(See Energy Level Diagrams for 8Be)
GENERAL: References to articles on general properties of 8Be published since the previous review (1988AJ01) are grouped into categories and listed, along with brief descriptions of each item, in the General Tables for 8Be located on our website at (nucldata.tunl.duke.edu/nucldata/General_Tables/8be.shtml).
The yield of γ1 has been measured for Eα = 32 to 36 MeV. The yield of γ0 for Eα = 33 to 38 MeV is twenty times lower than for γ1 , consistent with E2 decay: see (1979AJ01). Angular distributions were measured in the 4He(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 = [ΓT=0M1/ΓT=1M1]1/2 = +0.04 ± 0.02, δ0 = [ΓT=0E2/ΓT=1M1]1/2 = +0.21 ± 0.04, δ1 = [ΓT=1E2/ΓT=1M1]1/2 = +0.01 ± 0.03 and ΓT=1M1 = 2.80 ± 0.18 eV (1995DE18), and they note that earlier values (1978BO30) were troubled by a transformation error. The Ex of 8Be*(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 8Beg.s. has been calculated as a function of Ex over the 3 MeV state: the total Γγ for this transition is 8.3 meV, corresponding to 75 W.u. (1986LA05). A calculation of the Γγ 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 γ-ray transition within the 2+ resonance is calculated to be ≤ 2.5 nb at Ex ≈ 3.3 MeV (1986LA19). See also (2001CS04) for discussion of the impact of variation in the NN force on the nucleosynthesis rates of 8Be and 12C.
The cross sections for formation of 7Li*(0, 0.48) [Eα = 39 to 49.5 MeV] and 7Be*(0, 0.43) [39.4 to 47.4 MeV] both show structures at Eα ≈ 40.0 and ≈ 44.5 MeV: they are due predominantly to the 2+ states 8Be*(20.1, 22.2): see (1979AJ01). The excitation functions for p0, p2, d0, d1 for Eα = 54.96 to 55.54 MeV have been measured in order to study the decay of the first T = 2 state in 8Be: see 8.5 (in PDF or PS) in (1984AJ01). Cross sections for p0+1 are also reported at Eα = 37.5 to 140.0 MeV: see (1979AJ01, 1984AJ01). The cross sections for reaction (c) has been measured at three energies in the range Eα = 46.7 to 49.5 MeV: see (1979AJ01) and below.
The production of 6Li, 7Li and 7Be [and 6He] has been studied at Eα = 61.5 to 158.2 MeV by (1982GL01), at 198.4 MeV by (1985WO11), and at Eα = 160, 280 and 320 MeV by (2001ME13). The production of 7Li (via reactions (a) and (b)) and of 6Li is discussed. At energies beyond Eα ≈ 250 MeV the α + α reaction does not contribute to the natural abundance of lithium, reinforcing theories which produce 6Li in cosmic-ray processes and the "missing" 7Li in the Big Bang: thus the universe is open (1982GL01, 1985WO11). The measurements of (2001ME13) have observed smaller cross sections for 6Li production than previous extrapolations, and reduce uncertainty in extrapolation to higher energies.
The 8Beg.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 low-energy 4He(α, α) scattering process (1992WU09). A measurement that detected α - α coincidences at θ(α1, α2) = (45°, 45°) and (30°, 60°) was performed using a gas jet target, which permitted an energy resolution of 26 eV; the resulting parameters for 8Beg.s. are Eb = -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 Eb = -92.12 ± 0.05 keV and Γ = 6.8 ± 1.7 eV (1968BE02). For Eα = 30 to 70 MeV the l = 0 phase shift shows resonant behavior at Eα = 40.7 MeV, corresponding to a 0+ state at Ex = 20.2 MeV, Γ < 1 MeV, Γα/Γ < 0.5. No evidence for other 0+ states is seen above Eα = 43 MeV.
The d-wave phase shift becomes appreciable for Eα > 2.5 MeV and passes through a resonance at Eα = 6 MeV (Ex = 3.18 MeV, Γ = 1.5 MeV, Jπ = 2+): see 8.11 (in PDF or PS). Five 2+ levels are observed from l = 2 phase shifts measured from Eα = 30 to 70 MeV: 8Be*(16.6, 16.9) with Γα = Γ [see 8.11 (in PDF or PS)], and states with Ex = 20.1, 22.2 and 25.2 MeV. The latter has a small Γα. The l = 2 α - α phase shifts have been analyzed by (1986WA01) up to Eα = 34 MeV: intruder states below Ex = 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 Eα ≈ 11 MeV and indicates a broad 4+ level at Ex = 11.5 ± 0.3 MeV [Γ = 4.0 ± 0.4 MeV]. A rapid rise of δ4 at Eα = 40 MeV corresponds to a 4+ state at 19.9 MeV with Γα/Γ ≈ 0.96; Γ < 1 MeV and therefore Γα < 1 MeV, which is < 5% of the Wigner limit. A broad 4+ state is also observed near Eα = 51.3 MeV (Ex = 25.5 MeV). Over the range Eα = 30 to 70 MeV a gradual increase in δ6 is observed. Some indications of a 6+ state at Ex ≈ 28 MeV and of an 8+ state at ≈ 57 MeV have been reported; Γcm ≈ 20 and ≈ 73 MeV, respectively. A resonance is not observed at the first T = 2 state, 8Be*(27.49). See (1979AJ01) for references.
The elastic scattering has also been studied at Eα = 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 α-α correlations involving 8Be*(0, 3.0) see (1987CH33, 1987PO03). Resonances in α - α scattering and the role of α clustering in 8Be have been investigated in theoretical studies of 4He(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 γ-rays to 8Be*(17.64) [1+; T = 1] has been measured for Ed = 6.85 to 7.10 MeV. A resonance is observed at Ed = 6965 keV [Ex = 27495.8 ± 2.4 keV, Γcm = 5.5 ± 2.0 keV]; Γγ = 23 ± 4 eV [1.14 ± 0.20 W.u.] for this M1 transition from the first 0+; T = 2 state in 8Be, 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 [Ay(θ), Ayy(θ), T20(θ)] were measured at Epol. d = 9 MeV (1991WI19) and Epol. d = 2 and 9 MeV (1994WI08). In addition, (1994WI08) measured the excitation function from Ed = 7 - 14 MeV; capture to the 8Be ground state and 3.0 MeV state were observed. A transition matrix element analysis for 6Li(pol. d, γ0) at 9 MeV indicates a 13 - 21% E1 contribution in addition to the expected dominant E2 strength. This suggests ≈ 1.5% D-state admixture in the 8Be 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 Γγ0 should be listed as Γγ(27.5 to 17.6).
Yield curves and cross sections have been measured for Ed = 48 keV to 17 MeV: see (1979AJ01, 1984AJ01). At Ecm = 96.6 keV σ = 3.17 mb ± 3%(stat.) ± 7.5%(syst.) (2001HO23). Polarization measurements are reported at Ed = 0.27 to 3.7 MeV. Angular distributions were measured for 6Li(d, n) at Ed = 0.7 - 2.3 and 5.6 - 12.1 MeV and excitation functions for neutrons corresponding to 7Be*(0, 0.43, 4.57, 7.21) are reported (1996BO27). Comparisons of the populations of 7Be*(0, 0.43) and of 7Li*(0, 0.48) have been made at energies up to Ed = 7.2 MeV. The (d, n)/(d, p) ratios are closely equal for analog states, as expected from charge symmetry: see (1979AJ01). However, the n1/p1 yield ratio decreases from 1.05 at Ed = 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 7Be in (2002TI10) and (1988AJ01).
Excitation functions have been measured for Ed = 30 keV to 5.4 MeV: see (1979AJ01, 1984AJ01). The thick target yield of 0.48 MeV γ-rays is reported from ≈ 50 to 170 keV (1985CE12). An anomaly is observed in the p1/p0 intensity ratio at Ed = 6.945 MeV [see (1979AJ01)], corresponding to the first 0+; T = 2 state, Γ = 10 ± 3 keV, Γp0 << Γp1, Γp0 < Γd. The (d, p0)/(d, n0) ratio is measured in the astrophysical range from 65 keV < Ed < 200 keV (1993CZ01, 1997CZ04). In this region the subthreshold isospin mixed 2+ level at 8Be*(22.2; Γ ≈ 800 keV) could influence the (d, p0)/(d, n0) ratio, which is important in inhomogeneous Big Bang nucleosynthesis models. The observed ratio is Γn0/Γp0 = 0.95 ± 0.03 which is consistent with the presently accepted isospin mixing parameter ε = 0.20. The 6Li(d, p) and 6Li(d, α) reactions were measured at Ed = 20 - 135 keV (1993CE02), and a nearly constant σ(d, p0 + p1)/σ(d, α) ratio of 0.55 was observed indicating that there is no anomalous behavior in the low energy 6Li(d, p) cross section. Polarization measurements have been reported at Ed = 0.6 to 10.9 MeV: see (1979AJ01). See also 7Li in (2002TI10) and (1984KU15; theor.).
The yield of elastically scattered deuterons has been measured for Ed = 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 Ed = 191 and 395 MeV see (1986GA18).
Cross sections and angular distributions (reaction (a)) have been measured at Ed = 10 keV to 31 MeV: see (1979AJ01, 1984AJ01), (1992EN01, 1992EN04) for Ed = 10 - 1450 keV, and (1997CZ01) for Ed = 50 - 180 keV. A DWBA analysis by (1997CZ01) of data up to 1 MeV evaluated the impact of the subthreshold resonance 8Be*(22.2) on the measured cross sections. In the DWBA analysis, data was limited to energies above Ed = 60 keV in order to minimize the effect of screening; the analysis indicated an energy Eres = (-50 ± 20) keV for the subthreshold resonance. The 6Li(6Li, 2α)4He reaction was measured at E(6Li) = 6 MeV and was evaluated in the "Trojan Horse" method to extract the 6Li(d, α) reaction cross sections and S-factors in the astrophysically relevant range from Ecm = 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 6Li(d, α) and 2H(6Li, α) in the energy range of Ecm < 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 Ed = 0.8 MeV, Γlab ≈ 0.8 MeV and Ed = 3.75 MeV, Γlab ≈ 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 Ex = 22.2 and 25.2 MeV and a 4+ state at 25.5 MeV. A strong resonance is seen in the α* channel [to 4He(20.1), Jπ = 0+] presumably due to 8Be*(25.2, 25.5). In addition the ratio of the α*/α differential cross sections at 30° shows a broad peak centered at Ex ≈ 26.5 MeV (which may be due to interference effects) and suggests a resonance-like anomaly at Ex ≈ 28 MeV. Ayy = 1 points are reported at Ed = 5.55 ± 0.12 (θcm = 29.7 ± 1.0°) and 8.80 ± 0.25 MeV (θcm = 90.0 ± 1.0°) [corresponding to Ex = 26.44 and 28.87 MeV]. For references see (1974AJ01, 1979AJ01).
At Ed = 6.945 MeV, the α0 yield shows an anomaly corresponding to 8Be*(27.49), the 0+; T = 2 analog of 8Heg.s.. This T = 2 state has recently been studied using both polarized deuterons and 6Li ions. The ratio of the partial widths for decay into 6Li + d states with channel spin 2 and 0, Γ2/Γ0 = 0.322 ± 0.091 (1986SO07).
A measurement of angular distributions and the excitation function for 6Li(d, α) for Ed = 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 Ed = 1.2 to 8.0 MeV: the transition matrix element squared plotted as a function of Eαα* (the relative energy in the channel 4Heg.s. + 4He*(20.1) [0+]) shows a broad maximum at Ex ≈ 25 MeV. Analysis of these results, and of a study of 7Li(p, α)α* [see reaction 18] which shows a peak of different shape at Ex ≈ 24 MeV, indicate the formation and decay of overlapping states of high spatial symmetry, if the observed structures are interpreted in terms of 8Be resonances: see (1984AJ01). For other work see (1984AJ01). See also 6Li in (2002TI10) and references cited in (1988AJ01).
Angular distributions have been studied in the range E(3He) = 0.46 to 17 MeV and at E(pol. 6Li) = 21 MeV. 8Be*(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 Ay(θ) were measured for 6Li(pol. 3He, p0 and p1) at Epol. 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(3He) = 1 MeV. For reaction (b) see (1974AJ01) and (1987ZA07). See also 9B.
Deuteron groups have been observed to 8Be*(0, 3.0, 11.3 ± 0.4). Angular distributions have been measured at Eα = 15.8 to 48 MeV: see (1974AJ01, 1979AJ01). A study of reaction (b) shows that the peak due to 8Be*(3.0) is best fitted by using Γ = 1.2 ± 0.3 MeV. At Eα = 42 MeV the α - α FSI is dominated by 8Be*(0, 3.0). See also 8.11 (in PDF or PS) and (1983BE51; theor.).
At Emax(6Li) = 13 MeV reaction (a) proceeds via 8Be* (0, 3.0, 16.6, 16.9, 22.5). The involvement of a state at Ex = 19.9 MeV (Γ = 1.3 MeV) is suggested. Good agreement with the shapes of the peaks corresponding to 8Be*(16.6, 16.9) is obtained by using a simple two-level formula with interference, corrected for the effect of final-state 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 8Be*(16.6, 16.9) remains constant for E(6Li) = 4.3 to 5.5 MeV: I(16.6)/I(16.9) = 1.22 ± 0.08. Partial angular distributions for the α0 group have been measured at fourteen energies for E(6Li) = 4 to 24 MeV. See (1979AJ01) for the references. The reaction mechanism for 6Li(6Li, X) was studied by measuring charged particle angular distributions for E(6Li) = 2 - 16 MeV (1990LE05). Analysis in a statistical model indicated that the 6Li(6Li, α) reaction proceeds dominantly via direct, cluster transfer rather than an intermediate compound nucleus.
At E(6Li) = 36 to 46 MeV sequential decay (reaction (b)) via 8Be states at Ex = 3.0, 11.4, 16.9 and 19.65 MeV is reported: see (1984AJ01). (1987LA25) report the possible involvement of the 2+ state 8Be*(22.2). At E(6Li) = 6 MeV the "Trojan Horse" method was used to evaluate 6Li(6Li, 2α) data to extract the 6Li(d, α) reaction cross sections and S-factors (2001SP04, 2001MU30): see reaction 9
For reaction (a) electron/positron pair decay from 8Be*(17.6, 18.15) Jπ = 1+ levels was measured in a search for M1 de-excitation via pair production that would indicate the involvement of a short-lived isoscalar axion 4 - 15 MeV/c2 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 γ-ray ratio.
For reaction (b) cross sections and angular distributions have been reported from Ep = 30 keV to 18 MeV. Gamma rays are observed to the ground (γ0) and to the broad, 2+, excited state at 3.0 MeV (γ1) and to 8Be*(16.6, 16.9) (γ3, γ4). An R-matrix fit to the γ-ray spectrum obtained at Ep = 7.5 and 8 MeV yielded Ex = 2.91 MeV and Γ = 1.23 MeV for the 8Be first excited state (1990RI06). See also (1994DE09) for comments on model dependences for deduced widths. Resonances for both γ0 and γ1 occur at Ep = 0.44 and 1.03 MeV, and for γ1 alone at Ep = 2, 4.9, 6.0, 7.3, and possibly at 3.1 and 11.1 MeV. The excitation function was measured for γ0 and γ1 across the resonance at Ep = 441 keV; the peak cross section was σγ0 + γ1 = 5.0 ± 0.7 mb (yielding an average of 5.9 ± 0.5 mb when weighted with previous measurements). The branching ratio was σ(γ0)/σ(γ0 + γ1) = 0.72 ± 0.07 (1995ZA03). Broad resonances are reported at Ep ≈ 5 MeV (γ0), Γ ≈ 4 - 5 MeV, and at Ep ≈ 7.3 MeV (γ1), Γ ≈ 8 MeV: see 8.12 (in PDF or PS). The Ep ≈ 5 MeV resonance (Ex ≈ 22 MeV) represents the giant dipole resonance based on 8Beg.s. while the γ1 resonance, ≈ 2.2 MeV higher, is based on 8Be*(3.0). The γ0 and γ1 giant resonance peaks each contain about 10% of the dipole sum strength. The main trend between Ep = 8 and 17.5 MeV is a decreasing cross section.
At the Ep = 0.44 MeV resonance (Ex = 17.64 MeV) the radiation is nearly isotropic and has been interpreted as arising from p-wave formation, Jπ = 1+, with channel spin ratio σ(Jc = 2)/σ(Jc = 1) = 3.2 ± 0.5. Radiative widths for the γ0 and γ1 decay are displayed in 8.10 (in PDF or PS). A careful study of the α-breakup of 8Be*(16.63, 16.92) [both Jπ = 2+] for Ep = 0.44 to 2.45 MeV shows that the non-resonant part of the cross section for production of 8Be*(16.63) is accounted for by an extranuclear direct-capture process. The γ-ray transitions to 8Be*(16.63, 16.92) are observed at Ep = 0.44, 1.03 and 1.89 MeV [8Be*(17.64, 18.15, 18.9)]. The results are consistent with the hypothesis of nearly maximal isospin mixing for 8Be*(16.63, 16.92): decay to these states is not observed from the 3+ states at Ex = 19 MeV, but rather from the 2- state at Ex = 18.9 MeV. Squared T = 1 components calculated for 8Be*(16.6, 16.9) are 40 and 60%, and for 8Be*(17.6, 18.2) they are 95 and 5%, respectively. At Ep = 25 MeV, the capture cross section to the 16 MeV 2+ doublet was measured (σθ(γ)=90° < 0.04 μb/sr) via a triple coincidence γ + 2α method (1991BR11). The cross section for (γ3 + γ4) has also been measured for Ep = 11.5 to 30 MeV (θ = 90°) by detecting the γ-rays and for Ep = 4 to 13 MeV (at five energies) by detecting the two α-particles from the decay of 8Be*(16.6, 16.9): a broad bump is observed at Ep = 8 ± 2 MeV (1981MA33). The angle and energy integrated yield only exhausts 8.6% of the classical dipole sum for Ep = 4 to 30 MeV, suggesting that this structure does not represent the GDR built on 8Be*(16.6, 16.9). A weak, very broad [Γ ≥ 20 MeV] peak may also be present at Ex = 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 7Li(p, γ) angular distributions and cross sections, mainly for γ0 and γ1 capture, were measured at Ep = 40 - 180 keV (1992CE02), Epol. p = 80 keV (1994CH23, 1996GO01, 1997GO13), Ep = 100 - 1500 keV (1995ZA03), Ep = 80, 402 and 450 keV (1996HA06), and Epol. p = 40 - 100 keV (2000SP01). The angular dependent cross-section and analyzing power data indicate significant near-threshold contributions from p-wave capture. Estimates of the p-wave strength have been deduced from Transition Matrix Element (TME) fits to the polarization data (1994CH23, 1996GO01, 1997GO13), R-matrix fits to the data (1995BB21, 1996BB26, 2000BA89), and other direct-plus-resonances 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 p-wave strength was the result of interference in the extended tails of the two 1+ resonances at Ep = 441 keV and 1030 keV, while a more recent measurement (2000SP01) that observed a negative slope in the astrophysical S-factor, as the energy approaches zero, indicates that the sub-threshold 8Be state at Ex = 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 low-energy capture that include the subthreshold state and the two resonances at Ep = 441 and 1030 keV. Polarized proton capture to the 8Be*(16.6) state was measured at Epol. p = 80 keV (1996GO01). See (1995ZA03, 2000NE09) for thermonuclear reaction rates and (1994CH70) for applications. Thick target proton induced γ-ray yields, useful for elemental analysis, were measured at Ep = 2.2 - 3.8 MeV (1988BO37) and Ep = 7 - 9 MeV (1987RA23).
Measurements of cross sections have been reported for Ep = 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 Ep = 2.05 to 5.5 MeV, 30 and 50 MeV [see (1974AJ01)] and at Ep = 52.8 MeV (1988HE08) [Kzz' = 0.07 ± 0.02]. See also below.
The yield of ground state neutrons (n0) rises steeply from threshold and shows pronounced resonances at Ep = 2.25 and 4.9 MeV. The yield of n1 also rises steeply from threshold and exhibits a broad maximum near Ep = 3.2 MeV and a broad dip at Ep ≈ 5.5 MeV, also observed in the p1 yield. Multi-channel scattering length approximation analysis of the 2- partial wave near the n0 threshold indicates that the 2- state at Ex = 18.9 MeV has a width Γ = 50 ± 20 keV. See, however, reaction 23 here. The ratio of the cross section for 7Li(p, γ)8Be*(18.9) → 8Be*(16.6 + 16.9) + γ to the thermal neutron capture cross section 7Be(n, γ)8Be*(18.9) → 8Be*(16.6 + 16.9) + γ, provides a rough estimate of the isospin impurity of 8Be*(18.9): σp,γ/σn,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 Ep = 2.25 MeV is ascribed to a Jπ = 3+, T = (1), l = 1 resonance with Γn ≈ Γp and γn2/γp2 = 3 to 10: see (1966LA04). At higher energies the broad peak in the n0 yield at Ep = 4.9 MeV can be fitted by Jπ = 3(+) with Γ = 1.1 MeV, γn2 ≈ γp2. The behavior of the n1 cross section can be fitted by assuming a 1- state at Ex = 19.5 MeV and a J = 0, 1, 2, positive-parity state at 19.9 MeV [presumably the 20.1 - 20.2 MeV states reported in reaction 4]. In addition the broad dip at Ep ≈ 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 [7Be*(0, 0.43)] decreases inversely with Ep in the range 60.1 to 480.0 MeV (1984DA22) [note: the values of σt supersede those reported earlier in (1979AJ01)]. The transverse polarization transfer, DNN (0°), for the ground-state transition has been measured at Epol. p = 160 MeV (1984TA07). See also (1986MC09; Epol. p = 800 MeV) and references cited in (1988AJ01).
Absolute differential cross sections for elastic scattering have been reported for Ep = 0.4 to 12 MeV and at 14.5, 20.0 and 31.5 MeV. The yields of inelastically scattered protons (to 7Li*(0.48)) and of 0.48 MeV γ-rays have been measured for Ep = 0.8 to 12 MeV: see (1974AJ01). Polarization measurements have been reported at a number of energies in the range Ep = 0.67 MeV to 2.1 GeV/c [see (1974AJ01, 1979AJ01, 1984AJ01)], at Ep = 1.89 to 2.59 MeV (1986SA1P; p0) and at 65 MeV (1987TO06; continuum). See also (1983GLZZ).
Anomalies in the elastic scattering appear at Ep = 0.44, 1.03, 1.88, 2.1, 2.5, 4.2 and 5.6 MeV. Resonances at Ep = 1.03, 3 and 5.5 MeV and an anomaly at Ep = 1.88 MeV appear in the inelastic channel. A phase-shift analysis and a review of the cross-section data show that the 0.44 and 1.03 MeV resonances are due to 1+ states which are a mixture of 5P1 and 3P1 with a mixing parameter of +25°; that the 2- state at the neutron threshold (Ep = 1.88 MeV) has a width of about 50 keV [see also reaction 14]; and that the Ep = 2.05 MeV resonance corresponds to a 3+ state. The anomalous behavior of the 5P3 phase around Ep = 2.2 MeV appears to result from the coupling of the two 3+ states [resonances at Ep = 2.05 and 2.25 MeV]. The 3S1 phase begins to turn positive after 2.2 MeV suggesting a 1- state at Ep = 2.5 MeV: see 8.13 (in PDF or PS). The polarization data show structures at Ep = 1.9 and 2.3 MeV. A phase-shift analysis of the (p, p) data finds no indication of a possible 1- state with 17.4 < Ex < 18.5 MeV [see, however, reaction 15 in (1979AJ01)].
An attempt has been made to observe the T = 2 state [8Be*(27.47)] in the p0, p1 and p2 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 Γp0/Γ.
The proton total reaction cross section has been reported for Ep = 25.1 to 48.1 MeV by (1985CA36). (1987CH33, 1987PO03) have studied p - 7Li correlations involving 8Be*(17.64, 18.15, 18.9 + 19.1 + 19.2). Elastic proton scattering on 7Li was measured near the (p, n) threshold, Ecm = 1.2 - 2.4 MeV (1988GU10). Parameters for observed near-threshold resonances are in 8.13 (in PDF or PS). See also (1994DE09) for comments on model dependences for deduced widths. See also 7Li in (2002TI10) and references cited in (1988AJ01).
Angular distributions were measured for 7Li(p, d) at Ep = 18.6 MeV (1987GO27); neutron spectroscopic factors were deduced, via DWBA analysis, for deuterons corresponding to the 6Li ground state and first excited state. The excitation function for d0 measured for Ep = 11.64 to 11.76 MeV does not show any effect from the T = 2 state [8Be*(27.47)]: see (1979AJ01). See also (1984BA1T).
The cross section increases from (4.3 ± 0.9) × 10-5 mb at Ep = 28.1 keV to 6.33 mb at 998 keV. Astrophysical S-factors 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 2H(7Li, 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 Ep = 10 keV - 62.5 MeV: see (1979AJ01, 1984AJ01), Ep = 20 - 250 keV (1989HA14), and Ecm = 10 - 1450 keV (1992EN01, 1992EN04). Polarization measurements have been carried out for Ep = 0.8 to 22 MeV: see (1974AJ01), Ep = 9 - 22 MeV (1992TA21). In the range Ep = 23 keV to 62.5 MeV: see (1979AJ01, 1984AJ01). Polarization measurements have been carried out for Ep = 0.8 to 10.6 MeV [see (1974AJ01)]: in the range Ep = 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 Ep = 8.5 to 10 MeV. Above 10 MeV the asymmetry begins to decrease slowly.
Broad resonances are reported to occur at Ep = 3.0 MeV [Γ ≈ 1 MeV] and at ≈ 5.7 MeV [Γ ≈ 1 MeV]. Structures are also reported at Ep = 6.8 MeV and at Ep = 9.0 MeV: see (1979AJ01). The 9.0 MeV resonance is also reflected in the behavior of the A2 coefficient. The experimental data on yields and on polarizations appear to require including two 0+ states [at Ex ≈ 19.7 and 21.8 MeV] with very small α-particle widths, and four 2+ states [at Ex ≈ 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 Ep = 11.64 to 11.76 MeV the excitation function does not show any effect due to the T = 2 state at Ex = 27.47 MeV. See (1979AJ01) for references.
The population of 8Be*(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 8Be*(3.0) see (in PDF or PS) 8.4 in (1974AJ01). Angular distributions were measured for 7Li(d, n) at Ed = 0.7 - 2.3 and 5.6 - 12.1 MeV and excitation functions were reported for neutrons corresponding to 8Be*(0 + 3.0, 16.6 + 16.9, 17.6, 18.15) (1996BO27). The 8Be*(11.4) level is not observed. Angular distributions of n0 and n1 have been reported at Ed = 0.7 to 3.0 MeV and at Ed = 15.25 MeV [see (1974AJ01, 1979AJ01)], at 0.19 MeV (1983DA32, 1987DA25) and at 0.40 and 0.46 MeV (1984GA07; n0 only). The angular distributions of the neutrons to 8Be*(16.6, 17.6, 18.2) are fit by lp = 1: see (1974AJ01). At Ecm = 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 Ed = 2.85 to 14.97 MeV proceeds almost entirely through the excitation and sequential decay of 8Be*(16.6, 16.9) (1987WA21). See also (1988AJ01). At Ed = 19.7 MeV, 8Be*(11.4) was observed at Ex = 11.3 ± 0.2 MeV with Γ = 3.7 ± 0.2 MeV (1995AR25). At Ed = 7 MeV, population of the two T = 0 levels at 20.1, 2+ and 20.2, 0+ is reported with widths Γ20.1 = 0.85 ± 0.25 MeV and Γ20.2 = 0.75 ± 0.25 MeV (1991AR18), and Γ20.1 = 0.90 ± 0.20 MeV and Γ20.2 = 0.70 ± 0.20 MeV (1992DA22). A complete kinematics measurement of d3σ/(dΩθdΨdE12) at Ed = 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 7Li + p configuration of that state (1999GO15). See (2001LA35, 2003PI13, 2003SP02), and reaction 18 for measurements at Ep = 19 - 21 MeV that are evaluated in the "Trojan Horse" method to obtain information on the astrophysical 7Li(p, α) rate. See also (2000HA50) for fusion applications. See also 9Be.
Deuteron groups are observed to 8Be*(0, 3.0, 16.6, 16.9, 17.6, 18.2). For the Jπ = 2+ isospin mixed states see 8.11 (in PDF or PS). Angular distributions have been measured for E(3He) = 390 - 1130 keV (2003FR22), for E(3He) = 0.9 to 24.3 MeV and at E(pol. 3He) = 33.3 MeV: see (1974AJ01, 1979AJ01, 1984AJ01). Reaction (b) has been studied at E(3He) = 5.0 MeV (1985DA29) and at 9, 11 and 12 MeV (1986ZA09). 8Be*(0, 3.0) are reported to be involved (1985DA29). Implications of this reaction for destroying 7Li and 7Be in astrophysical environments is discussed in (2003FR22). See also 10B.
Angular distributions have been measured to Eα = 50 MeV: see (1974AJ01, 1979AJ01, 1988AJ01). The ground state of 8Be decays isotropically in the cm system: Jπ = 0+. Sequential decay (reaction (b)) is reported at Eα = 50 MeV via 8Be*(0, 3.0, 11.4, 16.6, 16.9, 19.9): see (1974AJ01). See also (1992KO26).
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 7Li*(0, 0.48) are 38400 ± 800 and 420 ± 120 b, respectively. A departure from a 1/v shape in σt is observed for En > 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 7Li in the Big Bang by as much as 20% (1988AJ01): see also (1998FI02). Results from a R-matrix analysis of reaction (a) over the range from Ecm = 10-8 - 9.0 MeV (2003AD05) are summarized in 8.14 (in PDF or PS). In their analysis, 8Be*(19.07) and 8Be*(19.24) are treated as a single resonance. A different R-matrix analysis (1988KO03) found a T = 1 impurity of ≈ 24% and Γ = 122 keV for the 2- 8Be*(18.9) state. The approach of (1988KO03) defines the resonance energy and width as a pole of the S-matrix on the so-called 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).
8Li decays mainly to the broad 3.0 MeV, 2+ level of 8Be, which decays into two α-particles. Both the β-spectrum and the resulting α-spectrum have been extensively studied: see (1955AJ61, 1966LA04). See also 8B(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 8Li] and that the ground state of 8Li has Jπ = 2+: see (1980MC07). Detailed calculations are necessary to obtain the log ft values for decay to 8Be*(3.0); values in the literature are: log ft = 5.37 (1986WA01), log ft = 5.72 (1989BA31).
The data of (1971WI05) for 8Li and 8B β-decay have been analyzed extensively (1986WA01, 1989BA31, 2002BH03). In (1986WA01) a many-level one-channel approximation R-matrix analysis of the β-delayed α particle spectra in the decay of both 8Li and 8B [as well as of the L = 2 α - α phase shifts] found that there was no need to introduce "intruder" states below Ex ≈ 26 MeV of 8Be in order to explain the data [see, e.g. (1969BA43, 1974AJ01, 1976BA67, 1979AJ01)]. Warburton extracted the GT matrix elements, for the decay to 8Be*(3.0) and the doublet near 16 MeV, and pointed out the difficulties in extracting meaningful Ex, Γ and log ft values from β± decay to the broad 8Be*(3.0) state. On the other hand, the R-matrix analysis of Barker (1989BA31) requires a broad 2+ intruder state at ≈ 9 MeV. See (1998FA05, 2000BA89, 2001CA50) for further comments on intruder states in 8Be.
Beta-α angular correlations have been measured for the decays of 8Li and 8B for the entire final-state distribution: see 8.10 (in PDF or PS) in (1979AJ01). (1980MC07) have measured β - α correlations as a function of Ex in the decay of 8Li and 8B; by detecting the β and both α particles involved in the 8Be decay, the β - ν - α correlations were determined. They find that the decay is GT for 2 < Ex < 8 MeV. The absence of Fermi decay strength is expected because the isovector contributions from the tails of 8Be*(16.6, 16.9) interfere destructively in this energy region: see (1980MC07). The measurement of the β-decay asymmetry as a function of Eβ is reported by (1985BIZZ, 1986BI1D. (1986NAZZ) have measured the β-spectrum and compared it with the spectrum predicted from the α-breakup data. See also references cited in (1988AJ01).
Angular distributions of 8Be from 1H(8Li, 8Be) were measured at Ecm = 1.5 MeV (1993CA04). The 8Beg.s. was reconstructed by detecting the coincident α particles and the data were transformed to represent the inverse kinematics 8Li(p, n) reaction. The observed cross section, σtot = 21 ± 2(stat.) ± 4.2(norm.) mb, was 2 times smaller than estimates based on a Hauser-Feshbach calculation and indicates that 8Li(p, n) does not contribute significantly to 8Li burning in nucleosynthesis. See also (2003IS12).
A dynamic semi-microscopic model study of 8Be(γ, p) considered dipole-dipole and quadrupole-quadrupole forces on the properties of Giant Dipole Resonances built on the ground state and first excited state of 8Be (1995GO21). See also reaction 14 here.
The decay [see reaction 1 in 8B] proceeds mainly to 8Be*(3.0). Detailed study of the high-energy portion of the α-spectrum reveals a maximum near Eα = 8.3 MeV, corresponding to transitions to 8Be*(16.63), for which parameters Ex = 16.67 MeV, Γ = 150 to 190 keV or Ex = 16.62 MeV, Γ = 95 keV are derived: see (1974AJ01). Analyses (1986WA01, 1989BA31) of the β± delayed α-spectra following 8B and 8Li decay are described in reaction 24. The analysis of (1989BA31) requires a 2+ intruder state in 8Be at Ex ≈ 9 MeV, while the analysis of (1986WA01) excludes intruder states below Ex = 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 8Be*(3.0) log ft = 5.6 (1974AJ01), log ft = 5.77 (1989BA31); for decay to 8Be*(16.63) log ft = 3.3 (1969BA43, 1979AJ01).
The β+ spectrum has been measured by (1987NA08) and by (2000OR04): see reaction 1 in 8B. 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 8B β-decay. See also (1994DE30).
Neutron groups to 8Be*(0, 3.0) have been studied for Eγ = 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 θlab = 90° photo-neutron emission excitation function (1989VA18). 9Be levels at Ex = 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 high-quality nearly mono-energetic γ-rays (2001UT01, 2001UT03, 2002SU19, 2003UT02); B(E1) and B(M1) values are deduced in (2001UT01, 2002IT07, 2002SU19). A measurement from neutron threshold to Eγ ≈ 20 MeV indicated that 8Be 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. γ-rays with Eγ = 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 9Be*(1.684) Jπ = 1/2+ resonance is presented in (2001ME11). A multicluster-model study of 9Be photodisintegration (1998EF05) and an R-matrix analysis of the situation (2000BA21) address discrepancies in the low-energy cross section measurements. See also (1994KA25; theor.) for 9Be Coulomb dissociation. Neutrons from 9Be(γ, n) were used to estimate the number of hard X-rays (with Eγ > 1.67 MeV) that are produced in the plasma that results from impinging a 5 × 108 W/cm2 laser on a Ta foil (2001SC12). See (1974AJ01, 1979AJ01) and 9Be.
Reaction (c) appears to proceed largely via excited states of 9Be with subsequent decay mainly to 8Be*(3.0): see (1966LA04, 1974AJ01), and 9Be and 10Be here. Neutrons from 9Be(n, 2n) for En < 10.3 MeV were analyzed to determine the neutron-neutron scattering length ann = -16.5 ± 1.0 fm (1990BO43). Measurements of 9Be(n, 2n) for En < 12 MeV were made to assess the possibility of using 9Be 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 reaction (a) angular distributions of deuteron groups have been reported at Ep = 0.11 to 185 MeV [see (1974AJ01, 1979AJ01, 1984AJ01)] and at 18.6 MeV (1986GO23, 1987GO27; d0 and d1) and 50 and 72 MeV (1984ZA07; to 8Be*(0, 3.0, 16.9, 19.2)). Angular distributions of cross sections and analyzing powers were measured for deuterons from 9Be(pol. p, d) at Epol. p = 60 MeV. Analyzing powers for deuterons corresponding to 8Be*(3.04, 11.4, 16.92, 19.24) were presented while peaks corresponding to 8Be 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 8Be*(0, 3.0, 16.9, 17.6, 18.2, 19.1) are consistent with ln = 1: see (1974AJ01). Neutron spectroscopic factors for n + 8Beg.s. and n + 8Be*(3.04) were extracted from a DWBA analysis of 9Be(p, d) at Ep = 18.6 MeV (1987GO27), and spectroscopic factors for n + 8Be*(0, 3.04, 16.626, 16.922, 17.640, 18.15, 19.07) were extracted from 9Be(p, d) at 33.6 MeV (1991AB04): see 9B. For other spectroscopic factor measurements see (1979AJ01, 1984ZA07).
An anomalous group is reported in the deuteron spectra between the d0 and the d1 groups. At Ep = 26.2 MeV, Ex = 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 Breit-Wigner tail of the Jπ = 0+ 8Beg.s.: it contains < 10% of the ground-state transfer strength. An analysis of reported Γcm widths for 8Be*(3.0) in this reaction shows that there is no Ep dependence. The average Γcm at Ep = 14.3 and 26.2 MeV is 1.47 ± 0.04 MeV. Γcm = 5.5 ± 1.3 eV for 8Beg.s. and 5.2 ± 0.1 MeV for 8Be*(11.4). Spectroscopic factors for 8Beg.s. (including the "ghost" anomaly) and 8Be*(3.0) are 1.23 and 0.22 respectively at Ep = 14.3 MeV, and 1.53 and 1.02 respectively at Ep = 26.2 MeV. The width of 8Be*(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: Eres = 3130 ± 25 keV (resonance energy in the α + α cm system) [Ex = 3038 ± 25 keV] and Γcm = 1.50 ± 0.02 MeV for 8Be*(3.0): the corresponding observed and formal reaction widths and channel radii are γres2 = 580 ± 50 keV, γλ2 = 680 ± 100 keV and rc = 4.8 fm. A study of the continuum part of the inclusive deuteron spectra is reported at Epol. p = 60 MeV (1987KA25). See (1979AJ01, 1984AJ01) for the earlier work.
The effects of electron screening were studied at around Ep = 16 - 390 keV. A direct-plus resonance model fit to the data result in the values of Eres = 336 ± 3 keV and Γlab = 205 ± 6 keV for 10B*(6.87) and Γα = 68 ± 2 keV and Γd = 90 ± 4 keV (1997ZA06). See also (2002BA77). At Ep = 77 - 321 keV, angular distributions and analyzing powers of deuterons were measured; an R-matrix evaluation of the data indicated that a direct-reaction model can adequately account for the observations (1998BR10) indicating that the sub-threshold state in 10B at Ex = 6.57 MeV does not contribute. An R-matrix analysis of 10B levels populated for Ep < 700 keV is reported in (2001BA47).
Reaction (b) has been studied at Ep = 45 and 47 MeV: the reaction primarily populates 8Be*(0, 3.0). At Ep = 70 MeV data were evaluated using a DWTA (T-matrix) approach to decompose the 1s and 1p shell contributions in the quasielastic knockout of neutrons (2000SH01). See (1979AJ01), and 9Be, 9B here. For work at Ep = 1 GeV see (1985BE30, 1985DO16). For reaction (c) [FSI through 8Be*(0, 3.0)] see (1974AJ01, 1984AJ01). See also (1992KO26; theor.) and 10B.
At astrophysically-relevant energies, Ecm = 57 - 139 keV, 9Be(d, t0) angular distributions and total cross sections were measured and are compared with DWBA calculations (1997YA02). At Ed = 8 - 50 MeV, angular distributions of t0 and t1 are evaluated in a DWBA analysis and vertex constants, |G|2, and neutron spectroscopic factors are deduced (1995GU22). Angular distributions of t0 were measured at Ed = 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 11B were observed in measurements of the excitation function and angular distribution for tritons from 9Be(d, t0) at Ed = 0.9 - 11.2 MeV (1994AB25) and Ed = 3 - 11 MeV (1995AB41, 2000GE16). A review of the 9Be(d, t0) excitation function for Ed = 237 keV to 11 MeV is given in (2000GE16). Angular distributions have been measured at Ed = 0.3 to 28 MeV [see (1979AJ01)], at Ed = 18 MeV (1988GO02; t0, t1) and at Epol. d = 2.0 to 2.8 MeV (1984AN16; t0). At Ed = 28 MeV angular distributions of triton groups to 8Be*(16.6, 16.9, 17.6, 18.2, 19.1, 19.2, 19.8) have been analyzed using DWUCK: absolute C2S 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 8Be*(17.6, 18.2): see (1979AJ01).
At Ed = 7 MeV a complete kinematics measurement of 9Be(d, t + 8Be) observed states participating in the sequential decay of 8Be (1991SZ06). The relative energy spectrum was reconstructed and yielded peaks corresponding to the ground state, Ex ≈ 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 single-level R-matrix formalism, best fit with rc = 4.5 ± 0.1 fm, indicates that the "ghost anomaly" structure at ≈ 0.6 MeV is the result of deformation in the high-energy tail of the 8Be ground state. While the cross section corresponding to the first excited state peaks at 3.00 MeV, the R-matrix fit indicates that the resonance energy is 3.12 ± 0.01 MeV (Ex = 3.03 ± 0.01 MeV) with Γres = 1.43 ± 0.06 MeV (1991SZ06). A kinematically complete study of reaction (b) at Ed = 26.3 MeV indicates the involvement of 8Be*(0, 3.0, 11.4, 16.9, 19.9 + 20.1): see (1974AJ01).
Angular distributions have been measured in the range E(3He) = 3.0 to 26.7 MeV and at E(pol. 3He) = 33.3 MeV (to 8Be*(16.9, 17.6, 19.2)) [S = 1.74, 0.72, 1.17, assuming mixed isospin for 8Be*(16.9)]. The possibility of a broad state at Ex ≈ 25 MeV is also suggested: see (1979AJ01). See also (1987VA1I).
Reaction (b) has been studied at E(3He) = 1.0 to 10 MeV [see (1979AJ01, 1984AJ01)], at E(3He) = 3 to 12 MeV (1986LA26) and at 11.9 to 24.0 MeV (1987WA25). The reaction is reported to proceed via 8Be*(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 8Be*(11.4) see (1987WA25). Angular distributions for 9Be(3He, α) were evaluated to determine the contributions from neutron pickup vs. heavy particle stripping; 9Be spectroscopic factors for Sn and Sα were calculated (1997ZH40). See also (1992KO26; theor.). See also 9Be here, 12C 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 9Be-actinide radioactive sources.
Angular distributions have been studied at E(6Li) = 32 MeV involving 8Be*(0, 3.0) and 7Li*(0, 0.48) (1985CO09). For reaction (b) see (1984KO25). For reaction (c) measurements at E(9Be) = 48 MeV were evaluated with a CCBA model; 8Be*(3.04, 11.3) played an important role in the reaction (2003AS04). Also see 10Be and (1985JA09). For the earlier work see (1979AJ01).
Optical model parameters for 8Be + 13C were deduced from 9Be(12C, 13C)8Be for E(12C) = 65 MeV. For 9Be + 12C and 8Be + 13C, energy-dependent optical model parameters are given for Ecm = 5 - 50 MeV (1999RU10).
The angular distribution for the transition to the first T = 2 state 8Be*(27.49) is very similar to the measured 10Be(p, 3He) angular distribution that is measured for population of the analog state, 8Li*(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 10B and 11B were measured at Eπ+ = 0, 100, 140 and 180 MeV, corresponding cross sections were σ[10B(π+, 2p)] = 8, 18, 17, 17 mb and σ[11B(π+, 2pn)] = 0.18, 0.80, 2.0, 3.4 mb, respectively (1992RA11).
Angular distributions were measured for 10B(K+, K+d) at EK+ = 130 - 268 MeV. A DWIA analysis indicated that direct knock-out and 2-step mechanisms are important (1991BE42).
Bremsstrahlung photons were used to measure the 10B(γ, pn) reaction at Eγ = 66 - 103 MeV in a study of two-body photon absorption and final state interactions (1988SU14).
The breakup of 10B by 14.4 MeV neutrons involves, among others, 8Beg.s. (1984TU02). The cross section of 10B(n, t)2α, for thermal neutrons is reported as σthermal = 7 ± 2 mb (1987KA32). See also (1979AJ01) and 11B in (1990AJ01).
Angular distributions of the 3He ions to 8Be*(0, 3.0, 16.6, 16.9) have been studied at Ep = 39.4 MeV [see (1974AJ01)] and at Ep = 51.9 MeV (1983YA05; see for a discussion of isospin mixing of the 16.8 MeV states).
Angular distributions have been reported at Ed = 0.5 to 7.5 MeV: see (1974AJ01, 1979AJ01). At Ed = 67 - 141 keV, angular distributions of α0 and α1 were measured and the 10B(d, α0) and 10B(d, α1) astrophysical S-factors were deduced (1997YA02). The angular-dependent cross sections for α0, α1 and 3α processes were measured for Ed = 120 - 340 keV and in each case the S-factor was observed to increase with decreasing energy (2001HO22). Yield ratios for 10B(d, p)/10B(d, α) were measured at Ed = 58 - 142 keV (1993CE02). At Ed = 7.5 MeV the population of 8Be*(16.63, 16.92) is closely the same, consistent with their mixed isospin character while 8Be*(17.64) is relatively weak consistent with its nearly pure T = 1 character. 8Be*(16.63, 16.92, 17.64, 18.15) have been studied for Ed = 4.0 to 12.0 MeV. Interference between the 2+ states 8Be*(16.63, 16.92) varies as a function of energy. The cross-section ratios for formation of 8Be*(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 Ex the 3+ state at Ex = 19.2 MeV is observed, the neighboring 3+ state at Ex = 19.07 MeV is not seen. Γ16.6 = 90 ± 5 keV, Γ16.9 = 70 ± 5 keV, ΔQ = 290 ± 7 keV: see 8.11 (in PDF or PS) and (1979AJ01). Relative widths of 8Be levels at 19.86 and 20.1 MeV, Γα/Γp = 2.3 ± 0.5 and Γα/Γp = 4.5 ± 0.6 respectively, were determined by a complete kinematics measurement of 10B(d, 2α) and 10B(d, 7Li + p) at Ed = 13.6 MeV (1992PU06). At Ed = 48 MeV evidence was observed for an 8Be state at Ex = 32 MeV with Γ = 1 MeV (1993PA31); levels were also seen at 8Be*(0, 3.0, 11.4, 16.6[u], 16.9[u], 17.6, ≈ 19, ≈ 20, 21.5, 22.2, 24, 25.2).
At Ed = 4.2 to 6.6 MeV measurements were carried out by detecting α coincidences in a kinematical star configuration (1992BO1H). 12C 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 8Be*(11.4) state, was intended to stimulate activity in 3-body interactions by invoking an alternative approach.
Reaction (b) [Ed < 5 MeV] takes place mainly by a sequential process involving 8Be*(0, 2.9, 11.4, 16.6, 16.9): see (1979AJ01). See also (1983DA11) [The work quoted in (1984AJ01) has not been published.] At Ed = 13.6 MeV in addition to 8Be*(16.6, 16.9), states with Ex ≈ 19.9 - 20.2 MeV with Γ ≈ 0.7 - 1.1 MeV are involved (1988KA1K). See also (1992KO26).
Angular distributions for the 8Be*(0, 3.0) are reported in a measurement of 10B(α, 6Li) at Eα = 27.2 MeV (1995FA21); it was deduced that direct processes are dominant in the reactions. See reaction 40 in (1984AJ01) and 6Li in (2002TI10).
Angular distributions have been measured at Ep = 0.04 to 45 MeV [see (1974AJ01, 1979AJ01, 1984AJ01)]. The α0 and α1 excitation functions and astrophysical reaction rates have been determined by measuring angular dependent differential cross sections and total cross sections at Ecm = 0.12 - 1.10 MeV (1987BE17), at Ep = 4.5 to 7.5 MeV (1983BO19), at Ep = 40 - 180 keV (1992CE02), at Ecm = 17 - 134 keV (1993AN06), at 1.7 - 2.7 MeV (1998MA54), and at Ep = 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 α0 and α1 particles were measured around the 12C*(16.1) resonance at Ep = 163 keV; Ecm = 148.3 ± 0.1 keV and Γ = 5.3 ± 0.2 keV were deduced (1987BE17). The 12C*(16.57) resonance was evaluated in (p, α) data and resonance parameters of Eres = 596 ± 30 keV and Γ = 383 ± 40 keV were deduced (1993AN06).
Reaction (b) has been studied for Ep = 0.15 to 20 MeV: see (1974AJ01, 1984AJ01). The reaction proceeds predominantly by sequential two-body decay via 8Be*(0, 3.0). See also 12C in (1990AJ01), and (1992KO26).
Reaction (c) was measured at Ep = 2 - 5.5 MeV by (1995BO35). A re-construction of the 2α relative energy spectrum was analyzed to evaluate parameters for 8Be*(3.0).
A DWIA calculation of 12C(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 Eπ+ = 30 - 135 MeV (2000GI07).
The first two of these reactions involve 8Be*(0, 3.0): see (1974AJ01, 1979AJ01, 1984AJ01) and (1985AJ01). For reaction (a), see (1986AN22). For reaction (b) α-spectroscopic factors in 12C for α + 8Be*(0, 3.0) are deduced in (1995NE11, 1997SA04, 1998YO09). The α-cluster 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 [iT11(θ), T20(θ), T21(θ) and T22(θ)] are reported for 12C(pol. d, 6Li)8Beg.s. at 18 and 22 MeV (1987TA07). DWBA analysis is used to evaluate α-spectroscopic factors from 12C(d, 6Li) at Ed = 41 MeV (1988RA20) and at Ed = 15 - 55 MeV (1988RA27). Angular distributions have been studied at Ed = 12.7 to 54.3 MeV [see (1974AJ01, 1979AJ01, 1984AJ01)] and at Epol. d = 18 and 22 MeV (1986YA12; to 8Beg.s.) and 51.7 MeV (1986YA12; to 8Be*(0, 3.0, 11.4) as well as at Ed = 50 MeV (1987GO1S), 54.2 MeV (1984UM04; FRDWBA) [Sα = 0.48, 0.51 and 0.82 for 8Be*(0, 3.0, 11.4)] and 78.0 MeV (1986JA14; to 8Be*(0, 3.0, 16.6, 16.9)). See also (1985GO1G; Ed = 50 MeV). For reaction (b) see (1984AJ01). See also (1984NE1A) and references cited in (1988AJ01).
Angular distributions have been obtained at E(3He) = 25.5 to 70 MeV [see (1979AJ01, 1984AJ01)] and at E(pol. 3He) = 33.4 MeV (1986CL1B; 8Beg.s.; also Ay). 8Be*(0, 3.0, 11.4, 16.6, 16.9, 17.6) have been populated.
These reactions have been studied at Eα to 104 MeV [see (1979AJ01, 1984AJ01) and 12C in (1985AJ01)] and at 31.2 MeV (1986XI1A; reaction (a)): 8Be*(0, 3.0, 11.4) are populated. See also references cited in (1988AJ01). Alpha spectroscopic factors 8Be*(0, 3.0) were measured by (α, 2α) knockout at 200 MeV (1999ST06) and 580 MeV (1999NA05). α-particle angular correlations were measured from the 12C* → α + 8Be decay to determine the polarization characteristics of the 12C*(9.64; 3-) state, which was excited by 12C(α, α')12C*(9.64) → α + 8Be (1989KO55).
For reaction (a) 12C(12C, 16O) was measured in a study of 24Mg excited states near 33 MeV at E(12C) = 27 - 36 MeV (1995AL25, 1996AL03, 1997SZ01). See also 16O in (1993TI07) and references cited in (1988AJ01). For reaction (b) see reaction 18 in 20Ne in (1987AJ02), (1985MU14) and (1988AL07; location of a 10+ state in 20Ne at Ex ≈ 27.5 MeV). Evidence for 11 states in 24Mg with excitation energy between 22 and 30 MeV is seen in reaction (c) at E(20Ne) = 110 and 160 MeV (2001FR03). For reaction (d) see (1987SI06). States in 28Si at Ex = 28.0 MeV [Jπ = 13-], 29.8 MeV [(11)], 33.4 MeV [8+(10+)] and 34.5 MeV [(12, 14)+] are observed in reaction (e) at E(24Mg) = 170 MeV (2001SH08).
See 7Li in (2002TI10).
See 14C in (1986AJ01).
See 7Li in (2002TI10).
The 16O(γ, 4α) reaction was studied with bremsstrahlung γ rays up to Eγ = 300 MeV (1995GO10). Evidence in the energy reconstruction spectra indicates that participation of the 8Be*(0, 3.0) states increases with increasing γ-ray energy.
See (1986VD04; Ep = 50 MeV).
Sequential-decay neutron spectroscopy of 7Be + n products from natAg + 14N at 35 MeV/A indicates the participation of 8Be*(19.24) with 19.234 ± 0.012 MeV and Γ = 210 ± 35 keV (1989HE24).