(See Energy Level Diagrams for 8Be)
Special states: (1981PL1A, 1983AD1B, 1983BI1C, 1983FE07, 1983FI11, 1983HA41, 1984DE24, 1984DU17, 1984LU1A, 1984LU1B, 1984VA06, 1984VAZS, 1984ZW1A, 1985FI1E, 1985GO1A, 1985PO19, 1985PU03, 1985RO1G, 1986AN10, 1987KA18, 1987KI1C, 1987SV1A, 1987WA36, 1988BA75, 1988KR01, 1988KW02, 1988KH03).
Complex reactions involving 8Be: (1982GU21, 1983DEZW, 1983EL1A, 1983SI1A, 1983WA1F, 1983XU1A, 1984AB1C, 1984PA13, 1985BU16, 1985HA1N, 1985KA1E, 1985KA1G, 1985KAZQ, 1985KW03, 1985PO11, 1985PO19, 1985WA22, 1986BA2D, 1986BL12, 1986BR26, 1986GA24, 1986GU1F, 1986IR01, 1986MA1O, 1986PO06, 1986PO12, 1986TA1M, 1987AR19, 1987BL16, 1987CH26, 1987CH33, 1987CH32, 1987DE1O, 1987DU07, 1987GE1B, 1987GL05, 1987HA45, 1987PE1B, 1987PO23, 1987RUZX, 1988AR05, 1988POZZ, 1988RU01, 1988SA09, 1988VA1E).
Ground-state properties of 8Be: (1983ANZQ, 1983DR09, 1984DU17, 1984LU1A, 1984LU1B, 1985AN28, 1985FI1E, 1985GO1A, 1985SH1A, 1987BL18, 1987BO42, 1987KI1C, 1987KO1U, 1987SA15, 1987SV1A, 1988AR05, 1988WO04).
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)]. 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)].
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 (1985BA45; theor.).
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) 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 for Eα = 61.5 to 158.2 MeV by (1982GL01) and at 198.4 MeV by (1985WO11). 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 (1985WO11, 1982GL01).
The α-α 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]. 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 8.5 (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.
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; Γc.m. ≈ 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; prelim.), 158.2 MeV, 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). See also (1985KR21, 1986FO04, 1986GOZY, 1986UC1A, 1987FO08) and the "General" section here. For inclusive cross sections see (1984AJ01) and (1984AL03; 218 MeV).
For studies at very high energies see reaction 3 and (1982AB1B, 1984SA39, 1984TA1D, 1984TA1G, 1985AB1A, 1985AK1A, 1985CA1C, 1986BE2N, 1986BE1S, 1986BE1T, 1986TA1N, 1986TA1P, 1987BA13). See also (1986CH1M), (1982NA1B, 1983FA1A, 1984FA1B, 1984FR1C, 1985CA41, 1985FA1A, 1985FR1E, 1985WI1B, 1986AN1F, 1986CH1J, 1986ST1D, 1987HE1B, 1987OT1D ), (1985NO1B, 1986LA16, 1987FU04, 1987MU1B; astrophysics) and (1982WE15, 1983AL1C, 1983BU15, 1983FI11, 1983GO25, 1983KO41, 1983MA73, 1983OK06, 1983PR09, 1983SA16, 1984DE24, 1984FI11, 1984FI13, 1984FR10, 1984HE1D, 1984KR10, 1984LI28, 1984MA16, 1984MA1H, 1984MA68, 1984NA11, 1984OK03, 1984TA1E, 1984VAZS, 1984ZA1B, 1985BA45, 1985FI1E, 1985FR1F, 1985HO1B, 1985KI11, 1985PR1A, 1985PR1B, 1985SP05, 1985TH08, 1985YA05, 1985YI1B, 1985YI1C, 1986CR1B, 1986FR12, 1986HO33, 1986LA12, 1986MA03, 1986OC1A, 1986SA30, 1986SU06, 1986WI04, 1986YU1A, 1987BA35, 1987FR1D, 1987KA1W, 1987KR03, 1987OC1B, 1987PR01, 1987SA37, 1987SH1M, 1987WA07, 1988BA75, 1988KR01, 1988MO05; 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 = 6965 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) in (1984AJ01). See also (1979AJ01).
Yield curves and cross sections have been measured for Ed = 48 keV to 17 MeV: see (1979AJ01, 1984AJ01). See also (1983SZZY). 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 for 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 polarization of the deuteron (1985CE12). See also 7Be, (1985WA1C) and (1984KU15; theor.).
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). See also (1983SZZY). 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 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 Epol. d = 191 and 395 MeV see (1986GA18).
Cross sections and angular distributions (reaction (a)) have been measured at Ed = 30 keV to 31 MeV: see (1979AJ01, 1984AJ01). See also (1983SZZY). 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: see (1984AJ01). Polarization measurements are reported in the range 0.4 to 11 MeV: see (1979AJ01, 1984AJ01) and see below.
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 (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]. 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/Γ1 = 0.322 ± 0.091 (1986SO07).
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, (1986ST1E), (1984VO1A, 1988KU1E; applications) and (1983HA1D, 1984KR1B, 1984KU15; theor.).
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). 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 Table 8.4 (in PDF or PS) in (1974AJ01) 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 Table 8.5 (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 = 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).
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). 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*(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 8.7 (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 Ex = 18.9 MeV. 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). A study of the γ-decay of 8Be*(17.64, 18.15) shows no evidence for a pseudoscalar particle postulated to account for narrow peaks in e+ spectra in heavy-ion reactions (1988SA2A). For the earlier references see (1979AJ01). See also (1983CH1C), (1986WE1D), (1984DA1H; astrophysics), (1988KI1C; applied) and (1983GO1B, 1984SE16, 1985GO1B, 1987KI1C; theor.).
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 Epol. p = 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 is virtual relative to the threshold and that its width Γ = 50 ± 20 keV. 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. See (1979AJ01, 1984AJ01).
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 8.8 (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 (1985BO1C). 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]. The transverse polarization transfer, DNN (0°), for the g.s. transition has been measured at Epol. p = 160 MeV (1984TA07). See also (1986MC09; Epol. p = 800 MeV), (1987WAZT), 1984BA1U), (1985CA41; astrophysics), (1983LO12; applications), (1986RA21, 1987TA22) and (1988GU1F; 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). 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 Epol. p = 1.89 to 2.59 MeV (1986SA1P; p0; prelim.) and at 65 MeV (1987TO06; continuum; prelim.). 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 Table 8.8 (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. Table 8.5 (in PDF or PS) in (1984AJ01) displays the upper limit for Γp0/Γ.
The proton total reaction 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). See also 7Li, (1984BA1U), (1986BA88), (1986RA1D; applications) and (1986HA1K, 1988GU1F; theor.) and the "General" section here.
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). For the earlier work see (1984AJ01).
Excitation functions and angular distributions have been measured at many energies 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.
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 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 9 and (1984AJ01). See also (1986ZA09), (1984HA1M, 1984YA1A, 1985BO1K, 1985CA41, 1985DE1K, 1986BO1H, 1987AS05, 1987KA1R, 1987RO25, 1988BA86, 1988FO1A; astrophysics), (1986RA1D, 1986ST1E, 1986TU1B; applications) and (1984BL21, 1984KR1B; 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 [see (1974AJ01, 1979AJ01)] and at 0.19 MeV (1983DA32, 1987DA25) and 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).
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). 8Be*(11.4) may also be involved [Ex = 11.4 ± 0.05 MeV, Γc.m. = 2.8 ± 0.2 MeV] as may state(s) at Ex ≈ 20 MeV: see (1979AJ01). See also 9Be, (1983BL17, 1986BA40), (1986LE1E; applications) and (1983MU13, 1984BL21; theor.).
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 = 2+ mixed isospin states see Table 8.5 (in PDF or PS). Angular distributions have been measured 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). See also 10B and (1983KU17; theor.).
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+. 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 (1983BE51, 1985PU03; theor.).
The total (n, p) cross section has been measured from 25 × 10-3 eV to 13.5 keV. For thermal neutrons the cross sections to 7Li*(0, 0.48) are 38 400 ± 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: this could lead to an increase in the calculated rate of production of 7Li in the Big Bang by as much as 20%. A multi-level R-matrix analysis of the data indicates Γ = 122 keV for the 2- state 8Be*(18.9), and a T = 1 impurity of ≈ 24% (1988KO03). 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 (1987GLZZ, 1987GL1D), (1979AJ01, 1988BO15) and (1984YA1A, 1985BO1K, 1985DE1K; astrophysics).
8Li decays 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).
(1986WA01) has performed a many-level one-channel approximation R-matrix analysis of the β-delayed α-particle spectra in the decay of both 8Li and 8B, obtained by (1971WI05) [as well as of the L = 2 α-α phase shifts]. Warburton finds that there is no need to introduce "intruder" states below Ex ≈ 26 MeV [see, e.g., (1974AJ01)]. He extracts the GT matrix elements for the decay to 8Be*(3.0) and the doublet near 16 MeV; and he points out the difficulties in extracting meaningful Ex and γ values from the β± decay for 8Be*(3.0), as well as the log ft values for the transitions to that state (1986WA01).
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). (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 measurement of the β-decay asymmetry as a function of Eβ is reported by (1986BI1D, 1985BIZZ; prelim.). (1986NAZZ; prelim.) have measured the β-spectrum and compared it with the spectrum predicted from the α-breakup data. See also (1984KO25, 1985GR1A), (1986HA1P, 1988WA1E), (1986MA1T, 1986NAZZ; astrophysics) and (1983KU17, 1984BA25, 1986QUZZ, 1987LY05, 1988BA75; 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: see (1974AJ01). Log ft for the transition to 8Be*(16.6) is 3.3. An analysis by (1986WA01) of the β+ delayed α-spectrum is described in reaction 24. See also (1988WA1E) and (1988BA75; theor.). The β+ spectrum has been measured by (1987NA08) for momenta greater than 9 MeV/c. Then using the α spectra from (1986WA01) the 8B neutrino spectrum is calculated. The average cross section for the "solar neutrino" 37Cl(νe, e-)37Ar reaction is then (1.07 ± 0.02) × 10-42 cm2 [certain corrections may increase this value by as much as 4%] (1987NA08). See also (1982BA1J, 1983CO1D, 1983FO1A, 1983HA1B, 1983VO1C, 1984DA1H, 1984HA1M, 1985BA1N, 1985BA1M, 1985CH1B, 1986BA21, 1986BE1K, 1986DE1H, 1986GR04, 1986HA1I, 1986MA1T, 1986RO1N, 1986WO1B, 1987BA1X, 1987BA89, 1987CH1G, 1987FR1C, 1987FU1G, 1987KR10, 1987RI1E, 1987WE1C, 1988BA86, 1988EW1A, 1988HA1M; astrophysics).
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. For work at Ep = 1 GeV see (1985BE30, 1985DO16). For reactions (d) and (e) see (1974AJ01) and 9Be. For reaction (e) see (1979AJ01).
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)). For spectroscopic factors see (1979AJ01, 1984ZA07). The angular distributions to 8Be*(0, 3.0, 16.9, 17.6, 18.2, 19.1) are consistent with ln = 1: see (1974AJ01).
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. An analysis of reported Γc.m. for 8Be*(3.0) in this reaction shows that there is no Ep dependence. 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. 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: 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 ΓR2 = 580 ± 50 keV, Γλ2 = 680 ± 100 keV and s = 4.8 fm. See (1979AJ01) for the earlier work. A study of the continuum part of the inclusive deuteron spectra is reported at Epol. p = 60 MeV (1987KA25). For reaction (b) see (1988BO47). For reaction (c) [FSI through 8Be*(0, 3.0)] see (1974AJ01, 1984AJ01). See also (1985PU03; theor.) and 10B.
Angular distributions have been measured for 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 Table 8.5 (in PDF or PS). An isospin amplitude impurity of 0.21 ± 0.03 is found for 8Be*(17.6, 18.2): see (1979AJ01).
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). (1986PAZN; prelim.) report Ex = 3.10 ± 0.15 MeV, Γ ≈ 0.9 - 1.3 MeV. See also (1988NE1A; theor.).
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). See also 9Be, and 12C in (1980AJ01), (1985MC1C, applications) and (1985PU03; theor.).
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) see 10Be (1985JA09). For the earlier work see (1979AJ01).
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, 1984AJ01) and Table 8.5 (in PDF or PS) in (1984AJ01).
See (1988RIZZ; prelim).
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 = 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 8.5 (in PDF or PS) and (1979AJ01).
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; prelim.). See also (1984SH1D, 1984SHZJ) and (1985PU03, 1988BA75, 1988KA1M; theor.).
Angular distributions have been measured at Ep = 0.78 to 45 MeV [see (1974AJ01, 1979AJ01, 1984AJ01)], at E = 0.12 to 1.10 MeV (1987BE17; 11B and p; α0, α1) and at Ep = 4.5 to 7.5 MeV (1983BO19; α0). 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 (1983CO1A, 1985MAZG, 1985PU03; theor.).
The first two of these reactions involve 8Be*(0, 3.0): see (1974AJ01, 1979AJ01, 1984AJ01), reactions 39 and 42 in 12C in (1985AJ01). See also (1986AN22) [reaction (a)] and (1982ZH06, 1985GA1B, 1986VD01; theor.). For reaction (c) see (1983LI18; theor.).
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.; also VAP, TAP) and 51.7 MeV (1986YA12; to 8Be*(0, 3.0, 11.4; also VAP) 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 (1983GA14, 1983SH39, 1985GA1B, 1987KA1L; theor.).
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; prelim.). 8Be*(0, 3.0, 11.4, 16.6, 16.9, 17.6) have been populated. See also (1986RA15; theor.).
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 (1984ZE1A, 1985GA1B, 1987KO1E; theor.).
For reaction (a) see 16O in (1986AJ04), (1983DEZW, 1984HU1E, 1984SP1C, 1986ALZN, 1986SH10) and (1984DA1B; theor.). 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). For reaction (c) see (1987SI06).
See 14C in (1986AJ01).
See (1986VD04; Ep = 50 MeV).