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