5He,7He,and

Yu. N. Kopatch

¹

,

M. Mutterer

²

,

D. Schwalm

³

et al.

Abstract

The neutron-unstable odd-N isotopes 5 He, 7 He, and 8 Li ͑in its excited state of E*ϭ2.26 MeV) were measured to show up as short-lived (Ӎ10 Ϫ21 Ϫ10 Ϫ20 s) intermediate light charged particles ͑LCPs͒ in ternary fission of 252 Cf. For the study a high-efficiency angular correlation measurement between neutrons, LCPs, and main fission fragments has been performed. The evidence for the ternary 5 He and 7 He particles ͑lifetimes: 1ϫ10 Ϫ21 s, and 4ϫ10 Ϫ21 s, respectively͒ was disclosed from the measured angular distributions of their decay neutrons focused by the emission in flight towards the direction of motion of 4 He and 6 He ternary particles. Similarly, neutrons observed to be peaked around Li-particle motion could be attributed to the decay of the second excited state at E*ϭ2.26 MeV ͑lifetime: 2ϫ10 Ϫ20 s) of 8 Li. The fractional yields of the intermediate 5 He and 7 He ternary fission modes relative to the ''true'' ternary 4 He and 6 He modes, respectively, were determined to be 0.21͑5͒ for both cases. The mean energy of the 4 He residues resulting from the 5 He decay was determined to be 12.4͑3͒ MeV, compared to 15.7͑2͒ MeV for all ternary ␣ particles registered, and to 16.4͑3͒ MeV for the true ternary ␣ particles. The mean energy of the 6 He residues from the 7 He decay is 11.0͑15͒ MeV, compared to 12.3͑5͒ MeV for all ternary 6 He particles. The population of 8 Li* was deduced to be 0.06͑2͒ relative to Li ternary fission, and 0.33͑20͒ relative to the yield of particle stable 8 Li. The perspective of using the observed intermediate LCPs for probing the ternary scission configuration in 252 Cf fission with the aid of trajectory calculations is briefly discussed.

Angular correlations in the prompt neutron emission in spontaneous fission of252Cf

“…The experimental setup "CORA" consists of a 4π detector for fission fragments CODIS [8], surrounded by a set of 60 DEMON liquid scintillator cells [9] for measuring prompt fission neutrons (see Fig. 1).…”

Spatial- and Time-Correlated Detection of Fission Fragments

“…Ref [4]. Due to technical constraints of conventional detectors so far charged-particle coincidence measurements such as angular correlations between rare and main fission fragments [5] could only be measured under certain circumstances (energy cutoff, low-Z).…”

Ternary fission of 260No in collinear configuration

“…In observed ternary fission modes, the detected two heavy fragments were accompanied by a light charged particle such as 4,5,7 He [5,6], 8 Li [6], 10 Be [3,7], and 14 C [8,9] isotopes, with a yield on the order of 10 4 per a binary fission event [10]. The 4 Heaccompanied ternary fission of the neutron rich isotopes 252.254,256 Cf is reported with high probability [5].…”