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GENERAL: See also Table 8.3 [Table of Energy Levels] (in PDF or PS).

Theory: See (1955HE1E, 1956KU1A, 1956PE1A, 1957BI1C, 1957FR1B, 1958WI1E).

1. 8Be → 4He + 4He

Qm = 0.094

Recent Q-values are 93.7 ± 0.9 keV (1957CO59: ⁹Be(p, d)⁸Be), 90 ± 5 keV (1955TR03: ¹¹B(p, α)⁸Be): the weighted mean of all measurements is 94.1 ± 0.7 keV (1957VA11). The width of the ground state is 4.5 ± 3 eV (1956RU41: 15% of Wigner limit), ≤ 3.5 eV (1956HE57). The second value leads to τ_m ≥ 2 × 10^-16 sec. (Combination of these values places the mean life in the range τ_m = 2 to 4.5 × 10^-16 sec.) An upper limit to the mean life is 6 × 10^-15 sec (1955TR03). See also (1955AJ61).

2. 4He(α, p)7Li

Qm = -17.347

Eb = -0.094

See ⁷Li.

3. 4He(α, α)4He

Eb = -0.094

Absolute differential cross sections are reported for E_α = 0.15 to 3.0 MeV (1956HE57), E_α = 3.0 to 5.9 MeV (1956RU41), E_α = 12.9 to 21.6 MeV (1953ST52), E_α = 12.3 to 22.9 MeV (1956NI20), E_α = 20 and 20.4 MeV (1951BR92, 1951MA1B), E_α = 30 MeV (1951GR45, 1952GR1A), E_α = 38.5 MeV (1957BU13), and E_α = 44.7 MeV (1957CO63). See also (1958CH35).

Phase shifts summarizing the work of (1956HE57), (1956RU41) and (1956NI20) are presented in (1956RU41) and (1958NI05). These three sets of data appear to join smoothly, but do not appear to fit well with the data of (1953ST52). For E_α < 3 MeV, only the s-wave phase shift is important. A careful survey in the range 146 - 202 keV reveals no effect of the ground state and places an upper limit of Γ ≤ 3.5 eV on this state (1956HE57): see Table 8.5 (in PDF or PS). Analysis of the 0 to 6 MeV data by effective range theory leads to a value Γ = 4.5 ± 3 eV for the ground-state width; θ² ≈ 0.15 of the Wigner limit (with R = 5.7 × 10^-13 cm). Some evidence of shape-dependence is found in this analysis (1956RU41). According to (1958NI05) a good account of the s-wave phase shift below 6 MeV is given by hard-sphere scattering plus resonance scattering from the ground state with a width θ² = 0.75 (R = 4.44 × 10^-13 cm). There is no indication of other S-states below E_x = 11.5 MeV (1958NI05).

The d-wave phase shift first becomes appreciable near E_α = 2.5 MeV (1956HE57) and appears to pass through resonance at 6.0 MeV (1956RU41). The g-wave shift rises continuously from E_α = 11 to 23 MeV; a broad ⁸Be level is indicated at E_x = 11.7 MeV (1956NI20, 1958NI05). The course of the phase shifts appears to be consistent with a simple two-body interaction with an attractive potential near R ≈ 5 × 10^-13 cm and a repulsive core at a smaller radius; some dependence of the well shape on l is required (1951HA1B, 1956HE1B, 1956RU41, 1958NI05, 1958VA1B). A detailed comparison with the model of (1951HA1B) is made by (1958NI05). At 38.5 MeV, the s and d phase shifts are large, while the δ₄, δ₆ and δ₈ phase shifts are small. These results are consistent with 0⁺ and 2⁺ states near 19 MeV (see ⁷Li(p, α)⁴He) and are not inconsistent with a 4⁺ state at ≈ 11 MeV (1957BU13). See also (1955AJ61), (1956HA1C, 1958MC1C; theor.) and (1954SN1A).

4. 6Li(d, γ)8Be

Qm = 22.279

Not observed: see (1953SA1A, 1954SI07).

5. (a) 6Li(d, n)7Be	Qm = 3.380	Eb = 22.279
(b) 6Li(d, n)4He + 3He	Qm = 1.796

The excitation 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). At this energy the neutron yield to the 0.43-MeV state of ⁷Be is isotropic, while at E_d = 600 keV and above, the angular distributions indicate a strong admixture of stripping process (1956NE13). A sharp resonance at E_d = 2.12 MeV is reported by (1952BA64). However, (1957SL01) find that 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. This is confirmed by (1954BU1B) who reports no appreciable change in slope at E_d ≈ 1.8 MeV and suggests that the increase in neutron yield observed by (1952BA64) might have been due to oxygen contamination.

The ratio of 430-keV γ-radiation from this reaction and 477-keV γ-radiation from the mirror reaction, ⁶Li(d, p)⁷Li, has been measured for E_d = 0.2 to 1.8 MeV. This ratio, which measures Γ_n/Γ_p, rises from 1.1 to about 1.13 at E_d = 0.45 MeV, falling to 0.98 at E_d = 1.8 MeV. The theoretical ratio, assuming charge symmetry, rises from 0.96 at low energy to 0.98 at E_d = 1.8 MeV. It is concluded that the predictions of charge independence are borne out within 15%, and that the slight deviation observed may be connected with the resonance near E_d = 0.45 MeV (1957WI24). See also (1954HI34).

6. (a) 6Li(d, p)7Li	Qm = 5.027	Eb = 22.279
(b) 6Li(d, p)4He + 3H	Qm = 2.561

Cross sections and angular distributions have been measured for E_d = 30 keV to 3 MeV by (1950KR1A, 1953SA1A: see (1950WH02, 1954NI10, 1957JA37)). A broad maximum near E_d = 1.0 MeV is interpreted by (1950WH02) as indicating a level at E_d = 0.4 MeV, Γ ≈ 0.5 MeV. The angular distributions at E_d > 1 MeV indicate stripping effects, with l_n = 1 (1954NI10). See also the discussion of the work of (1957WI24) in the preceding section. See also (1955AJ61).

7. 6Li(d, d)6Li

Eb = 22.279

See ⁶Li.

8. 6Li(d, t)5Li

Qm = 0.765

Eb = 22.279

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.

9. 6Li(d, 3He)5He

Qm = 0.839

Eb = 22.279

See ⁵He.

10. 6Li(d, α)4He

Qm = 22.373

Eb = 22.279

Cross sections have been measured for E_d = 30 keV to 1.6 MeV (1953SA1A: see (1950WH02, 1954HI34, 1957JA37)). A broad maximum is observed at E_d = 0.6 MeV which is interpreted in terms of a resonance at E_d = 0.35 MeV, Γ ≈ 0.5 MeV (1950WH02: see, however, (1954HI34)). See also (1956PO1A), (1956SA1B; theor.) and (1952AJ38).

11. 6Li(t, n)4He + 4He

Qm = 16.115

See (1952CU1B).

12. 6Li(3He, p)8Be

Qm = 16.786

At E(³He) = 1.25 MeV, proton groups are observed to the ground state, the 2.9-MeV state and possibly to a state at ≈ 12.3 MeV (Γ ≈ 2 MeV, intensity ≈ 6% of 2.9-MeV transition). It is suggested that the 12.3-MeV state may be that observed in ⁴He(α, α)⁴He. No other states are observed with E_x ≲ 14 MeV. The upper limits on the intensities of groups leading to such states are 1% (of 2.9-MeV transition) for sharp states and 3% for levels 1 MeV wide (1956MO19). These results are confirmed by (1956SC01) at E(³He) = 1.5 and 2 MeV: no group of width ≲ 1 MeV appears for E_x < 14 MeV with an intensity as much as 2% of the ⁸Be*(2.9) group. See also (1953KU24, 1955AL57).

13. 6Li(α, d)8Be

Qm = -1.565

This reaction has been observed at E_α = 31.5 MeV (1956WA29).

14. 7Li(p, γ)8Be

Eb = 17.253

The cross section has been studied from E_p = 30 keV (1957JA37) to 7.7 MeV. Resonances are observed at E_p = 0.44, 1.03 and 2.1 MeV: see Table 8.6 (in PDF or PS). There is no further structure up to 5 MeV (1952BA1B). The radiation comprises two components, one from the ground-state transition, with E_γ = 17.2 + 7/8 E_p and the other from the transition to the 2.9-MeV broad excited state, with E_γ ≈ 14.3 + 7/8 E_p. Both are resonant at the 0.44-MeV resonance, but only the lower energy transition shows the 2.1-MeV resonance (1957NE22). The intensity ratio of the higher to the lower-energy radiation increases from 0.5 at E_p = 0.2 MeV to 1.7 at E_p = 0.44 MeV and falls to 1.0 at E_p = 0.6 MeV (1956CA1A: θ = 90°). Between E_p = 1.0 and 3.5 MeV the ratio is constant within 30% at 2/3 (1955WI1D, 1957NE22). Evidence for a component at ≈ 12 MeV is discussed by (1953TI1C: see also (1955CA19)). A broad resonance appears near E_p = 5.8 MeV probably corresponding to the "giant" (γ, p) resonance, E_x = 22.3 MeV (1959GE33).

The angular distributions of both γ-rays show small deviations from isotropy at the E_p = 0.44 MeV resonance and exhibit strong interference effects nearby. The observed distribution of the 17.6-MeV radiation at resonance is consistent with p-wave formation if the channel spin ratio χ ≡ σ(1)/σ(2) = 1/4: this ratio implies an intermediate coupling with a/K = 2 to 3 (1958NE17: see also (1950DE1A, 1957FR1B)). Angular distributions in the range E_p = 0.9 to 1.2 MeV are reported by (1954KR06) an 0°/90° cross sections for E_p = 1.5 to 3.5 MeV by (1957NE22). The latter observations indicate that some process other than direct s-wave capture is responsible for the background between resonances (1954WI1A, 1957NE22).

A study of (γ - α) coincidences at E_p = 0.45 MeV yields an angular correlation which rules out the assignment J = 0⁺ to the 2.9-MeV ⁸Be level and indicates that the 14.7-MeV γ-radiation contains a mixture of E2 and M1 radiation (1956BO1H: see also (1954DE1D)). The alpha spectra, taken singly (1956LA1A) and in coincidence with γ-rays (1958ME78) show no evidence of weakly excited levels reported by (1954IN1A: see also (1955TI1B)). In the work of (1958ME78), the 2.9-MeV level appears to have a width of 1.9 MeV; compare (1950BU1B). There is some evidence for a broad level near E_x = 10 MeV (1956LA1A).

See also (1955RI1A, 1956PO1A) and (1957FR1B, 1957KU58; theor.).

15. 7Li(p, n)7Be

Qm = -1.646

Eb = 17.253

The cross section has been studied from the threshold at E_p = 1.8811 MeV (see ⁷Be) to 10 MeV (1957BO1F, 1957JA37, 1957KA1C: see also (1958TA03)). Resonances are indicated at E_p = 1.93, 2.25, (3.0) and 5.0 MeV (see Table 8.7 (in PDF or PS)). Absolute cross sections are given by (1948TA16) and (1958MA07): see also (1959MA20: footnote 14). Angular distributions in the range E_p = 2.0 to 2.5 MeV show strong (cos θ) terms, suggesting interference of states of opposite parity (1948BR1A, 1948TA16). (1954AD1A) has shown that the behavior in this region can be accounted for by ascribing the 2.25-MeV resonance to p-wave formation, with J = 3⁺ and γ²_p = γ²_n = 0.8 × 10^-13 MeV-cm (presumably the T = 1 analogue of ⁸Li*(2.28)), and assuming a background due to s-wave, J = 1^- and 2^-, levels of undetermined location. According to (1957NE22), a better account of the cross section below 2.4 MeV is obtained with the J = 3⁺ level assumed to have γ²_n/γ²_p = 5.5 and a single s-wave J = 2^- level at E_p = 1.9 MeV, with γ²_n/γ²_p = 5.5. With this large ratio the low energy cross section can be accounted for in detail and can be made to agree with that derived from the inverse reaction ⁷Be(n, p)⁷Li (1957NE22, 1958MA07: see also (1955HA34)). [It is of interest to note that a similar apparent deviation from charge independence occurs in ¹⁰B(α, n)¹³N and ¹⁰B(α, p)¹³C (see ¹⁴N). On the other hand, see ⁶Li(d, p)⁷Li and ⁶Li(d, n)⁷Be.] Using the stacked-foil method, (1957KA1C) report structure in the excitation function corresponding to ⁸Be levels at 21.5, 22.5, 23.85, (24.9) and (25.6) MeV. At E_p = 10 MeV, the cross section for production of ⁷Be is 120 ± 20 mb (1957KA1C), 100 ± 20 mb (1957BO1F).

The relative intensity of the low-energy neutrons (to ⁷Be*(0.43)) to the high-energy (ground state) neutrons varies with energy: see Table 8.8 (in PDF or PS). In the range E_p = 2.5 to 2.9 MeV, the low-energy neutrons are practically isotropic (c.m. system). From the shape of the excitation function, (1955BA1L) conclude that the reaction to ⁷Be* proceeds by s-wave protons in and s-wave neutrons out.

It is pointed out by (1954AD1A) that the existence of the J = 3⁺ level, apparently well separated from the other components J = 1⁺ and 2⁺ which can be formed with channel spin 2, indicates a strong spin-orbit interaction, which should lead to polarization of the neutrons and scattered protons. Polarization measurements are reported by (1954AD1A, 1954WI42, 1955OK01, 1956WI1E, 1958CL98, 1958CR85, 1958ST28). See also (1957RO1C, 1958GI15).

16. 7Li(p, p)7Li

Eb = 17.253

Absolute differential scattering cross sections are reported for E_p = 0.4 to 1.4 MeV (1953WA27), E_p = 1.4 to 3.0 MeV (1956MA12), and E_p = 14.5, 20.0 and 31.5 MeV (1956KI54). Anomalies appear at E_p = 0.44, 1.03, 1.88, 2.1 and 2.5 MeV (see Table 8.7 (in PDF or PS)). Both the 0.44- and the 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, 1953LI1A, 1955LI1B: compare ⁷Li(p, γ)⁸Be).

The anomaly at E_p = 1.88 MeV coincides with the ⁷Li(p, n)⁷Be threshold and is ascribed to the abrupt change in total width of a broad (2^- ?) resonance when neutron emission becomes possible (1956MA12, 1957NE22). The observed structure at 2.0 - 2.25 MeV may reflect interference of the p-wave 2.25-MeV (J = 3⁺) resonance with one at E_p = 2.1 MeV, also formed by p-waves (1956MA12). Preliminary results of a phase shift analysis suggest, on the other hand, interference between a J = 3^- level at E_p = 2.1 MeV with a 2^- level at E_p = 1.9 MeV, and interference of the 3⁺ level at E_p = 2.25 MeV with a broad 1⁺ level near 3 MeV (J. Olness quoted in (1957NE22)).

17. (a) 7Li(p, p')7Li*		Eb = 17.253
(b) 7Li(p, p'γ)7Li

A pronounced resonance appears in the yield of inelastically scattered protons (1951BR10, 1954MO04) and 0.48-MeV γ-rays (1954KR06) at E_p = 1.030 ± 0.005 MeV, Γ = 168 keV. The angular distribution of the protons is approximately isotropic at resonance, σ = 42 mb, and asymmetric above it, consistent with an s- or p-wave resonance interfering with a non-resonant wave of opposite parity (1954MO04: see also (1955LI1B)).

The yield of 480-keV radiation rises smoothly from E_p = 1.5 to 3.0 MeV except for a pronounced cusp at 1.881 MeV (1955HA34, 1957NE22). Analysis of the excitation function suggests that the inelastic process is enhanced by the J = 2^- level at 1930 keV and that the cusp results from the sudden increase in the total width when neutron emission becomes possible (1957NE22). See also (1951BA79).

18. 7Li(p, d)6Li

Qm = -5.026

Eb = 17.253

See ⁶Li.

19. 7Li(p, t)5Li

Qm = -4.261

Eb = 17.253

See ⁵Li.

20. 7Li(p, α)4He

Qm = 17.347

Eb = 17.253

The cross section, which has been measured to 3.8 MeV, exhibits a broad maximum at E_p = 3 MeV which is interpreted in terms of a level ≈ 1 MeV wide, with J = 2⁺, at E_p ≈ 3 MeV, and a several-MeV broad level of J = 0⁺, underlying the region: see (1948HE01, 1948HE1B, 1948IN1A, 1953SA1A, 1957JA37). Absolute differential cross sections are reported by (1958FR03) for E_p = 1.0 to 1.5 MeV: at 1.01 MeV, dσ/dω (lab, 90°) = 0.67 mb/sr, see also (1956MA12). Differential cross sections have also been measured at E_p = 15.0 and 18.5 MeV; there are indications of a triton pickup process at these energies (1957MA1F). See also ⁴He(α, p)⁷Li, (1955AJ61, 1955RI1A, 1956BA1E, 1956CR47, 1958BU38).

21. 7Li(d, n)8Be

Qm = 15.026

A careful study of the neutron spectrum at E_d = 2 MeV at several angles reveals only two distinct groups, corresponding to ⁸Be(0) and ⁸Be*(2.9). No other levels below E_x = 10 MeV appear in this work: upper limits for groups leading to levels near E_x = 4 to 5 MeV and E_x = 7.5 MeV are 10% and 20%, respectively, of the ground state group. Angular distributions of the ground state and 3-MeV state neutrons exhibit l_p = 1 stripping patterns at forward angles (1954TR1A, 1955TR1B). Other workers have reported neutron groups corresponding to levels at 2.2, 2.9, 4.1, 5.1 and 7.6 MeV: see for instance, (1953TR1B, 1954RE1A, 1955BE1D, 1955GI1B, 1955IH1A, 1955IH1B), as well as states at 10 MeV (1941RI1A), 11.1 and 14.7 MeV (1950WH1B).

Thresholds for slow neutron production indicate ⁸Be levels at 16.08, 16.67, 17.61 and 18.20 MeV (1954BO79, 1957SL01) (see Table 8.9 (in PDF or PS)). It is suggested that the 16.67-MeV level is the lowest T = 1 level of ⁸Be, and that the levels at 17.61 and 18.20 MeV correspond to those seen in (⁷Li + p) at E_p = 0.44 and 1.03 MeV (1954BO79). A search for nuclear pairs from possible pair-emitting states of ⁸Be yielded an upper limit of 2 × 10^-5 mb at E_d = 0.33 MeV for excitation of such states in the range E_x = 5.0 to 8.5 MeV (1955BE62). See also (1955CA1A, 1955CA1C, 1955PE1C, 1956BO1F, 1956BO43, 1956CA1B, 1956RI37, 1957CA14).

22. 7Li(3He, d)8Be

Qm = 11.759

See (1954MO92) and (1955AL57).

23. 7Li(α, t)8Be

Qm = -2.560

Not observed.

24. 7Li(7Li, 6He)8Be

Qm = 7.247

See (1957NO17).

25. (a) 7Be(n, p)7Li	Qm = 1.646	Eb = 18.899
(b) 7Be(n, α)4He	Qm = 18.993

At thermal energies, the (n, p) cross section is (5.1 ± 0.6) × 10⁴ b (1955HA34) while the (n, α) cross section is < 25 mb (1958SE08). These observations are consistent with the odd parity of ⁷Be. Less than 10% of transitions involve ⁷Li*(0.48). Comparison of the (n, p) cross section with the cross section for ⁷Li(p, n)⁷Be gives evidence for an l = 0 level in ⁸Be within 20 keV below the neutron threshold, with Γ < 30 keV (1955HA34). See, however, (1957NE22, 1958MA07), and see also (1954AD1A). Comparison of the thermal cross section with the (p, n) cross section observed in the inverse reaction supports the assignment J = 3/2 for ⁷Be_g.s. (1957NE22).

26. 7Be(d, p)8Be

Qm = 16.672

At E_d = 0.85 MeV, θ = 30°, 90° and 270°, proton groups are observed corresponding to ⁸Be_g.s. and the broad level, E_x = 2.95 MeV, Γ = 1.6 ± 0.4 MeV. No other prominent groups appear for E_x < 5.8 MeV (1958SP1A).

27. 8Li(β-)8Be	Qm = 16.001
	Q0 = 15.94 ± 0.08 (1958VE20).

The observed β-spectrum closely matches the mean of reported α-spectra (1955FR29) for E_β > 3 MeV and is consistent with 89% branching via ⁸Be*(2.9), with log ft = 5.67 and 11% to higher states, possibly ⁸Be*(11.7), log ft = 4.6. Less than 1% of transitions involve ⁸Be_g.s.: log ft > 8 (1958VE20: see also (1955AJ61)). Upper limits to transitions to sharp states in ⁸Be with E_x = 2, 4 and 6 MeV are, respectively, 2.5, 1 and 0.5% (1955FR29: see also (1956AR21)).

The α - β angular correlation is isotropic within a few per cent for all β-energies: see (1955AJ61). It is pointed out by (1955MO1A) that a small, ≈ 0.5%, anisotropy may be expected at high β-energies because of the increased importance of l = 1 and 2 emission, even in an allowed transition. Anisotropy in the β-decay from partially oriented ⁸Li nuclei is reported by (1957BU44: see also (1958SH1A)). The distribution of recoil momenta and the neutrino-recoil correlation establish that the decay is at least 90% Gamow-Teller and that the Gamow-Teller portion is at least 90% axial vector in character. The observations also require J = 2⁺ for the ⁸Li ground state (1958BA1E, 1958LA07, 1958LA08: see also (1958MO1D)). An upper limit of 0.2 ± 0.1 % is reported by (1956TA07) on the number of disintegrations leading to 4.9-MeV γ-radiation: see also (1953BU35). See also (1955GI1A) and (1955JA1C, 1955LA1D; theor.).

28. 8B(β+)8Be

Qm = 17.978

The observed positron spectrum matches the ⁸Li - ⁸B α-spectra for E_β⁺ > 6 MeV. About 80% of transitions involve ⁸Be*(2.9), log ft = 5.72, with ≈ 19% to higher states, possibly ⁸Be*(11.7), log ft = 4.6. Less than 5% go to ⁸Be_g.s., log ft > 7.3 (1958VE20). See (1950AL57, 1952KI1A, 1954GI1A). See also (1955GI1A).

29. (a) 9Be(γ, n)8Be	Qm = -1.667
(b) 9Be(n, 2n)8Be	Qm = -1.667
	Q0 = -1.664 ± 0.004 (1956CO56).

At E_γ = 6 MeV, most of the transitions are to the 2.9-MeV state (1954CA1A). See also ⁹Be and (1956CO56). For reaction (b), see ⁹Be and ¹⁰Be.

30. 9Be(p, d)8Be

Qm = 0.560

Angular distributions of ground-state deuterons are remarkably similar for E_p = 5, 10, 16.5 and 22 MeV and show strong contributions from the pickup process (1951HA1A, 1953CO1C, 1955SU1A, 1956RA32, 1956RE04, 1956SU1A, 1958SU14). The significance of this result, which is not consistent with the simple Butler theory, is discussed by (1955DA1D, 1956GL25: see also (1955DA1E, 1955SA1D, 1956DA1D, 1956KO1B, 1957GR1C)). At E_p = 16.5 MeV, the distribution is consistent with l_n = 1, R₀ = 3.0 × 10^-13 cm, and θ² = 0.024 for ⁸Be(0) + n (1956RE04). At higher energies, the distributions appear to be affected by pickup from within the nuclear volume (1956BE14, 1956SE1A). For E_p = 31 and 95 MeV, unresolved ⁸Be states near 17 MeV appear, possibly representing pickup of a 1s neutron in ⁹Be (1956BE14, 1956SE1A: see ⁹Be).

At E_p = 7.4 MeV, a search for ⁸Be levels revealed only the ground-state and the 2.9-MeV state in the range E_x = 0 to 6.5 MeV (1956CA1C). See also (1954FI35, 1955GI1A, 1956ST30, 1957BE49) and (1955LA1C; theor.).

31. (a) 9Be(d, t)8Be	Qm = 4.592
(b) 9Be(d, t)4He4He	Qm = 4.686

At E_d ≈ 1.2 and 3.5 MeV, the ground and first excited states are observed: see (1952CU1A, 1953CU1B, 1953GE01, 1956GE1A, 1956JU1D). For the first excited state, (1955CU16) finds E_x = 2.8 ± 0.1 MeV, Γ = 0.8 MeV. At E_d = 0.5 MeV (θ = 60° and 90°), there is no evidence for excited states of ⁸Be with E_x = 3.4 to 4.8 MeV: the upper limit to the intensity of the corresponding groups is 2% of the 2.9-MeV group (1956GE1A). At E_d = 14.8 MeV (θ = 15°), there is no evidence for states with E_x = 7.1 to 15.4 MeV (1956CA1C).

Recent studies of the angular distribution of ground-state tritons for E_d = 0.1 to 15 MeV have been reported by (1955JU10, 1955JU1B, 1956HA90, 1957SM78: see also (1955AJ61)). Below E_d ≈ 0.5 MeV, the tritons show strong backward peaking, suggestive of interference of compound nucleus states of opposite parity (1957SM78: see ¹¹B). At high energies, the reaction proceeds mainly by pickup, with l_n = 1 (1956HA90). See also (1955DA1E; theor.), (1957HA1F) and ⁹Be.

32. 9Be(3He, α)8Be

Qm = 18.911

At E(³He) = 0.90 MeV, the ground (weak) and 2.9-MeV (strong) states are observed: see (1955AJ61).

33. 10B(γ, d)8Be

Qm = -6.025

⁸Be states up to E_x = 10 MeV are reported to be involved in this reaction: see (1954TI1C, 1955AJ61, 1955TI1A).

34. 10B(n, t)8Be

Qm = 0.234

See (1951PE1B, 1954RI15, 1955JA18, 1956FR18, 1957TI1A) and ¹¹B.

35. 10B(p, 3He)8Be

Qm = -0.532

See (1952CR30, 1955RE16).

36. (a) 10B(d, α)8Be	Qm = 17.819
(b) 10B(d, α)4He4He	Qm = 17.913

All observers agree that transitions occur to the ground state and a state at E_x ≈ 2.87 ± 0.06 MeV, Γ = 0.93 ± 0.15 MeV, (weighted mean of (1951WH1A, 1953CU1C, 1953TR04)). However, there is conflicting evidence on whether other states with E_x < 15 MeV are involved in this reaction. (1954CU1A) report additional states at (4), 5.1 and 7.5 MeV (see also (1955AJ61)). However, (1953TR04: E_d = 0.6 to 1.07 MeV) report no other low lying states; (1956BO1J: E_d = 5 MeV, θ = 50° and 90°) have not observed any other states below E_x = 9 MeV; (1955HO48: E_d = 1.4 to 3.2 MeV, several angles) find no evidence for excited states other than the 2.9-MeV level below E_x ≈ 10 MeV; and (1956KA1A, 1958KA31: E_d = 1.7 MeV) find no groups corresponding to ⁸Be states with E_x = 9.8 to 14.8 MeV above the continuum attributed to ¹⁰B(d, α)⁴He⁴He.

The observed α-spectrum corresponding to the 2.9-MeV level may be reasonably well accounted for by the Breit-Wigner formula with l_α = 2, E_λ = 5.29 MeV, γ²_α = 13.4 × 10^-13 MeV-cm, R = 4.48 × 10^-13 cm [θ² ≈ 2] (1953TR04).

37. (a) 11B(γ, t)8Be	Qm = -11.230
(b) 11B(γ, t)4He4He	Qm = -11.136

These reactions have been observed in boron-loaded photoplates. Six states of ⁸Be below E_x = 5 MeV are reported to be involved in reaction (a) (1953ER1A). See also (1955TI1A).

38. 11B(p, α)8Be

Qm = 8.582

Alpha-particle groups corresponding to the ground state and to the 2.9-MeV state are reported; E_x = 2.94 ± 0.06 MeV, Γ = 0.84 MeV (1951LI1B, 1953BE61: see (1955AJ61)). Excitation of several additional levels is reported by (1953GL1A); however, a careful search by (1955HO48) reveals no evidence for any levels with E_x < 7 MeV except the ground state and that at 2.9 MeV.

The alpha particles leading to the ground state are strongly anisotropic at the E_p = 163-keV resonance (¹²C* = 16.11, J = 2⁺; T = 1); it is thus unlikely that J = 2 (1952TH1B). The directional correlation of successively emitted α-particles at E_p = 163 keV indicates isotropic breakup of ⁸Be(0) and hence J = 0, with J = 2 excluded. From the angle between the α-particles resulting from the breakup, Q = 90 ± 5 keV is obtained; the half-life is < 4 × 10^-15 sec (1955TR03). The angular correlation of alpha particles leading to the 2.9-MeV state with those resulting from the subsequent breakup is consistent with J = 2⁺ for the 2.9-MeV state (1955GE1A). Certain peculiarities in the relative yields of ground state and 2.9-MeV excited state α-particles suggest that the latter level may have a significant T = 1 admixture: see (1953BE61, 1955HO48).

Nuclear pairs have been reported with E(π) = 7 MeV (1951PH1B); see, however, (1955BE62). See also (1955TI1B).

39. 12C(γ, α)8Be

Qm = -7.375

For E_γ < 40 MeV, the reaction involves mainly states of ⁸Be at 0, 2.9, (4.1) (16.5 ± 0.2; Γ < 0.4), 16.8 ± 0.2 (Γ < 0.3), 17.6 ± 0.2 (Γ < 0.3) MeV, with indications of further states near 6, 10 and 15 MeV. There is no evidence for three-body reactions in this work (1955GO59). Evidence for levels at 3.2, 4.0, (7.5) and 9.0 MeV is reported by (1955GL1A: see also (1954TI1C)). The ground state decay energy is given as 87 ± 8 keV; for the first excited state, E_x = 3.06 MeV, Γ = 0.9 MeV (1955GO59). The excitation function is characterized by a number of resonances, suggesting that the process takes place via definite energy levels of ¹²C (see ¹²C); the principal types of levels involved being J = 1^-; T = 1, (E1 absorption) and J = 2⁺; T = 0, 1 (E2) (1955GO59: see also (1953GE1B, 1955TI1A, 1957MU1C)). For E_γ < 25 MeV, the reaction proceeds mainly to ⁸Be(0) and ⁸Be*(2.9); angular correlations indicate J = 0 and J = 2, respectively for these states. Wide variations in the branching ratio with energy are attributed to differences in isobaric spin impurities, estimated as 0.05 × 10^-3 for the ground state, and ≥ 10^-3 for ⁸Be*(2.9).

For E_γ > 26 MeV the reaction changes radically, now involving the 17 to 18 MeV states of ⁸Be, with E1 absorption. The fact that these levels are so strongly excited in this manner suggests that they have T = 1. Angular distributions indicate J = 2 for ⁸Be*(16.8) and J = 2 (or possibly 0) for ⁸Be*(17.6). It is noted that the latter level cannot be identified with the well-known 17.63-MeV, J = 1⁺ level (see ⁷Li + p) (1955GO59: see, however, (1953WA27)). Excitation of proton-emitting levels near E_x = 18 and 22 MeV is reported by (1956LI05). See also (1953GU1A, 1955HA1D, 1955TI1A).

40. (a) 12C(n, n')4He4He4He	Qm = -7.281
(b) 12C(p, p')4He4He4He	Qm = -7.281

Reaction (a) has been studied for E_n = 12.3 to 20.1 MeV by (1955FR35) who find evidence for transitions through the ground state and the 2.9-MeV level. See also (1955AJ61) and ¹²C.

Reaction (b) at E_p = 29 MeV appears to proceed predominantly through the ground state and the 2.9-MeV level. It is not clear whether higher levels in ⁸Be are involved (1955NE18). See also (1955CU1C, 1956SA1C, 1956SA1D, 1957JA1B).

41. 16O(γ, α)12C* → 8Be + 4He

Qm = -14.524

At E_γ ≈ 22 MeV, the reaction appears to proceed mainly via the 9.6 and 10.8-MeV states of ¹²C to the ground state of ⁸Be. For E_γ > 24 MeV, transitions through the 15(?) and 16-MeV T = 1 state(s) of ¹²C, to the 2.9-MeV state of ⁸Be appear to dominate: see (1955AJ61) and (1955HA1D, 1955TI1A, 1956DA1C).

42. 16O(p, p')4He4He4He4He

Qm = -10.822

At E_p = 29 MeV, more than half the transitions are through the ground state of ⁸Be; there is no evidence for participation of any excited states of ⁸Be (1955KO1A). See also (1957JA1B).