Spontaneous fission decay constant of 238U determined by SSNTD method using CR-39 and DAP plates

This paper presents a simple method for determining the spontaneous fission decay constant (λf) of 238U using a combination of CR-39 and diallyl phthalate (DAP) plates as solid-state nuclear track detectors (SSNTD). In this method, thin U-sources were prepared by depositing natural uranium onto 10-cm2 stainless steel plates. Alpha-particle tracks originated from 238U were detected in the 2π geometry of CR-39 detectors that had been attached to U-sources for 120–426 min. Spontaneous fission tracks, on the other hand, were detected using DAP detectors in the same geometry that had been attached to U-sources for 50–238 days. Based on precise measurements of bulk-etching and track-etching rates of the two detectors, track registration efficiencies and critical angles were determined to be 0.740±0.072 and 15.1° for CR-39, and 0.995±0.035 and 0.26° for DAP, respectively. Using these correction values and specific activities (or track densities) measured for each detector, a mean value of λf was calculated to be (8.51±0.18)×10−17 yr−1 in proportion to the alpha emission decay constant of 1.55±1.25×10−10 yr−1.