while compound nucleus mechanisms were most important at backward angles (1989SZ02). Levels of ^{11}B were observed in measurements of the excitation function and angular distribution for tritons from ^{9}Be(d, t_{0}) at E_{d} = 0.9  11.2 MeV (1994AB25) and E_{d} = 3  11 MeV (1995AB41, 2000GE16). A review of the ^{9}Be(d, t_{0}) excitation function for E_{d} = 237 keV to 11 MeV is given in (2000GE16). Angular distributions have been measured at E_{d} = 0.3 to 28 MeV [see (1979AJ01)], at E_{d} = 18 MeV (1988GO02; t_{0}, t_{1}) and at E_{pol. d} = 2.0 to 2.8 MeV (1984AN16; t_{0}). At E_{d} = 28 MeV angular distributions of triton groups to ^{8}Be*(16.6, 16.9, 17.6, 18.2, 19.1, 19.2, 19.8) have been analyzed using DWUCK: absolute C^{2}S are 0.074, 1.56, 0.22, 0.17, 0.41, 0.48, 0.40, respectively. See also 8.11 (in PDF or PS). An isospin amplitude impurity of 0.21 ± 0.03 is found for ^{8}Be*(17.6, 18.2): see (1979AJ01). At E_{d} = 7 MeV a complete kinematics measurement of ^{9}Be(d, t + ^{8}Be) observed states participating in the sequential decay of ^{8}Be (1991SZ06). The relative energy spectrum was reconstructed and yielded peaks corresponding to the ground state, E_{x} ≈ 0.6 MeV and 3.00 ± 0.01 MeV; the observed width for the 3 MeV state was Γ = 1.23 ± 0.02 MeV. Analysis in a singlelevel Rmatrix formalism, best fit with r_{c} = 4.5 ± 0.1 fm, indicates that the "ghost anomaly" structure at ≈ 0.6 MeV is the result of deformation in the highenergy tail of the ^{8}Be ground state. While the cross section corresponding to the first excited state peaks at 3.00 MeV, the Rmatrix fit indicates that the resonance energy is 3.12 ± 0.01 MeV (E_{x} = 3.03 ± 0.01 MeV) with Γ_{res} = 1.43 ± 0.06 MeV (1991SZ06). A kinematically complete study of reaction (b) at E_{d} = 26.3 MeV indicates the involvement of ^{8}Be*(0, 3.0, 11.4, 16.9, 19.9 + 20.1): see (1974AJ01).
Angular distributions have been measured in the range E(^{3}He) = 3.0 to 26.7 MeV and at E(pol. ^{3}He) = 33.3 MeV (to ^{8}Be*(16.9, 17.6, 19.2)) [S = 1.74, 0.72, 1.17, assuming mixed isospin for ^{8}Be*(16.9)]. The possibility of a broad state at E_{x} ≈ 25 MeV is also suggested: see (1979AJ01). See also (1987VA1I). Reaction (b) has been studied at E(^{3}He) = 1.0 to 10 MeV [see (1979AJ01, 1984AJ01)], at E(^{3}He) = 3 to 12 MeV (1986LA26) and at 11.9 to 24.0 MeV (1987WA25). The reaction is reported to proceed via ^{8}Be*(0, 3.0, 11.4, 16.6, 16.9, 19.9, 22.5): see (1979AJ01) and (1986LA26, 1987WA25). For a discussion of the width of ^{8}Be*(11.4) see (1987WA25). Angular distributions for ^{9}Be(^{3}He, α) were evaluated to determine the contributions from neutron pickup vs. heavy particle stripping; ^{9}Be spectroscopic factors for S_{n} and S_{α} were calculated (1997ZH40). See also (1992KO26; theor.). See also ^{9}Be here, ^{12}C in (1980AJ01), and (1988AJ01).
A summary of the (α, α'n) cross sections used in the SOURCES code is given in (2003SH22). The SOURCES code (2002WI1K) is used, for example, to calculate neutron energies and doses from ^{9}Beactinide radioactive sources.
Angular distributions have been studied at E(^{6}Li) = 32 MeV involving ^{8}Be*(0, 3.0) and ^{7}Li*(0, 0.48) (1985CO09). For reaction (b) see (1984KO25). For reaction (c) measurements at E(^{9}Be) = 48 MeV were evaluated with a CCBA model; ^{8}Be*(3.04, 11.3) played an important role in the reaction (2003AS04). Also see ^{10}Be and (1985JA09). For the earlier work see (1979AJ01).
Optical model parameters for ^{8}Be + ^{13}C were deduced from ^{9}Be(^{12}C, ^{13}C)^{8}Be for E(^{12}C) = 65 MeV. For ^{9}Be + ^{12}C and ^{8}Be + ^{13}C, energydependent optical model parameters are given for E_{cm} = 5  50 MeV (1999RU10).
The angular distribution for the transition to the first T = 2 state ^{8}Be*(27.49) is very similar to the measured ^{10}Be(p, ^{3}He) angular distribution that is measured for population of the analog state, ^{8}Li*(10.82). They are both consistent with L = 0 using a DWBA (LZR) analysis: see (1979AJ01, 1984AJ01) and 8.5 (in PDF or PS) in (1984AJ01).
Total proton emission cross sections following π^{+} absorption on ^{10}B and ^{11}B were measured at E_{π+} = 0, 100, 140 and 180 MeV, corresponding cross sections were σ[^{10}B(π^{+}, 2p)] = 8, 18, 17, 17 mb and σ[^{11}B(π^{+}, 2pn)] = 0.18, 0.80, 2.0, 3.4 mb, respectively (1992RA11).
Angular distributions were measured for ^{10}B(K^{+}, K^{+}d) at E_{K+} = 130  268 MeV. A DWIA analysis indicated that direct knockout and 2step mechanisms are important (1991BE42).
Bremsstrahlung photons were used to measure the ^{10}B(γ, pn) reaction at E_{γ} = 66  103 MeV in a study of twobody photon absorption and final state interactions (1988SU14).
The breakup of ^{10}B by 14.4 MeV neutrons involves, among others, ^{8}Be_{g.s.} (1984TU02). The cross section of ^{10}B(n, t)2α, for thermal neutrons is reported as σ_{thermal} = 7 ± 2 mb (1987KA32). See also (1979AJ01) and ^{11}B in (1990AJ01).
Angular distributions of the ^{3}He ions to ^{8}Be*(0, 3.0, 16.6, 16.9) have been studied at E_{p} = 39.4 MeV [see (1974AJ01)] and at E_{p} = 51.9 MeV (1983YA05; see for a discussion of isospin mixing of the 16.8 MeV states).
Angular distributions have been reported at E_{d} = 0.5 to 7.5 MeV: see (1974AJ01, 1979AJ01). At E_{d} = 67  141 keV, angular distributions of α_{0} and α_{1} were measured and the ^{10}B(d, α_{0}) and ^{10}B(d, α_{1}) astrophysical Sfactors were deduced (1997YA02). The angulardependent cross sections for α_{0}, α_{1} and 3α processes were measured for E_{d} = 120  340 keV and in each case the Sfactor was observed to increase with decreasing energy (2001HO22). Yield ratios for ^{10}B(d, p)/^{10}B(d, α) were measured at E_{d} = 58  142 keV (1993CE02). At E_{d} = 7.5 MeV the population of ^{8}Be*(16.63, 16.92) is closely the same, consistent with their mixed isospin character while ^{8}Be*(17.64) is relatively weak consistent with its nearly pure T = 1 character. ^{8}Be*(16.63, 16.92, 17.64, 18.15) have been studied for E_{d} = 4.0 to 12.0 MeV. Interference between the 2^{+} states ^{8}Be*(16.63, 16.92) varies as a function of energy. The crosssection ratios for formation of ^{8}Be*(17.64, 18.15) vary in a way consistent with a change in the population of the T = 1 part of the wave function over the energy range: at the higher energies, there is very little isospin violation. At higher E_{x} the 3^{+} state at E_{x} = 19.2 MeV is observed, the neighboring 3^{+} state at E_{x} = 19.07 MeV is not seen. Γ_{16.6} = 90 ± 5 keV, Γ_{16.9} = 70 ± 5 keV, ΔQ = 290 ± 7 keV: see 8.11 (in PDF or PS) and (1979AJ01). Relative widths of ^{8}Be levels at 19.86 and 20.1 MeV, Γ_{α}/Γ_{p} = 2.3 ± 0.5 and Γ_{α}/Γ_{p} = 4.5 ± 0.6 respectively, were determined by a complete kinematics measurement of ^{10}B(d, 2α) and ^{10}B(d, ^{7}Li + p) at E_{d} = 13.6 MeV (1992PU06). At E_{d} = 48 MeV evidence was observed for an ^{8}Be state at E_{x} = 32 MeV with Γ = 1 MeV (1993PA31); levels were also seen at ^{8}Be*(0, 3.0, 11.4, 16.6[u], 16.9[u], 17.6, ≈ 19, ≈ 20, 21.5, 22.2, 24, 25.2). At E_{d} = 4.2 to 6.6 MeV measurements were carried out by detecting α coincidences in a kinematical star configuration (1992BO1H). ^{12}C was excited into the excitation energy region near 30 MeV, which was then followed by 3α decay. The analysis, which indicated sequential decay through the ^{8}Be*(11.4) state, was intended to stimulate activity in 3body interactions by invoking an alternative approach. Reaction (b) [E_{d} < 5 MeV] takes place mainly by a sequential process involving ^{8}Be*(0, 2.9, 11.4, 16.6, 16.9): see (1979AJ01). See also (1983DA11) [The work quoted in (1984AJ01) has not been published.] At E_{d} = 13.6 MeV in addition to ^{8}Be*(16.6, 16.9), states with E_{x} ≈ 19.9  20.2 MeV with Γ ≈ 0.7  1.1 MeV are involved (1988KA1K). See also (1992KO26).
Angular distributions for the ^{8}Be*(0, 3.0) are reported in a measurement of ^{10}B(α, ^{6}Li) at E_{α} = 27.2 MeV (1995FA21); it was deduced that direct processes are dominant in the reactions. See reaction 40 in (1984AJ01) and ^{6}Li in (2002TI10).
Angular distributions have been measured at E_{p} = 0.04 to 45 MeV [see (1974AJ01, 1979AJ01, 1984AJ01)]. The α_{0} and α_{1} excitation functions and astrophysical reaction rates have been determined by measuring angular dependent differential cross sections and total cross sections at E_{cm} = 0.12  1.10 MeV (1987BE17), at E_{p} = 4.5 to 7.5 MeV (1983BO19), at E_{p} = 40  180 keV (1992CE02), at E_{cm} = 17  134 keV (1993AN06), at 1.7  2.7 MeV (1998MA54), and at E_{p} = 0.4  1.6 MeV (2002LI29). A DWBA evaluation of data at 398, 498 and 780 keV indicated that direct mechanisms dominated over exchange processes at astrophysical energies (1995YA07). A calculation of the expected influence of electron screening, due to using atomic nuclei, indicates that the astrophysical S(0)factor deduced from lab measurements may be 2.5 times greater than the rate when bare ions participate in the reaction (1993AN06). See also (2002BA77, 2002HA51). The effects of higher order processes including vacuum polarization, relativity, bremsstrahlung, atomic screening and atomic polarization are reviewed in (1997BA95). See also (1996RA14) for DWBA analysis of data from 10  1000 keV. Angular distributions of α_{0} and α_{1} particles were measured around the ^{12}C*(16.1) resonance at E_{p} = 163 keV; E_{cm} = 148.3 ± 0.1 keV and Γ = 5.3 ± 0.2 keV were deduced (1987BE17). The ^{12}C*(16.57) resonance was evaluated in (p, α) data and resonance parameters of E_{res} = 596 ± 30 keV and Γ = 383 ± 40 keV were deduced (1993AN06). Reaction (b) has been studied for E_{p} = 0.15 to 20 MeV: see (1974AJ01, 1984AJ01). The reaction proceeds predominantly by sequential twobody decay via ^{8}Be*(0, 3.0). See also ^{12}C in (1990AJ01), and (1992KO26). Reaction (c) was measured at E_{p} = 2  5.5 MeV by (1995BO35). A reconstruction of the 2α relative energy spectrum was analyzed to evaluate parameters for ^{8}Be*(3.0).
At E(^{3}He) = 71.8 MeV angular distributions of the ^{6}Li ions to ^{8}Be*(0, 3.0, 16.6, 16.9, 17.6, 18.2) are reported (1986JA14). For the earlier work at 25.6 MeV see (1979AJ01). See also (1986JA02).
The work reported in (1984AJ01) has not been published. See also ^{7}Li in (2002TI10) and references cited in (1988AJ01).
See (1984DA17) and ^{12}B in (1990AJ01).
The ^{8}Be ground state and excited 0^{+} and 2^{+} states are reported to participate in the ^{12}C photodisintegration reaction ^{12}C(γ, pt) at energies up to E_{γ} = 150 MeV; see (1989VO04, 1990DO03).
A DWIA calculation of ^{12}C(e, e'α) at 500  650 MeV qualitatively evaluated the restructuring of excited clusters following knockout reactions (1999SA27).
The energy and mass dependence of pion (π^{+}) absorption leading to multiple protons in the final state was measured at E_{π+} = 30  135 MeV (2000GI07).
The first two of these reactions involve ^{8}Be*(0, 3.0): see (1974AJ01, 1979AJ01, 1984AJ01) and (1985AJ01). For reaction (a), see (1986AN22). For reaction (b) αspectroscopic factors in ^{12}C for α + ^{8}Be*(0, 3.0) are deduced in (1995NE11, 1997SA04, 1998YO09). The αcluster knockout reaction mechanism is evaluated in (1987ZH10, 1994NE05, 1995GA39, 1995NE11, 1995TC01, 1997SA04, 1998YO09, 1999HA27). For reaction (c) see (1983LI18; theor.).
Measurements of angular distributions and polarization observables [iT_{11}(θ), T_{20}(θ), T_{21}(θ) and T_{22}(θ)] are reported for ^{12}C(pol. d, ^{6}Li)^{8}Be_{g.s.} at 18 and 22 MeV (1987TA07). DWBA analysis is used to evaluate αspectroscopic factors from ^{12}C(d, ^{6}Li) at E_{d} = 41 MeV (1988RA20) and at E_{d} = 15  55 MeV (1988RA27). Angular distributions have been studied at E_{d} = 12.7 to 54.3 MeV [see (1974AJ01, 1979AJ01, 1984AJ01)] and at E_{pol. d} = 18 and 22 MeV (1986YA12; to ^{8}Be_{g.s.}) and 51.7 MeV (1986YA12; to ^{8}Be*(0, 3.0, 11.4) as well as at E_{d} = 50 MeV (1987GO1S), 54.2 MeV (1984UM04; FRDWBA) [S_{α} = 0.48, 0.51 and 0.82 for ^{8}Be*(0, 3.0, 11.4)] and 78.0 MeV (1986JA14; to ^{8}Be*(0, 3.0, 16.6, 16.9)). See also (1985GO1G; E_{d} = 50 MeV). For reaction (b) see (1984AJ01). See also (1984NE1A) and references cited in (1988AJ01).
Angular distributions from ^{12}C(t, ^{7}Li) and ^{13}C(t, ^{8}Li) were evaluated in a DWBA analysis to deduce spectroscopic factors in ^{12}C for α + ^{8}Be_{g.s.} (1989SI02). See also ^{7}Li in (2002TI10).
Angular distributions have been obtained at E(^{3}He) = 25.5 to 70 MeV [see (1979AJ01, 1984AJ01)] and at E(pol. ^{3}He) = 33.4 MeV (1986CL1B; ^{8}Be_{g.s.}; also A_{y}). ^{8}Be*(0, 3.0, 11.4, 16.6, 16.9, 17.6) have been populated.
These reactions have been studied at E_{α} to 104 MeV [see (1979AJ01, 1984AJ01) and ^{12}C in (1985AJ01)] and at 31.2 MeV (1986XI1A; reaction (a)): ^{8}Be*(0, 3.0, 11.4) are populated. See also references cited in (1988AJ01). Alpha spectroscopic factors ^{8}Be*(0, 3.0) were measured by (α, 2α) knockout at 200 MeV (1999ST06) and 580 MeV (1999NA05). αparticle angular correlations were measured from the ^{12}C* → α + ^{8}Be decay to determine the polarization characteristics of the ^{12}C*(9.64; 3^{}) state, which was excited by ^{12}C(α, α')^{12}C*(9.64) → α + ^{8}Be (1989KO55).
Angular distributions involving ^{8}Be_{g.s.} + ^{13}C_{g.s.} (reaction (a)) have been reported at E(^{9}Be) = 20 to 22.9 MeV and E(^{12}C) = 10.5 to 13.5 MeV: see (1984AJ01). For both reactions see also (1983DEZW).
For reaction (a) ^{12}C(^{12}C, ^{16}O) was measured in a study of ^{24}Mg excited states near 33 MeV at E(^{12}C) = 27  36 MeV (1995AL25, 1996AL03, 1997SZ01). See also ^{16}O in (1993TI07) and references cited in (1988AJ01). For reaction (b) see reaction 18 in ^{20}Ne in (1987AJ02), (1985MU14) and (1988AL07; location of a 10^{+} state in ^{20}Ne at E_{x} ≈ 27.5 MeV). Evidence for 11 states in ^{24}Mg with excitation energy between 22 and 30 MeV is seen in reaction (c) at E(^{20}Ne) = 110 and 160 MeV (2001FR03). For reaction (d) see (1987SI06). States in ^{28}Si at E_{x} = 28.0 MeV [J^{π} = 13^{}], 29.8 MeV [(11)], 33.4 MeV [8^{+}(10^{+})] and 34.5 MeV [(12, 14)^{+}] are observed in reaction (e) at E(^{24}Mg) = 170 MeV (2001SH08).
See ^{7}Li in (2002TI10).
See (1984SH1D, 1988SH1F; E_{α} = 27.2 MeV) and ^{9}Be in (1979AJ01).
See ^{14}C in (1986AJ01).
See ^{7}Li in (2002TI10).
The ^{16}O(γ, 4α) reaction was studied with bremsstrahlung γ rays up to E_{γ} = 300 MeV (1995GO10). Evidence in the energy reconstruction spectra indicates that participation of the ^{8}Be*(0, 3.0) states increases with increasing γray energy.
See (1986VD04; E_{p} = 50 MeV).
See (1987CZ02).
Sequentialdecay neutron spectroscopy of ^{7}Be + n products from ^{ nat}Ag + ^{14}N at 35 MeV/A indicates the participation of ^{8}Be*(19.24) with 19.234 ± 0.012 MeV and Γ = 210 ± 35 keV (1989HE24).
