
^{12}Be (1990AJ01)(See Energy Level Diagrams for ^{12}Be) GENERAL: See also (1985AJ01) and 12.1 [Table of Energy Levels] (in PDF or PS) here. General theoretical papers: (1984FR13, 1985AN28, 1985BA51, 1985WI1B, 1986WI04, 1987BL18, 1987GI1C, 1987SA15, 1987YA16, 1988RU01, SU88C, 1989BE03). Hypernuclei: (1984IW1B, 1984YA04, 1985BE31, 1985GA1C, 1985IK1A, 1985WA1N, 1985YA01, 1985YA07, 1986BA1W, 1986BI1G, 1986DO1B, 1986GA14, 1986GA33, 1986GA1H, 1986HA26, 1986MA1J, 1986ME1F, 1986MI1N, 1986PO1H, 1986YA1T, 1986ZO1A, 1987DA30, 1986FA1A, 1987HA40, 1987IK1B, 1987PO1H, 1987WU1B, 1988BA24, 1988HA07, 1988MA09, 1988PO1H, 1988TA14, 1988WA1B, 1988YA05). Other topics: (1989SU05). Secondary beams of ^{12}Be produced in the fragmentation of ^{20}Ne accelerated to 800 MeV/A have been used to measure interaction cross sections in Be, C and Al. The interaction radius and the r.m.s. radius for the nucleon distribution in ^{12}Be have also been derived (1988TA10). See also (1989SA10, 1989TA1K).
The halflife of ^{12}Be is 24.4. ± 3.0 ms (1978AL10), 21.3 ± 2.2 ms (1986CU01), 24.0 ± 1.0 ms (1984DU15): the mean of these values is 23.6 ± 0.9 ms. Log ft = 3.834 ± 0.017 (M.J. Martin, private communication), assuming the decay is to ^{12}B_{g.s.}. The upper limit of the branching to a state which subsequently decays by neutron emission is 1% (1978AL10, 1984DU15).
At E_{t} = 12 MeV ^{12}Be*(2.10) is populated [E_{x} = 2110 ± 15 keV] and (p, γ) angular correlations lead to J = 2 (1978AL10). At E_{t} = 17 MeV proton groups are observed to the states shown in 12.1 (in PDF or PS). The energy of ^{12}Be*(2.10) is measured to be 2089 ± 20 keV. The two highest states have an appreciable intrinsic width. 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. See also (1980AJ01).
At E(^{14}C) = 60 MeV ^{12}Be*(0, 2.10, 2.68 ± 0.03) have been populated, the latter weakly. Angular distributions are poorly fitted by DWBA. An assignment of 0^{+} is plausible but not proven for ^{12}Be*(2.70) (1982BE42).
