(See Energy Level Diagrams for 10Be)
GENERAL: See (1956KU1A, 1957FR1B, 1959BA1F, 1960KU1B, 1960TA1C, 1961BA1E, 1961TR1B, 1963BU1C, 1963VL1A, 1963WA1M, 1964FR1D, 1964GR1J, 1964VO1B, 1964WA1F, 1964WA1K). See also Table 10.1 [Table of Energy Levels] (in PDF or PS).
The neutron yield exhibits broad resonances at Et = 0.84 and 1.70 MeV (1951CR01), 0.71 ± 0.02 MeV (1962SE1A), 0.765 and 1.735 MeV (1961VA43), and a weak structure at Et = 0.24 MeV (1960SE12). The width of the 0.77 MeV resonance is 160 ± 50 keV (1962SE1A).
Excitation functions for α0, α1 and α2 (corresponding to 6He*(0, 1.8, 3.4) see, however, (1965AJ01) for evidence relevant to the existence of a state at 3.4 MeV in 6He) show a weak maximum at 1.10 MeV, a weak minimum at 1.30 MeV and a broad maximum at 1.80 MeV (Γ ≈ 0.5 MeV). Angular distributions are complex and suggest direct interaction: the maximum at Et = 1.80 MeV may result from interference effects (1961HO23). Angular distributions of α0 and α1 at Et = 0.24 MeV suggest J = 2+ for the 17.8 MeV state (1954AL38). See also (1963JA1E) and (1959AJ76).
Angular distributions of p0 at Eα = 13.6 and 14.7 MeV (1962KO13) and 30 MeV (1960KL03) show an oscillatory character with strong peaking in the back hemisphere. The p1 distributions are smoother, but they also show backward peaks (see also (1956WA29)). An explanation in terms of heavy-particle stripping is discussed by (1962HO1C). See also (1962MA59) and (1960MA15).
The total cross section data is summarized in (1964ST25). Angular distributions are summarized in (1963GO1M). The coherent scattering length (thermal, bound) is 7.7 fm (1961WI1A). The spin dependent thermal cross section is < 30 mb (1952PA1A).
Polarization and differential cross sections are reported for En = 0.2 to 2 MeV by (1961LA1A, 1962EL01, 1964LA04). Analysis of these data indicates that the En = 0.62 MeV (Ex = 7.37 MeV) resonance has Jπ = 3-, formed by l = 2, with equal participation of channels Jc = 1 and 2. Interference with hard-sphere (R = 5.6 fm) s-wave background and with a broad l = 1, J = 3+ state is observed. Below En = 0.5 MeV, the scattering cross section reflects the effect of bound 1- and 2- states with Eλ ≈ -0.2 MeV, γ2 ≈ 0.05 MeV, presumably to be identified with 10Be*(5.96, 6.26). The resonant behavior near 0.815 MeV is consistent with Jπ = 2+, formed by l = 1 (1964LA04). See also (1964GO1L). The finding that the level at Ex = 7.37 MeV has J = 3- is in good accord with comparisons of reduced widths with the presumed T = 1, Tz = 0 analogue in 10B at Ex = 8.89 MeV; for R = 5.8 fm,
The structure at En = 2.73 MeV is ascribed to two levels: a broad state at about 2.85 MeV with J = 2+, and a narrow one, Γ ≈ 100 keV, at En = 2.73 MeV with a tentative assignment of J = 4- (1951BO45, 1959FO1A). A weak dip near 4.3 MeV is ascribed to a level with J ≥ 1 (1961FO07).
Data on non-elastic cross sections are summarized by (1964ST25). The processes involved include (n, 2n) and (n, n')9Be* → n + 8Be; the (n, α) process is relatively weak. The total non-elastic cross section rises rapidly from threshold at En ≈ 2.5 MeV to ≈ 600 mb at En = 6 MeV, and then falls slowly to 500 mb at 14 MeV. In the range 3.5 to 6.0 MeV, 9Be(n, n')9Be*(2.43) accounts for about half of the non-elastic cross section (1959MA34: see (1964ST25)): see also 9Be. At En = 14 MeV, 8Be*(2.9) is frequently involved (1959CH1E, 1961MY01).
The cross section for production of 6He has been measured for En = 0.7 to 8.6 MeV (1957ST95, 1958VA33, 1961BA53); see also (1964ST25). (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. No indication of resonance is found at En = 2.7 MeV. From En = 3.9 to 8.6 MeV, the cross section decreases smoothly from 100 mb to 32 mb (1961BA53). The cross section at En = 14 MeV is 10 ± 1 mb (1953BA04). See also (1960BU1C, 1963CH1C, 1964GA11).
Parameters of levels observed in this reaction are listed in Tables 10.4 (in PDF or PS) and 10.5 (in PDF or PS). Angular distributions of proton groups have been studied at many energies: see (1958ZE01, 1959AJ76, 1960MA32, 1961IS01, 1961RE04, 1962SL04, 1964SC12). Except at the lowest energies, the stripping process appears to dominate: see (1959BO1C, 1960BE1B, 1960LU04, 1960LU1B, 1960NA1A, 1963SM05, 1963TA1A, 1964BA1V). See also (1964ZA1B).
The mean life of the 3.37 MeV level is 0.15 ± 0.03 psec (1965WA1P), some ten times shorter than the single-particle value. On the I.P.M. an effective charge [1 + (0.5 ± 0.2)]e is required; strong collective effects are indicated (1963WA03, 1963WA1M): see also (1959BO49, 1959KO1B). For the 6.18 MeV level, τm > 0.5 psec, consistent with an E0 transition (1963WA17). Internal pair correlations establish the multipolarities of the transitions: 3.37 (E2), 5.96 (E1), and 6.18 (E0) (1964WA05); however, (1965FO1G) report that Jπ(5.96) = 2- from γ-γ correlation studies †. The mean life of 10Be*(5.96) is < 0.08 psec (1965WA1P). The absence of a ground-state transition from 10Be*(6.26) supports the assignment Jπ = 2- for this level (1958ME81, 1963WA17): see also (1959CH28, 1959GO78).
† See Note added in proof section in the Introduction.
The (p-γ) correlation through 10Be*(3.37) has the form 1 + AP2(cos θγ), where θγ is measured from the recoil direction. Reported values of A lie in the range -0.2 to -0.4 (1957CO54, 1959TA01, 1959ZA01, 1960GO18, 1961RE04, 1962KO14, 1963AC01, 1963NE09, 1964ZA03). These values are consistent with the assumption of a 3P2 state in LS coupling, but not with 1D2. Pure jj coupling leads to A = 0, as does the collective model. Approximate agreement can be obtained in intermediate coupling with a/k = 4.5 (1962PI1A): see also (1960KU1B, 1961RO1K). Polarization of the protons has been studied by (1959HI1E, 1960GR11, 1960HI09, 1961VA03, 1962AL10, 1962PA12, 1963NE09, 1963NE16, 1964RE04, 1965HE1B). See also (1961TE02).
In the summed proton spectrum, structure is observed corresponding to Q = -10.9 ± 0.35, -14.7 ± 0.4, -21.1 ± 0.4, -35 ± 1 MeV (1958TY49, 1962GA09, 1962GA23, 1962GO1P, 1964TI02, 1965RI1A, 1966TY01). See also (1958MA1B, 1963BE42, 1963RI1B, 1964BA1C), and 11B.