
^{11}Be (1980AJ01)(See Energy Level Diagrams for ^{11}Be) GENERAL: See also (1975AJ02) and Table 11.1 [Table of Energy Levels] (in PDF or PS). Model calculations: (1974TA1E, 1975MI12, 1976IR1B, 1977SE1D, 1978BO31, 1979BE1H). Special reactions: (1975FE1A, 1976OS04, 1977AR06, 1977YA1B). Muon capture (See also reaction 2.): (1978DE15). Pion reactions: (1975CO06, 1976CO1M, 1977DO06, 1977GE1D). Ground state of ^{11}Be: (1975BE31, 1978BO31).
The decay proceeds to ^{11}B*(0, 2.12, 5.02, 6.79, 7.98, 9.88) with J^{π} = 3/2^{}, 1/2^{}, 3/2^{}, 1/2^{+}, 3/2^{+}, 3/2^{+}, respectively: see Table 11.15 (in PDF or PS) (1971AL07). The halflife is 13.81 ± 0.08 sec (1970AL21). The nature of the decay indicates J = 1/2 or 3/2, even parity for the ground state of ^{11}Be: see (1971AL07). See also (1977TE01; theor.).
Proton groups have been observed to many states of ^{11}Be: see Table 11.2 (in PDF or PS) (1962PU01, 1972AJ01, 1978AJ02). The first excited state has an excitation energy of 319.8 ± 0.2 keV and τ_{m} = 0.18 ± 0.06 psec corresponding to a very strong E1 transition of 0.33 W.u. (1971HA25). The J^{π} of ^{11}Be*(0.32) is 1/2^{}, as determined by a study of the yield of 320 keV γrays as a function of time in μ^{} capture by ^{11}B (1968DE20). The strength of the E1 transition fixes J^{π} of ^{11}Be_{g.s.} to be 1/2^{+} or 3/2^{+}, using the parity information obtained from the nature of the β^{} decay of the ground state [see reaction 1]. ^{11}Be*(5.24, 6.71, 8.82) are strongly populated at E_{t} = 20 MeV indicating that these states have a large overlap with ^{9}Be_{g.s.} + two neutrons (1972AJ01).
See (1975AJ02).
Angular distributions of the p_{0} and p_{1} groups have been measured at E_{d} = 6 MeV (1970GO11: p_{1} only) and 12 MeV (1970AU02): l_{n} = 0 [and therefore J^{π} = 1/2^{+} for ^{11}Be(0)] and 1, S = 0.73 ± 0.06 and 0.63 ± 0.15, respectively (1970AU02). At E_{d} = 25 MeV ^{11}Be*(0, 0.32, 1.78) are strongly populated: S = 0.77, 0.96 and 0.50, respectively, J^{π} = (5/2, 3/2)^{+} for ^{11}Be*(1.78) [l_{n} = 2] (1979ZW01).
See ^{11}Li.
See ^{12}B.
At E(^{6}Li) = 80 MeV, ^{11}Be*(0.32) is strongly populated and the angular distribution to this state has been measured (1977WE03). ^{11}Be*(2.69, 4.0) are also observed. It is suggested that these states have odd parity (1976WE09) [see, however, reaction 2 for evidence concerning the positive parity of ^{11}Be*(2.69)]. See also (1977WE1B).
See (1974BA15).
