(See Energy Level Diagrams for 9Be)
GENERAL: See (1958BL57, 1959BA1D, 1959BR1E, 1959PI45, 1959TH16, 1960HE04, 1960KU1B, 1960PH1A, 1960SP08, 1960TA1C, 1960VA1H, 1961BA1G, 1961BA1E, 1961CL10, 1961GU1B, 1961KU1C, 1962BA1C, 1962IN02, 1962SC12, 1962TA1H, 1963HI1B, 1963MA1E, 1963SC1P, 1964AM1D, 1964BA29, 1964BA1Y, 1964BE1M, 1964GR1J, 1964NE1E, 1964RE1C, 1964ST1B, 1965BO1M, 1965KU1E, 1965MU1A, 1965NE1C, 1965RO1H, 1965WO01).
Ground state: μ = -1.1776 nm; Q = ± 0.03 b (1965FU1G).
The differential cross section for reaction (a) at 90° measured up to Et = 1.90 MeV increases rapidly with energy below the coulomb barrier and then approaches a constant value. At 1.50 MeV, the total cross section for formation of the ground state of 7Li is 190 mb; that for the first excited state is 4 times less (1961HO21: see also (1957JA37)). Angular distributions for both groups show maxima in the forward hemisphere. It is suggested that the large cross section indicates a cluster exchange process - here the exchange of t and d (1961HO1F, 1961HO21).
The 0° differential cross section for reaction (c) increases monotonically between 0.10 and 2.4 MeV (1960SE12, 1961VA43, 1962SE1A) except for a resonance at Et = 1.875 MeV, corresponding to an excited state of 9Be at 18.937 MeV. The total cross section for neutron production at Et = 2.12 MeV is 324 ± 32 mb (1961VA43). See also (1963JA1E).
The 90° differential cross section for reaction (d) 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 (see (1957JA37)). See also 5He, 7Li, 8Li and 8Be.
Angular distributions of ground-state protons have been measured at Eα = 10.15, 11.5 and 13.5 MeV (1960MA15) 13.6 and 14.7 MeV (1962KO13) and 30 MeV (1960KL03). At 30 MeV, strong backward peaking is evident (1960KL03). A qualitative account of the observations can be given if heavy-particle stripping (p + 5He + α) is assumed (1962HO1C). See also (1956WA29).
In the region Ed = 0.1 to 1.1 MeV, a resonance in the yield of capture γ-rays is observed at Ed = 362 ± 3 keV (1965WO01), 361 ± 2 keV (1965IM01), corresponding to an excited state in 9Be at 16.973 ± 0.002 MeV. The width of the level is less than 470 eV (c.m.). The small width of the level and the correspondence with 9Li*(2.69) argues for T = 3/2 (1965WO01). The angular distribution of the γ-rays to the ground state is isotropic to within 7%. The branching ratios to the ground state, and to the levels at 1.67, 2.43, 3.03 and 4.70 MeV are 100/8.5 ± 4.3/10.6 ± 5.3/ ≤ 4.5/9.6 ± 4.8. An upper limit for non-resonant, direct capture is 1.6 μb. The neutron decay of 9Be*(2.43) and 9Be*(4.70) is observed (1965IM01).
The cross sections for reactions (a) and (b) have been measured for Ed = 70 to 110 keV (1955RA14), 30 to 250 keV (1953SA1A) and 330 to 400 keV (1965IM01). The 0.36 MeV resonance is observed here also, in the yield of neutrons with En > 10 MeV: the ratio of the partial width of the 16.97 MeV level for emission of neutrons to 8Beg.s. to that for emission of γ-rays is ≈ 1.5, while Γα0/Γγ < 20 (1965IM01).
The yield of neutrons has been measured from 0.2 to 4.8 MeV by (1952BA1A, 1957SL01: see also (1947BE1A, 1949WH1A)), and the yield of α-particles has been measured from Ed = 0.2 to 0.3 MeV by (1964MA60) and for 0.7 to 3.0 MeV by (1963PA04). Resonances for neutron production are observed at Ed = 0.68, 0.98 and (1.8) MeV (Table 9.4 (in PDF or PS)). At Ed = 0.90 MeV, α-particles from reaction (b) are isotropic within 2%, consistent with formation by s-wave deuterons (1957RI39). The angular correlation of ground-state α-particles with those resulting from the breakup of 5He indicates J = 5/2- for the 9Be level mainly responsible for the reaction at Ed = 0.9 MeV (1956RI37); a similar observation at Ed = 0.16 MeV suggests J = 3/2- for the responsible level (1957FA10). See also (1964FE01). At Ed = 0.9 MeV, reactions (a) and (c) account for less than 10% of the disintegrations at this energy (1956RI37). Polarization of ground-state neutrons has been measured by (1962HE06).
The excitation function for reaction (b) shows indications of the Ed = 0.7 and 1.0 MeV resonances (unresolved in this work) as well as broad structure at Ed = 2.5 MeV. There is no indication of resonance at 1.8 MeV in this ground-state α-yield. Also reported are α-particles from reaction (a) associated with the 8Be excited states at 11.3, 16.6 and 16.9 MeV; the α-particles from the decay of the 11.3 MeV state seem to show resonance behavior at Ed = 0.7, 1.0 and 1.75 MeV. It is not clear whether the α-particles corresponding to 8Be*(16.6) show resonance at Ed = 2.5 MeV or whether the 8Be*(16.9) α-particles are appearing at this point (1963PA04). See also (1964BI10, 1965BI1F, 1965JO19), 5He and 8Be.
The yield of 8Li (ground-state protons) has been measured for Ed = 0.29 to 0.78 MeV. A resonance is observed at Ed = 360 ± 3 keV with Γ < 2 keV. The ratio Γp/Γγ is ≈ 0.5 (1965IM01, 1965WO01): see also 7Li(d, γ)9Be.
The yield of 8Li(p0 + p1) has been measured in the range Ed = 0.4 to 3.3 MeV by (1952BA1A, 1954BA46, 1960KA05) and from 1.1 to 4 MeV by (1956BE1A: stacked foils). Ground-state protons have been examined from Ed = 1.0 to 4.0 MeV by (1960SE08, 1963SE1F). Resonances are reported at 0.77, 1.02, (1.375), 2.0, 2.5 and 3.7 MeV (Table 9.4 (in PDF or PS)), apparently superposed on a rising background. The total cross section at Ed = 0.77 MeV is 150 ± 35 mb (1954BA46), 176 ± 15 mb (1960KA05), From Ed = 1.0 to 4.0 MeV, angular distributions are unusually well described by stripping theory; the resonance at Ed = 1.375 MeV shows no effect on the angular distribution (1960SE08, 1963SE1F).
The yield of 0.95 MeV γ-rays from 7Li(d, p)8Li* rises smoothly from Ed = 1.9 to 3.3 MeV. Above Ed = 2.3 MeV, the isotropy of the γ-rays is taken to indicate predominance of the stripping process (1962CH14).
The upper limit for the relative partial width for elastic scattering at Ed = 0.36 MeV (9Be* = 16.97), Γd0/Γγ, is 400 (1965IM01).
The elastic scattering has been studied from Ed = 0.4 to 1.8 MeV by (1964FO13). The scattering cross sections lie below the Rutherford values at the lower energies. A marked increase occurs in the range Ed = 0.8 to 1.0 MeV, and a conspicuous anomaly occurs at Ed = 1.0 MeV. A rising background is ascribed to other overlapping resonances. The scattering below Ed = 1.0 MeV can be satisfactorily accounted for by s-waves: the variation of parameters is consistent with - but does not require - a level at Ed = 0.8 MeV. The resonance at 1 MeV appears to be due to p-wave deuterons (1964FO13). See also 7Li and (1958RO49).
Observed proton groups are listed in Table 9.5 (in PDF or PS) (1955AL57, 1958MO99, 1963CA02, 1965CO1F, 1965MA1E). The γ-decay of the narrow 14.39 MeV state to the ground and 2.4 MeV states indicates Γγ0/Γp = 0.023 ± 0.005, Γγ1/Γp = 0.04 ± 0.01. Assuming Γγ0 = 18 eV (see 9Be(e, e')), Γ = 0.8 ± 0.3 keV for the 14.39 MeV state. This level is presumed to be the lowest T = 3/2 state of 9Be, analogous to the 9Li ground state (1965GR08, 1965LY01). There is some evidence also for the γ-decay of a state at ≈ 17 MeV, presumably the T = 3/2 analogue of the first excited state of 9Li (1965GR08: see also 7Li(d, γ)). See also (1961WO05) and 10B.
At E(7Li) = 2.9 MeV, α-particle groups are observed corresponding to 9Be*(0, 1.75, 2.4, 3.0, 11.9 ± 0.2 MeV); the last has Γ = 500 ± 100 keV. No other levels are observed for Ex < 13.0 MeV (1964ME07). See also (1963GA02, 1963HU02, 1964KI02, 1965BE1X).
9Li decays to the ground state (25 ± 15 %) and to 9Be*(2.4) (75 ± 15 %): log ft = 5.5 ± 0.2 and 4.7 ± 0.2, respectively. The allowed character of the transition is consistent with 9Be*(2.4) = 5/2- and 9Li(0) = 3/2- or 5/2- (1963AL18). See also 9Li.
The photoneutron cross section has been measured from threshold (Eγ = 1664 ± 4 keV: (1956CO56)) to 320 MeV: see Table 9.6 (in PDF or PS). A sharp peak occurs just above threshold, at Eγ = 1.70 MeV (1960WA06, 1961JA13) followed by a weak maximum at 2.4 MeV, a strong sharp peak at 2.95 MeV, and a broad maximum at 4.6 MeV (1961JA13). (1959TH15) find well-defined peaks at 11.3 ± 0.2 and 13.3 ± 0.2 MeV, with integrated cross sections of 4.0 and 3.9 MeV · mb. A considerable yield in the range 8 - 11 MeV is also indicated (1959TH16). The giant resonance occurs at 20 - 22 MeV (1953JO1B, 1953NA1A, 1956CO59). At Eγ = 6.1 MeV, the main processes appear to involve 9Be(γ, n)8Be*(2.9) and reaction (b) (1954CA1A). For Eγ = 18 to 25 MeV, ≈ 80% of (γ, n) processes lead to 8Be*(16.6) (1964BE30). See also (1960SE1D, 1965KO08, 1965KO1B).
The total nuclear absorption cross section is about 2 mb at Eγ = 10 MeV: a deep minimum at ≈ 13 MeV is followed by a rise to ≈ 5 mb at 18 MeV and a slow decrease to ≈ 3 mb at 35 MeV (1965WY02). Fine structure is reported at Eγ = 20.47 ± 0.04 and 20.73 ± 0.04 MeV (1964TE04). See also (1962MI15).
Measurements involving time-of-flight analysis of the neutron energies show the 1.7 and 3 MeV resonances in ground-state neutrons (n0), but ascribe the 4.6 MeV structure to slow neutrons, arising from reactions (b), (c) or from n1 to 8Be*(2.9): ground-state neutrons account for < 10% of the total at this energy. The yield of n0 remains essentially constant from 5 to 16 MeV, aside from a broad maximum near 10 MeV and a shallow minimum at 13 MeV. The yield of n1 rises sharply near 6 MeV, showing signs of a sharp peak at 7 MeV and remains high until about 10 MeV where it falls rapidly to a minimum at 13 - 14 MeV. There is evidence of a broad peak near 12 MeV (1963DE1J). For Eγ = 5.6 to 8.5 MeV, the relative contribution of n0 ranges from 0.5 to 0.3 (1963BO32).
Angular distributions of neutrons from the 1.67 and 4.6 MeV levels are isotropic; those from the 2.4 MeV level show slightly higher yield at θ = 90°. Neutrons from the 3.0 MeV level have the distribution σ(θ) = 1 + (1.0 ± 0.2)sin2θ, compatible with E1 excitation to a 5/2+ D-state (1961JA13: see also (1949HA1A, 1961BA1G)). Some fore and aft asymmetry may indicate the presence of odd-parity amplitudes (1965PH1B). The fact that the 3.0 MeV state is strongly excited in (γ, n) and not in 180° (e, e') (M1 excitation) also indicates positive parity (1961BL1D). The same argument suggests positive parity (E1 transitions) for levels at 1.7, 6.8, 7.9, 9.2, 11.3 and 13.3 MeV (1959TH16). For Eγ = 5.6 to 8.5 MeV, angular distributions are of the form 1 + Asin2θ, with A = 0.20 to 0.27, consistent with P3/2 → D3/2 transitions (1962BO08, 1962BO21, 1963BO32). Evidence for polarization of neutrons is reported by (1964CO17). See also (1959KU84, 1961VA09, 1964AL33).
Calculations of the (γ, n) cross section near threshold have been made by (1960FR1B), using a single-particle model with a diffuse-surface Saxon-Woods potential and assuming a 1/2+ level at Ex = 1.70 MeV. A good account of the observations is obtained, but with a rather large diffuseness parameter, a = 1.2 fm, in the final state. If the parameter is taken to be a = 0.6 fm, the calculated cross section is about 1.6 times too high. According to (1961BL1D), a model in which the neutron in 9Be(0) is strongly coupled to a deformed 8Be core leads to a sizable probability of excitation of the core to the 2+ state, reducing the calculated cross section at 1.7 MeV. The 4.7 MeV structure is then ascribed to transformations in which 8Be is left in the excited 2+ state. A calculation of the low-energy excitation function has been made by (1963CO05) using the same model as (1960FR1B) but fixing the final state diffuseness parameter at a = 0.6 fm, and varying the final state potential depth. The slope and magnitude of the observed (γ, n) cross section are best accounted for by a bound s-state, with energy 19+9-5 keV below threshold (1963CO05). (1961BA1G) considers couplings of 1s and 1d neutrons to 8Be(0) and 8Be(2+). With the 1.7 MeV level assumed 1/2+, 3/2+ and 5/2+ levels are predicted at 4.88 and 4.05 MeV, respectively. It is suggested that the 3.03 MeV level is an unresolved combination of 1/2- and 5/2+. See also (1961GU1C, 1961KO1J, 1962CU05, 1962KO11, 1963CO1D, 1963SA09, 1964BI1E, 1964FR1C, 1964MA2E, 1965WE1E).
The yield shows structure in the energy region corresponding to the 9Be levels at 17 - 19 MeV (1962CL06), followed by the giant resonance at Eγ = 22.2 MeV (1953HA1A: Γ = 4.7 MeV, σ = 2.72 mb), ≈ 23 MeV (1962CL06: σ = 2.64 ± 0.30 mb). The angular and energy distributions of photoprotons in various energy intervals have been studied by (1956CO59, 1956KL19, 1962CH26, 1963KI1C, 1965KO08). At Ebrems.(peak) = 335 MeV, the polarization of photoprotons at 45°, 56° and 90° is small and is consistent with zero (1962LI13). See also (1959CH25, 1961MA36, 1962CU05, 1962MI15, 1962VO1D) and (1959AJ76).
The cross section for reaction (a) is appreciable only for γ-energies greater than the sum of the threshold energy and the binding energy of the most weakly bound nucleon in 7Li. The main processes involved are then thought to be those in which the emission of deuterons is accompanied by one or more nucleons (1962BA62, 1962CH26, 1962VO1D). See also (1959CH25, 1960SH1D, 1962CU05, 1962MA1F, 1963BA1K, 1964SH1B, 1965KO08) and (1959AJ76).
Elastic scattering of electrons has been studied at Ee = 42, 80, 125, 150, 190 and 300 MeV (1953HO79, 1954MC45, 1959ME24, 1963GO04). Analysis of the 190 and 300 MeV results has been carried out in terms of various models for the charge distribution; the r.m.s. radius is about 2.60 ± 0.2 fm, depending on the model. At large values of momentum transfer, a static spherical distribution seems inadequate and a contribution from the quadrupole distribution may be required (1959ME24). According to (1960WA1J) the 300 MeV data can be matched with a Fermi distribution plus a quadrupole distortion consistent with Q = 0.02 b. See also (1961WA1C, 1963GU1A). Magnetic scattering at θ = 180° gives indication of both M1 and M3 contributions (1965RA1C: see also (1963GO04)).
Inelastic scattering reveals a number of levels from 1.6 to 16.9 MeV (see Table 9.7 (in PDF or PS)). Of these, only the 2.43, (14.7), and (16.9) MeV levels are strong in 180° scattering, where M1 transitions should dominate (1960BA47, 1962BA1D, 1962ED02). Studies of the 2.4 and 6.7 MeV levels at smaller angles reveal strong E2 components; quantitative comparison with form factors and absolute cross sections predicted by the α-rotational model (1960IN1A) indicate Jπ = 5/2- and 7/2-, respectively, for these two levels. The excitation energies and transition widths are consistent with the assumption that they are members of a K = 3/2- rotational band based on the ground state. The derived intrinsic g.s. quadrupole moment Q0 = 0.26 ± 0.01 b is nearly twice that obtained from the spectroscopic value Q0 = 5 × 0.029 b (1963NG01). In both this work and calculations of (1962KU1C) the rotational α-model shows increasing deviations from experiment for momentum transfer q > 1 fm-1; the Nilsson model has the same fault, but in opposite sense. An intermediate coupling model with enhanced quadrupole charge distribution is superior (1962KU1C). See also (1961WA1C, 1965RA1D).
Comparison of the inelastic scattering from the 1.6 MeV level at two angles indicates that this level is most probably excited by E1 (1963NG01). The fact that the 1.6, 3.0 and 4.7 MeV levels appear strongly in (γ, n) but not in (e, e') at 180° suggests that these levels are excited by E1 transitions (1962ED02). [The 14.7 MeV level is presumably the T = 3/2, J = (3/2)- analogue of the 9Li ground state; the 16.9 MeV level may correspond to the first excited state.] In the range 17 to 49 MeV, inelastic scattering appears to be largely via E1, E3, M2 to the exclusion of M1, E2, M3 (1962NG02, 1963NG1B, 1964NG1A).
The neutron spectrum observed when 9Be is bombarded with 3.7 MeV neutrons exhibits a structure which is consistent with the excitation of the ground states and the levels at 1.7, 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 9Be (1957HU14, 1958WA05). Time-of-flight studies from En = 2.6 to 6.0 MeV show that about 1/2 of the inelastic processes involve 9Be*(2.43). A continuous distribution may be ascribed either to 9Be*(1.7) or to (n, 2n). Examination of the spectra at En = 3.5 MeV yields the result that the 2.43 MeV level decays only 12 ± 5 % via 8Beg.s. (1959MA34). At En = 14 MeV, evidence is found for the participation of the 6.8 MeV level. A search for an angular correlation between outgoing neutrons yielded a negative result (1963JE05). At En = 14 MeV, the cross section for production of 9Be*(2.4) is 200 ± 45 mb (1961CO1E), 200 ± 100 mb (1961MY01), 170 ± 30 mb (1958AN32) comparison with σ(n, 2n) = 500 mb (1964ST25) indicates that about 1/3 of the (n, 2n) processes proceed via 9Be*(2.4) (1958AN32). Elastic and inelastic neutron angular distributions show forward peaking at En = 14 MeV (1958AN32, 1958NA09). See also (1958BE1E, 1959CH1E, 1959SA04, 1959WI41, 1960BA24, 1960BA28, 1960LU1B, 1960MC04, 1963OP1A, 1964BO31, 1964CR1B, 1965LO1K, 1965RO1U) and 10Be.
Elastic scattering has been studied at Ep = 6 MeV (1963BL20), 5 to 15 MeV (1964BI19), 10 MeV (1956RA32), 6, 8 and 12 MeV (1963TE1B), 12 MeV (1958SU14), 14.5, 20 and 31.5 MeV (1956KI54), 16.6 to 36.6 MeV (1965AR1E), 18.9 MeV (1956DA03), 31 MeV (1953WRZZ, 1954FI35, 1956BE14), 48 MeV (1965WI1H), 142 MeV (1961TA06), 143 MeV (1964ST16), 160 MeV (1965RO1T), 316 MeV (1956CH80) and 725 MeV (1965MC04). All angular distributions show pronounced diffraction maxima characteristic of the optical model. Analysis in terms of the diffuse-surface optical model is discussed by (1957ME21). See also (1956KL55, 1959HI1H, 1959JO43, 1960NE09, 1960NE11, 1960SA28, 1961IS05, 1961JO18, 1961RE03, 1964CR1B, 1964SA1L, 1964VE1A).
Inelastic scattering is observed to states at 1.7, 2.4, 3.1, 4.8, 6.8, 7.9, 11.3 MeV and others: see Table 9.8 (in PDF or PS). The structure at 9Be*(1.7) is unsymmetrical, rising abruptly from threshold at Q = -1.669 MeV to a peak within < 14 keV (1962BR09). The width at half-maximum is 175 ± 25 keV (c.m.), indicating dominant s-wave emission of neutrons (1960SP08). According to (1960SP08) the structure does not represent a true state, but results from the spatial localization of the low-energy neutron and 8Be after emission of the inelastically scattered proton. Using a specialized density-of-states function, they obtain a good match to the experimental shape in this hypothesis. See also (1963PH1A). On the other hand, (1962BA1C) find an equally good fit with a density-of-states function of Breit-Wigner shape, corresponding to a Jπ = 1/2+ level at Ex = 1.75 MeV with width γ20 = 1.01 MeV (R = 4.35 fm), parameters which also fit the (γ, n) cross section. At Ep = 18.9 MeV, the 1.7 MeV group is not observed; the upper limit to the intensity of the group is < 2% of that to the 2.4 MeV state (1962SC12). See also (1955GO48, 1956BO18, 1958MI1C, 1958SU14, 1964BI19, 1964SC1F, 1965WI1H).
The energy of the 2.4 MeV level is given as 2433 ± 5 (1951BR72), 2434 ± 5 (1956BO18), 2432 ± 4 (1955GO48), 2430 ± 5 keV (1960SP08); the width is ≤ 1 keV (1955GO48), ≤ 3 keV (1960SP08). Angular distributions of protons leading to the 2.4 MeV state are not well matched by plane wave direct interaction calculations (1962SC12). The 12 MeV data suggest l = 0 and 2 (Jπ = 1/2- or 5/2-) (1958SU14) while the 31 MeV data are best fitted by l = 2 (1956BE14, 1958SU14, 1962SC12). It appears that the relative inelastic cross sections for various levels are largely independent of bombarding energy or particle; in particular, the 2.4 and 6.8 MeV levels are always strong and the 1.7, 3.0 and 4.8 MeV levels always weak. It is suggested that the strong excitation of the former is relative to a collective enhancement of electric multipole transition strengths connecting them to the ground state (1958BL57, 1959PI45, 1962SC12). The excitation energies and inelastic cross sections are consistent with the assumption that they have Jπ = 5/2- and 7/2-, respectively. On the collective model, they are members of the ground state K = 3/2- band: the J = 9/2- member is then expected at 10 - 11 MeV (1958BL57). See also (1964JA03, 1965HA17).
The 3 MeV state has a width 250 ± 50 keV (1960SP08): Ex = 3.03 ± 0.03 MeV (1956BO18), 3.04 ± 0.05 MeV (1960SP08). Comparison of the width with that of the mirror level 9B*(2.79) suggests that the level decays either to 8Be(0) via d-wave or to 8Be(2+) via s-wave: J = 3/2+, 5/2+ (1960SP08). See also (1955GR12, 1958TY46, 1960LU1B, 1961IS05, 1963BA1R, 1963BL20, 1963RU05).
Angular distributions of ground-state deuterons have been studied at Ep = 4.9, 5.5 MeV (1961RE03), 5 to 8 MeV (1951HA1A), 6.8 MeV (1960NE09, 1960NE11), 7 MeV (1964YA1A), 10 MeV (1956RA32), 12 MeV (1958SU14), 16.5 MeV (1956RE04), 22 MeV (1953CO1C), 31 MeV (1956BE14), 95 MeV (1956SE1A) and 155 MeV (1963BA1R, 1963RA01). The distributions in the range Ep = 5 to 31 MeV are substantially identical, contrary to the prediction of the simple Butler theory with fixed cut-off radius (1956GL25). An analysis by (1961RE03) (see Table 9.9 (in PDF or PS)), shows good agreement for the 12 to 31 MeV data with inclusion of a volume interaction, leading to θ2n = 1.2%. Polarization of the deuterons has been studied at Ep = 3 MeV (1961LA17). See also (1960BA26, 1965MO27).
At Ep = 95 MeV, states of 8Be near 16 to 18 MeV are strongly excited (1956SE1A). At Ep = 155 MeV, states at ≈ 16.6 and ≈ 18.9 MeV are excited with 0° differential cross sections of 3.6 and 1.15 mb/sr, respectively (1963BA1R, 1963RA01).
Angular distributions and excitation functions for Ep = 3 to 12 MeV suggest direct interaction. Analysis with DWBA in terms of 9Be → 6Li + t (l = 1) yields fair agreement for α0 but not for α1 (1963BL20). The observed large cross section at back angles suggests that 9Be is better described as 4He + 5He (1963SC1P). See also (1964YA1A, 1965MO27).
The summed proton spectrum in reaction (a), observed at Ep = 155 to 450 MeV shows two peaks, with Q = -16.7 ± 0.3 and Q = -25.8 ± 0.4 MeV, corresponding to removal of a p-proton and an s-proton respectively (1958MA1B, 1958TY49, 1961PU1A, 1962GA09, 1962GA23, 1962IN1A, 1963BE1A, 1963BE42, 1963BO1R, 1963RI1B, 1964BA1C, 1964TI02, 1965RI1A, 1966TY01).
At Ep = 155 MeV, p - α correlations (reaction (c)) give evidence for a substructure 9Be = 5He + 4He in a relative s-state with a probability of 7% (1963RU05).
For reaction (b), see 7Li.
Elastic scattering has been studied at intermediate energies by (1961BA06, 1962GR14: 7.8 MeV), (1963FR1F: 12.8 MeV), (1961IS04, 1963SA1G: 14.7 to 18.1 MeV), (1964HE01: 15.8 MeV), (1958SU14: 24 MeV), (1962SL03: 27.7 MeV). All show pronounced diffraction patterns. See also (1947GU1A, 1952EL01, 1959ZA01) and 11B.
Inelastic groups are reported to states at 1.7, 2.4, 3.0, 4.8 and 6.8 MeV (1955RA41, 1956GR37, 1958MI1C, 1958SU14). The angular distributions to the 2.4 MeV state have been studied at Ed = 15, 24 and 27.7 MeV (1956HA90, 1958SU14, 1962SL03). Analysis by direct interaction theory yields l = 2, J = 1/2-, 5/2- or 7/2-. See also (1958BL57, 1959BL31, 1960EL09, 1960LU1B).
Elastic scattering has been studied at Eα = 9.5 to 20 MeV (1965TA1C), 18.4 MeV (1964LU02), 23.8 MeV (1964GR39), 28 MeV (1964YA1A), 42 MeV (1956FA02: see (1958BL57)) and 48 MeV (1958SU14). Inelastic groups are observed to 9Be*(1.8, 2.4, 3.0, 6.8, 11.3) (1955RA41, 1958SU14, 1964LU02, 1964YA1A). The angular distribution of the groups corresponding to the 1.8 MeV "level" is consistent with Jπ = 1/2+ (1964LU02). The angular distribution of the Q = -2.4 MeV group, at Eα = 48 MeV, indicates l = 2, J = 1/2-, 5/2- or 7/2- (1958SU14). Analysis based on the rotational model leads to a deformation coefficient β2 = 0.46 (1959BL31), 0.34 ± 0.01 (1964GR39).
Measurement of the momentum and angular distributions of α-particles from the breakup of 9Be*(2.4) indicates that the decay proceeds mainly via 4He + 5He, or by direct three-body breakup. Gamma decay is < 1%, neutron emission to 8Be(0) is < 10% (1957BO83: see also (1959MA34) in 9Be(n, n')9Be*, and (1962ST12)). At Eα = 25.4 MeV, the continuum has been analyzed in terms of a combination of three- and four-body breakup. At low energies the results are consistent with a mixture of 9Be + α → 8Be(0) + α + n, 9Be*(2.4) → 2α + n or 5He + 4He (1962BR14). The third excited state is located at Ex = 3.04 ± 0.03 MeV, with Γ = 300 ± 50 keV (1964LU02). See also (1958BL57, 1959PI45, 1962ST12, 1964GO1K, 1965SA1K) and 13C.
Angular distributions of 8Li nuclei observed for E(7Li) = 2 to 4.0 MeV, show pronounced peaks at θlab = 60° to 30°. The decrease of peak angle with increasing energy suggests a neutron transfer process (1957NO17, 1959NO40, 1960NO1A). The radial distribution of the 9Be neutron is deduced for R = 15 to 30 fm (1960AL1H, 1960GE1B). See also (1963LE10, 1965PO1F).
Elastic scattering in reactions (a) and (b) for Ec.m. = 3 to 15 MeV has been studied for angles near 90° (c.m.). The fact that no diffraction structure was found may reflect a more diffuse surface for 9Be than for 12C (1961KU1D, 1963KU1L). At E(14N) = 27.3 MeV no agreement is found with the predictions of a sharp cut-off model for elastic scattering (1959HA28). See also (1963WI1G).
At En = 14 MeV, groups are observed corresponding to 9Be*(0, 2.43); no other groups are observed below Ex ≈ 5.5 MeV. The angular distributions of the deuterons indicate odd parity, 1/2 < J ≤ 9/2 for both states (1954RI15). See also (1955FR1F, 1956FR18, 1963CE1B, 1964TO1C) and 11B.
The summed proton spectrum at Ep = 460 MeV yields Q = -6.7 ± 0.5, -11.9 ± 0.5, -17.1 ± 0.6 (all l ≠ 0), and Q = -30.5 ± 0.6 MeV (l = 0) (1966TY01). See also (1958TY49, 1961PU1A, 1962GA09, 1962GA23). See also (1963RI1B, 1964TI02) and 10B.
At Ed = 10 MeV, θ = 30°, groups corresponding to 9Be*(0, 1.7, 2.4, 3.0) are observed with relative intensities 1.0/0.07/0.70/0.16 (1965SY02).
At E(14N) = 27.5 MeV, the ground state angular distribution shows a single maximum at θc.m. = 30° (σ(θ) = 1.3 mb/sr). The total ground-state transfer cross section is 1.34 ± 0.30 mb, corresponding to an interaction radius Rmin ≈ 2.2(A1/31 + A1/32) fm (1962NE01).
Not reported. For reaction (b), see (1964BA1C).
Alpha groups are reported corresponding to states at (1.75), 2.4 and 3.0 MeV (1956BO18, 1958KA31, 1958MI1C). The width of the 1.75 MeV structure is 224 ± 25 keV (1958KA31, 1966PU02). The energy of the 2.4 MeV state is 2422 ± 5 keV (1951VA08), 2431 ± 6 keV (1954EL10), 2424 ± 5 keV (1956BO18). The next state is at 3.02 ± 0.03 MeV (1955LE36), 3.05 ± 0.03 MeV (1956BO18). Its width is ≈ 0.3 MeV (1956BO18), Γc.m. = 257 ± 25 keV (1958KA31, 1966PU02). See also (1955HO48, 1961TE02, 1963RO22, 1964GR19, 1964YA1A).
The ratio of the γ-decay width to the total width, Γrad/Γ, of the 2.4 MeV state is (1.15 ± 0.15) × 10-4 (1964PU04). Since Γrad is known from (e, e') (see (1962ED02) and Table 9.4 (in PDF or PS)), Γ = 1.0 ± 0.2 keV. For the 1.7 MeV state Γrad/Γ < 2.6 × 10-5 (1964PU04, 1966PU02).
Analysis of 128 cloud chamber stars involving 9Be*(2.4) leads to the conclusion that the probability of 9Be*(2.4) → n + 8Be(0) is 13 ± 5 % (1965MO09). See also (1955GR21, 1962BA15, 1962BA25, 1963AL10, 1963DA12, 1963SE08, 1964BR25, 1964CH28).