(See the Energy Level Diagram for 6He)
Spin of 6He: In a Stern-Gerlach experiment, (CO58H) find μ(6He) < 0.16 nuclear magnetons if J is taken as 1; it is concluded that J(6He) = 0.
The β-spectrum is simple, with an end point Eβ(max) = 3.50 ± 0.05 (WU52), 3.50 ± 0.02 MeV (SC56I). Recently reported half-lives are 0.852 ± 0.016 sec (VE56), 0.83 ± 0.02 sec (HE58C), 0.85 ± 0.03 sec (RU55). The weighted mean of half-lives cited here and in (HO50B, 55AJ61) is 0.813 ± 0.007 sec. Using Qm, log ft is 2.92.
The electron-neutrino correlation is found to be W(θ) = 1 + α(p/W)cosθ, with α = -(0.39 ± 0.02), in good agreement with the value α = -1/3 for pure axial vector interaction (HE58C, HE59, PL59). An earlier report by (RU55) appears to have been in error: see (AL58A, WU58). See also (BA55S, LA55A, LE57F; theor.).
At Et = 1.9 MeV, the α-spectrum, observed at 30°, extends from 1 to 7 MeV, with peaks at Eα = 2 and 5 MeV. The same general shape is observed at other angles and for Et = 0.95 to 2.1 MeV. These peaks are attributed to a two-stage process involving formation and breakup of 5He in the P3/2 and P1/2 states and are superposed on the three-body spectrum, reaction (b). Structure observed near the end point may indicate a correlation between the two neutrons (JA58). At Et = 1.48 MeV, the neutron spectrum shows a continuum from 0 to 12 MeV with a broad peak at 11.3 MeV, corresponding to formation of 5He in the ground state (BA57E).
Differential scattering cross sections have been measured at Et = 1.58 to 2.01 MeV by (HO56A). At Et = 1.90 MeV, θ(lab) = 30°, σ(θ) = 286 mb/sr (± 5%) (AL58B). A phase-shift analysis shows that the distributions at Et = 1.80 and 2.01 MeV are adequately accounted for by a 1S phase shift corresponding to a hard sphere of radius 2.35 x 10-13 cm. There is no evidence of p-waves or of resonance in this region (FR55E).
A γ-emitting level at Ex = 1.6 ± 0.2 MeV is reported by (TI54A). This evidence, based on the colinearity of p and 6He tracks in photoplates, appears to conflict with other indications that this state decays predominantly to 4He + 2n (AL54E: see, however, (MA56O)). See 7Li(t, α)6He.
The summed proton spectrum at Ep = 185 MeV shows two peaks, attributed to formation of 6Heg.s. by removal of a p-proton from 7Li and 6He* ~ 15 MeV, formed by removal of an s-proton (TY57C, MA58H, TY58B).
At Ed = 14.5 MeV, the ground state and the 1.71-MeV level are observed. The angular distributions analyzed by pick-up theory indicate even parity for both states. Peak differential cross sections are 8.0 mb/sr at θc.m. = 17° and 2.0 mb/sr at θc.m. = 16.5° for the ground and 1.7-MeV states, respectively (LE55); θ2 = 0.055 and 0.017 (FR57).
The energy of the first excited state is 1.71 ± 0.01 MeV, Γ < / ~ 100 keV (AL54E, AL55A). Preliminary results may indicate a state at 3.4 MeV, Γ < 0.3 MeV (AL54E, AL55A). (MA56O) report evidence for a state at (6.0 ± 0.9 MeV) and for one or more states at 9.3 ± 0.7 MeV (3.8-MeV tritons from 9Be(d, t)8Be were used). Angular distributions at Et = 240 keV are consistent with J = 0 and 2 for the ground state and the 1.7-MeV level, respectively (AL54D: see 10Be). At Et = 0.84 MeV, θ = 90°, the cross sections for formation of 6He(0) and 6He*(1.7) are 16 and 26 mb/sr, respectively (MA56K).