Speaker
Description
A better quantitative understanding of $\beta$-delayed neutron emission rates and spectra is relevant for nuclear structure, astrophysics, and reactor applications: $\beta$-delayed neutrons provide valuable information on the $\beta$-decay process, are needed in network calculations for understanding the stellar nucleosynthesis process, and can improve the understanding of the kinematics and safety of new reactor concepts loaded with new types of fuels. The field has experienced an increased activity during the last decades [1] thanks to the advances in nuclear experimental techniques and the radioactive ion beam facilities. More accurate measurements of $\beta$-delayed neutron emission properties like the emission probability, $\beta$-feeding, and energy spectrum from individual precursors are being made with advanced neutron detectors [2, 3, 4], digital data acquisition systems [5], and high intensity ion beams [6, 7, 8, 9].
The $\beta$-delayed neutron emission in the $^{85}$As decay has been measured at the Ion Guide Isotope Separator On-Line (IGISOL) facility [9] of the JYFL Accelerator Laboratory of the University of Jyväskylä. The $^{85}$As isotopes were produced by proton-induced fission reactions in $^{238}$U, separated from the rest of the fission fragments with IGISOL, and implanted onto a tape. The complete decay has been studied with the help of a complex setup which consists of a plastic scintillator detector for the emitted $\beta$-particles, a HPGe Clover and four LaBr$_3$ detectors for the emitted $\gamma$-rays, and the \textbf{MO}dular \textbf{N}eutron \textbf{S}pectrome\textbf{TER} (MONSTER) [4, 10] for the detection of the emitted neutrons. MONSTER consists of an array of 48 cylindrical cells of 200 mm diameter and 50 mm height, filled with BC501A or EJ301 scintillating liquid. Each cell is coupled through a light guide of 31 mm thickness to a R4144 or R11833 PMT. The neutron energy is determined by the time-of-flight technique, using the signals from the plastic detector and MONSTER as the start and stop signals, respectively.
In this conference, we report the results obtained from the measurement at JYFL. The $\beta$-delayed neutron energy distribution of the $^{85}$As $\beta$-decay has been determined by unfolding the time-of-flight spectrum with the iterative Bayesian unfolding method [11], and their partial branching ratios to the excited states in the final nucleus by applying $\beta$-n-$\gamma$ coincidences. We also compare the results of this work to existing data [12, 13].
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Nuclei in the Cosmos, 138, Proceedings of Science, (2008) 1–5
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[5] D. Villamarin et al., In preparation
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[13] D. Rudstam et al., At. Data and Nucl. Data Tables, 53, (1993) 1