
^{9}Be (1959AJ76)(See the Energy Level Diagram for ^{9}Be) GENERAL: See also Table 9.1 [Table of Energy Levels] (in PDF or PS). Theory: See (1955DA1E, 1955FR1F, 1956BL1B, 1956DE1C, 1956KU1A, 1957BA1H, 1957PA1A, 1958KU1B).
The differential cross section at 90° for reaction (a) rises steeply from 8.8 mb/sr at E_{t} = 0.72 MeV to 19 mb at 0.90 MeV, and then more slowly to 21 mb at E_{t} = 1.15 MeV. For reaction (d), the differential cross section at 90° rises from 0.75 mb/sr at 0.62 MeV to 5.7 mb/sr at 1.8 MeV and then decreases slowly to 5.3 mb/sr at 2.2 MeV (R.W. Crews, quoted in (1957JA37)). See also (1952PE02), ^{5}He, ^{7}Li, ^{8}Li and ^{8}Be.
See (1956WA29).
Cross sections have been measured for E_{d} = 0.4 to 1.8 MeV by (1952BA64), and for E_{d} = 0.7 to 3.3 MeV by (1954BA46); see (1957JA37). The yield for E_{d} = 1.1 to 4.0 MeV has been measured by (1956BE1A). Resonances are observed at 0.80 and 1.04 MeV (1952BA64, 1954BA46), 1.4 MeV (1952BA64: see, however, (1954BA46)), 2.0, 2.5 and 3.7 MeV (1956BE1A: see, however, (1954BA46)). See also (1955AJ61).
The cross section for (a) has been measured for E_{d} = 70 to 110 keV by (1955RA14) and that for (b) has been measured for E_{d} = 30 to 250 keV by (1953SA1A). Resonances for neutron production occur, in the range E_{d} = 0.2 to 4.8 MeV, at E_{d} = 0.68 (Γ = 250 keV), 0.98 (Γ = 60 keV) and 1.8 MeV (Γ = 400 keV) (1952BA64, 1957SL01). At E_{d} = 0.90 MeV, the αparticles in reaction (b) are isotropic to within 2%, consistent with formation by swave deuterons. No evidence is found for direct interaction effects at this energy (1957RI39). The angular correlation of groundstate αparticles with those resulting from breakup of ^{5}He indicate J = 5/2^{} (1956RI37), J = 3/2^{} (1957FA10), for the ^{9}Be level mainly responsible for this reaction at E_{d} = 0.9 MeV. Reactions (a) and (c) account for less than 10% of the disintegrations at this energy (1956RI37). See also ^{5}He, ^{8}Be and (1956CA1B).
The cross section for reaction (b) rises steeply from threshold to 95 mb at E_{d} = 2.4 MeV, and then more slowly to about 165 mb at E_{d} = 4.1 MeV (1955MA20). See also ^{6}He and ^{7}Li.
Not observed.
At E_{d} = 0.7 and 1 MeV, proton groups are observed corresponding to excited states of ^{9}Be at 1.83 ± 0.04 MeV (Γ < 0.4 MeV), 2.39 ± 0.08 MeV (Γ < 0.2 MeV), 3.10 ± 0.04 MeV (Γ < 0.3 MeV), 4.74 ± 0.08 MeV (Γ = 1.25 ± 0.25 MeV) and (9.1 ± 0.2 MeV) (Γ = 1.2 MeV) (1954MO92, 1955AL57, 1958MO99). The 1.8MeV level admits a description in terms of an swave n  ^{8}Be interaction with a scattering length a = 23 × 10^{13} cm (1958MO99: see ^{11}B(d, α)^{9}Be).
Not observed.
See ^{9}Li.
The photoneutron cross section has been studied from threshold (E_{γ} = 1.664 ± 0.004 MeV: (1956CO56)) to 320 MeV: see Table 9.2 (in PDF or PS). A sharp peak, Γ < 50 keV, σ ≈ 100 mb, occurs at E_{γ} = 1.70 MeV (1956CO56). A further broad maximum appears at E_{γ} ≈ 10 MeV, followed by the giant resonance at 20  22 MeV (1953JO1B, 1953NA1A: see (1956CO59)). Measurements from 6 to 18 MeV show pronounced peaks at 11.3 and 13.3 MeV and a broad, low peak at 16 MeV, immediately preceding the giant resonance (1959SP1B). At E_{γ} = 6.1 MeV the main processes appear to involve ^{9}Be(γ, n)^{8}Be*(2.9) and ^{9}Be(γ, α)^{5}He (1954CA1A). Angular distributions for E_{γ} = 1.7 and 1.8 MeV are spherically symmetric; at E_{γ} = 2.76 MeV, W(θ) = 1.2 + sin^{2}θ (1949HA1A: see also (1954NI1B, 1956FA30)). Calculations of (1949GU1A) and (1956MA1M) envisage E1 transitions to p^{4}s and p^{4}d configurations, with levels at ≈ 1.8 and ≈ 5 MeV (assuming a fixed well depth). The angular distributions and general trend of the cross section are well accounted for, as is the ratio of σ(γ, n)/σ(e, e'n) (1958BA60: 6 to 17 MeV). (1956CO56) state, on the other hand, that the 1.70MeV peak is to be attributed to an M1 transition. See also (1954ER1B, 1955JO1B, 1958BA60, 1958CH31) and (1956CZ1B, 1956CZ1C, 1956DE1C, 1957KO1B; theor.). The cross section for reaction (c) is < 1 mb at E_{γ} = 1.63 MeV (1952AL26, 1952AL30). For reaction (d) see (1957LO1A).
The yield has a broad maximum, Γ = 4.7 MeV, at E_{γ} = 22.2 MeV where σ = 2.72 mb (1953HA1A). The angular and energy distributions of photoprotons produced by bremsstrahlung with E_{max} = 25 to 80 MeV has been studied by (1956CO59, 1956KL19). The angular distributions can be accounted for by the direct interaction of γrays with individual nucleons (1956KL19). The energy distributions indicate that transitions to levels in the residual nucleus play an important part in the direct photo effect (1956KL19). (1956CO59) suggest, on the other hand, that the relatively large proportion of lowenergy protons indicates predominance of a (γ, n) process, followed by proton emission from ^{8}Be levels at high excitation. See also (1953HE1B, 1953NA1A, 1957CH24, 1958CH31, 1958PA1B, 1958ST1A, 1958WH35).
See (1955AJ61), (1956CO59, 1958WH35) and ^{9}Be(γ, n)^{8}Be.
Elastic scattering has been studied at E_{e} = 125, 150 and 190 MeV (1953HO79, 1954MC45). An r.m.s. radius of (2.2 ± 0.2) × 10^{13} cm is obtained (1957HO1E: see also (1956HO93)). Inelastic peaks corresponding to levels at 2.54 and 6.96 MeV are reported by (1954MC45). Comparison of σ(γ, n) and σ(e, e'n) for E_{e} = 6 to 17 MeV indicates that the transitions are mainly E1 (1958BA60). See also (1957EH1A, 1958EH1A).
The neutron spectrum observed when ^{9}Be is bombarded with 3.7MeV neutrons exhibits a structure which is consistent with the excitation of the known states at 0, 1.5, 2.4 and 3.1 MeV, with subsequent neutron emission from the latter two. It is concluded that the (n, 2n) process at this energy proceeds mainly via discrete states of ^{9}Be (1957HU14, 1958WA05). At the same bombarding energy (1955FO1B) observe two discrete groups in coincidence, suggesting the process ^{9}Be(n, n')^{9}Be*(2.43) → n + ^{8}Be: see, however, (1957BO83: ^{9}Be(α, α')^{9}Be*). Using monochromatic neutrons with E_{n} = 2.6 to 3.25 MeV, (1957FI52) finds a sharp threshold for (n, 2n) at E_{n} = 2.7 MeV, corresponding to excitation of ^{9}Be*(2.43). On the other hand, (1958MA22) find evidence for (n, 2n) at E_{n} = 2.6 MeV, below the threshold for (n, n'); at E_{n} = 5 to 6 MeV, the spectra show neutrons from the direct (n, 2n) process. At E_{n} = 14 MeV, the cross section for production of ^{9}Be* is 170 ± 30 mb; comparison with σ(n, 2n) = 530 ± 40 mb indicates that about 1/3 of the (n, 2n) processes proceed via ^{9}Be*(2.4) (1958AN32). See also (1957RO57) and (1958BE1E; theor.). A search for γtransitions from the 1.8 and 2.4MeV levels yields upper limits of 0.3 and 0.2 mb, respectively, for E_{n} = 2.56 MeV and 1.8 and 0.3 mb for E_{n} = 2.74 MeV (1956DA23). Elastic and inelastic neutron angular distributions show forward peaking at E_{n} = 14 MeV (1958AN32, 1958NA09): see ^{10}Be, (1958RE1A, 1958TO1A).
Elastic scattering has been studied at E_{p} = 14.5, 20 and 31.5 MeV by (1956KI54), at 10 MeV by (1956RA32), at 12 MeV by (1958SU14), at 17 MeV by (1956DA03), at 31 MeV by (1953WRZZ, 1954FI35, 1956BE14): see also ^{10}B. All angular distributions show pronounced diffraction maxima characteristic of the optical model. Analysis in terms of the diffusesurface optical model is discussed by (1957ME21). See also (1956KL55, 1956SH1C). Inelastic scattering is observed corresponding to levels at (1.8), 2.43, 3.1, 5.0, 6.8, 7.9, 11.3, (14.5), (17.5), (19.9) and (21.7) MeV: see Table 9.3 (in PDF or PS). It is not clear whether the structure observed near 1.8 MeV is properly to be attributed to a level at this energy or to a threebody breakup, modified by the proximity of the neutron threshold. If the former is correct, the level width is 0.15 MeV and J = 1/2^{+} (1955GO48, 1958SU14). If a threebody breakup is involved, some interaction between the neutron and the ^{8}Be must be involved: (1956BO18) find a satisfactory fit to the observed shape with an swave scattering length of 20 × 10^{13} cm; see also (1958MI1C) and ^{11}B(d, α)^{9}Be. It is suggested by (1956SU67, 1958SU14) that the observed structure is to be understood in terms of a heavy particle stripping process and it is conjectured that the 4.8MeV level may reflect the same effect, involving ^{8}Be*(2.9); see, however, (1958MI1C). A continuous distribution of neutrons, observed for E_{p} > 4.5 MeV is attributed to formation of ^{9}Be*(2.4) with subsequent breakup into n + ^{8}Be*(2.9) (1959MA20). Breakup into (^{8}Be + n) occurs in 12 ± 5 % of transitions (J.B. Marion, private communication). The energy of the 2.4MeV level is given as 2433 ± 5 (1951BR72), 2434 ± 5 (1956BO18), 2432 ± 4 keV (1955GO48); the width is ≤ 1 keV (1955GO48). Analysis of angular distributions at E_{p} = 12 MeV in terms of direct interaction plus compound nucleus formation indicate J = 1/2^{} or 5/2^{} (1958SU14). At E_{p} = 31 MeV, analysis indicates J = 1/2^{+}, 3/2^{+} or 5/2^{+} (1956BE14: see, however, (1958SU14)). Results at E_{p} = 10 MeV are consistent with odd parity (1956RA32). See also ^{10}B(n, d)^{9}Be and (1952DA1B). The 3.03 ± 0.03 MeV level has a width > 0.28 MeV; the Wigner limit then restricts l_{n} to 0 or 1, J ≤ 3/2 (1956BO18: see, however, ^{11}B(d, α)^{9}Be). Angular distributions for the higher levels have been studied by (1956BE14); the resulting spin assignments are given in Table 9.3 (in PDF or PS). See also (1954FI35, 1955GR12, 1958TY46) and (1956BL1B; theor.).
Elastic scattering angular distributions have been studied at E_{d} = 24 MeV by (1958SU14). See also (1947GU1A, 1952EL01) and ^{11}B. Inelastic groups are reported corresponding to levels at (1.7), 2.4, 3.01 ± 0.1 (Γ ≈ 0.3), 4.8 and 6.8 MeV (1955RA41, 1956GR37, 1958MI1C, 1958SU14). The structure at Q = 1.7 MeV may be accounted for as a threebody breakup with an swave (n  ^{8}Be) interaction characterized by a scattering length of 20 × 10^{13} cm, or by a resonance of about singleparticle width. In either case a J = 1/2^{+} level of ^{9}Be is indicated near the binding energy (1955RA41, 1958MI1C: see also ^{11}B(d, α)^{9}Be). The angular distribution of the Q = 2.43 MeV group has been studied at E_{d} = 15 MeV (1956HA90) and E_{d} = 24 MeV (1958SU14). Analysis by direct interaction theory yields l = 2, J = 1/2^{}, 5/2^{} or 7/2^{} (1958SU14: see, however, (1956HA90)). See also (1956SU1A).
Elastic scattering has been studied at E_{α} = 48 MeV by (1958SU14). Inelastic groups are observed corresponding to ^{9}Be* = (1.8), 2.4, (3.1), 6.8 and 11.3 MeV (1955RA41, 1956FA02, 1958SU14). The group corresponding to the 1.8MeV "level" has a peak at Q = 1.83 ± 0.03 MeV, Γ ≈ 200 keV. It is suggested, however, that just such a structure would be expected from a heavy particle stripping process in which the proton also escapes, preferentially with the maximum possible energy. In this case, the 4.8MeV "level" might arise from a similar process, in which the final nucleus is now ^{8}Be*(2.9). The angular distribution of the Q = 2.4 MeV group at E_{α} = 48 MeV indicates l = 2, J = 1/2^{}, 5/2^{} or 7/2^{} (1958SU14). Measurement of the momentum and angular distributions of αparticles from the breakup of ^{9}Be*(2.4) indicate that the decay proceeds mainly via ^{4}He + ^{5}He, or by direct threebody breakup. Gamma decay is < 1%, neutron emission to ^{8}Be(0) is < 10% (1957BO83). See also (1956BL1B, 1958PI1B; theor.).
At E_{p} = 95 MeV, two groups of deuterons are observed from reaction (a), corresponding to ^{8}Be_{g.s.} and to states near 17 MeV. It is suggested that these reflect the "snatching" of the loosely bound neutron or of one of the tightly bound "alphaparticle" neutrons, respectively. Angular distributions lend some support to the αparticle model of ^{9}Be; the occurrence of high momenta for the tightly bound neutrons indicates the operation of strong shortrange twobody forces (1956SE1A). Angular distributions at E_{p} = 6.5 and 22 MeV, and at E_{d} = 7.7 MeV are analyzed in terms of pickup theory, using a squarewell (n  ^{8}Be) interaction to represent the ground state of ^{9}Be (1955DA1D, 1955DA1E). See also ^{10}B, ^{11}B.
For reaction (a) see (1956GO1F, 1956GO1G). For reaction (b) see ^{8}Be and ^{10}B.
At E_{n} = 14.4 MeV, the ground state and the level at 2.43 MeV are observed. No other deuteron groups were detected below E_{x} ≈ 5.5 MeV. The angular distribution of the deuterons, analyzed by pickup theory, indicate odd parity, 1/2 < J ≤ 9/2 for both states (1954RI15). See also (1956FR18), (1955FR1F; theor.) and ^{11}B.
Not observed.
At E_{t} = 1 MeV, αgroups are observed corresponding to ^{9}Be levels at 2.39 and 3.06 MeV (1955AL57).
Not observed.
Not observed.
Alphaparticle groups are reported to states at (1.75), 2.4 and 3.0 MeV. The structure corresponding to the 1.75MeV state can be explained in terms of an (n  ^{8}Be) interaction with a scattering length a of 20 × 10^{13} cm or in terms of a resonance near threshold, with θ^{2} ≈ 1 (1956BO18, 1958MI1C). (1958KA31) find, on the other hand, that a value of a ≥ 80 × 10^{13} cm is required to fit their distribution and suggest that the (n  ^{8}Be) interaction must be very near resonance on this model. The energy of the 2.4MeV state is given as 2422 ± 5 keV by (1951VA08), 2431 ± 6 keV (1954EL10), 2424 ± 5 keV (1956BO18). The next state is located at 3.02 ± 0.03 (1955LE36), 3.05 ± 0.03 MeV (1956BO18). The width is ≈ 0.3 MeV (1956BO18), Γ_{c.m.} = 161 ± 15 keV (1958KA31). See also (1955HO48).
At E_{n} = 14 MeV, the cross section to the ground state of ^{9}Be is 80 ± 20 mb; that to the 2.43MeV level, σ_{2.43}, is 10 ≤ σ_{2.43} ≤ 210 mb (1955GR21).
See (1953MI31).
