
^{12}Be (1980AJ01)(See Energy Level Diagrams for ^{12}Be) GENERAL: See also (1975AJ02) and Table 12.1 [Table of Energy Levels] (in PDF or PS). Special reactions: (1975VO09, 1977AR06, 1979NA1E). General reviews: (1973TO16, 1974CE1A). Theoretical papers: (1975BE31, 1976BA24, 1976BE1G, 1976IR1B, 1977SE1D). Mass of ^{12}Be: The Qvalue of the ^{10}Be(t, p) reaction (4809 ± 15 keV) (1978AL29) leads to an atomic mass excess of 25078 ± 15 keV for ^{12}Be which we adopt. See also (1975AJ02, 1975JE02).
The halflife of ^{12}Be is 24.4 ± 3.0 msec (1978AL10): log ft = 3.84 ± 0.06 (M.J. Martin, Nuclear Data Project, ORNL.) assuming the decay is to ^{12}B_{g.s.}. The upper limit to a branch involving delayed neutrons is 1% (1978AL10). See also (1975AJ02) and (1973TA30; theor.).
This reaction has been studied at E(^{7}Li) = 25.0 to 30.1 MeV (1971HO26).
At E_{t} = 12 MeV, ^{12}Be*(2.10) is populated and (p, γ) angular correlations lead to an assignment of J = 2 [it is not excluded that a 0^{+} state might be unresolved; it would not, of course, γdecay to ^{12}Be_{g.s.}] (1978AL10). At E_{t} = 17 MeV proton groups are observed to the states shown in Table 12.1 (in PDF or PS). Assignment of a possible group to a state at ≈ 2.24 MeV is very tentative. The energy of ^{12}Be*(2.10) is measured to be 2089 ± 20 keV. The two highest states have an intrinsic width. There is no evidence for a state at E_{x} = 0.81 MeV suggested in reaction 2. From the measured atomic mass excess of ^{12}Be, d, the cubic factor in the IMME, is calculated to be +2.8 ± 8.6 keV and the first T = 2 state in ^{12}N should occur at E_{x} = 12.27 ± 0.04 MeV (1978AL29): compare with ^{12}O. (1976BA24) suggests that first two T = 2 states do not belong exclusively to the lowest configuration (1s^{4}1p^{8}), for which the first 2^{+}; T = 2 excited state is expected to have E_{x} ≈ 4.4 MeV but is observed at 2.1 MeV. Model calculations suggest a 0^{+} state at E_{x} ≈ 2.35 MeV (1976BA24). See also ^{12}O.
At E_{π} = 164 MeV, ^{12}Be*(0, 2.10 + 2.71 (?)) are populated (1978SE07).
At E(^{18}O) = 88.7 MeV, ^{12}Be*(0, 2.09 ± 0.05) are populated (1974BA15).
