(See Energy Level Diagrams for 8Be)
Cluster and α-particle models: (1970YU02, 1973AB1A, 1973AR1C, 1974CH01, 1974DR05, 1974KA11, 1975AB1E, 1975SC1K, 1976BA1N, 1976ST04, 1977AR08, 1977BE50, 1977FU1D, 1977FU1F, 1977HE10, 1977HE1C, 1977KA1K, 1977KI10, 1977SE1D, 1977SM1A, 1977ZA04, 1978AR1M, 1978ST10, 1978TO09).
Special levels: (1973DO1B, 1974HA1G, 1974IR04, 1974KA11, 1974KU06, 1974MC04, 1974NE1B, 1975SH01, 1976IR1B, 1976JI1A, 1977BA62, 1977FU1F, 1977KA1K, 1978AR1M, 1978BA31, 1978BA66, 1978SE1C, 1978SH04, 1978ST10).
Other topics: (1973DO1B, 1973KR1B, 1973PE05, 1974BE1L, 1974BEYR, 1974CH01, 1974DZ03, 1974IR04, 1974KU06, 1974MC04, 1975AR10, 1975AR28, 1975ER09, 1975GO07, 1975KH1A, 1975KO1C, 1975SH01, 1976AR07, 1976IR1B, 1976KH04, 1976KU07, 1976SA16, 1977AR08, 1977BE1U, 1977HE10, 1977TR07, 1978BA31, 1978JE1B, 1978KA1G, 1978MC04, 1978RO01, 1978RO17, 1978SH04).
The yield of γ1 has been measured for Eα = 32 to 36 MeV: see (1975NA12, GA77F, 1977PA26). An angular correlation measurement at the resonances corresponding to 8Be*(16.6 + 16.9) [2+; T = 0 + 1] gives δ = 0.19 ± 0.03 (1978BO30); Γγ(M1) = 6.1 ± 0.53 eV (1978BO30), 7.4 ± 1.0 eV (1977PA26), 5.50 ± 0.60 eV (1977LO1D, 1977LO1E). On the basis of these results there is no evidence for violation of CVC or for the existence of second-class currents: see (1978BO30). (1977PA26) find Ex = 3.18 ± 0.05 MeV for the energy of the first excited state (see also Table 8.4 (in PDF or PS) in (1974AJ01)). The yield of γ0 for Eα = 33 to 38 MeV is twenty times lower than that for γ1, consistent with E2 decay (1977GAZZ). See also (1975NA1C) and (1977GA1E).
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). The cross sections for (a) and (b) are of interest in accounting for the abundance of 7Li in the galaxy (1977KI12). Cross sections for p0+1 are also reported at Eα = 60.2, 92.4 and 140.0 MeV (1975KI14). See also (1977RA1B). The cross section for reaction (c) has been measured at three energies in the range Eα = 46.7 to 49.5 MeV (1977KI12). See also (1977KI05). (1976HI04) have measured the excitation functions for p0, p2, d0, d1 for Eα = 54.96 to 55.54 MeV to study the decay of the first T = 2 state in 8Be: see Table 8.4 (in PDF or PS). See also (1975MA1G), (1977AU1B, 1977KO1J; astrophys.) and 6Li, 7Li and 7Be.
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) × 10-16 sec] (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 (1972BA83): see also (1974AJ01).
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+) (1963TO02): 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 (1978HI04) and Table 8.5 (in PDF or PS)], and states with Ex = 20.2, 22.2 and 25.2 MeV. The latter has a small Γα (1972BA83).
The l = 4 shift rises from Eα ≈ 11 MeV and indicates a broad 4+ level at Ex = 11.4 ± 0.3 MeV (1959BR71), 11.7 ± 0.4 MeV [Γ = 4.0 ± 0.4 MeV] (1974CH45). 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) (1972BA83, 1978LE13).
Over the range Eα = 30 to 70 MeV a gradual increase in δ6 is observed (1972BA83). Some indications of a 6+ state at Ex ≈ 28 MeV and of an 8+ state at ≈ 57 MeV have been reported by (1965DA1A) with Γc.m. ≈ 20 and ≈ 73 MeV, respectively. A resonance is not observed at the first T = 2 state, 8Be*(27.49): see Table 8.4 (in PDF or PS) (1976HI04). The elastic scattering has also been studied at Eα = 160 MeV (1978RO1G), at 650 and 850 MeV (1976FO03), 850 and 1370 MeV (1977TE1A) and at 4.30 and 5.05 GeV/c (1977BE1R, 1977BE1T). The total cross section has been measured at 0.87 and 2.1 GeV/A (1975JA1A).
See also (1975IG1A, 1975TO1A, 1976SL02, 1977KI05, 1978BR1E, 1978CH1G, 1978FI1E) and (1973CO1C, 1973FA1C, 1973HA1F, 1973TA1B, 1974AT1A, 1974BA1P, 1974FR1B, 1974FR06, 1974LU05, 1974RA16, 1974TH04, 1974WA02, 1974WA1D, 1975AN1F, 1975BA76, 1975BE1M, 1975BE16, 1975CL1C, 1975DU09, 1975GR05, 1975GR41, 1975GR1C, 1975HE07, 1975HO1E, 1975KU09, 1975MA27, 1975TA1D, 1976AL1E, 1976BA1E, 1976BR32, 1976CO18, 1976CU07, 1976GO12, 1976HA18, 1976HA1L, 1976HO1A, 1976JA1F, 1976LE1J, 1976LI1E, 1976ME1C, 1976MI17, 1976MO31, 1976RA1E, 1977AL1G, 1977AN1B, 1977BA17, 1977BE50, 1977BU01, 1977CA06, 1977CH1C, 1977DA20, 1977FL13, 1977FR12, 1977FR18, 1977FU1E, 1977HO1D, 1977HO1E, 1977HU1A, 1977IK1A, 1977KO1K, 1977LA1D, 1977MA1J, 1977SA1C, 1977ST1G, 1977TH09, 1977ZA04, 1977ZI01, 1978AR1M, 1978FO1G, 1978FR1F, 1978FR1H, 1978LE13, 1978MA20, 1978NO1B, 1978SA24, 1978SA2B, 1978ST10, 1978TO09, 1978VA03, 1978YA1A; 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 (1976NO07). The γ1 transition from 8Be*(27.49) to 8Be*(2.9) is not observed: assuming Γd0/Γ = 0.78, ΓΔT = 2γ/Γ < 2 × 10-6. If Γc.m. = 5.5 keV, ΓΔT = 2γ < 0.01 eV [< 1.5 × 10-3 W.u.] for this E2, ΔT = 2 transition (1977LO1F).
The yield curve has been measured for Ed = 0.06 to 5.5 MeV and 12 to 17 MeV: see (1974AJ01) and (1977SZ05: 0.10 to 0.18 MeV; activation cross section), (1977EL09: 0.20 to 0.90 MeV; cross sections for n0 and n1) and (1974MCZS, 1975MC02: 0.5 to 3.0 MeV; n1γ). Polarization measurements have been reported at Ed = 0.27 to 0.60 MeV (1966MI06: n1) and Ed-bar = 0.6, 0.8 and 1.0 MeV (1977GL05; n1) and at Ed = 2.5 to 3.7 MeV (1970TH08; n0, n1). See also 7Be.
Comparisons of the populations of 7Be*(0, 0.43) and of 7Li*(0, 0.48) have been made at many energies, up to Ed = 7.2 MeV. The n/p ratios are closely equal for analog states, as expected from charge symmetry: see (1974AJ01) and (1977EL09). See also (1973GL1A, 1974AU1B) and (1976MO23, 1977EL11, 1977MC1C; applications).
Excitation functions have been measured for Ed = 30 keV to 5.4 MeV: see (1974AJ01). Recent cross-section measurements are reported at Ed = 0.1 to 1.0 MeV (1977EL09; p0, p1) and 0.5 to 3.4 MeV (1974MCZS, 1975MC02; p0, p1, p1γ). There is no resonance at Ed = 0.4 MeV: see (1976MO23). An anomaly is observed in the p1/p0 intensity ratio at Ed = 6.945 MeV, corresponding to the first 0+; T = 2 state: Ex = 27.483 ± 0.010 MeV, Γ = 10 ± 3 keV, Γp0 << Γp1, Γp0 < Γd (1969BL14). See also (1975GE1F).
Polarization measurements for p0 and p1 have been reported at Ed-bar = 0.6 and 0.96 MeV (1977GL05) and Ed = 2.1 to 10.9 MeV (1968DU09, 1968FI07, 1970FI07). The latter report pronounced differences in the angular distributions of the vector analyzing power of the two ln = 1 transitions to 7Li*(0, 0.48). See also 7Li, (1974AU1B, 1978VA1D), (1974AJ01, 1975SE07, 1976MO23) and (1977EL11; applications).
The yield of elastically scattered deuterons has been measured for Ed = 2 to 7.14 MeV [see (1974AJ01)]: no resonances are observed, except, possibly, for a very weak anomaly at Ed = 6.96 MeV (1975GE1F; abstract). See also 6Li and (1974CH58; theor.).
The cross section for tritium production rises rapidly to 190 mb at 1 MeV, then more slowly to 290 mb near 4 MeV. There is evidence of deviation from isotropy near 0.4 MeV (1955MA20). See also 5Li. For reaction (b) see 5He.
Cross sections and angular distributions (reaction (a)) have been measured at Ed = 0.03 to 12 MeV [see (1974AJ01)] and at Ed = 0.118 to 0.975 MeV (1977EL09: very accurate total reaction cross sections), 0.50 to 3.4 MeV (1974MCZS, 1975MC02; σR), 1.0 to 11.5 MeV (1977RI09; σ(θ): see below) and 13.6 MeV (1978FU03; ang. distrib. to 4He*(20.1, 21.1, 25.5)) and E(6Li) = 10 to 31 MeV (1979WA02: 30° yield of α0 and α* to 4He*(20.08) [0+]). A critical analysis of the low energy data has led to a calculation of the reaction rate parameter for thermonuclear reactions for plasma temperatures of 2 keV to 1 MeV (1978CL07). Polarization measurements are reported at Ed = 0.40 to 11.8 MeV and at E(6Li) = 0.6 MeV [see (1974AJ01)] and at Ed-bar = 1.5 to 11.5 MeV (1977RI09: vector and tensor analyzing powers). At Ed-bar = 5, 6, 8 and 9 MeV, Ayy = 1 is observed at certain angles: see (1978SE01).
Pronounced variations are observed in the cross sections and in the analyzing powers (1977RI09). Maxima are seen at Ed = 0.8 MeV, Γlab ≈ 0.8 MeV and Ed = 3.75 MeV, Γlab ≈ 1.4 MeV (1963ME09, 1964PA06). 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 (1977RI09). The results of this and other experiments are in good agreement with the results of (1972BA83) [4He(α, α): reaction 4], that is with two 2+ states at Ex = 22.2 and 25.2 MeV and a 4+ state at 25.5 MeV (1977RI10). A strong resonance is seen in the α* channel [to 4He*(20.08), 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). At Ed = 6.945 MeV, the α0 yield shows an anomaly corresponding to 8Be*(27.49), the 0+; T = 2 analog of 8Heg.s. (1969BL14) [(1975GE1F; prelim.) find Ed = 6962 ± 7 keV, Γ ≈ 10 keV.]
For reaction (b) see (1977RO18: Ed = 0.465; evidence for QSI) and (1977MI13: Ed = 7.5, 9, 10, 10.5 MeV; see 5Li, 7Li). For reaction (c) see (1974AJ01). For reaction (d) see (1977MI13, 1978FU03). See also 6Li.
Proton groups are observed to 8Be*(0, 2.9, 16.63, 16.92, 17.64): see Tables 8.4 (in PDF or PS) and 8.5 (in PDF or PS) in (1974AJ01). The excitation of 8Be*(18.15, 19.0, 19.4, 19.9) is also reported by (1971GL07). Angular distributions have been measured at E(3He) = 1.4 to 17 MeV [see (1974AJ01)] and at 3, 4.5 and 6 MeV (1976GO1F; p0, p1) and 14 MeV (1977IR01; p0, p1).
Reaction (b) proceeds via 8Be*(16.63, 16.92): Γ = 117 ± 10 and 85 ± 10 keV, respectively. Interference effects are reported (1969VI05): see also Table 8.5 (in PDF or PS). See also (1976GO1F, 1977AR09), (1977AS04; theor.) and 9B.
Deuteron groups have been observed to 8Be*(0, 2.9, 11.3 ± 0.4). Angular distributions have been measured at Eα = 20 to 48 MeV [see (1974AJ01)] and at Eα = 15.8 to 25.1 MeV (1974KO24; d0, d1), 17.3, 23.3, 25.1 MeV (1974LE14; d0, d1), 20 and 24 MeV (1974GR21; d0) and 29.4 MeV (1974MA9; d0, d1). Large differential cross sections at back angles are analyzed by (1974GR21) using both direct and exchange amplitudes.
A study of reaction (b) shows that the peak due to 8Be*(2.9) is best fitted by using Γ = 1.2 ± 0.3 MeV (1969BA18): see also Table 8.4 (in PDF or PS) in (1974AJ01). At Eα = 42 MeV the α-α FSI is dominated by 8Be*(0, 2.9) (1977BO22). See also (1974MA49, 1976LE1K).
This reaction proceeds via 8Be*(0, 2.9, 16.6, 16.9, 22.5), and there is indication also that the direct three-body break-up (reaction (b)) is possible (1971GA21, 1972GA32: Emax(6Li) = 13.0 MeV). The involvement of a state at Ex = 19.9 MeV (Γ = 1.3 MeV) is suggested by (1966MA40). 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 8.5 (in PDF or PS) (1971NO04). 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 (1966MA40, 1966KI09). Partial angular distributions for the α0 group have been measured at fourteen energies for E(6Li) = 4 to 24 MeV (1970FR06). See also (1975NO1C; theor.) and (1974AJ01).
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 2.9 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 8.6 (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*(2.9). The γ0 and γ1 giant resonance peaks each contain about 10% of the dipole sum strength (1976FI1C). The main trend between Ep = 8 and 17.5 MeV is a decreasing cross section (1976FI1C). (1977UL02) have studied the analyzing power for Ep-bar = 0.38 to 0.96 MeV: the data indicate some possibility of a 1- state at 17.70 MeV.
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 (1961ME10). Radiative widths for the γ0 and γ1 decay are displayed in Table 8.7 (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 (1969SW01). (1968PA09) find squared T = 1 components of 40% and 60% in 8Be*(16.6, 16.9) and of 95% and 5% in 8Be*(17.6, 18.2). See also (1974SO1D, 1978GO1F, 1978ZI1A; applied work), (1974VA1C; astrophys.) and (1977BA62, 1978BA66; theor.).
Measurements of cross sections have been reported for Ep = 1.9 to 52 MeV: see (1974AJ01) and the review article by (1975LI1E). Recent measurements have been carried out at Ep = 1.9 to 3.8 MeV (1974BU16: n0; dσ/dΩ(0°)), 4.2 to 25.9 MeV (1976PO06: n0, n1; 3.5°), and for neutron production at 0° at 14.3, 19.4 and 29.6 MeV (1975MC18), 29.4, 39.2 and 50.6 MeV (1976RO10), and 24.7 to 44.7 MeV (1977SC37). Polarization measurements have been reported at Ep = 2.05 to 5.5 MeV and 30 and 50 MeV: see (1974AJ01). See also (1976DOZW, 1978LE10). For angular distributions see 7Be.
The yield of ground state neutrons (n0) rises steeply from threshold and shows pronounced resonances at Ep = 2.25 and 4.9 MeV (1963BO06). The yield of n1 also rises steeply from threshold (1964BU08) and exhibits a broad maximum near Ep = 3.2 MeV (1961BE05, 1972PR03) and a broad dip at Ep ≈ 5.5 MeV, also observed in the p1 yield (1972PR03).
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 (1974AR10). The ratio of the cross section for 7Li(p, γ)8Be*(18.9) γ /→ 8Be*(16.6 + 16.9) [obtained by (1969SW01)] to the thermal neutron capture cross section 7Be(n, γ)8Be*(18.9)γ /→ 8Be*(16.6 + 16.9) [obtained by (1973BA1J)], provides a rough etsimate of the isospin impurity of 8Be*(18.9): σp,γ/σn,γ ≈ 1.5 × 10-5 and therefore the T = 1 isospin impurity is < 4% in intensity (1974AR10). See, however, (1977BA62; theor.) who estimates ≈ 10% isospin mixing.
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 (1963BO06). 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 (1972PR03). See Table 8.8 (in PDF or PS).
The ratio of the cross sections of the (p, n1) reaction to 7Be*(0.43) to that for the (p, p1) reaction to the analog state 7Li*(0.48) has been measured for Ep = 2.4 to 10 MeV and 23 to 52 MeV [see (1974AJ01)] and at Ep = 3 to 25.9 MeV (1976PO06): at the lower energies the ratio varies very strongly with energy. [An average value for the ratio over the range 5 to 26 MeV is ≈ 0.3.] See also (1973AT01, 1974AR05, 1976CY1A), (1974LE1E, 1974LO1B, 1975SO1C, 1976RI1B, 1976SL02), (1976BR42, 1976CAZG, 1977LO10, 1977ME1C; applications) and (1974CO1B, 1976AR1F, 1977ST18, 1978BA66, 1978DE37; theor.).
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). (1976SOZW; prelim.) reports total cross-section meeasurements at Ep = 25, 30, 35, 40, 45 and 48 MeV. Polarization measurements have been reported at Ep = 0.67 to 10.6 MeV and at 14.5, 49.8, 152 and 155 MeV: see (1974AJ01). The polarization has also been studied by (1974DE45; p0) for Ep = 1.8 to 3.0 MeV. For angular distribution see 7Li.
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 existing cross-section data by (1973BR13) 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 16]; and that the Ep = 2.05 MeV reosnance 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 (1973BR13): see Table 8.9 (in PDF or PS), (1972PR03) and (1977BA62, 1978BA66; theor.). The polarization data of (1974DE45) show structures at Ep = 1.9 and 2.3 MeV. See also (1974AR10, 1976MA64).
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. Table 8.4 (in PDF or PS) displays the upper limit for Γp0/Γ (1976HI04). See (1973GO41, 1978FR12), (1976IK01) and (1975MA1H, 1977ST18, 1978DE37; theor.).
The cross section follows the expression E-1e-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 (1967FI05). Taking into account 8Be Jπ = 2+ levels at 16.7, 16.9 and 20.6 MeV, (1972BA41) has made an R-matrix fit to the revised data of (1971SP05) for Ep = 131 to 561 keV and has obtained 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 (1966LA04, 1974AJ01). Recent measurements include those of (1976SAZR: 1.6 to 12.0 MeV) and (1976HI04: 11.64 to 11.76 MeV). 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 (1968PL01, 1969KI04) [see Fig. 12 in (1969KI04) and Fig. 6 (1968PL01) for contour maps of the asymmetry].
Broad resonances are reported to occur at Ep = 3.0 MeV [Γ ≈ 1 MeV] and at ≈ 5.7 MeV [≈ 1 MeV]. Structures are also reported at Ep = 6.8 MeV and at Ep = 9.0 MeV: see (1974AJ01) and (1976SAZR). The 9.0 MeV resonance is also reflected in the behavior of the A2 coefficient (1968PL01). The experimental data on yields and on polarization have been analyzed by (1971KU10): the data 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 and (1972BA83). 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 (1971KU10). 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 (1976HI04).
The population of 8Be*(0, 2.9, 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*(2.9) 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 [see (1974AJ01)] and at Ed = 15.25 MeV (1975AZ02; also n to 8Be*(16.6 + 16.9); spectroscopic factors). The angular distributions of the neutrons to 8Be*(16.6, 17.6, 18.2) are fit by lp = 1: see (1974AJ01). See also (1978BA66; theor.).
Reaction (b) appears to proceed primarily via 8Be*(2.9, 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 (1969HO11), 3.4 ± 0.1 MeV (1976FO21)] as may state(s) at Ex ≈ 20 MeV (1978AR10). Attempts to observe n-α rescattering ("proximity scattering") proceeding via 8Be*(16.6, 16.9) have been unsuccessful: see (1974AJ01). See, however, (1975GR43). See also (1973HU12, 1974DA28, 1974GR44, 1975DA15, 1977LO10), (1976EA1A, 1976NE1B; applications) and 5He and 9Be.
Deuteron groups are observed to 8Be*(0, 2.9, 16.6, 16.9, 17.6). For the parameters of 8Be*(2.9) see Table 8.4 (in PDF or PS) in (1974AJ01). The Jπ = 1+ mixed isospin states have been studied by (1967MA12): see Table 8.5 (in PDF or PS). Angular distributions have been measured at a number of energies in the range E(3He) = 0.9 to 24.3 MeV [see (1974AJ01)] and at 1.2 to 2.5 MeV (1975BO56, 1977BO29). For reaction (b) see (1976DA24). See also (1977SL1B), (1974AL07), (1975KU27, 1975TR02, 1976KU07, 1977BA62; theor.) and 9Be.
Angular distributions have been measured up to Eα = 50 MeV [see (1966LA04, 1974AJ01)] and at 23.2 and 25.0 MeV (1974DM01; t0, and t1 at higher energy) and 29.4 MeV (1974MA49; t0, t1). The ground state of 8Be does decay isotropically in the cm system: Jπ = 0+ (1970LA14). At Eα = 10 MeV an anomaly ("ghost") is observed at Ex ≈ 0.5 MeV: see (1971BE52) and reaction 31. Sequential decay (reaction (b)) is reported at Eα = 50 MeV via 8Be*(0, 2.9, 11.4, 16.6, 16.9, 19.9) (1970LA14). See also (1974MA49). See also (1976LE1K) and (1977BE51; theor.).
At E(7Li) = 1.4, 1.7 and 1.8 MeV, the angular distributions of 6He ions leaving 8Be in its ground and 2.9 MeV states are essentially isotropic (1968ST12).
At thermal energies, the (n, p) cross section is (4.8 ± 0.9) × 104 b (1973MU14), the (n, α) cross section is ≤ 0.1 mb and the (n, γα) cross section is 155 mb (1963BA34). These values, and comparison of the (p, n) cross section with that of reaction (a), support the Jπ = 3/2- assignment for 7Be(0) (1957NE22, 1963BA34). See also (1974AJ01) and (1977BA62; theor.).
8Li decays mainly to the broad 2.9 MeV, 2+ level of 8Be, which decays into two α particles. Both the β-spectrum and the resulting α-spectrum have been extensively studied. There appears to be an increasing excess of α-particles with Eα which may reflect transitions into the tail of the Jπ = 2+ level at Ex = 16.63 MeV. See (1955AJ61, 1966LA04) for earlier references. 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 (1966LA04).
Angular correlations have been measured for the decays of 8Li and 8B as a test of the conserved vector current theory of β-decay. The values of the coefficients are displayed in Table 8.10 (in PDF or PS) (1962NO02, 1963GR11, 1966EI02, 1975TR06). The experimental value of δ [δ ≡ B(8Li) - B(8B)] is (5.4 ± 0.4) Wβ, consistent with CVC theory (1966EI02). There is no evidence for second class currents in this decay: see, e.g., (1975TR06). See also (1973AN11, 1974TR01, 1978FO1H, 1978HA1K, 1978MC1E), (1973BR1C, 1975CA1F, 1976CA1E, 1977GA1E, 1978BO30) and (1973KU1D, 1973TA30, 1974HO1D, 1974KU06, 1975KR14, 1975WI1E, 1976KU1B, 1977KU1E, 1977KU20, 1977OK1A, 1977SA23, 1977TE1B, 1977WI02, 1978KH03; theor.).
The decay proceeds mainly to 8Be*(2.9) [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 = 2.9 (1964MA35), 3.33 (1969BA43). The log ft value is consisatent with the identification Jπ = 2+, T = 1 for 8Be*(16.63) (1964MA35) [actually this state is of mixed T = 0 and 1 isospin]. The energy distribution of α-particles has also been measured by (1969CL10). 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 of Γ = 14-3+4 MeV (a2 = 6.0 ± 0.5 fm) (1969CL10).
For angular correlation measurements see reaction 28 and Table 8.10 (in PDF or PS) (1962NO02, 1966EI02, 1975TR06). See also (1974TR01). There is no evidence for second-class currents in this decay: see, e.g., (1975TR06). See also (1973BR1C, 1975CA1F, 1976CA1E, 1977GA1E, 1978BO30) and (1974HO1D, 1974KU06, 1975KR14, 1975WI1E, 1976KU1B, 1976KU07, 1977KU1E, 1977OK1A, 1977TE1B, 1977WI02, 1978KH03; theor.).
Neutron groups to 8Be*(0, 2.94) have been studied for Eγ = 18 to 26 MeV (1977BU02). See also (1974AJ01) and 9Be. Reaction (b) appears to proceed largely via excited states of 9Be with subsequent decay mainly to 8Be*(2.9): see (1966LA04, 1974AJ01), 9Be and 10Be. Reaction (c) has been studied at Ep = 45 and 47 MeV: the reaction primarily populates 8Be*(0, 2.9) (1977WA05). See also (1977JE01, 1978CH07), 9Be and 9B. For reactions (d) and (e) see (1974AJ01) and 9Be. For reaction (e) see (1974GR42).
Angular distributions of deuteron groups have been reported at Ep = 0.11 to 185 MeV [see (1974AJ01)] and at Ep = 4.6 MeV (1974YA1C; d0), 17.7 MeV (1977GU14; d0, d1) and Ep-bar = 15 MeV (1976DA15; d0, d1). In the latter work S for 8Be*(0, 2.9) are 0.80 and 1.05 (see also reaction 32) (1976DA15). For other work on spectroscopic factors see (1974AJ01).
Besides 8Be*(2.9) [see Table 8.4 (in PDF or PS) in (1974AJ01)] 8Be*(11.4, 16.6, 16.9, 17.6, 18.2, 18.9, 19.2, (20.0), 21.5, 22.0, 23.0, (24.5), 26.0) are populated. See also Table 8.5 (in PDF or PS). (1969SU02) report Ex = 11.3 ± 0.3 MeV for the 4+ state. At Ep = 46 and 100 MeV the angular distributions to 8Be*(16.9, 17.6, 18.2, 19.1) are consistent with l = 1 (1967VE01, 1968LE01, 1971SC26).
An anomaly has been reported in deuteron spectra between the d0 and d1 groups. At Ep = 39.9 MeV it is seen at Ex ≈ 0.6 MeV. An R-matrix analysis using a three-level approximation for both the 0+ and the 2+ contributions shows that the anomaly is due to a "ghost" of the 0+ state which produces the ground state group (1976BA67). See (1974AJ01) for the earlier work. Reaction (b) at Ep = 9 MeV is dominated by strong FSI through 8Be*(0, 2.9) and 6Li*(2.19) with little or no yield from a direct three-body decay (1971EM01). See also (1974AD1B, 1974LO1B), (1978PR1A; applied) (1976BO15, 1978BA66; theor.) and 10B.
Angular distributions have been measured for Ed = 0.3 to 20 MeV [see (1966LA04, 1974AJ01)] and at 0.15 to 2.5 MeV (1974CH1L; t0), 0.6 to 2.2 MeV (1974FR02; t0), 0.9 to 2.5 MeV (1974BO42, 1975BO1C; t0), 0.9 to 3.1 MeV (1975ZW01; t0), 12.35 and 14.06 MeV (1978TA04; t0, t1), 13.6 MeV (1973ZA06; t0), 28.0 MeV (1977OO01: see below) and at Ed-bar = 15 MeV (1976DA15; t0, t1; S = 0.37, 0.55: see also reaction 31).
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 8.5 (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 18] in 8Li and (1978BA66; theor.).
A kinematically complete study of reaction (b) at Ed = 26.3 MeV indicates the involvement of 8Be*(0, 2.9, 11.4, 16.9, 19.9 + 20.1) (1973SO08). See also (1974SO1C, 1975DO04, 1975ZA06, 1976HE1F), (1974AJ01) and 11B in (1980AJ01).
Angular distributions have been measured in the range E(3He) = 3.0 to 26.7 MeV [see (1974AJ01)] and at E(3He) = 1.75, 2.12, 2.43 and 2.95 MeV (1974SA1K; α0), 4, 5 and 7 MeV (1975BI14: to 8Be*(17.6, 18.2)), 4 to 7 MeV (1978BI15; α0), 9 and 10 MeV (1975RO09; α0) and at E(3He-bar) = 33.3 MeV (1976KA23: to 8Be*(16.9, 17.6, 19.2)) [S = 1.74, 0.72, 1.17, assuming mixed isospin for 8Be*(16.9)]. The parameters of observed states are displayed in Table 8.4 (in PDF or PS) of (1974AJ01) and Table 8.5 (in PDF or PS) here. In a recent experiment (1974CA32) suggest Ex = 2.80 ± 0.05 and 11.8 ± 0.5 MeV for the first two excited states of 8Be. In addition to three relatively sharp states reported in the range 22 < Ex < 23 MeV [see Table 8.5 (in PDF or PS)] (1976AJ01) suggest the possibility of a broad state at Ex ≈ 25 MeV. See also (1978BA66; theor.).
Reaction (b) has been studied at E(3He) = 3.0 and 4.0 MeV (1966SU04, 1968MO05, 1972TA04, 1975KA05) and at 2.9 to 10 MeV (1975RO09). See also (1976AR11). The reaction proceeds via 8Be*(0, 2.9, 11.4, 16.6, 16.9, 19.9, 22.5) (1972TA04). See, however, (1975RO09): Γc.m. for 8Be*(2.9) is reported to be 0.94 ± 0.04 MeV. Jπ = 2+ is indicated for 8Be*(16.6, 16.9) (1966SU04, 1968MO05). See also (1976STYX), (1976RO1L) and 12C in (1980AJ01).
At E(6Li) = 5.5 and 6.5 MeV angular distributions involving 8Beg.s. and 7Li*(0, 0.48) have been measured (1974VO06). For reaction (b) see (1974KE1C). For reaction (c) see (1977UH1A, 1978CH02). For reaction (d) see (1975SE03, 1975SE04). Reaction (e) has been studied at E(18O) = 16 and 20 MeV (1971KN05). See also (1974AJ01) for the earlier work.
At Ep = 34 MeV tritons are observed to the first T = 2 state, Ex = 27.4922 ± 0.0026 MeV, Γc.m. = 12 ± 3 keV: the angular distributions for the transitions to this state 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 (1975RO01). The particle decay of the T = 2 state has been studied by (1975ADZV; abstract).
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 (1977BA51).
At Ep = 39.4 MeV angular distribution measurements have been carried out for the 3He groups to 8Be*(0, 2.9, 16.6, 16.9): the ratio dσ(16.63)/dσ(16.91) has a mean value of 0.65 ± 0.05 for θ = 15° to 30°, suggesting possibly a preferential excitation of the T = 1 components of these two states. The ratio of the differential cross sections dσ(p, t) [to 8Bg.s.] to dσ(p, 3He) [to 8Be*(16.63, 16.92)] (15° to 30°) seems to also suggest this (1971SQ01).
Angular distributions have been reported at Ed = 0.5 to 7.5 MeV [see (1974AJ01)] and at Ed = 0.8 to 9.0 MeV (1978BU04), 1.83 MeV (1974LA29; α0, α1) and 5 MeV (1975RO09; α0). At Ed = 7.5 MeV the total cross section for formation of 8Be*(16.63), σt(16.63), is about 1.15σt(16.92), consistent with the mixed isospin character of these two states. σt(18.15) is ≈ 0.85σt(16.92), but the other nearby 1+ state 8Be*(17.64) has σt(17.64) ≈ 0.07σt(16.92), consistent with the nearly pure T = 1 nature of 8Be*(17.64) (1966BR08). These four states [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 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 (1970CA12). There is some question as to whether a two-level fit can be made for the α groups to 8Be*(16.63, 16.92). ((1970CA12) and W.D. Callender, private communication) are dubious about this, feeling that other 2+ states have to be brought into the calculation. Based onn a two-level fit they find the following average values: Γ16.6 = 113 keV, Γ16.9 = 80 keV, ΔQ = 302 keV. However, (1971NO04) state that the two-level fit is appropriate of the spectra are properly corrected for effects of final state Coulomb interactions: Γ16.6 = 90 ± 5 keV, Γ16.9 = 70 ± 5 keV, ΔQ = 290 ± 7 keV: see (1978HI04) and Table 8.5 (in PDF or PS). See also Table 8.4 (in PDF or PS) in (1974AJ01) and (1977BA62, 1978BA66; theor.).
Reaction (b) [Ed < 5 MeV] takes place mainly by a sequential process involving 8Be*(0, 2.9, 11.4, 16.6, 16.9): see (1975RO09, 1975VA04) and the earlier work in (1974AJ01). See also (1970HU1B, 1976GR22, 1977LA13, 1977NO10), (1974AD1B), and 12C in (1980AJ01).
At E(3He) = 2.45 and 6.00 MeV this reaction proceeds primarily by sequential decay via 8Be*(0, 2.9) and via 5Li, 9B and 12C states (1966WA16).
Angular distributions have been obtained at E(7Li) = 24 MeV to 8Be*(0, 2.9, 11.4) (1977KO27).
See 11B in (1980AJ01).
Angular distributions have been measured at Ep = 0.78 to 45 MeV [see (1974AJ01)] and at Ep = 5.08 to 38 MeV (1975BU1B, 1978BU1D; α0) and 7.3 MeV (1974KA1J; α0, α1). Observed parameters for 8Be*(2.9) are shown in Table 8.4 (in PDF or PS) of (1974AJ01). (1977FU09) find that the width of this state varies with Ep. 8Beg.s. decays isotropically, as expected from its 0+ character (1976KO18).
Reaction (b) has been studied for Ep = 0.15 to 10.5 MeV. The reaction proceeds predominantly by sequential two-body decay via 8Be*(0, 2.9): see (1974AJ01), 12C in (1975AJ02, 1980AJ01) and (1974KA1J, 1975VA04, 1976GR22, 1977LA13, 1977OH1A). See also (1972TH1C, 1977GR10) and (1978BI1E; applied).
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] (1974DE25). For the earlier work see (1974AJ01), (1972YO02) and 6Li.
Angular distributions have been reported at Eα = 28.4 and 29.0 MeV for 8Beg.s. + 7Lig.s., 8Beg.s. + 7Li*0.48 and 8Be*2.9 + 7Li (29 MeV only) by (1968KA24) and at 42 MeV for 8Beg.s. + 7Lig.s. and 8Beg.s. + 7Li*0.48 by (1968MI05). At Eα = 65 MeV 8Be*(16.6 + 16.9, 20.0) are apparently also excited (1973WO06). See also (1974WO1C, 1974WO1D), (1973SC1B) and 7Li.
Reaction (a) has been studied for 13 < Ep < 160 MeV. At low energies it involves 8Beg.s.; at higher energies 8Be*(0, 2.9): see (1974AJ01) and (1969EP01, 1977IO1A, 1977RO02). See also 12C in (1975AJ02, 1980AJ01), (1978CH1G, 1978DE1J) and (1977CH02; theor.). For reaction (b) see (1977CO07; 100 MeV; 8Be(0)) [Sα = 0.56 ± 0.12].
Angular distributions have been obtained at Ed = 19.5, 28 and 51.8 MeV [see (1974AJ01)] and at Ed = 12.7 and 13.2 MeV (1975GO36; 8Beg.s.), 13.6 and 14.6 MeV (1974GA30; 8Beg.s.), at Ed-bar = 16 MeV (1976JA1G; 8Beg.s.), at Ed = 35 MeV (1975BE01; 8Beg.s.) and at 54.3 MeV (1977TA1D: to 8Be*(0, 2.9, 11.4, 16.6 + 16.9)). See also (1973FO1A) and (1974DO03, 1976NA05, 1978TA1F; theor.).
Angular distributions have been measured involving 8Beg.s. + 7Beg.s. and 8Beg.s. + 7Be*(0.43) at E(3He) = 25.5, 27.0 and 29.0 MeV (1976PI10) and at 28 MeV (1970DE12). In addition at E(3He) = 70 MeV the distributions involving 8Be*(2.9, 11.4, 16.6) and 7Be0+1, 8Be*(16.9) and 7Be*(0.43), and 8Be*(17.6) and 7Be*(0, 0.43) have been studied by (1976ST11). See also (1975AU01), (1974DO03; theor.) and 7Be.
This reaction has been studied up to Eα = 104 MeV: see (1974AJ01). Angular correlations involving 8Be*(0, 2.9) 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 (1976SH02).
At E(12C) ≈ 37 MeV angular distributions (reaction (b)) are reported involving 8Beg.s. + 16Og.s. (1975EB02, 1976EB01). See also 16O in (1977AJ02), 24Mg in (1978EN06), (1974AJ01) and (1974HO30, 1976AR02, 1977WA04). For reaction (a) see (1978FR20) and 15N in (1981AJ01).
See 16O in (1977AJ02).
See 20Ne in (1978AJ03).