Evidence for264108, the heaviest known even-even isotope
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We have observed the decay of one atom of the doubly even isotope 108. We observed α-decay with a halflife, of (76−36+364) Μs. The full α-decay energy could not be measured, as the α escaped the detector. With the knowledge of the halflife, an estimate on the α-decay energy can be made.
From the formula of Rasmussen9 and a reduced α-width of 1, a value which has been measured for260106 and also for the doubly even isotones of N=156, we obtain Q=(11.0−0.3+0.1 MeV. This value is higher than given by Moeller10 (10.35 MeV), and agrees with that of Uran and Zeldes11 (10.9 MeV). A hindrance factor wα of 0.5 increases the Qα-value by 0.14 MeV. The mass excess of264108 follows as (120.0±0.3) MeV. The groundstate shell effect amounts to (−5.0±0.3) MeV using the macroscopic mass values of Ref. 10. The formation cross section of (3.2−2.6+6.1) pb overlaps with the value of ∼ 5 pb from Dubna for the 6 ms sf-activity mentioned initially but is considerably lower than an extrapolation from the reaction58Fe (208Pb,n)265108 which gave 10 pb with the lower limit of 4 pb.
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