(See Energy Level Diagrams for 8Be)
Cluster and α-particle models: (1977WU1A, 1979GO24, 1979GR1F, 1979PA22, 1979ZH1C, 1980FU1G, 1980HA1M, 1980IK1B, 1981GA1J, 1981KA1P, 1981KN12, 1981KR1J, 1981ST22, 1982HA1M, 1982TS1A, 1982VA11, 1983KA1K, 1983RO1G).
Special states: (1978CA1D, 1978LA1D, 1978RA1B, 1979AR03, 1979GA1E, 1979HA1E, 1979IN07, 1979KA40, 1980KA28, 1980OK01, 1981BA2P, 1981BO1Y, 1981GA1G, 1981GA1J, 1981KU1H, 1981RA06, 1981SE06, 1981ST22, 1982BI09, 1982FI13, 1982HA1M, 1982OR03, 1983AR07, 1983JO03).
Complex reactions involving 8Be: (1978BE1G, 1978GU16, 1978VO1A, 1979BE1M, 1979BO22, 1979GE05, 1979HA1E, 1979SI09, 1981BL1G, 1981CH18, 1981GU1B, 1981GU1E, 1981WO1A, 1982GU1E, 1982GU1K, 1982KO17, 1982SH01).
Reactions involving pions and other mesons: (1978GI14).
Other topics: (1978FI1C, 1978LA1D, 1978RO17, 1978UL02, 1979AR03, 1979BE1H, 1979EL04, 1979GO24, 1979KA40, 1979KA43, 1979VA1A, 1980AM1B, 1980FI09, 1981BA2P, 1981CA1H, 1981KU1H, 1981SE06, 1981SU1D, 1982BE17, 1982BO01, 1982DE1N, 1982NG01, 1982VA1C, 1983AG1C, 1983AR07, 1983BA2F, 1983FI1J, 1983JO03).
Ground-state properties of 8Be: (1978FI1C, 1978OV1A, 1978RO17, 1978SM02, 1978UL02, 1979IN07, 1979KA40, 1979PA22, 1981AV02, 1981CH18, 1981ST22, 1982BO01, 1982FI13, 1982HA1M, 1982NG01, 1982TS1A, 1982ZE1A, 1983AR07).
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. An angular correlation measurement at the resonances corresponding to 8Be*(16.6 + 16.9) [2+; T = 0 + 1] gives δ = 0.19 ± 0.03, γγ(M1) = 6.4 ± 0.5 eV [weighted mean of the two published measurements listed in (1979AJ01)]. See also (1982NA1L). On the basis of these results there is no evidence for violation of CVC or for the existence of SCC. The Ex of 8Be*(3.0) is determined in this reaction to be 3.18 ± 0.05 MeV [see also Table 8.4 (in PDF or PS) in (1974AJ01)]. For all references see (1979AJ01). See also (1979AL1F).
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 Table 8.5 (in PDF or PS). Cross sections for p0+1 are also reported at Eα = 60.2, 92.4 and 140.0 MeV [see (1979AJ01)] and at Eα = 37.5 to 43.0 MeV (1982SL01; p0, p1). The cross section for reaction (c) has been measured at three energies in the range Eα = 46.7 to 49.5 MeV: see (1979AJ01).
The production of 6Li, 7Li and 7Be [and 6He] has been studied for Eα = 61.5 to 158.2 MeV by (1982GL01). The production of 7Li (via reactions (a) and (b)) in the interaction of cosmic rays with the interstellar medium is discussed: it appears that the cross section is too small to account for the observed 7Li abundance and it is suggested that the "missing" 7Li was produced in the Big Bang, thus supporting the theory of an open universe (1978GL03, 1982GL01). Inclusive proton and deuteron spectra have been measured at Eα = 110, 130, 158 and 172 MeV (1981PA15). A study of the (α, αp) reaction at Eα = 119 MeV is reported by (1981KA1V) [see for excited states of 4He]. See also (1979AL1F), (1979RA1C; astrophysics) and (1978SL02).
The αα scattering reveals the ground state as a resonance with Q0 = 92.12 ± 0.05 keV, γc.m. = 6.8 ± 1.7 eV, [τ = (0.97 ± 0.24) x 10-16 sec]. 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 resonance at Eα = 6 MeV (Ex = 3.18 MeV, γ = 1.5 MeV, Jπ = 2+): see Table 8.4 (in PDF or PS) in (1974AJ01). 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 Table 8.6 (in PDF or PS)], and states with Ex = 20.2, 22.2 and 25.2 MeV. The latter has a small γα.
The l = 4 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; γc.m. ≈ 20 and ≈ 73 MeV, respectively. A resonance is not observed at the first T = 2 state, 8Be*(27.49): see Table 8.5 (in PDF or PS). See (1979AJ01) for references.
The elastic scattering has also been studied at Eα = 650 and 850 MeV [see (1979AJ01)] and at Eα = 158.2 MeV (1978NA16), as well as at 4.32 and 5.07 GeV/c (1980BE14). Total cross sections are reported at 0.87 and 2.1 GeV/c (1978JA16). Inclusive inelastic cross sections have been measured at 4.32 and 5.07 GeV/c (1981BA1Q, 1981DU08). Elastic and quasielastic cross sections are reported at 17.9 GeV/c (1980AB1C). At 31, 44, 88 and 125 GeV elastic (at the two higher energies) and inelastic collisions have been studied by (1982BE1T, 1982BE1X). For a study of excited states of 4He see (1980KA20). The bremstrahlung cross section has been measured for Eα = 9.35 to 18.7 MeV: see (1974AJ01).
See also (1978BR1A, 1978CH1C, 1981SY1A, 1982FA1B, 1982FA1F, 1982YA1A) and (1978SA24, 1978FI1D, 1978SC1B, 1978TA1A, 1979BA18, 1979DY03, 1979FE1B, 1979GH01, 1979LU1A, 1979SA08, 1979SA1E, 1980CH1R, 1980DY1A, 1980KO1M, 1980LI1K, 1980MA30, 1980RA1D, 1980RE1C, 1980SH1M, 1980SI1M, 1980TO1E, 1980VI01, 1980ZH1B, 1981DY02, 1981ER11, 1981FR1N, 1981KI03, 1981KR15, 1981LI1V, 1981SH1A, 1981SU1D, 1982AO1A, 1982AO06, 1982BA29, 1982DR1C, 1982FI16, 1982HA1M, 1982LE1G, 1982LI1G, 1982OR03, 1982SC16, 1982SH08, 1982TI1A, 1983BA1T, 1983BR1F, 1983FI1K, 1983HO1F, 1983KO14, 1983VI1D; theor.).
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 = 6962.8 ± 3.0 keV [Ex = 27495.8 ± 2.4 keV, γc.m. = 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 Table 8.5 (in PDF or PS). See also (1979AJ01). [The energy at resonance, Ed is ≈ 6965 keV, based on the new Qm.]
Yield curves and cross sections have been measured for Ed = 60 keV to 5.5 MeV and 12 to 17 MeV [see (1979AJ01)], for 48 to 170 keV (1982CE02; n1γ; deduced S(E)), for 0.4 to 1.0 MeV (1979RU07; activation) and 1.3 to 11.9 MeV (1980GU26). Polarization measurements are reported at Ed = 0.27 to 3.7 MeV. Comparisons of the populations of 7Be*(0, 0.43) and of 7Li*(0, 0.48) have been made at many energies, to Ed = 7.2 MeV. The n/p ratios are closely equal for analog states, as expected from charge symmetry. See (1979AJ01) for references. See also 7Be, (1979EL03) in reaction 10, and (1981HO1E).
Excitation functions have been measured for Ed = 30 keV to 5.4 MeV [see (1979AJ01)], for 36 to 170 keV (1981CE04; p0, p1 [from 47 keV]) and for 100 to 180 keV (1979BO33; σt). An anomaly is observed in the p1/p0 intensity ratio at Ed = 6.945 MeV, corresponding to the first 0+; T = 2 state, γ = 10 ± 3 keV, γp0 « γp1; γp0 < γd. Polarization measurements have been reported at Ed = 0.6 to 10.9 MeV: see (1979AJ01). See also 7Li, (1974FI1D), (1979EL03, 1981HO1E), (1979SE04; theor.) and reaction 10.
Cross sections and angular distributions (reaction (a)) have been measured at Ed = 30 keV to 13.6 MeV [see (1979AJ01)], at 47 to 147 keV (1981GO19; σt), at 100 to 180 keV (1979BO33; σt) and at E(6Li) = 10 to 31 MeV (1979WA02: 30° yield of α0 and α* to 4He*(20.1)[0+]). A critical analysis of the low-energy data has led to a calculation of the reaction rate parameters for thermonuclear reactions for plasma temperatures of 2 keV to 1 MeV (1978CL07). See also (1981GO19). Polarization measurements are reported at Ed = 0.4 to 11.8 MeV and at E(6Li) = 0.6 MeV [see (1979AJ01)], at E(pol. 6Li) = 0.4 and 0.6 MeV (1981UL1A; TAP), at Epol. d = 5.0 to 6.5 MeV and 8.0 to 10.0 MeV (1979RI03; VAP, TAP) and at Epol. d = 7.92 MeV (1981KA21; analyzing powers at θlab = 65°).
Pronounced variations are observed in the cross sections and in 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. See also (1979EL03). 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° show a broad peak centered at Ex ≈ 26.5 MeV (which may be due to interference effects) and suggest a resonance-like anomaly at Ex ≈ 28 MeV (1979WA02). See also the discussion in (1974AJ01). Ayy = 1 points are reported at Ed = 5.55 ± 0.12 (θc.m. = 29.7 ± 1.0°) and 8.80 ± 0.25 MeV (θc.m. = 90.0 ± 1.0°) [corresponds to Ex = 26.44 and 28.87 MeV] (1979RI03). At Ed = 6.945 MeV, the α0 yield shows an anomaly corresponding to 8Be*(27.49), the 0+; T = 2 analog of 8Heg.s.. See also (1979SO1A).
An R-matrix analysis of the very accurate differential and cross-section measurements by (1977EL09) for 6Li(d, n), (d, p) and (d, α) [Ed = 0.1 to 1.0 MeV] has been presented by (1979EL03): non-negligable direct and direct-compound interference are present in the (d, n) and (d, p) processes.
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 19] 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 (1978GE12, 1980CA13). Cross sections have been measured for reactions (b) [Ed = 117 to 772 keV] and (c) [Ed = 204 to 779 keV] (1979HO04). For reaction (d) see (1980LU1C). See also 6Li, (1974AJ01, 1979AJ01) for earlier references, (1983KU1H; applied) and (1978FI1D, 1979SE04, 1980LE07, 1981KU1B; theor.).
Angular distributions have been reported at E(3He) = 1.4 to 17 MeV [see (1974AJ01, 1979AJ01)] and in the range E(3He) = 0.46 to 1.85 MeV (1980EL02; very accurate σ(θ); to 8Be*(0, 3.0, 16.63, 16.92) and for the protons from reaction (b)) and E(pol. 6Li) = 21 MeV (1983KO04; p0). The population of 8Be*(17.64, 18.15, 19.0, 19.4, 19.9) has also been reported: see (1974AJ01).
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 Table 8.4 (in PDF or PS) in (1974AJ01), (1983GO07) and (1978ZE03, 1980ZE05, 1982BE1K, 1982BE17, 1983BE1P; 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 Table 8.6 (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.
At E(6Li) = 36 to 46 MeV sequential decay (reaction (b)) via 8Be states at Ex = 11.4, 16.9 and 19.65 MeV, with γlab = 7.8, 2.4 and 3.7 MeV [(Primarily experimental widths. I am grateful to Prof. F.C. Barker for calling this to my attention.)], and 8Be*(3.0), is reported by (1979WA13).
Reaction (c) has been studied at E(6Li) = 36 to 47 MeV: enhancements in the yield have been observed in the yield of d-d and α-α but not of α - d. These enhancements are due to double spectator poles. Their widths are smaller than predicted from the momentum distribution of α + d clusters in 6Li. The enhancements are not due to phase space, FSI, or the involvement of states in 4He, 6Li or 8Be. The strengths of the DSP peaks suggest qualitatively that quasi-free scattering is the basic mechanism producing the d-d or α-α detected pairs (1980WA10, 1981WA15). See also (1982WA07, 1983LA1J; theor.).
Cross sections and angular distributions have been reporteed from Ep = 30 keV to 18 MeV. Gamma rays are observed to the ground (γ0) and the the broad, 2+, excited state at 3.0 MeV (γ1) and to 8Be*(16.6, 16.9) (γ3, γ4). Resonances for both γ0 and γ1 occur at Ep = 0.44 and 1.03 MeV, and for γ1 alone at 2, 4.9, 6.0, 7.3, and possibly at 3.1 and 11.1 MeV. In addition broad resonances are reported at Ep ≈ 5 MeV (γ0), γ ≈ 4 - 5 MeV, and at Ep ≈ 7.3 MeV (γ1), γ ≈ 8 MeV: see Table 8.7 (in PDF or PS). The Ep ≈ 5 MeV resonance (Ex ≈ 22 MeV) represents the giant dipole resonance based on 8Be(0) 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 consistent with 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 Table 8.8 (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. Resonances for production of 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 18.9 MeV excitation. Squared T = 1 components calculated for 8Be*(16.6, 16.9) are 40 and 60%, and 95 and 5% for 8Be*(17.6, 18.2). 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 earlier references see (1979AJ01). See also (1982SC1H; applications) and (1979BA1V; theor.).
Measurements of cross sections have been reported for Ep = 1.9 to 52 MeV [see (1974AJ01, 1979AJ01)] and at 60.1 to 199.1 MeV (1982WA02; activation σ). Polarization measurements have been reported at Ep = 2.05 to 5.5 MeV, 30 and 50 MeV: see (1974AJ01).
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 is virtual relative to the threshold and that its width γ = 50 ± 20 keV. The ratio of the cross section 7Li(p, γ)8Be*(18.9) γ/→ 8Be*(16.6 + 16.9) to the thermal-neutron-capture cross section 7Be(n, γ)8Be*(18.9) γ/→ 8Be*(16.6 + 16.9), provides a rough estimate of the isospin impurity of 8Be*(18.9): σp, γ/σn, γ ≈ 1.5 x 10-5 and therefore the T = 1 isospin impurity is < 4% in intensity. See, however, (1979AJ01) and (1977BA62) who finds a 10% impurity.
The structure at Ep = 2.25 MeV is ascribed to a 3+, T = (1), l = 1 resonance with γn ≈ γp and γ2n/γ2p = 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, γ2n ≈ γ2p. 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 Table 8.9 (in PDF or PS). The total reaction cross section goes down exponentially from Ep = 23 to 199.1 MeV: see (1982WA02). See also 7Be, (1977KO46, 1980AU02, 1982AB1D), (1979AJ01, 1982TA03), and (1979CH1C, 1979DU1A; applications).
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 to 155 MeV [see (1974AJ01, 1979AJ01)] and at 2.1 GeV/c (1979ZH1A).
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 exisitng 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 a neutron threshold (Ep = 1.88 MeV) has a width of about 50 keV [see also reaction 16]; 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 postive after 2.2 MeV suggesting a 1- state at Ep = 2.5 MeV: see Table 8.10 (in PDF or PS). The polarization data show structures at Ep = 1.9 and 2.3 MeV. (1979AR10) have performed a phase-shift analysis of the (p, p) data: they find no indication of a possible 1- state with 17.4 < Ex < 18.5 MeV [see, however, reaction 15 in (1979AJ01)]. The absence of a 1- state in this Ex region indicates that the shell-model residual interaction for negative-parity, S = 0, T = 0 states of 8Be is deficient (1979AR10).
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 effects of the T = 2 state. Table 8.5 (in PDF or PS) displays the upper limit for γp0/γ. The inclusive cross section has been reported at Ep = 640 MeV (1981ER07). See also (1982AB1D), (1979AJ01) and (1979VE08, 1981BA36, 1983BA2H; theor.).
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). Poalrization measurements are reported at Ep = 200 and 400 MeV (1981LI1B) and 450 to 530 MeV (1981IR1A) [both prelim.]. See also (1979VE08; theor.).
The cross section follows the expression E-1 e-B√E(square root of E), with B = 91.5 ± 4.5 keV1/2, in the range Ep = 23 to 50 keV. The cross section in that interval rises from 0.013 to 2.4 μb. Taking into account 8Be Jπ = 2+ levels at 16.7, 16.9 and 20.6 MeV, an R-matrix fit for Ep = 131 to 561 keV leads to a quadratic energy dependence for the S-factor: S = 0.065[1 + 1.82E - 2.51E2] MeV · b, over the energy range Ep = 0 to 600 keV.
Excitation functions and angular distributions have been measured at many energies in the range Ep = 23 keV to 45.2 MeV [see (1979AJ01)] and at Ep = 47.8, 53.5, 58.5 and 62.5 MeV (1982BA1V). 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.
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 the yields and on polarization 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.
A study of the 7Li(p, α)4He* reaction to 4He*(20.1) [0+] at Ep = 4.5 to 12.0 MeV shows a broad maximum at Ex ≈ 24 MeV: see reaction 10 (1978GE12, 1980CA13). See also (1981BA1R), (1975ZI1A, 1980PE1N; astrophysics) and (1978FI1D, 1979DO19; theor.).
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 Table 8.4 (in PDF or PS) in (1974AJ01). Angular distributions of n0 and n1 have been reported at Ed = 0.7 to 3.0 MeV and at Ed = 15.25 MeV. The angular distributions of the neutrons to 8Be*(16.6, 17.6, 18.2) are fit by lp = 1: see (1974AJ01, 1979AJ01).
Reaction (b) appears to proceed primarily via 8Be*(3.0, 16.6, 16.9) and 5Heg.s.: see (1974AJ01). However, 8Be*(11.4) may also be involved [Ex = 11.4 ± 0.05 MeV, γc.m. = 2.8 ± 0.2 MeV] as many state(s) at Ex ≈ 20 MeV: see (1979AJ01). See also (1980NE1B), (1978BA1F; applied) and 9Be.
Deuteron groups are observed to 8Be*(0, 3.0, 16.6, 16.9, 17.6, 18.2). For the parameters of 8Be*(3.0) see Table 8.4 (in PDF or PS) in (1974AJ01). For the Jπ = 1+ mixed isospin states see Table 8.6 (in PDF or PS). Angular distributions have been measured for E(3He) = 0.9 to 24.3 MeV [see (1974AJ01, 1979AJ01)] and at E(pol. 3He) = 33.3 MeV (1981BA1P; to 8Be*(16.6, 17.6, 18.2)). See also 10B and (1982AR08).
Angular distributions have been measured to Eα = 50 MeV: see (1966LA04, 1974AJ01, 1979AJ01). The ground state of 8Be decays isotropically in the c.m. system: Jπ = 0+. At Eα = 10 MeV an anomaly ("ghost") is observed at Ex ≈ 0.5 MeV. 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 (1978ZE03, 1979ZE1B, 1980ZE05, 1982BE1K, 1983BE1P; theor.).
At thermal energies, the (n, p) cross section is (4.8 ± 0.9) x 104 b (1981MUZQ), the (n, α) cross section is ≤ 0.1 mb and the (n, γα) cross section is 155 mb. See also (1974AJ01) and (1983BA2H; theor.).
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 correlation 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).
Beta-α angular correlations have been measured for the decays of 8Li and 8B for the entire final-state distribution: see Table 8.10 (in PDF or PS) in (1979AJ01). No evidence was seen for second-class currents. Recently (1980MC07) have measured the β - ν - α correlations as a function of Ex in the decay of 8Li and 8B, detecting both α-particles involved in the 8Be decay. 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 results are consistent with the CVC predictions (1980MC07). See also (1978FO31), (1982BO1T) and (1979DE15, 1980OK01, 1981HO06; theor.).
The decay [see reaction 1 in 8B] proceeds mainly to 8Be*(3.0) [see Table 8.4 (in PDF or PS) in (1974AJ01) for its parameters]. 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. Log ft = 3.3. The energy distribution of the α-particles has been measured. Analysis of this data and of data from α-α scattering in a three-level R-matrix formalism indicate a 2+ state of 8Be at Ex = 12.0-3.0+3.5 MeV and γ = 14-3+4 MeV (a2 = 6.0 ± 0.5 fm): see (1974AJ01). For β+-α angular correlation studies see reaction 27. See also (1982BO1T).
Neutron groups to 8Be*(0, 3.0) have been studied for Eγ = 18 to 26 MeV: see (1974AJ01, 1979AJ01) and 9Be. Reaction (b) appears to proceed largely via excited states of 9Be with subsequent decay mainly to 8Be*(3.0): see (1966LA04, 1974AJ01), 9Be and 10Be. Reaction (c) has been studied at Ep = 45 and 47 MeV: the reaction primarily populates 8Be*(0, 3.0): see (1979AJ01), 9Be and 9B. See also (1978JE01). For reactions (d) and (e) see (1974AJ01) and 9Be. For reaction (e) see (1979AJ01).
Angular distributions are reported to 8Be*(0, 3.0, 11.4) (unresolved) at Eπ+ = 50 MeV (1980BA43).
Angular distributions of deuteron groups have been reported at Ep = 0.11 to 185 MeV [see (1974AJ01, 1979AJ01)], 14.3 and 26.2 MeV (1981BE53; d0, d1; and see below), 18.6 MeV (1983BE1D; d0) and 50 and 72 MeV (1982ZA1B; d0, d1 and d) to 8Be*(16.9 ± 17.6, 19.2). For spectroscopic factors see (1979AJ01). The angular distributions to 8Be*(0, 3.0, 16.9, 17.6, 18.2, 19.1) are consistent with ln = 1: see (1974AJ01) and (1982ZA1B). For spectroscopic factors see (1979AJ01).
An anomalous group is reported in the deuteron spectra between the d0 and the d1 groups. At Ep = 26.2 MeV, its (constant with θ) Ex = 0.6 ± 0.1 MeV. 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 g.s. transfer strength (1981BE53). See also (1981OV02). An analysis of reported γc.m. for 8Be*(3.0) in this reaction shows that there is no Ep dependence: (1981BE53) report that the average γc.m. at Ep = 14.3 and 26.2 MeV is 1.47 ± 0.04 MeV. γc.m. = 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 (1981BE53). Studies of the width of 8Be*(3.0) in this reaction and in reactions 32, 42, 47 and 51 are reported by (1981OV02): the width 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. (1981OV02) find a mean ER = 3130 ± 25 keV (resonance energy in the α + α c.m. system) [Ex = 3038 ± 25 keV] and γc.m. = 1.50 ± 0.02 MeV for 8Be*(3.0): the corresponding observed and formal reaction widths and channel radii are γ2R = 580 ± 50 keV, γ2λ = 680 ± 100 keV and s = 4.8 fm. See (1979AJ01) for the earlier work. For reaction (b) [FSI through 8Be*(0, 3.0)] see (1974AJ01) and (1982LA11; Ep = 30 MeV).
Angular distributions have been measured for Ed = 0.3 to 28 MeV: see (1979AJ01). At Ed = 27.97 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 Table 8.6 (in PDF or PS). An isospin amplitude impurity of 0.21 ± 0.03 is found for 8Be*(17.6, 18.2) (1977OO01). See also 9Be(d, 3He) [reaction 13] in 8Li. For a study of the parameters of 8Be*(3.0) see reaction 31 (1981OV02).
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 isopsin for 8Be*(16.9)]. The possibility of a broad state at Ex ≈ 25 MeV is also suggested. See (1979AJ01) and Table 8.5 (in PDF or PS) here.
Reaction (b) has been studied at E(3He) = 2.9 to 10 MeV [see (1979AJ01)] and at 1.0 to 2.8 MeV (1978AR21, 1979BA27, 1981FA02, 1981FA07). The reaction has been reported to proceed via 8Be*(0, 3.0, 11.4, 16.6, 16.9, 19.9, 22.5): see (1979AJ01) and (1978AR21, 1981FA07). In addition, observation of the quasi-free reaction process is reported by (1981FA07). See also 9Be and 12C in (1980AJ01).
Angular distributions (reactions (c) and (e)) have been studied at E(12C) = 12 and 15 MeV and E(16O) = 11, 15 and 18 MeV (1970BA49). See also (1982HU06) for reaction (c). See (1979AJ01) for earlier references.
Angular distributions for the transition to the first T = 2 state 8Be*(27.49), and to 8Li*(10.82) reached in the (p, 3He) reaction, are very similar. They are both consistent with L = 0 using a DWBA (LZR) analysis: see (1979AJ01). The particle decay of this state has been studied by (1979FR04): see Table 8.5 (in PDF or PS).
Using stopped pions, 8Be states at ≈ 3 and ≈ 19 MeV are populated. The 19 MeV structure may be due to a superposition of three peaks at 17, 19 and 22 MeV: see (1979AJ01).
At Ep = 39.4 MeV angular distribution measurements have been carried out for the 3He groups to 8Be*(0, 3.0, 16.6, 16.9): see (1974AJ01).
Angular distributions have been reported at Ed = 0.5 to 7.5 MeV: see (1974AJ01, 1979AJ01). 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 only 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 Table 8.6 (in PDF or PS).
In reaction (b) at Ed = 13.6 MeV sequential decay is indicated via 8Be*(0, 3.0, 11.4, 16.6 + 16.9, 19.9 + 20.2, 25.2, 27.4, 28.6) and possibly via a state with Ex = 15 MeV, γ = 1.0 ± 0.2 MeV (1981NE08). See (1974AJ01, 1979AJ01) for the earlier work, 12C in (1980AJ01) and (1981DU1F; theor.).
Angular distributions have been obtained at E(7Li) = 24 MeV to 8Be*(0, 3.0, 11.4): see (1979AJ01).
Angular distributions have been measured at Ep = 0.78 to 45 MeV [see (1974AJ01, 1979AJ01)] and at Ep = 125 to 498 keV (1979DA03; α0) and 6 to 18 MeV (1983BU06; α0, α1). For the parameters of 8Be*(3.0) see reaction 31 (1981OV02). Reaction (b) has been studied for Ep = 0.15 to 10.5 MeV [see (1974AJ01)] and at 20 MeV (1981LA07). The reaction proceeds predominantly by sequential two-body decay via 8Be*(0, 3.0). See also 12C in (1980AJ01), (1981HO13) and (1981DU1F; theor.).
At E(3He) = 25.6 MeV angular distributions have been obtained for the 6Li ions to 8Be*(0, 16.6, 16.9, 17.6). In the range E(3He) = 25.2 to 26.3 MeV, the group to 8Be*(18.2) [Jπ = 1+; T = 0] is not observed: its intensity is < 0.15 of the intensity to 8Be*(17.6) [Jπ = 1+; T = 1]: see (1979AJ01).
At Eα = 27.2 MeV angular distributions involving 7Li*(0, 0.48) and 8Beg.s. as well as the "ghost" state [see e.g. reaction 31] have been studied by (1983DO1F): the cross section for formation of the "ghost" state is anomalously large. See (1979AJ01) and 7Li.
These reactions involve 8Be*(0, 3.0): see (1974AJ01, 1979AJ01), (1983AN02; reaction (a) at En = 10 - 35 MeV) (1981DE08; reaction (b) at Ep = 45 MeV) and 12C in (1980AJ01). See also (1978GO14; theor.) and 13C in (1981AJ01, 1986AJ01) and 13N in (1981AJ01, 1886AJ01).
Angular distributions have been obtained at Ed = 12.7 to 51.8 MeV [see (1974AJ01, 1979AJ01)] and at Ed = 13.6 MeV (1981DO15; to 8Be*(0) and to "ghost" anomaly), 54.25 MeV (1980YA02: to 8Be*(0, 3.0, 11.4)). Sα = 0.79, 1.08, 1.27 for 8Be*(0, 3.0, 11.4) [FRDWBA] (1980YA02). For the parameters of 8Be*(3.0) see reaction 31 (1981OV02). For reaction (b) see (1979HE06). See also (1978BE1H) and (1983GA1J; theor.).
This reaction has been studied up to Eα = 104 MeV: see (1979AJ01). Angular correlations involving 8Be*(0, 3.0) have been studied at Eα = 90 MeV: Sα (PWIA) = 2.9 ± 0.4 and 2.8 ± 0.3, respectively; Sα (DWIA) for 8Beg.s. = 2.4 ± 0.4. Angular distributions at Eα = 65 MeV (reaction (b)) lead to Sα = 0.55 and 0.75 (DWBA) for 8Be*(0, 3.0). 8Be*(11.4) was also observed. Reaction (a) has also been studied at Eα = 65 MeV (1983YA01). See also (1981RU10), (1978BE1G), (1981BA20; theor.), 12C in (1985AJ01) and 16O in (1982AJ01).
Angular distributions involving 8Beg.s. + 16Og.s. have been reported at E(12C) = 11.9 to 22 MeV (1980WA16, 1982TA21) and at ≈ 37 MeV (see (1979AJ01)). See also 16O in (1977AJ02, 1982AJ01). For 8Be*(3.0) see (1981OV02). See also (1979GO1C).
An angular distribution involving 8Beg.s. and 14Cg.s. has been obtained at E(9Be) = 28.8 MeV (1980BO21).