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11Be (1968AJ02)(See Energy Level Diagrams for 11Be) GENERAL: See Table 11.1 [Table of Energy Levels] (in PDF or PS). Mass of 11Be: The Q-value of the 9Be(t, p)11Be reaction is given as Q = -1.164 ± 0.015 MeV by (1962PU01) (based on 12C(t, p)14C*). This value has been adjusted by (1965RY01) to -1.170 MeV, leading to M - A for 11Be = 20.181 ± 0.015 MeV (relative to 12C) (1965MA54). See (1960TA07, 1960TA1C, 1961DO03, 1966RO11, 1967DE1V). The ground state of 11Be has even parity (1964AL22).
The decay proceeds to the 11B states at 0, 2.12, 6.79 and 8.00 MeV (Jπ = 3/2-, 1/2-, 3/2+, 3/2+, respectively); the half-life is 13.68 ± 0.14 sec. The nature of the decay indicates even parity, Jπ = 1/2+, 3/2+ or 5/2+ for 11Beg.s. (1961DO03, 1964AL22): see 11B.
Proton groups have been observed corresponding to seven states of 11Be: see Table 11.2 (in PDF or PS) (1962PU01). Angular distributions measured at Et = 6, 10 and 14 MeV do not show a clear stripping pattern for the ground-state protons. At Et = 14 MeV, the distribution of protons corresponding to 11Be*(0.319) exhibits an L = 2 pattern indicating Jπ = 1/2-, 5/2- or 7/2- (1962PU01, 1964HI08). (1960TA07) suggest Jπ = 1/2+ and 1/2- for the ground and first excited states, respectively. The dimensionless reduced widths θ2n for Ex = 1.8, 2.7 and 3.4 MeV indicate l = 0, 1 or 2 decay to 10Be + n, Jπ = 1/2±, 3/2± or 5/2+ (1962PU01). See also (1968HO1F).
At En = 14.8 MeV, σ(nα)/σ(np) = 10.0 ± 1.5 (1958NU40).
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