
^{10}Be (1959AJ76)(See the Energy Level Diagram for ^{10}Be) GENERAL: See also Table 10.1 [Table of Energy Levels] (in PDF or PS). Theory: See (1956KU1A, 1957FR1B, 1958FR1C).
The weighted mean endpoint energy is 0.556 ± 0.003 MeV (1951LI26). The mean halflife is (2.7 ± 0.4) × 10^{6} y (1949HU19): log ft = 13.65 (1951FE1A). The spectrum is of the D_{2} type (1950WU1A).
The neutron yield (elemental Li) at 0° exhibits two broad resonances, at E_{t} = 0.84 and 1.70 MeV. The angular distributions are not isotropic (1951CR01). The cross section for reaction (a) has been measured for E_{t} = 0.6 to 2.3 MeV (θ = 90° and 165°): both the yield of ^{6}He(0) and ^{6}He*(1.71) αparticles show a broad resonance at E_{t} ≈ 1.7 MeV. At E_{t} = 1.8 MeV, θ = 90°, the differential cross section is 2.6 mb/sr for ^{6}He(0) and 8 mb/sr for ^{6}He*(1.71) (1957JA37). At E_{t} = 0.24 MeV the ground state αparticles are distributed as W(θ_{c.m.}) = 1  (0.66 ± 0.06)cos^{2}θ, while those corresponding to the 1.7MeV state of ^{6}He are isotropic within 8%. The formation of the 1.7MeV state is 8 times more probable than the formation of the ground state. These results indicate pwave formation of the 0.84MeV resonance and J = 2^{+} for the 17.83MeV state (1952DE1B, 1953CH1A, 1954AL38). See also ^{6}He and (1956MA09).
At E_{α} = 31.5 MeV, proton groups are observed leading to the ground and first excited state of ^{10}Be (1956WA29).
The thermal capture cross section is 10 ± 1 mb (1958HU18). In addition to the groundstate transition, a 3.41 ± 0.06MeV γray is observed, attributed to a cascade through the 3.4MeV state. The intensity of the cascade transition is ≈ 0.25 photon/capture (1953BA18), 0.27 photon/capture (1955GR1E). See also (1953WI1C).
The total cross section is constant at 6.04 ± 0.03 b from 0.1 eV to 100 keV (1958HU18): the spin dependent scattering is < 0.003 b (1952PA1A). In the region E_{n} = 0 to 18 MeV, three resonances are reported at 0.62, 0.81 and 2.73 MeV. The parameters of these resonances are exhibited in Table 10.2 (in PDF or PS). Angular distributions have been measured for E_{n} = 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 0.62MeV resonance has J = 3; a satisfactory fit to the angular distribution is obtained with the assumption of pwave formation in channel spin 2, with swave potential scattering all in channel spin 1. It is observed that the assumption of spindependent potential scattering is at variance with observation at thermal energies (see also (1956LA1B)). The possibility of dwave formation is not excluded. The cross section at the 0.81MeV resonance is consistent with J = 2 (1955WI25). A comparison of reduced widths suggests a close correspondence between ^{10}Be*(7.37), (7.54) and the two ^{10}B levels at 8.89 MeV (1956MA55). Differential elastic scattering cross sections have been measured in the nonresonant regions from E_{n} = 0.7 to 3.0 MeV (1957FO1B, 1958FO46) and analyzed in terms of phase shifts (1957FO1B). For E_{n} = 1.0 to 2.0 MeV, an appreciable pwave contribution is observed (1958FO46). The shape of the 2.73MeV structure suggests that there may actually be two levels involved, at E_{p} = 2.73 MeV, Γ ≈ 0.1 MeV, and a broad state at E_{p} = 2.85 MeV (1951BO45: see, however, the similar situation in ^{10}B (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 ^{9}Be(n, α)^{6}He results of (1957ST95) probably identifies the broad 2.9MeV resonance as formed by pwave neutrons with J = 2^{+} for ^{10}Be*(9.4) (1958FO46). Polarization measurements at E_{p} = 3.1 MeV indicate interference between a broad d_{3/2} resonance and s_{1/2} hardsphere scattering (1957MC1B). Other measurements of differential cross sections from E_{n} = 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 opticalmodel 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 E_{n} = 12.7 MeV, σ_{t} = 1.60 b (1953NE01, 1955TA29, 1958BR16) and at E_{n} = 14.1 MeV, σ_{t} = 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 E_{n} = 18.0 MeV (1954CO16). Nonelastic cross sections are given by (1955BE1D, 1955BF01, 1955MA1G, 1955TA29, 1955WA27, 1956BE32, 1956FL1B, 1957RO57, 1958BA03, 1958MA22, 1958MA54, MC58C). See also (1957HU1D), ^{9}Be(n, n')^{9}Be*, ^{9}Be(n, 2n)^{8}Be and ^{9}Be(n, α)^{6}He. See also (1956HE1D, 1956LA1C, 1957ST1D, 1957ZA1A).
The cross section for reaction (a) has been measured for E_{n} = 2.6 to 3.2 MeV. A sharp increase is reported at E_{n} = 2.70 MeV, threshold for process (b): ^{9}Be(n, n')^{9}Be*(2.4) → n + ^{8}Be; the resonance at E_{p} = 2.73 MeV (see ^{9}Be(n, n)^{9}Be) 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 E_{n} = 2.6 to 6 MeV. See ^{9}Be. 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 E_{n} = 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 E_{n} = 2 to 11 MeV is 0.20 ± 0.12 b (1957VA12). At E_{n} = 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 E_{n} = 14.1 MeV. See also (1950HO80, 1952AG1A, 1957DU1B, 1958AN32, 1958BE1E, 1958HO1C).
At E_{n} = 14 MeV, σ(n, t) = 18 ± 1.5 mb (1958WY67). See also (1957VA12).
The cross section for production of ^{6}He has been measured for E_{n} = 0.7 to 4.4 MeV by (1957ST95), for E_{n} = 1 to 6 MeV by (1957VA1D) and for E_{n} = 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 ^{9}Be(n, 2n)^{8}Be. No indication of resonance is found at E_{n} = 2.7 MeV. Weak resonances are reported at E_{n} = 3.73 and 4.27 MeV by (1955SA1E). The cross section at E_{n} = 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 E_{d} = 7 MeV the group corresponding to ^{10}Be*(6.18) is only 5% as intense as that corresponding to ^{10}Be*(6.26). The upper limit to the intensity of other groups is 3% (1954JU23: θ = 90°, E_{d} = 5.4  7.4 MeV). Angular distributions of the protons to ^{10}Be(0) and ^{10}Be*(3.37) have been studied at many energies from E_{d} = 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 E_{d} = 9 MeV, the ratio of the maximum differential cross sections of the ^{9}Be(d, p)^{10}Be(0) and ^{9}Be(d, n)^{10}B*(1.74) reactions is 1.64 ± 0.25; γ^{2}_{n}/γ^{2}_{p} = 2.16 (calculated from stripping theory; predicted value = 2) (1956CA1D). See also ^{11}B and (1956GR1D; theor.). The 3.37MeV 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 E_{d} = 2.5 to 3.9 MeV confirms this assignment and fixes the channel spin mixture (for capture of l = 1 neutrons) as 10% J_{c} = 1, 90% J_{c} = 2. This mixture is just that expected in pure L  S coupling for a ^{3}P_{2} state (1957CO54). Similar results are reported at E_{d} = 7.7 MeV by (1958PA1C). The gammaray energy is 3351 ± 27 (1953MA1A), 3400 ± 30 (1957MC35), 3360 ± 30 keV (1958ME81). Comparison of the γenergy at E_{d} = 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 singleparticle E2 transition (1959KO1B). It thus appears that shifts of some 20  30 keV should be subtracted from the observed γenergies. From the stripping pattern, the 5.96MeV 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: ^{10}Be*(5.96 → 3.37)). The fact that the cascade and direct transitions are roughly comparable in intensity fixes J = 1^{} (1958ME81). The 6.26MeV level (J = 1^{} or 2^{}) appears to decay only to the 3.37MeV level: the absence of the ground state transition indicates J = 2^{} (1958ME81). The 7.37MeV level presents some difficulty. From stripping results l_{n} = 1, J = 2^{+}, 3^{+} (see, however, (1958CA12)); from ^{9}Be(n, n), J = 3 and l_{n} = 1, possibly 2. The reduced width appears to be nearly the same as that of the 3.37MeV level and J = 2^{+} is suggested. Shellmodel calculations indicate a vanishing width if J = 3^{+} (1956GR37, 1957FR1B). The polarization of groundstate protons has been studied by (1958HI74). See also (1956GE1A, 1956TU1A, 1957HA1F).
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See ^{14}C.
