A=8Be (1966LA04)

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⁸Be (1966LA04)

(See Energy Level Diagrams for ⁸Be)

GENERAL: See (1956KU1A, 1957FR1B, 1958WI1E, 1959BA1F, 1959BA1D, 1959BR1E, 1959WI1B, 1960BI1E, 1960KU05, 1960PE11, 1960PH1A, 1960PH1C, 1960TA1C, 1961BA1E, 1961CL10, 1961VA17, 1962IN02, 1962IN1A, 1962IW1A, 1963BR1N, 1963BU1C, 1963DA1C, 1963FR1G, 1963KU03, 1963MA1E, 1963MO1H, 1963NA1E, 1963SH1G, 1964AM1D, 1964BA1Y, 1964BE1N, 1964BE1M, 1964BR1H, 1964DA1G, 1964DU1D, 1964GR1J, 1964MA1G, 1964VO1B, 1965BA2H, 1965BE1H, 1965MA2B, 1965MA1G, 1965NE1C, 1965TR1B, 1965YU1D).

See also Table 8.5 [Table of Energy Levels] (in PDF or PS).

1. ⁸Be → ⁴He + ⁴He Q_m = 0.095

The weighted mean of direct Q determinations to 1957 is Q = 94.1 ± 0.7 keV (1957VA11). Reported widths are 4.5 ± 3 eV (1956RU41), 6.8 ± 0.6 eV (1962BA1C), ≤ 3.5 eV (1956HE57), > 0.1 eV (1955TR03): see Table 8.8 (in PDF or PS). (1966BE05) find Q = 92.12 ± 0.05 keV, Γ = 6.8 ± 1.7 eV.

2. ⁴He(α, n)⁷Be Q_m = -18.991 E_b = -0.095

At E_α = 39 MeV, σ < 0.7 mb (1952WA31).

3. ⁴He(α, p)⁷Li Q_m = -17.347 E_b = -0.095

See ⁷Li.

4. ⁴He(α, α)⁴He E_b = -0.095

Reported differential cross section measurements are cited in Table 8.7 (in PDF or PS). The course of the derived phase shifts with increasing energy from E_α = 0.15 to 120 MeV is exhibited in (1956RU41, 1958NI05, 1960JO03, 1963TO02, 1965DA1A).

The s-wave phase shift, δ₀, decreases smoothly from 180° at 0.3 MeV. The absence of measurable effects in the range E_α = 0.15 to 0.2 MeV yields an upper limit of 3.5 eV on the width of the ground state (1956HE57). Analysis of the 0 - 6 MeV data leads to Γ(g.s.) = 4.5 ± 3 eV (1956RU41), 6.8 ± 0.6 eV (1962BA1C): see Table 8.8 (in PDF or PS).

The d-wave phase shift becomes appreciable for E_α > 2.5 MeV and passes through resonance at E_α = 6 MeV (J = 2⁺, E_x = 3.18 MeV, Γ = 1.5 MeV). The g-wave shift rises from E_α ≈ 11 MeV and indicates a broad J^π = 4⁺ level at E_x = 11.4 MeV. The l = 6 and l = 8 phase shifts become active above E_α ≈ 30 and 50 MeV respectively. Dispersion formula fits are somewhat unsatisfactory, but indicate J^π = 6⁺ and 8⁺ levels at E_x ≈ 28 and ≈ 57 MeV respectively. Both the excitation energies and the reduced widths for all five levels are approximately proportional to J(J + 1) (1965DA1A).

Sharp oscillations in the excitation functions at 15° and 45° are observed corresponding to ⁸Be*(16.6) and (16.9). Since no oscillations were observed at 27.8°, these states are assigned J^π = 2⁺ (1964SH19).

Optical model analysis of α - α scattering is discussed by (1960IG02, 1965DA1A); analysis in terms of two-nucleon forces is given by (1959VA1F, 1961SC1B). See also (1959BU07, 1959WI1F, 1960BI1E, 1961GO1T, 1961SH1F, 1962IG1B, 1962SH1F, 1963WI1H, 1964EN1C, 1965OK1B).

5. ⁶Li(d, γ)⁸Be Q_m = 22.280

Not observed: (1953SA1A, 1954SI07).

6. (a) ⁶Li(d, n)⁷Be Q_m = 3.384 E_b = 22.280
(b) ⁶Li(d, n)⁴He + ³He Q_m = 1.797

The yield curve has been measured for E_d = 0.06 to 5.5 MeV (1952BA64, 1954HI34, 1956NE13, 1957SL01). A broad s-wave resonance is indicated at E_d = 0.41 MeV, Γ = 0.45 MeV (1952BA64, 1956NE13). The forward cross section rises from ≈ 22 mb/sr at E_d = 1.1 MeV to ≈ 57 mb/sr at 5.5 MeV without sharp resonances (1957SL01). Above E_d = 0.6 MeV, angular distributions indicate a strong admixture of stripping process (1956NE13).

Comparison of the yields n₀/n₁ (⁷Be(0) and ⁷Be*(0.43)) and p₀/p₁ (⁷Li(0) and ⁷Li*(0.48)) over the energy range E_d = 0.4 to 3.2 MeV shows that the angular distributions are closely similar for n and p. The yield ratios are also closely equal over this range, consistent with the assumption of charge symmetry. The ratio n₀/n₁ increases rapidly as E_d falls below 0.8 MeV, suggesting a change in the reaction mechanism there (1957WI24, 1963BI27, 1963CR08).

7. (a) ⁶Li(d, p)⁷Li Q_m = 5.028 E_b = 22.280
(b) ⁶Li(d, p)⁴He + ³H Q_m = 2.561

Cross sections and angular distributions have been measured for E_d = 30 keV to 5.4 MeV ( 1959AJ76, 1963BI27, 1963ME09, 1964PA06). A broad maximum near E_d = 1.0 MeV is interpreted as indicating a level at E_d = 0.4 MeV (1950WH02). In the range E_d = 1 to 5 MeV there is evidence for both direct interaction and compound nucleus formation (1963BI27, 1963ME09, 1964PA06): at back angles the (d, p₁) data show evidence of the E_d = 3.7 MeV resonance (see ⁶Li(d, α)⁴He). See also ⁶Li(d, n)⁷Be and (1964FE01).

8. ⁶Li(d, d)⁶Li E_b = 22.280

Excitation functions have been measured for E_d = 2 to 4.8 MeV; they do not show any clear resonance behavior (1964PA06). See also ⁶Li.

9. ⁶Li(d, t)⁵Li Q_m = 0.595 E_b = 22.280

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.

10. ⁶Li(d, ³He)⁵He Q_m = 0.839 E_b = 22.280

See ⁵He.

11. ⁶Li(d, α)⁴He Q_m = 22.375 E_b = 22.280

Cross sections and angular distributions have been measured for E_d = 0.03 to 12 MeV (1948HE01, 1950WH02, 1962HA15, 1962JE02, 1963AN10, 1963ME09, 1964MA2D, 1964PA06, 1965MA13). Maxima are observed at E_d = 0.8 MeV, Γ_lab ≈ 0.8 MeV, and E_d = 3.75 MeV, Γ_lab ≈ 1.4 MeV. Analysis of the angular distributions in terms of two-level interference favors J^π = 2⁺ for the upper level, and J^π = 0⁺ or 2⁺ for the lower (1963ME09, 1964PA06). The upper level appears to have a large deuteron width, θ²_d ≈ 0.2, and small θ²_α ≈ 0.025 and θ²_p < 0.005 (1964PA06). A more elaborate analysis appears to require that both levels, E_x = 22.54 and 25.23 MeV, have J^π = 2⁺ and that a third broad J^π = 0⁺ level exist at E_x = 24.02 MeV (1965FR02): see Table 8.10 (in PDF or PS). The same parameters give a good account of the data up to E_d = 9.5 MeV. There is no evidence of further resonances (1965MA13). See also (1959HA29, 1960HA14, 1963EL1D, 1963FR1G, 1964FE01).

12. ⁶Li(t, n)⁸Be Q_m = 16.023

See (1959AJ77, 1962SE1A).

13. ⁶Li(³He, p)⁸Be Q_m = 16.787

At E(³He) = 1.2 to 2 MeV, proton groups are reported corresponding to ⁸Be(0), ⁸Be*(2.9) and possibly ⁸Be*(12.3) (1956MO19, 1956SC01). At E(³He) = 3.5 to 4.2 MeV, groups with Q = 0.163, -0.143 and -0.854 MeV (± 10 keV) are observed, corresponding to the 16.6, 16.9 and 17.6 MeV states (1961ER01): see Table 8.11 (in PDF or PS).

The differential cross sections for ground-state protons show backward peaking at E(³He) = 5, 6 and 7 MeV, forward peaking at E(³He) = 13 and 17 MeV, and both forwards and backward peaks in the intermediate region (1963MA02). Analysis of the angular distribution of protons leading to the E_x = 16.6 MeV level indicates stripping, with L = 0 and a large deuteron width (1963MO1K, 1964MO1L). See also (1963WE1B, 1965KA1F, 1965RO1R, 1965YO1D).

14. ⁶Li(α, d)⁸Be Q_m = -1.567

At E_α = 43 MeV, deuteron groups corresponding to ⁸Be(0) and ⁸Be*(2.9) are reported (1959ZE1A); at E_α = 48 MeV, an additional group ascribed to ⁸Be*(11.3 ± 0.4) is observed (1962CE01). Angular distributions of d₀ and d₁ show forward peaking, with that of d₀ exhibiting pronounced oscillatory characteristics. Attempts to fit the observations with direct interaction theory are only moderately successful (1959ZE1A, 1962CE01). See also (1959ST30, 1962KO13, 1963BL20, 1963DE1G, 1963DE29, 1963WE1B, 1964DE1K).

15. ⁶Li(⁶Li, α)⁸Be Q_m = 20.808

In addition to α-groups to the ground and 2.9 MeV states, there is evidence for a cluster reaction mechanism in which ⁶Li combines with a deuteron cluster to produce a state of ⁸Be at 20.95 ± 0.3 MeV, Γ = 3.4 MeV. At E(⁶Li) = 1.9 MeV, the cross section is 1.3 mb, or 23 times that for ground-state alpha particles (1963KA20). On the other hand (1964QU01) find that the α-particle spectrum is consistent with the involvement of a ⁸Be level near 22 MeV, with Γ ≈ 0.4 MeV. See also (1962CO05). The ⁸Be state decays by proton and α emission: Γ_p/Γ_α = 1.64 (1962GA21). At E(⁶Li) = 3.2 MeV, alpha groups corresponding to ⁸Be* = 16.6, 16.9, (17.6), 18.15 MeV are reported (1964CA1G). See also (1960SH01, 1962CO21, 1963LE19, 1963TA1B, 1964GA1E, 1964SH05, 1965MA2A, 1965NO1A).

16. ⁷Li(p, γ)⁸Be E_b = 17.252

Cross sections and angular distributions have been reported from E_p = 30 keV to 14.5 MeV. Two γ-rays are observed, γ₀ to the ground state and γ₁ to the broad, 2⁺, excited state at 2.9 MeV: E_γ = (17.2, 14.3) + 7/8 E_p. Resonances for both γ₀ and γ₁ occur at E_p = 0.44 and 1.03 MeV, and for γ₁ alone at 2 MeV (see, however, (1963PE15)): see Table 8.12 (in PDF or PS). In the range E_p = 2.5 to 9 MeV, broad resonances are reported at E_p ≈ 5 MeV (γ₀), Γ ≈ 5 MeV (1959GE33, 1963MI08, 1963PE15 (Γ = 5.5 MeV)), at E_p ≈ 7.3 MeV (γ₁), Γ ≈ 8 MeV, and possibly at E_p ≈ 6 MeV (γ₁). The E_p ≈ 5 MeV resonance (E_x ≈ 21.6 MeV) is presumed to represent the giant dipole resonance based on ⁸Be(0), while the γ₁ resonance, 2.0 ± 0.5 (1963MI08), 3 ± 0.5 MeV (1963RE09) higher is similarly related to ⁸Be*(2.9). Angular distributions from E_p = 2.0 to 7.5 MeV are approximately isotropic (except at 2.59 MeV), suggesting l = 0 capture (1963MI08, 1963PE15). The integrated (γ, p) cross section, determined by reciprocity is 22 ± 4 MeV · mb (1963RE09), 20 MeV · mb (1964TA05). See also (1965TA1E).

Angular distributions near the E_p = 0.44 MeV resonance show strong cos θ interference terms which vanish at resonance. At resonance the radiation is nearly isotropic, consistent with p-wave formation, J^π = 1⁺, with channel spin ratio σ(J_c = 2)/σ(J_c = 1) = 5. A detailed study of the angular distributions of γ₀ and γ₁ yields a small cos²θ term for γ₀: A₂ = 0.067 ± 0.025 (1961ME10), A₂ = 0.028 ± 0.003 (1958NE17, 1961BR02), while γ₁ is isotropic: A₂ = -0.004 ± 0.008 (1961ME10); see, however, (1958NE17, 1961BR02). Analysis of these data together with γ-α correlations leads to Γ(E2)/Γ(M1) for γ₁ = 0.018 ± 0.009 (1961ME10), 0.044 ± 0.014 (1960GR21). With Γ_γ = 25 eV, one obtains Γ(γ₀) = 16.7 eV, Γ(γ₁, M1) = 8.15 ± 0.07 eV, Γ(γ₁, E2) = 0.15 ± 0.07 eV. The observed E2 strength is about 15 times smaller than predicted by intermediate coupling shell model (1961ME10). See (1957KU58). The channel spin mixture σ(2)/σ(1) is 3.2 ± 0.5 (1961ME10), 4.1 ± 0.1 (1958NE17).

The relative intensity of γ₀/γ₁ at resonance is 2.0 (1961ME10), 2.3 ± 0.04 (1960MA23: θ = 90°), 1.8 ± 0.2 (1963BA58); the ratio falls rapidly above resonance and is approximately constant at 0.54 ± 0.08 for E_p = 0.8 to 1.0 MeV (1960MA23: see also (1961BR02)). There is evidence for an increase in the ratio at E_p = 1.03 MeV (1964SC19). At E_p = 5.4, 6.5, 7.5 and 8.6 MeV, the ratios are 0.5 ± 0.07, 0.3 ± 0.04, 0.2 ± 0.04 and 0.2 ± 0.04, respectively (1964TA05). Angular distributions in the range E_p = 0.2 to 1.1 MeV indicate interference with s-wave and d-wave non-resonant radiation (1960MA33: see also (1961BR02)); at E_p = 1.03 MeV the resonant radiation is isotropic, suggesting p-wave, J = 1⁺, σ(2)/σ(1) = 5 (1960MA33).

Angular distributions from E_p = 0.8 to 1.7 MeV appear to require interference of the E_p = 0.44 and 1.03 (1⁺) MeV levels with at least two odd-parity levels, possibly those at E_p = 2.1 and 5.8 MeV (1964SC19).

A pair-spectrometer measurement yields E_γ = 17.647 ± 0.015 MeV for γ₀ at the E_p = 440 keV resonance: from the spectrum of γ₁ an excitation energy of E_x = 2.6 ± 0.15, Γ = 0.7 ± 0.1 MeV is obtained for the first excited state (1963BA58). See Table 8.9 (in PDF or PS).

At E_p = 440 keV, α-particles from ⁸Be*(16.63) are observed, indicating the existence of the γ-transition ⁸Be*(17.64 → 16.63). The total resonant cross section is 6.45 ± 0.7 μb (1965WIZZ). The coincidence spectrum at resonance shows the 1.02 MeV γ-ray (17.64 → 16.63), and a weak branch (5.9 ± 2)% (1965WI07), (7.5 ± 2)% (1965KO05), to the 16.92 MeV state. There is no indication of resonance in the yield of α-particles from ⁸Be*(16.6) at E_p = 1.03 MeV (1965WI07). Evidence from this and other reactions involving ⁸Be*(16.6) and (16.9) indicates that neither has a pure isospin character (1965KO05, 1965MA1G). See also (1964PA13).

A careful study of γ - α coincidence spectra at E_p = 441 keV reveals only the 2.9 MeV level in the range E_x = 2 to 7 MeV; the α-spectra can be matched with a single-level dispersion formula with E_λ = 5.95 MeV, γ²_α = 11.9 MeV · fm, θ² = (1.7), R = 4.48 fm (1960GE07). A report of other γ - α groups by (1962CA13) is ascribed to contamination (1964MA25, 1964MI10, 1964PR04, 1964WE1C).

For a review of earlier work, see (1959AJ76). See also (1960SI10, 1960SI1D, 1963FE03, 1963SC1N, 1963TR08)

17. ⁷Li(p, n)⁷Be Q_m = -1.644 E_b = 17.252

This reaction is widely used as a source of monochromatic neutrons: see summary by (1960GI1A). The threshold is E_p = 1880.36 ± 0.22 keV (1963MA1R: see ⁷Be); a second threshold, for neutrons leading to ⁷Be*(0.43), occurs at E_p = 2376 ± 2 keV (1960MA1G), and above E_p = 7 MeV, neutrons corresponding to ⁷Be*(4.55) may be produced (1963BO06).

Reaction cross sections and angular distributions have been reported by (1948TA16: to 2.55 MeV), (1964BU08: 2.4 to 3.0 MeV; n₁), (1957NE22, 1958MA07: to 5.5 MeV), (1959GA08: to 3.25 MeV), (1961BE05: 2.6 to 4.2 MeV; n₀ and n₁ groups separately), (1961NI04: 2.7 to 3.5 MeV), (1963BO06: 3 to 13 MeV; n₀, n₁, n₂), (1964BA16: 4 to 14 MeV) and by (1960HI04: 8 to 14 MeV; n₀, n₁, n₂). See also (1959AJ81, 1960GI1A, 1962AU01, 1963PA1K). The yield of ground state neutrons (n₀) rises steeply from threshold and shows pronounced resonances at E_p = 2.25 (σ ≈ 0.57 b) and 4.9 MeV (σ ≈ 0.36 b) (1963BO06). The yield of n₁ also rises steeply from threshold (1964BU08) and exhibits a broad maximum near E_p = 3.5 MeV (1961BE05).

The behavior of the cross section near the n₀ threshold indicates a broad resonance with J^π = 2^-, T = (0), (l = 0) at E_p = 1.9 MeV with γ²_n/γ²_p ≈ 5.0 (Table 8.13 (in PDF or PS)). The structure at E_p = 2.25 MeV is ascribed to a 3⁺, T = (1), l = 1 resonance with Γ_n ≈ Γ_p and γ²_n/γ²_p = 3 to 10 (1957NE22, 1958MA07, 1959WE1A, 1960GI1A, 1961BE05). The broad peak at 4.9 MeV can be fitted by J^π = 3⁽⁺⁾ with Γ = 1.1 MeV, γ²_n ≈ γ²_p (1963BO06). An additional resonance at E_p = 3.0 MeV may be indicated (1957NE22, 1961BE05). The behavior of the n₁ cross section can be fitted in terms of a single level with J^π = 1^- at E_p = 3.55 MeV (1964BU08).

Polarization of the neutrons has been measured by (1961DA04, 1962EL01: 2.0 to 2.4 MeV), (1959CR84: 3.5 to 5 MeV), (1961AU02: 2 to 3 MeV), (1965MO1L: 3.1 to 3.3 MeV), (1965AN09: 3.0 to 4.0 MeV), (1959BA34, 1960BA27: 3 to 6 MeV), (1963MI01, 1963MI06, 1963MI20, 1964MI14: 4 to 5 MeV), (1962BE11: 4 to 10 MeV) and others (1959AJ76, 1963HA1G). Dominant effects are ascribed to the narrow 3⁺ level at E_p = 2.25 MeV and a broad 2^- background level. At least one level is needed near threshold, and at the higher energies (E_p > 2.6 MeV) two additional levels are indicated (1961AU02).

Neutron spectra and polarizations have been measured at E_p = 143 MeV by (1962BO33, 1963BO1N). Some contribution from quasi-free scattering is indicated: see (1963VA1C, 1965VA23).

18. ⁷Li(p, p)⁷Li E_b = 17.252

Absolute differential cross sections are reported for E_p = 0.4 to 12 MeV (1953WA27, 1956MA12, 1965GL03) and for E_p = 14.5, 20.0 and 31.5 MeV by (1956KI54). Anomalies appear at E_p = 0.44, 1.03, 1.88, 2.1, 2.5, 4.2 and 6.0 MeV (see Table 8.14 (in PDF or PS)). Both the 0.44 and 1.03 MeV resonances are ascribed to p-waves, J = 1⁺, with channel spins 1 and 2 in a ratio of 1 to 5 (1953CH1A, 1955LI1B: compare ⁷Li(p, γ)⁸Be). The structure at E_p = 2.1 MeV may indicate a state with J^π ≤ 3⁺ (1956MA12), 3^- (1957NE22). The E_p = 4.2 MeV resonance is ascribed to an almost pure single-particle level in ⁸Be at 20.9 MeV (1965GL03).

The polarization of 14.5 and 40 MeV protons scattered from ⁷Li has been studied by (1962RO20) and (1963HW01). See also (1961RO20).

See also (1961JO17, 1961JO18, 1965AN12) and (1959AJ76).

19. ⁷Li(p, p')⁷Li* E_b = 17.252

A pronounced resonance appears in the yield of inelastically scattered protons (1951BR10, 1954MO04) and 0.48 MeV γ-rays (1954KR06) at E_p = 1.03 MeV (see Table 8.14 (in PDF or PS)); it is an s- or p-wave resonance interfering with a non-resonant wave of opposite parity (1954MO04: see also (1955LI1B)). Excitation functions for the proton group to the 0.48 MeV state have been measured for E_p = 2.3 to 12 MeV: a peak is observed at 5.6 MeV (1965GL03). See also (1964FA08). The yield of 0.48 MeV γ-rays rises smoothly from E_p = 1.5 to 3.0 MeV except for a pronounced cusp at 1.881 MeV (1955HA34, 1957NE22). See also (1962CA13).

20. ⁷Li(p, d)⁶Li Q_m = -5.028 E_b = 17.252

See ⁶Li.

21. ⁷Li(p, t)⁵Li Q_m = -4.433 E_b = 17.252

See ⁵Li.

22. ⁷Li(p, α)⁴He Q_m = 17.347 E_b = 17.252

Excitation functions and angular distributions have been reported by (1962LU01: 0.4 to 3.3 MeV), (1948HE01: 0.5 to 3.8 MeV), (1958CO62: 0.1 to 0.6 MeV), (1963SA10: 3.0 to 5.5 MeV), (1962CA12: 1.5 to 4.8 MeV), (1960AL18: 12 MeV), (1961HA27: 2.8 to 12 MeV), (1962TE04, 1962TE07: 3.3 to 6.6 MeV), (1964MA51: 4 to 12 MeV), (1962MA40: 15, 18.6 MeV) and (1962CA13, 1963CA1K: 0.5 to 2.5 MeV; see, however, (1964MA25, 1964MI10)). Polarization effects have been studied by (1964AN08: 0.5 to 2.0 MeV), (1962BE14: 1 to 3.2 MeV), (1964AS04: 2 to 3.5 MeV), (1965BO07: 3.2 to 5.3 MeV).

A broad resonance occurs at E_p = 3.0 MeV, Γ ≈ 1 MeV, σ_max ≈ 90 mb (1948HE01): see Table 8.15 (in PDF or PS). A second prominent peak appears at E_p = 5.6 MeV, Γ ≈ 1 MeV (1961HA27, 1962TE04, 1964MA51). Some structure is reported near E_p = 6.0 to 6.5 MeV, and a further peak occurs at E_p = 9.0 MeV (1964MA51).

An earlier suggestion that a J = 0 resonance near E_p ≈ 0 is involved appears to be contradicted by polarization data (1962BE14). The states at E_x = 19.9 MeV and 22.1 MeV (E_p = 3.0 and 5.5 MeV resonances) appear to have J = 2⁺ (1959AJ76, 1961HA27, 1962TE04, 1962TE07, 1965FR02) and to have ⁶Li + d parentage (1962TE01, 1965FR02). Levels at E_x = 23 MeV (E_p = 6.5 MeV) and 25.2 MeV (E_p = 9.0 MeV) are assigned J^π = 4⁺ and 2⁺, respectively (G. Temmer, private communication).

See also (1960BO13, 1962PE20, 1962WE13, 1963AN09, 1964MA2D).

23. ⁷Li(d, n)⁸Be Q_m = 15.028

For E_d = 3.6 to 7.3 MeV, neutron time-of-flight spectra indicate states in ⁸Be at 0, 2.9, 16.64 ± 0.015, 16.9 ± 0.05, 17.64 and 18.15 MeV. Angular distribution of neutrons corresponding to the 16.6, 17.6 and 18.15 MeV states are strongly forward; l_n = 1 for the 16.6 MeV state, consistent with J = 2⁺ (1960DI02). At E_d = 2 MeV, recoil proton spectra show only the ground state and E_x = 2.9 MeV groups; in the range E_x < 9 MeV, no others appear with intensity > 10% of the ground-state group. The spectrum yields E_x = 3.1 ± 0.1, Γ = 1.75 ± 0.1 MeV; comparison with the shape calculated from known α - α phase shifts suggest a considerable contribution of three-body processes (1964JO04). Reported slow neutron thresholds are listed in Table 8.16 (in PDF or PS). See also (1964JO1D, 1964JO1F, 1965DI1F).

Alpha-particle spectra indicate groups corresponding to the break up of ⁸Be*(16.6) and (16.9) (1963BI22, 1963PA04, 1964GL03). Alpha particles attributed to ⁸Be*(11.4) are also reported (1963PA04). In the range E_x = 15.0 to 18.5 MeV, no α-emitting states other than the 16.6 and 16.9 MeV levels are observed (1964GL03). See also (1965BI1F, 1965JO19, 1965MA1G, 1965MA1K).

A large number of additional states with E_x < 16.1 MeV has been suggested in addition to ⁸Be*(0, 2.9, 11.4): for a listing of early references, see (1959AJ76, 1964JO04). See also (1958CA1E, 1960AG03, 1960JU04, 1963MI1M, 1964MI1J).

24. ⁷Li(³He, d)⁸Be Q_m = 11.759

At E(³He) = 24.3 MeV, angular distributions of deuterons corresponding to the ground and first excited states of ⁸Be have been measured (1963WE1B). At E(³He) = 9 to 10 MeV, excitation of ⁸Be*(17.6) is observed (1965GR08). See also (1964DU1E).

25. ⁷Li(α, t)⁸Be Q_m = -2.562

The angular distributions of the tritons to the ground state of ⁸Be have been determined at a number of energies up to 48 MeV; the distributions indicate strong contribution of direct interaction (1959ST1B, 1960GO04, 1960MA15, 1960VL03, 1962MA59, 1963WE1B). At E_α = 40 MeV, higher states are also observed (1960VL03).

26. ⁷Li(⁷Li, ⁶He)⁸Be Q_m = 7.272

See (1957NO17, 1964CA16).

27. (a) ⁷Be(n, p)⁷Li Q_m = 1.644 E_b = 18.896
(b) ⁷Be(n, α)⁴He Q_m = 18.991
(c) ⁷Be(n, γα)⁴He

At thermal energies, the (n, p) cross section is (5.1 ± 0.6) × 10⁴ b (1955HA34), the (n, α) cross section is ≤ 0.1 mb (1962BA1B, 1963BA34) and the (n, γα) cross section is 155 mb (1963BA34). These observations are consistent with odd parity of ⁷Be; the small value of σ(n, α) leads to an estimated F² < 4 × 10^-10 for the intensity of a positive parity admixture (1963BA34). Comparison of the thermal cross section for reaction (a) with the (p, n) cross section observed in the inverse reaction supports the assignment J = 3/2 for ⁷Be(0) (1957NE22). See also (1959AJ76).

28. ⁷Be(d, p)⁸Be Q_m = 16.672

For E_d = 0.8 to 1.7 MeV, proton groups are observed corresponding to the ground state and the 2.9 MeV level: Γ(2.9) = 1.6 ± 0.4 (1959SP1A), 1.53 ± 0.04 MeV (1960KA17). A dispersion formula fit yields parameters E_x = 2.90 ± 0.06 MeV, γ² = 0.60 MeV, θ² = 0.64, R = 5.75 fm (1960KA17): see Table 8.9 (in PDF or PS).

29. ⁸Li(β^-)⁸Be Q_m = 16.002

⁸Li decays mainly to the broad 2.9 MeV, 2⁺ level of ⁸Be, which decays into two α-particles. The β-spectrum, which extends to ≳ 14 MeV, has been studied by (1950HO01), (1960FA02) and others, while the α-spectrum, extending to ≈ 10 MeV, has been reported by (1938RU01, 1948BO20, 1955FR29, 1960BI10, 1960BI06, 1960FA04, 1961DE1E) and others: see (1955AJ61). The two spectra correspond well, except perhaps for low β-energies (1960GR10). For E_α ≲ 5 MeV, the spectrum is closely matched by a density-of-states derived from the experimental d-wave phase shift of α - α scattering; at higher energies, an increasing excess of α-particles appears which may reflect transition into the tail of the J^π = 2⁺ level at E_x = 16.67 MeV (1960GR10, 1963AL19, 1963DA05). See also ⁸B(β⁺).

Studies of the distribution of recoil momenta and neutrino-recoil correlation indicate that the decay is at least 90% GT, and that the GT portion is at least 90% axial vector. The observations indicate J = 2⁺ for ⁸Li (1958BA1E, 1958LA08, 1959LA11, 1959LA05).

The angular correlations W(θ_βα) have been measured for the decays of ⁸Li and ⁸B as a test of the conserved vector current theory of β-decay. The observed correlation is of the form W(θ) = 1 + Acos θ + Bcos²θ; reported values of A and B are listed in Table 8.17 (in PDF or PS). With shell model calculations of the matrix element Γ_γ(M1) for ⁸Be*(T = 1) → ⁸Be*(2.9 MeV), the CVC theory predicts δ ≡ B(⁸Li) - B(⁸B) = (7 ± 2) × 10^-3 W_β (1960KU05, 1960WE1A); conversely, if CVC is assumed correct, the experiment yields Γ(M1) = 1.9 ± 0.6 eV (1962NO02). See also (1963IS04).

30. ⁸B(β⁺)⁸Be Q_m = 17.979

The decay proceeds mainly to ⁸Be*(2.9). The α and β spectra correspond closely to those of ⁸Li, when account is taken of the different Q-values (1960FA04). The ratio ft(⁸B)/ft(⁸Li) = 1.096 (1964TO1D). Detailed study of the high energy portion of the α-spectrum reveals a maximum near E_α = 8.3 MeV, corresponding to transitions to ⁸Be*(16.62). The observed shape is reproduced with a Breit-Wigner density-of-states function with parameters E_x = 16.67 MeV, Γ = 150 to 190 keV; parameters E_x = 16.62, Γ = 95 keV are less good, but acceptable. With the former set, log ft = 2.9 (using τ_1/2 = 0.774 ± 0.005 sec); with the latter, log ft = 3.03. In either case, the low ft-value supports the identification T = 1, J = 2⁺ for ⁸Be*(16.63) (1964MA35). See, however, (1965MA1G).

See also (1960FA02, 1960GR10, 1963DI17) and see ⁸Li(β^-)⁸Be for a discussion of the work on β - α angular correlations.

31. (a) ⁹Be(γ, n)⁸Be Q_m = -1.665
(b) ⁹Be(n, 2n)⁸Be Q_m = -1.665
(c) ⁹Be(α, αn)⁸Be Q_m = -1.665

For reaction (a), see ⁹Be. The (n, 2n) reaction appears to proceed largely via excited states of ⁹Be, with subsequent decay to ⁸Be, mainly ⁸Be*(2.9) (1959CH1E, 1961MY01, 1963JE05, 1964BO31): see ⁹Be and ¹⁰Be. For reaction (c), see (1962ST12) and ⁹Be. See also (1959WI41, 1960KO1G, 1961JE01, 1962CU05, 1965LO1K).

32. ⁹Be(p, d)⁸Be Q_m = 0.559

At E_p = 5.2 MeV, the α-spectrum shows a sharp ground-state group α₀, and a broad group, α₁, corresponding to ⁸Be*(2.9). A pronounced anomaly appears at E_x ≈ 0.75 MeV, on the side of the α₁ group, which is apparently a "ghost" of α₀. A quantitative account is given with a density-of-states function derived from α - α scattering phase shifts (1961BE1E: see also (1962BA1C, 1962HA23, 1963AL19)).

At E_p = 95 to 155 MeV, ⁸Be states at 0, 2.9, 11.4, 16.6, 18.8 and (23) MeV are excited (1956SE1A, 1963BA1R, 1963RA01). See also (1959AJ76, 1959FI1B, 1960PH1B, 1964SH07, 1964TO1D, 1964YA1A), ⁹Be and ¹⁰B.

33. (a) ⁹Be(d, t)⁸Be Q_m = 4.592
(b) ⁹Be(d, t)⁴He + ⁴He Q_m = 4.687

Angular distributions of ground-state tritons have been measured at a number of energies up to 20 MeV: see (1959AJ76) and (1959VL24, 1960NE09, 1960NE11, 1961RE03, 1962BI11, 1965JA07). The width of the 2.9 MeV state is 0.8 MeV (1955CU16), 1.35 ± 0.15 MeV (1959VL24).

See also (1959FI1B, 1959KU1C, 1959ZA01, 1962HA23, 1963OG1A).

34. ⁹Be(³He, α)⁸Be Q_m = 18.913

At E(³He) = 3.0 and 4.0 MeV, angular distributions of the α-particles to the ground-state of ⁸Be and to the levels at 2.9, 16.6, 16.9 and 17.6 MeV have been measured. The excitation energy and width of the first excited state are found to be 2.90 ± 0.04 MeV and 1.35 ± 0.15 MeV (1963DO08): see Table 8.9 (in PDF or PS). The parameters of the higher states (from (1961ER01) and (1963DO08)) are given in Table 8.11 (in PDF or PS). The angular distributions are amenable to analysis by direct interaction except in the case of the 16.6 MeV state which appears to involve compound nucleus formation (1963DO08) (compare ⁷Li(d, n)⁸Be). For angular distribution data at lower energies, see (1955AJ61) and (1963WE08).

The α-particles corresponding to the 2.9 MeV excited state are superposed on a broad, intense continuum extending to E_x > 16 MeV. Some part of this spectrum may be ascribed to a broad level at E_x = 12.5 MeV, with Γ ≈ 5 MeV, but the main contribution appears to be due to a direct 3α breakup (1963DO11: see also (1963WE08)). (1964MO19) find, on the other hand, that the sequential decay, via ⁸Be*(2.9) and (16.93) dominates the reaction. See, however, (1965MO1M). Angular correlation studies confirm J^π = 2⁺ for ⁸Be*(16.9) (1964MO19, 1965MO1N).

See also (1962WE1C, 1964BL12, 1965MA1G).

35. (a) ⁹Be(⁶Li, ⁷Li)⁸Be Q_m = 5.587
(b) ⁹Be(⁷Li, ⁸Li)⁸Be Q_m = 0.367

For reaction (a) see (1960MA1H, 1961LE1K). For reaction (b) see ⁹Be.

36. ¹⁰B(γ, d)⁸Be Q_m = -6.028

See ¹⁰B and (1955AJ61).

37. ¹⁰B(n, t)⁸Be Q_m = 0.229

Angular distributions of the tritons to the ground and 2.9 MeV states of ⁸Be have been measured at E_n = 14.4 MeV (1964VA14). See also (1959AJ76, 1964VA1E) and ¹¹B.

38. (a) ¹⁰B(p, ³He)⁸Be Q_m = -0.534
(b) ¹⁰B(p, pd)⁸Be Q_m = -6.028

See ¹¹C and (1964BA1C).

39. (a) ¹⁰B(d, α)⁸Be Q_m = 17.819
(b) ¹⁰B(d, α)⁴He + ⁴He Q_m = 17.914

Alpha groups are reported corresponding to ⁸Be states at 0, 2.9 (1960BE15, 1960BI11, 1961CI02, 1961LE10, 1963PU02, 1964YA1A; and see (1959AJ76)), 16.6 and 16.8 MeV (1961ER01: see Table 8.11 (in PDF or PS)). A coincidence study of the α₁ group yields the following parameters for the level shape: E_res = 3.15 MeV, Γ = 2.04 MeV, E_λ = 4.00 MeV, γ² = 3.4 MeV · fm, θ² = 0.60, R = 5.5 fm (1963PU02: E relative to E(2α)). (1953TR04) reports E_λ = 5.29 MeV (relative to 2α), γ² = 13.4 MeV · fm, θ² ≈ 2, R = 4.48 fm: see Table 8.9 (in PDF or PS).

Arguments are presented for the assignments J = 2⁺, T = 1 for E_x = 16.63 and J^π = 0⁺ or 2⁺, T = 0 for E_x = 16.93 MeV. Comparison of yields with ⁶Li(³He, p)⁸Be* indicates gross violation of the isospin selection rule, possibly to be ascribed to intermixture in the compound nucleus stage (1961ER01). See, however, (1965MA1G). There is no evidence for an earlier reported level at E_x = 16.08 MeV (1961ER01). See also (1961TE02, 1962TE02, 1965LE09).

40. ¹⁰B(³He, pα)⁸Be Q_m = 12.326

See (1964ET02, 1965AL1B, 1965ET1A, 1965WA1M) and ¹²C.

41. (a) ¹¹B(γ, t)⁸Be Q_m = -11.226
(b) ¹¹B(γ, t)⁴He + ⁴He Q_m = -11.132

See ¹¹B.

42. ¹¹B(p, α)⁸Be Q_m = 8.588

Alpha groups are reported corresponding to the ground and 2.9 MeV state: see (1959AJ76) and (1962AL20). At E_p = 3 to 5 MeV, the α-spectrum shows an anomaly at E_x ≈ 0.75 MeV, ascribed to successive two-body decays with a final density-of-states related to α - α scattering phase shifts (1961BE1E: see ⁹Be(p, d)⁸Be and (1963BR03, 1964BR05, 1964DE1H)). See also ¹²C and (1959KA12, 1959KA13, 1961KO08, 1962BE21, 1963PH1A, 1964BA1C, 1964YA1A, 1965DU1C, 1965LE09, 1965PH1A, 1965SW1B).

43. ¹¹B(d, nα)⁸Be Q_m = 6.363

See (1965OL01).

44. ¹¹B(³He, ⁶Li)⁸Be Q_m = 4.566

At E(³He) = 3.0 MeV, ⁸Be*(2.9) is produced with an intensity 20 times that of the ground state (1964YO06).

45. (a) ¹²C(γ, α)⁸Be Q_m = -7.369
(b) ¹²C(α, 2α)⁸Be
(c) ¹²C(p, pα)⁸Be
(d) ¹²C(n, nα)⁸Be

Reaction (a) involves states of ⁸Be at 0, 2.9, 16.6, 16.9 and (17.6) MeV: see (1955GO59, 1959AJ76, 1964TO1A). See also (1961SE13, 1963SH04, 1964LE1C).

At E_α = 25.4 MeV, the four-body breakup (¹²C + α → 4α) is greatly favored over reaction (b) (1962BR14: see also (1961VA38, 1962VA25)). See also (1961GO1T, 1962IG1B, 1963LA02).

Reaction (c) at E_p = 15 to 29 MeV proceeds predominantly through the ground state and the 2.9 MeV level. It is not clear whether higher levels of ⁸Be are involved (1955NE18, 1960VA10, 1962VA1A, 1963VA04). See also (1963JA07, 1964BA1C, 1964KE1F, 1964SY02, 1965YU1C, 1965YU1D).

For reaction (d) see (1955FR35, 1960VA10, 1964BR25).