(See Energy Level Diagrams for 11Be)
The decay proceeds to 11B*(0, 2.12, 5.02, 6.79, 7.98, 9.88) with Jπ = 3/2-, 1/2-, 3/2-, 1/2+, 3/2+, 3/2+, respectively: see Table 11.15 (in PDF or PS) (1971AL07). The half-life 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 11Be: see (1971AL07). See also (1977TE01; theor.).
Proton groups have been observed to many states of 11Be: 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 τm = 0.18 ± 0.06 psec corresponding to a very strong E1 transition of 0.33 W.u. (1971HA25). The Jπ of 11Be*(0.32) is 1/2-, as determined by a study of the yield of 320 keV γ-rays as a function of time in μ- capture by 11B (1968DE20). The strength of the E1 transition fixes Jπ of 11Beg.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]. 11Be*(5.24, 6.71, 8.82) are strongly populated at Et = 20 MeV indicating that these states have a large overlap with 9Beg.s. + two neutrons (1972AJ01).
Angular distributions of the p0 and p1 groups have been measured at Ed = 6 MeV (1970GO11: p1 only) and 12 MeV (1970AU02): ln = 0 [and therefore Jπ = 1/2+ for 11Be(0)] and 1, S = 0.73 ± 0.06 and 0.63 ± 0.15, respectively (1970AU02). At Ed = 25 MeV 11Be*(0, 0.32, 1.78) are strongly populated: S = 0.77, 0.96 and 0.50, respectively, Jπ = (5/2, 3/2)+ for 11Be*(1.78) [ln = 2] (1979ZW01).
At E(6Li) = 80 MeV, 11Be*(0.32) is strongly populated and the angular distribution to this state has been measured (1977WE03). 11Be*(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 11Be*(2.69)]. See also (1977WE1B).