A=5He (1974AJ01)

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⁵He (1974AJ01)

(See Energy Level Diagrams for ⁵He)

GENERAL: See also (1966LA04) and Table 5.1 [Table of Energy Levels] (in PDF or PS) here.

Shell model calculations: (1966FR1B, 1967BO1C, 1967EL03, 1967YA1A, 1968EL1A, 1968GO01, 1968GO36, 1969EL1B, 1970IR01, 1970RA1D, 1970ZO1A, 1971RA15, 1971WA08, 1972KA38, 1972LE1L, 1973HA49).

Cluster calculations: (1965NE1B, 1966HO06, 1967BE1G, 1969ME1C, 1969WI1C, 1971LE1N, 1972DE30).

Special levels: (1971RA15, 1973FE1J).

Electromagnetic transitions: (1966HO06, 1973HA49).

General reviews: (1966DE1E).

Reactions involving pions: (1969GO1C, 1969KO30, 1972GA11, 1973EI01).

Special reactions: (1971CH31, 1972CH31, 1972PN1A, 1973GR22).

Other topics: (1967BO1C, 1967EL03, 1968GO01, 1968HE1D, 1969GI1A, 1969HE1L, 1969SC1J, 1970SU1B, 1970ZO1A, 1971BA2Y, 1971CH50, 1971ZA1D, 1972CA37, 1972GI11, 1972JA14, 1972KA38, 1972LE1L, 1972MA57, 1972RI10, 1973MA20, 1973RA1E, 1973RO1R).

States of ⁵He^b:

^b Similar considerations prevail for ⁵Li.

Ground state: The ground and first excited states of ⁵He comprise the components ²P_3/2 and ²P_1/2 formed by l = 1 scattering of a neutron by an α-particle. Shape parameters of the state are best described by tabulated phase shifts, but it is sufficiently narrow to appear as a distinct group in many reactions. The central energy of this group is generally taken as defining the "mass" of ⁵He.

First excited state: Ordinarily appears as a broad continuum in particle spectra, centered several MeV (3 - 5) above the ground state. The resonant phase shift goes through 1/2π at E_c.m. = 6.43 MeV, about 5.5 MeV above the ground state.

16.8 MeV: Conspicuous in the ³H + d reactions, the state is almost entirely of a 3 + 2 configuration, with relative angular momentum zero, and a quite small reduced width for neutron (l_n = 2) emission. Properties of the state are listed in Table 5.2 (in PDF or PS).

19.9 MeV: In the range E_x = 20 - 25 MeV, there appears to be a number of broad overlapping states, principally of 3 + 2 configuration, with even parity. There is some indication from ⁷Li(p, ³He), [⁷Li(p, t)] that they have mainly S = 3/2. Among this manifold, a level at 19.9 ± 0.4 MeV is reported to form a well-defined group (Γ = 3 MeV) in ⁷Li(p, ³He). There are indications of another structure near E_x = 24 - 25 MeV.

1. ³H(d, γ)⁵He Q_m = 16.70

At low energies the reaction is dominated by a resonance at E_d = 107 keV; the mirror reaction shows resonance at E_d = 430 keV. (1969BE56) have measured the cross section for emission of 16.7 MeV γ-rays for E_d = 25 to 100 keV: the ratio σ(d, γ)/σ(d, n) is approximately constant at (2.1 ± 0.6) × 10^-4, leading to Γ_γ = 14 ± 4 eV, where Γ_n is taken as 66 keV. (1963BU07) have measured thick target yields from E_d = 150 to 1300 keV. The derived cross sections are analyzed into resonant and direct-capture contributions: the cross section at resonance is here reported as 60 μb [vs. 1 mb reported by (1969BE56)]. At E_d = 1025 ± 47 keV, the differential cross section id 0.44 ± 0.12 μb/sr (90°) and the γ to n branching ratio is an order of magnitude smaller: 2.3 × 10^-5. The angular distribution of the γ-rays is forward peaked and the total cross section is estimated to be 4.8 μb (1970KO09). A cluster model calculation of major even parity states predicts a broad peak in dipole strength due mainly to a 5/2⁺ state in a cluster of positive parity states some 4 MeV above the 3/2⁺ state (1971WA08).

2. (a) ³H(d, n)⁴He Q_m = 17.5900 E_b = 16.70
(b) ³H(d, 2n)³He Q_m = -2.9885
(c) ³H(d, pn)³H Q_m = -2.2246

Below E_d = 100 keV, the cross section for reaction (a) follows the Gamow function, σ = (A/E)exp(-44.40 E^-1/2) (1953JA1A, 1954AR02). A strong resonance, σ(peak) = 5.0 b, appears at E_d = 107 keV: see Table 5.2 (in PDF or PS). From E_d = 10 to 500 keV, the cross section is well fitted with the assumption of s-wave formation of a J^π = 3/2⁺ state (1952AR30, 1952CO35, 1955KU03). Excitation curves and angular distributions for reaction (a) have been measured from E_d = 8 keV to 21 MeV: see (1966LA04) for earlier references and (1966KO19: differential cross section (90°); E_d = 0.115 to 1.65 MeV), (1968IV01: excitation functions at 3 angles; E_d = 3.97 to 10.99 MeV), (1973MC05: angular distributions, at ≈ 1 MeV intervals; absolute 0° cross sections to within ± 3.1%; E_d = 5.0 to 15.7 MeV) and (1968SI1B: differential cross sections (0°), angular distributions; E_d = 7.0, 11.4, 15.0 and 19.0 MeV; relative cross sections at 1 MeV intervals, E_d = 7.0 to 21.0 MeV). There is some evidence of resonant behavior between E_d = 3 and 9 MeV (1960ST25). See also (1968SI1B, 1973MC05).

A study of reaction (a) with polarized deuterons at E_d = 0.2 to 1.0 MeV indicates intervention of the s-wave, J^π = 1/2⁺ channel, as well as possible p-waves above E_d = 0.3 MeV (1965TR01, 1971GR32). This effect is evidently very small below E_d = 100 keV (1971OH1B). At higher energies, the neutron polarization P₁(θ₁) shows an angular distribution that peaks typically at θ₁ = 30° lab, then goes negative with increasing angle and has a minimum between 90° and 130°, depending upon energy. (1971MU04) have made an extensive study of P₁(30°) for E_d = 5 to 15 MeV and, with deuterium as target, for E_t = 4.5 to 19.5 MeV (neutrons near 135° lab). The polarization increases monotonically from 0.03 at E_d = 3 MeV to ≈ 0.5 at E_d = 6.5 MeV and then with a lower slope to 0.69 at E_d = 13 MeV. The change in the slope may be caused by excited states of ⁵He near 20 MeV. Comparison with the ³He(d, p)⁴He mirror reaction at corresponding cm energies shows excellent agreement between the polarization values in the two reactions up to E_d = 6 MeV, but then the proton polarization becomes ≈ 15% higher, converging back to the neutron values at E_d ≈ 12 - 13 MeV. This may be due to experimental factors (1971MU04). Using polarized deuterons (1971HI07) find that the average ratio of vector analyzing power of ³He(d, p) to ³H(d, n) is 1.016 ± 0.015 at E_d = 6 MeV and 1.035 ± 0.020 at 10 MeV. The vector analyzing power of the two reactions agree to within ± 0.025 at all angles. This agreement between the mirror reactions is in apparent conflict with the result of (1971MU04). See also reaction 3 in ⁵Li. For other polarization measurements see Table 5.3 (in PDF or PS).

(1968BO35) have examined the parity non-conserving effects inn this strong reaction with polarized deuterons (E_d = 0.14 MeV). The experiment measured the ratio of the number of neutrons emitted parallel and anti-parallel to the direction of the initial polarization vector. The magnitude of the real part of the parity violating amplitude, F, is ≲ 3.8 × 10^-3.

The energy spectrum of ³He particles in reaction (b) has been studied at E_d = 10.9 MeV at several angles: no evidence was found for a bound dineutron [ < 5 μb/sr at 6° and 7.5°]. Strong variations of the spectral shape with angle indicate that the Watson-Migdal approximation is inadequate and that several other first-order processes must be included. The determination of the nn scattering length is ambiguous (1970LA10, 1970LA1K). This problem is also discussed by (1971GR45: E_d = 13.4 MeV), (1970SL1A: E_d = 31.9 MeV), (1966BA1H: E_d = 29.8, 32.5 MeV), (1971GR12: E_t = 22 MeV) and (1972BA32: E_d = 83 MeV). A discussion and comparison of attempts to measure the ¹S₀ nn scattering length is presented by (1971GR45): based on kinematically complete measurements and using the Watson-Migdal treatment, they find a_nn = -16.0 ± 1.0 fm. Intervention of n - ³He final state interactions is believed to be small in this work (1971GR45). See also (1973GR1L, 1973JE02). At E_t = 22 MeV no clear evidence is seen for sequential processes via excited states of ⁴He (1971GR12).

Analysis of reaction (c) at E_d = 20 MeV is consistent with the existence of a broad resonance in the ³H + p system correspoding to ⁴He*(22.) (1968NE1D): see (1973FI04) for a general discussion of the states of ⁴He. n-p final-state interaction enhancement has been studied by (1973SL03) at E_d = 35 MeV. They find that only when E_n,p ≤ 1 MeV is agreement with the Watson-Migdal theory obtained, even if the data far from dominant n-t final-state interaction and p-t quasi-free scattering is chosen. See also (1966LA04).

3. ³H(d, p)⁴H → ³H + n Q_m = -2.2246 E_b = 16.70

See (1967JA07, 1973SL03) and (1973FI04).

4. ³H(d, d)³H E_b = 16.70

The elastic scattering has been studied for E_d = 2.6 to 11.0 MeV. The excitation curves show an interference at E_x ≈ 19 MeV and a braod (Γ > 1 MeV) resonance corresponding to E_x = 20.0 ± 0.5 MeV, also seen in ³He(d, d) [see ⁵Li]. Together with data from ³H(d, n)⁴He, this work favors an assignment D_3/2 or D_5/2 with a mixture of doublet and quartet components (channel spin 1/2 and 3/2) if only one state is involved (1967TO02, 1968IV01) [any appreciable doublet component would, however, be in conflict with results from ⁷Li(p, ³He)⁵He]. Measurements of differential cross section and analyzing power using polarized deuterons with E_d = 3.2 to 12.3 MeV show resonance-like behavior in the vector analyzing power near E_d = 5 MeV. The anomaly appears in the odd Legendre coefficients and is interpreted in terms of a (1/2, 3/2)^- excited state of ⁵He with E_x ≈ 19.6 MeV. Broad structure in the differential cross section near 6 MeV, principally in the even Legendre coefficients, corresponds to an even parity state ⁵He*(20.0) (1971KI02)^c. See also (1966BA1J, 1966BA1M, 1966DE1F, 1969BE1M, 1970HE1C, 1973CH27, 1974CH02; theor.) and (1966LA04).

^c Tensor analyzing powers have been measured for E_d = 5.0 to 11.5 MeV by (1973DE51).

5. (a) ³H(t, n)⁵He Q_m = 10.44
(b) ³H(t, 2n)⁴He Q_m = 11.3324

At E_t = 0.5 MeV, the reaction appears to proceed via three channels: (i) direct breakup into ⁴He + 2n, the three-body breakup shape being modified by the n-n interaction; (ii) sequential decay via ⁵He(0); (iii) sequential decay via a broad excited state of ⁵He. The branching ratios at θ = 90° are 0.7: 0.2: 0.1. The width of ⁵He(0) is estimated to be 0.74 ± 0.18 MeV. Some evidence is also shown for ⁵He* at E_x ≈ 2 MeV, Γ ≈ 2.4 MeV (1965WO03). For reaction (b), see reaction 2 in ⁶He.

6. (a) ³He(t, p)⁵He Q_m = 11.20
(b) ³He(t, pn)⁴He Q_m = 12.0963

Some evidence is reported at E_t = 22.25 MeV in reaction (a) for a broad state of ⁵He at E_x ≈ 20 MeV, in addition to a sharp peak corresponding to ⁵He*(16.7) (1968YO06). For reaction (b) see reaction 1 in ⁶Li. See also (1966LA04).

7. ⁴He(n, n)⁴He E_b = -0.89

The coherent scattering length (thermal, bound) is 3.0 ± 0.1 fm (1973MU14). The thermal scattering cross section is 0.773 ± 0.009 b and the absorption cross section at 2200 m/sec σ⁰_nγ, is < 0.05 b (1969RO16). (1973MU14) adopt 0.76 ± 0.01 b for σ-bar_s. Total cross sections for E_n = 4 × 10^-4 eV to 147 MeV are summarized in (1958HU18, 1960HU08, 1964ST25, 1966LA04). Recent measurements include those by (1969RO16: E_n = 0.187 to 6.195 eV), (1973GO38: E_n = 0.7 to 20.0 MeV), (1966ME14: 77.2, 88.2, 110.0, 129.4, 150.9 MeV) and (1968EN1A: 10 GeV/c).

Earlier angular distribution studies are summarized in (1970GA1A). Other recent work is reported by (1968MO26, 1970MO31: E_n = 0.2 to 7.0 MeV), (1969CR1B, 1972CR01: E_n = 0.55, 0.84, 1.16, 1.33 MeV) and (1971NI06: 17.6, 20.9 and 23.7 MeV). Recent polarization studies are listed in Table 5.4 (in PDF or PS).

The total cross section has a peak of 7.6 b (1973GO38) [see also (1960VA04)] at E_n = 1.15 ± 0.05 MeV, E_c.m. = 0.92 ± 0.04 MeV, with a width of about 1.2 MeV (1964ST25). A second resonance is observed at E_n = 22.15 ± 0.12 MeV, corresponding to the 16.7 MeV J^π = 3/2⁺ state (1959BO54, 1964SH30): Γ_c.m. = 100 ± 50 keV, Γ_n = Γ_d = 50 ± 35 keV (1960HU08) [(1966HO07) find that the data are fitted best by Γ_n < Γ_d although Γ_n > Γ_d is not excluded]. Attempts to detect additional resonances in the total cross section have been unsuccessful: see (1966LA04).

The P_3/2 phase shift shows strong resonance behavior near 1 MeV, while the P_1/2 shift changes more slowly, indicating a broad P_1/2 level at several MeV excitation (1952DO30, 1966HO07, 1970AR1B, 1972ST01). (1966HO07) have constructed a set of phase shifts for E_n = 0 to 31 MeV, l = 0, 1, 2, 3 using largely p-α phase shifts. They have measured differential cross sections from 6 to 30 MeV, with special attention to the region near 22.15 MeV and have fitted the data with the assumed phase shifts. At the 3/2⁺ state the best fit to all data is given by E_res = 17.669 MeV ± 10 keV, γ²_d = 2.0 MeV ± 25%, γ²_n = 50 keV ± 25% (see Table 5.2 (in PDF or PS)). The polarization has been calculated from the phase shifts and is presented as a contour plat (1966HO07).

(1968MO26) have carried out accurate angular distribution measurements for E_n = 0.2 to 7.0 MeV and deduced an independent set of p-wave phase shifts, assuming that s-wave shifts are those those of a hard sphere, R = 2.44 fm. The derived total cross sections fit existing data satisfactorily, and polarization results of (1968SA25) and (1963MA29) are well accounted for. Both single-level dispersion formula and Woods-Saxon potential parameters are deduced. A more extensive optical model analysis for E_n = 0 to 20 MeV has been carried out by (1968SA1B).

(1970AR1B, 1973AR1N, 1973AR1P) have analyzed existing differential cross sections and polarization data with phase shifts constrained to analytic (effective range) energy dependence, for E_n = 0 to 21 MeV. As compared with the (1966HO07) values, the P_1/2 phase shift is higher in the range 3 to 10 MeV, and both S_1/2 and P_3/2 are larger for E_n = 10 to 16 MeV. D- and F-wave phase shifts are also determined (1973AR1P).

A single-level-with-background R-matrix parameterization has been carried out by (1972ST01), fitting differential cross section data for E_n = 0 to 20 MeV and polarization analyzing power for 0 to 15 MeV. Parameters for P_3/2 and P_1/2 levels are E_res = 0.97 and 6.43 MeV, and γ² = 7.55 and 12.30 MeV, respectively. See also (1973NI1B). Polarization measurements at six energies from E_n = 11 to 30.3 MeV are reported by (1972BR10) together with derived phase shifts. Partial waves as high as l = 4 are required, but none shows resonance, other than the D_3/2. See also (1969RO20).

8. ⁴He(n, d)³H Q_m = -17.5900 E_b = -0.89

See (1964DE1B, 1966ME03) and (1966LA04).

9. (a) ⁴He(d, p)⁵He Q_m = -3.12
(b) ⁴He(d, pn)⁴He Q_m = -2.2246

A typical proton spectrum consists of a peak corresponding to formation of the ground state of ⁵He, plus a lower continuum of protons ascribed to deuteron breakup (reaction (b)). Ground-state protons show pronounced azimuthal asymmtery when the reaction is induced by 8.5, 10 and 11 MeV vector polarized deuterons. A DWBA calculation is in only qualitative agreement (1967TR05, 1971KE16). See also (1972AV1E).

Coincidence studies of the final state interactions (α + p) and (α + n) have been carried out at E_d = 14.2 MeV (1967FU1D), E_α = 18.0 and 24.0 MeV (1970AS02), 42 MeV (1967WA08, 1968WA01), E_α = 70 MeV (1973TR04) and E_d = 78 MeV (1968BO1M). Spectra of α-particles in coincidence with protons exhibit peaks corresponding to ⁵He_g.s. as well as broad spectator peaks which occur where the neutron laboratory energy is a minimum (1967WA08, 1968WA01)): see ⁵Li. [For earlier work see (1966LA04)]. See also (1971LE02).

At E_α = 70 MeV, a kinematically complete experiment shows evidence for sequential decay in reaction (a), proceeding through excited states of ⁵He. Peaks in the coincident yield of protons and deuterons are ascribed to narrow states at E_x = 16.7 ± 0.1 MeV, Γ = 80 ± 30 keV, at E_x = 18.6 ± 0.1, 18.8 ± 0.1 and 19.2 ± 0.1 MeV, all with Γ = 180 ± 60 keV (1973TR04).

See also (1968TA11, 1971AL1B, 1972LA1L) and (1966HE1B, 1967NA1D, 1969NA09, 1972BL1F, 1972NA1D, 1973DE2B; theor.).

10. ⁴He(t, d)⁵He Q_m = -7.15

Not reported.

11. ⁶Li(γ, p)⁵He Q_m = -4.59

At E_γ = 60 MeV, the proton spectrum shows prominent peaks attributed to ⁵He*(0 + 4.0, 20 ± 2) (1973GA16). See also (1973DE17) and ⁶Li.

12. ⁶Li(e, ep)⁵He Q_m = -4.59

At E_e = 1180 MeV, two values of Q are observed: Q = -3.5 ± 1.0 MeV, corresponding to ⁵He(0), and Q = -19.0 ± 1.0 MeV, corresponding to ⁵He*(16.7). Angular distributions at E_p = 1158 MeV show that the first represents ejection of a proton with l > 0 and the second, an s-proton (1972AN24, 1972AN27, 1972AN29).

13. (a) ⁶Li(n, d)⁵He Q_m = -2.37
(b) ⁶Li(n, nd)⁴He Q_m = -1.4737

The angular distribution of ground state deuterons has been studied at E_n = 14.4 MeV (1965VA05). DWBA analysis does not reproduce either its shape or the cross section: this may be due to neglect of the deuteron knock-on process (1971MI12). At E_n = 152 MeV, two broad structures in the forward spectrum are interpreted as being due to transitions to ⁵He*(0, 14). The Q = -17 MeV peak is the stronger of the two (1966ME03, 1967ME11). For reaction (b) see (1967VA12). See also (1970VA1L, 1971HE1M, 1973BO1Y) and (1966WE1B). See also (1966LA04).

14. ⁶Li(p, 2p)⁵He Q_m = -4.59

At E_p = 100 to 460 MeV, the summed proton spectra show two peaks [Q = -4.9 ± 0.3 and -22.7 ± 0.3 MeV (1966TY01)]. The lower peak corresponds to ejection of an l = 0 proton, presumably leaving ⁵He in the 3/2⁺ state at 16.7 MeV. See also (1966LA04). At E_p = 100 MeV, the 1/2^- first excited state of ⁵He is weakly excited (1972MA61). At E_p = 100 and 155 MeV, transitions to states above 20 MeV are reported by (1965RO15, 1967RO06, 1972MA61). See also (1965CO1E, 1966BE1B, 1968ZU1A, 1969RU1A, 1973BH1A), (1967KO1B, 1967SH1C, 1968SA1C, 1972KO13, 1973CH1Q; theor.) and ⁶Li.

15. (a) ⁶Li(d, ³He)⁵He Q_m = 0.90
(b) ⁶Li(d, n³He)⁴He Q_m = 1.795

At E_d = 14.5 MeV, the ground state group is observed (1955LE24). See also (1960HA14, 1971IN1C). A study of the proximity process ³He(n, p)³H in the final state of reaction (b) has led to an estimate of the lifetime of ⁵He_g.s., τ = 1.4 × 10^-21 sec (to within a factor of 2 or 3) (1972KA44). See also (1968LE15).

16. ⁶Li(t, α)⁵He Q_m = 15.22

The width of the ground state is 605 ± 45 keV (1966BI1A). See also (1967BE13) and (1966LA04).

17. ⁷Li(π⁺, 2p)⁵He Q_m = 128.51

The two-proton spectrum shows broad structures attributed to the ground state of ⁵He, and to p^-1s^-1 and s^-2 states at ≈ 20 and (≈ 35) MeV excitation (1965CH12).

18. (a) ⁷Li(n, t)⁵He Q_m = -3.36
(b) ⁷Li(n, tn)⁴He Q_m = -2.4668

The angular distriibution of ground state tritons has been measured at E_t = 14.4 MeV: it is fairly well reproduced by DWBA (1970MI05). Reaction (b) mainly proceeds as a sequential process through ⁵He_g.s. (1967VA12). See also (1972AN1Q, 1973LI02), (1967BA1E; theor.) and (1966LA04).

19. ⁷Li(p, ³He)⁵He Q_m = -4.12

At E_p = 43.7 MeV, angular distributions of the ³He groups to the ground state of ⁵He (Γ = 0.80 ± 0.04 MeV) and to levels at 16.7 and 19.9 ± 0.4 MeV (Γ = 2.7 MeV) have been determined. The angular distribution of the ⁵He ground state group indicates substantial mixing of L = 0 and L = 2 transfer. The distribution to ⁵He*(16.7) is consistent with L = 1. Since no transitions are observed in the ⁷Li(p, t)⁵Li reaction to the analogue 20 MeV state in ⁵Li [see ⁵Li], the transition is presumably S-forbidden and the putative states in ⁵He - ⁵Li near 20 MeV are ⁴D_3/2 or ⁴D_5/2 [compare ³H(d, d)] (1966CE05). Particle-particle coincidence data have been obtained at E_p = 43.7 MeV. They suggest the existence of ⁵He*(20.0) with Γ = 3.0 ± 0.6 MeV and of a broad state at ≈ 25 MeV. No T = 3/2 states decaying via T = 1 states in ⁴He were observed (1968MC02). See also (1967JO1B, 1969DE04, 1970CO1M).

20. (a) ⁷Li(d, α)⁵He Q_m = 14.23
(b) ⁷Li(d, n)⁴He⁴He Q_m = 15.1233

At E_d = 24 MeV, the α-particle spectrum from reaction (a) shows structures corresponding to the ground and 16.7 MeV states and to states at E_x ≈ 20.2 and 23.8 MeV with Γ ≈ 2 MeV and ≈ 1 MeV, respectively (1972BA30). See also (1966BI1A, 1966MI09, 1966PO1D) and ⁹Be.

Spectra measured in reaction (b) suggest the involvement of a ⁵He state with E_x = 2.6 ± 0.4 MeV, Γ = 4.0 ± 1.0 MeV (1964FE01), E_x = 5.2 ± 0.2 MeV, Γ = 5.6^+0.3_-0.6 MeV (1965AS06, 1966AS04), E_x = 2.6 ± 0.2 MeV, Γ = 7 ± 2 MeV (1972GI10). See also (1972ST08, 1973HE26). Study of n-α coincidences for E_d = 2.6 to 4.0 MeV shows that reaction (b) proceeds mainly by sequential decay, primarily via ⁵He(0) and excited states of ⁸Be (1967VA11). See also (1966AS04, 1966MI09, 1967JE01, 1972DE44, 1973HE26). Attempts to observe n-α rescattering effects, following formation of ⁸Be*(16.63, 16.91) have been unsuccessful at E_d = 1.90 to 2.10 MeV (1972BR08), 2.07 and 2.09 MeV (1971SW10) and 3.0, 3.2 and 3.6 MeV (1968VA12). The upper limit for the rescattering yield is 1% of the yield from sequential decay via intermediate states in ⁵He and ⁸Be (1968VA12). Positive results are reported for E_d = 2.07 to 2.25 MeV by (1969TH02). See also (1967BE13, 1967FL12, 1967WI1C, 1968GA1E, 1968WI1E, 1971HU1H, 1973HE06, 1973KA32), ⁸Be, ⁹Be and (1966LA04).

21. ⁷Li(⁶Li, 2α)⁵He Q_m = 12.76

See (1965BE1C).

22. ⁹Be(γ, α)⁵He Q_m = -2.46

See ⁹Be.

23. ⁹Be(p, pα)⁵He Q_m = -2.46

Studies of this reaction have been carried out at E_p = 26.0, 35.0 and 46.8 MeV (1972QU01) and at 57 MeV (1968RO19). Observation of protons and alphas in coincidence at selected angles shows quasifree scattering of the incident protons by S-state α-clusters in ⁹Be (1968RO19, 1972QU01): see ⁹Be. See also (1969YA1B, 1970GO12).

24. ⁹Be(α, 2α)⁵He Q_m = -2.46

The population of ⁵He(0) has been observed at E_α = 28 MeV (1965YA02) and at 32.3 and 37.4 MeV (1968YA02). See also (1965HI1B, 1965KU1B, 1966HI1A, 1967ME1C) and ⁹Be.

25. ¹¹Be(d, n)⁴He⁴He⁴He Q_m = 6.4577

At E_d = 10.4 and 12.0 MeV, this reaction involves ⁵He(0) and states in ⁸Be and ⁹Be (1971RE19).

26. ¹²C(n, n)⁴He⁴He⁴He Q_m = -7.2748

See ¹²C in (1968AJ02).