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USNDP

8He (1984AJ01)


(See the Isobar Diagram for 8He)

GENERAL: See also (1979AJ01) and Table 8.1 [Table of Energy Levels] (in PDF or PS).

Complex reactions involving 8He (See (1979AJ01) for comments on the 18O(α, 8He) and 26Mg(α, 8He) reactions.): (1978VO10, 1978MA1D, 1979BE60, 1979BO22, 1980BO31, 1981BO1X, 1981SE1B, 1982BO35, 1982BO1Y, 1982GU1H, 1982OG02).

Hypernuclei: (1978PO1A, 1978SO1A, 1981WA1J).

Other topics: (1979BE1H, 1981AV02, 1982NG01).

Mass of 8He: A study of the 64Ni(α, 8He)60Ni reaction leads to an atomic mass excess of 31595 ± 9 keV for 8He (1980TR1E) [(Using the new Wapstra masses for 64Ni and 60Ni.)] The value adopted by Wapstra, and by us, based on this and on some earlier measurements [see (1979AJ01)], is 31598 ± 9 keV. 8He is then stable with respect to decay into 6He + 2n by 2.137 MeV.

1. 8He(β-)8Li Qm = 10.648

The half-life of 8He is 122 ± 2 msec [see (1974AJ01)], 117.5 ± 1.5 msec (1981BJ03): the weighted mean is 119.0 ± 1.5 msec. The decay takes place (84 ± 1)% to 8Li*(0.98) [log ft = 4.20] and (16 ± 1)% via the neutron unstable states 8Li*(3.21, 5.4) [assignments to these states from an interpretation of the energy spectrum of the delayed neutrons]; (32 ± 3)% of the emitted neutrons populate 7Li*(0.48). Changed-particle emission (e.g. t, α) was not observed. The decay to 8Li*(3.21, 5.4) suggest π = + for 8Li*(3.21) and 0+ or 1+ for 8Li*(5.4) (1981BJ03). See also (1979DE15; theor.).

2. 9Be(7Li, 8B)8He Qm = -28.264

At E(7Li) = 83 MeV, θ = 10°, the population of 8Heg.s. and of an excited state at 2.6 ± 0.2 MeV (presumably Jπ = 2+) are reported by (1982AL08): the differential cross section is 0.1 μb/sr.