(See the Energy Level Diagram for 10Be)
The neutron yield (elemental Li) at 0° exhibits two broad resonances, at Et = 0.84 and 1.70 MeV. The angular distributions are not isotropic (1951CR01). The cross section for reaction (a) has been measured for Et = 0.6 to 2.3 MeV (θ = 90° and 165°): both the yield of 6He(0) and 6He*(1.71) α-particles show a broad resonance at Et ≈ 1.7 MeV. At Et = 1.8 MeV, θ = 90°, the differential cross section is 2.6 mb/sr for 6He(0) and 8 mb/sr for 6He*(1.71) (1957JA37).
At Et = 0.24 MeV the ground state α-particles are distributed as W(θc.m.) = 1 - (0.66 ± 0.06)cos2θ, while those corresponding to the 1.7-MeV state of 6He are isotropic within 8%. The formation of the 1.7-MeV state is 8 times more probable than the formation of the ground state. These results indicate p-wave formation of the 0.84-MeV resonance and J = 2+ for the 17.83-MeV state (1952DE1B, 1953CH1A, 1954AL38). See also 6He and (1956MA09).
At Eα = 31.5 MeV, proton groups are observed leading to the ground and first excited state of 10Be (1956WA29).
The thermal capture cross section is 10 ± 1 mb (1958HU18). In addition to the ground-state transition, a 3.41 ± 0.06-MeV γ-ray is observed, attributed to a cascade through the 3.4-MeV state. The intensity of the cascade transition is ≈ 0.25 photon/capture (1953BA18), 0.27 photon/capture (1955GR1E). See also (1953WI1C).
Angular distributions have been measured for En = 0.54 to 0.70 MeV by (1955WI25). The patterns are symmetric about 90° in this range, indicating absence of interference between resonance and potential scattering waves of opposite parity. The 0.62-MeV resonance has J = 3; a satisfactory fit to the angular distribution is obtained with the assumption of p-wave formation in channel spin 2, with s-wave potential scattering all in channel spin 1. It is observed that the assumption of spin-dependent potential scattering is at variance with observation at thermal energies (see also (1956LA1B)). The possibility of d-wave formation is not excluded. The cross section at the 0.81-MeV resonance is consistent with J = 2 (1955WI25). A comparison of reduced widths suggests a close correspondence between 10Be*(7.37), (7.54) and the two 10B levels at 8.89 MeV (1956MA55).
Differential elastic scattering cross sections have been measured in the non-resonant regions from En = 0.7 to 3.0 MeV (1957FO1B, 1958FO46) and analyzed in terms of phase shifts (1957FO1B). For En = 1.0 to 2.0 MeV, an appreciable p-wave contribution is observed (1958FO46).
The shape of the 2.73-MeV structure suggests that there may actually be two levels involved, at Ep = 2.73 MeV, Γ ≈ 0.1 MeV, and a broad state at Ep = 2.85 MeV (1951BO45: see, however, the similar situation in 10B (1959MA20)).
The elastic scattering in this region changes from being nearly symmetric at 2.4 MeV to being peaked forward at 2.9 MeV. This evidence also suggests two resonances and, together, with the 9Be(n, α)6He results of (1957ST95) probably identifies the broad 2.9-MeV resonance as formed by p-wave neutrons with J = 2+ for 10Be*(9.4) (1958FO46). Polarization measurements at Ep = 3.1 MeV indicate interference between a broad d3/2 resonance and s1/2 hard-sphere scattering (1957MC1B). Other measurements of differential cross sections from En = 0.06 to 1.80 MeV are reported by (1956LA1B, 1957LA14), from 2.30 to 3.66 MeV by (1953ME1A), at 4.1 MeV by (1955WA27), 7.0 MeV by (1956BE32), and 14.2 MeV by (1957AN52) and (1958NA09). At the higher energies, the neutrons show strong optical-model effects.
The total cross section decreases from 2.14 b at 3.8 MeV to 1.7 b at 8.7 MeV (1955WA27, 1956BE98, 1957BO13, 1958BR16, 1958MA22); see also (1958HU18). At En = 12.7 MeV, σt = 1.60 b (1953NE01, 1955TA29, 1958BR16) and at En = 14.1 MeV, σt = 1.55 b (1955TA29), 1.49 ± 0.02 b (1954CO16), 1.53 ± 0.03 b (1952CO41), 1.46 ± 0.03 b (1957KH1A), 1.51 ± 0.02 b (1958BR16). The cross section then decreases monotonically to 1.38 ± 0.03 b at En = 18.0 MeV (1954CO16). Non-elastic cross sections are given by (1955BE1D, 1955BF01, 1955MA1G, 1955TA29, 1955WA27, 1956BE32, 1956FL1B, 1957RO57, 1958BA03, 1958MA22, 1958MA54, MC58C). See also (1957HU1D), 9Be(n, n')9Be*, 9Be(n, 2n)8Be and 9Be(n, α)6He. See also (1956HE1D, 1956LA1C, 1957ST1D, 1957ZA1A).
The cross section for reaction (a) has been measured for En = 2.6 to 3.2 MeV. A sharp increase is reported at En = 2.70 MeV, threshold for process (b): 9Be(n, n')9Be*(2.4) → n + 8Be; the resonance at Ep = 2.73 MeV (see 9Be(n, n)9Be) does not appear (1957FI52: see, however, (1956ED15)). It is suggested that the (n, 2n) reaction mainly proceeds via process (b) in this energy region (1955FO1B, 1957FI52). On the other hand (1958MA22) report evidence from energy spectra that the direct (n, 2n) process occurs for En = 2.6 to 6 MeV. See 9Be. The absolute cross section σ(n, 2n) rises linearly from 0.1 b at 2.8 MeV to 0.7 b at 3.25 MeV (1957FI52). The 90° differential cross section at En = 3.7 MeV is 39 ± 8 mb/sr (1957HU14, 1958WA05), 27 ± 6 mb/sr (1955FO1B: quoted in (1957HU14)). The cross section for Ra - Be and Po - Be neutrons is 0.37 ± 0.06 b (1956ED15). The average cross section for En = 2 to 11 MeV is 0.20 ± 0.12 b (1957VA12). At En = 14 MeV, the cross section is 0.42 ± 0.07 b (1957RO57, 1957ST1C), in agreement with predictions of (1956SA1E) but not of (1953MA1C). (1958AS63) finds σ = 0.54 ± 0.04 b at En = 14.1 MeV. See also (1950HO80, 1952AG1A, 1957DU1B, 1958AN32, 1958BE1E, 1958HO1C).
The cross section for production of 6He has been measured for En = 0.7 to 4.4 MeV by (1957ST95), for En = 1 to 6 MeV by (1957VA1D) and for En = 3.3 to 6.1 MeV by (1955SA1E). (1957ST95) find only a smooth rise to a broad maximum of 104 ± 7 mb at 3.0 MeV, followed by a gradual decrease to 70 mb at 4.4 MeV, possibly to be attributed to competition by 9Be(n, 2n)8Be. No indication of resonance is found at En = 2.7 MeV. Weak resonances are reported at En = 3.73 and 4.27 MeV by (1955SA1E). The cross section at En = 14 MeV is 10 ± 1 mb (1953BA04). See also (1947AL1A, 1957VA12).
Levels reported by (1954JU1C, 1954JU23, 1956GR37, 1958CA12) are listed in Table 10.3 (in PDF or PS). At Ed = 7 MeV the group corresponding to 10Be*(6.18) is only 5% as intense as that corresponding to 10Be*(6.26). The upper limit to the intensity of other groups is 3% (1954JU23: θ = 90°, Ed = 5.4 - 7.4 MeV).
Angular distributions of the protons to 10Be(0) and 10Be*(3.37) have been studied at many energies from Ed = 1 to 14.9 MeV: see (1952AJ38, 1954EB02, 1955AJ61, 1955JU10, 1955JU1B, 1956GR37, 1956JU1E, 1956VA17, 1956ZE1A, 1957CO54, 1957JU1A, 1957SM78, 1958CA12, 1958MI93). Except at the lowest energies, the stripping process appears to dominate. At Ed = 9 MeV, the ratio of the maximum differential cross sections of the 9Be(d, p)10Be(0) and 9Be(d, n)10B*(1.74) reactions is 1.64 ± 0.25; γ2n/γ2p = 2.16 (calculated from stripping theory; predicted value = 2) (1956CA1D). See also 11B and (1956GR1D; theor.).
The 3.37-MeV level has J = 2+, established by the (p, γ) correlation (J ≥ 2), the stripping pattern (J ≤ 3+) and the internal pair formation coefficient (E1, M1 or E2): see (1955AJ61, 1958CH1A). Detailed study of the (p, γ) correlation at Ed = 2.5 to 3.9 MeV confirms this assignment and fixes the channel spin mixture (for capture of l = 1 neutrons) as 10% Jc = 1, 90% Jc = 2. This mixture is just that expected in pure L - S coupling for a 3P2 state (1957CO54). Similar results are reported at Ed = 7.7 MeV by (1958PA1C). The gamma-ray energy is 3351 ± 27 (1953MA1A), 3400 ± 30 (1957MC35), 3360 ± 30 keV (1958ME81). Comparison of the γ-energy at Ed = 3.2 MeV with recoils in vacuum and recoils stopped in Ta reveals no effect on the Doppler shift and sets an upper limit of 3.0 × 10-13 sec on the mean lifetime. A value of 0.4 to 1.0 × 10-12 sec is expected for a single-particle E2 transition (1959KO1B). It thus appears that shifts of some 20 - 30 keV should be subtracted from the observed γ-energies.
From the stripping pattern, the 5.96-MeV level is assigned J = 1- or 2- (Table 10.3 (in PDF or PS)). A gamma ray of energy 5.98 ± 0.04 (1953MA1A), 6.035 ± 0.04 (1955BE81, 1957MC35), 6.01 ± 0.06 MeV (1958ME81) is assigned to this level, as is another, of energy 2.54 ± 0.04 MeV (1958ME81: 10Be*(5.96 → 3.37)). The fact that the cascade and direct transitions are roughly comparable in intensity fixes J = 1- (1958ME81).
The 6.26-MeV level (J = 1- or 2-) appears to decay only to the 3.37-MeV level: the absence of the ground state transition indicates J = 2- (1958ME81). The 7.37-MeV level presents some difficulty. From stripping results ln = 1, J = 2+, 3+ (see, however, (1958CA12)); from 9Be(n, n), J = 3 and ln = 1, possibly 2. The reduced width appears to be nearly the same as that of the 3.37-MeV level and J = 2+ is suggested. Shell-model calculations indicate a vanishing width if J = 3+ (1956GR37, 1957FR1B). The polarization of ground-state protons has been studied by (1958HI74). See also (1956GE1A, 1956TU1A, 1957HA1F).