Recent developments for an active UF6 gas target for photon-induced fission experiments

Recent developments for an active uranium-hexafluoride-loaded gas target as well as results on the detector gas properties are presented. The gas of choice is a mixture of argon with small amounts of UF6. This contribution presents the experimental setup and focusses on the electron drift velocity with increasing UF6 content. A time-dependent decrease in electron drift velocity is observed in our setup.JRC.D.4-Standards for Nuclear Safety, Security and Safeguard

Elaboration of a computer system for determining the energy of laser pulse

This work investigates the neutron-induced fission of U-234 and the fission-fragment properties for neutron energies between E-n = 0.2 and 5.0 MeV with a special highlight on the prominent vibrational resonance at E-n = 0.77 MeV. Angular, energy, and mass distributions were determined based on the double-energy technique by means of a twin Frisch-grid ionization chamber. The experimental data are parametrized in terms of fission modes based on the multimodal random neck-rupture model. The main results are a verified strong angular anisotropy and fluctuations in the energy release as a function of incident-neutron energy

Development and test of the high-precision gamma-beam monitor at the ESFRI facility ELI-NP

This document describes the development of a fission chamber for gamma beam intensity monitoring at the high-energy gamma line at ELI-NP. The fission chamber foreseen for monitoring the gamma beam intensity on the high-energy beam line at ELI-NP is an ionization chamber with several 238U deposits of a thickness in the range from 100 to 150 μg/cm2 in a compact design. The innovative design of the chamber allows measuring for each individual micro pulse arriving at a time interval of 1.6x10^-8 s.JRC.G.2-Standards for Nuclear Safety, Security and Safeguard

Energy dependant neutron multiplicity in 235U(n,f)

Experimental activities at JRC-Geel on prompt-fission-neutron (PFN) emission in response to OECD/NEA nuclear data requests are presented in this report. Specifically, investigations of PFN emission from the reaction 235U(n,f) in the region of the resolved resonances are presented. The experiment employs a scintillation detector array for neutron detection, while fission fragment properties are determined via the double kinetic energy technique using a position sensitive twin ionization chamber. This setup allows us to study several correlations between properties of neutron and fission fragments simultaneously. Results on PFN correlations with fission fragment properties from the present study differ significantly from earlier studies on this reaction, induced by thermal neutrons.JRC.G.2-Standards for Nuclear Safety, Security and Safeguard

Digital Signal Processing Application in Nuclear Spectroscopy

Digital signal processing algorithms for nuclear particle spectroscopy are described along with a digital pile-up elimination method applicable to equidistantly sampled detector signals pre-processed by a charge-sensitive preamplifier. The signal processing algorithms provided as recursive one- or multi-step procedures which can be easily programmed using modern computer programming languages. The influence of the number of bits of the sampling analogue-to-digital converter to the final signal-to-noise ratio of the spectrometer considered. Algorithms for a digital shaping-filter amplifier, for a digital pile-up elimination scheme and for ballistic deficit correction were investigated using a high purity germanium detector. The pile-up elimination method was originally developed for fission fragment spectroscopy using a Frisch-grid back-to-back double ionisation chamber and was mainly intended for pile-up elimination in case of high alpha-radioactivity of the fissile target. The developed pile-up elimination method affects only the electronic noise generated by the preamplifier. Therefore, the influence of the pile-up elimination scheme on the final resolution of the spectrometer investigated in terms of the distance between piled-up pulses. The efficiency of developed algorithms compared with other signal processing schemes published in literature. Keywords: x- and gamma-ray spectroscopy, computer data analysis, ionization chambers, interpolation; curve fitting, numerical differentiation and integration, integral and integrodifferential equations.JRC.DDG.D.5-Neutron physic

The energy dependence of fission-fragment characteristics for neutron-induced fission on Pu-239

This report is in response to a nuclear data request on the OECD-NEA high priority request list for new measurements of prompt neutron multiplicities from 239Pu(n,f) in the incident neutron energy range from thermal to 5 eV. There exists experimental evidence for strong fluctuations of the average neutron multiplicity from resonance to resonance in 239Pu(n,f). These fluctuations have been shown to impact nuclear reactor benchmarks by reducing the criticality. One explanation for the fluctuating neutron multiplicity may be the competition between direct fission and the (n,γf) process. However, there is also evidence for fluctuations of the fission fragment mass yields from resonance to resonance. The mass yield fluctuations may also contribute to fluctuations of the neutron multiplicity averaged over all fission fragment masses. In order to model the contribution to the neutron multiplicity fluctuations by the fission fragment mass yield fluctuations new data on the correlations between fission fragment properties and neutron multiplicities are in need. In this report we present an experiment carried out to determine prompt neutron multiplicity correlations with fission fragment masses and total kinetic energies. The experiment has been carried out at the GELINA facility at JRC-Geel. Correlations between average neutron multiplicities and fission fragment properties have been measured with improved resolution in both mass and TKE, compared to data from the literature. Results show that the dependence of average neutron multiplicity per fission and fission fragment mass split is weak.JRC.G.2-Standards for Nuclear Safety, Security and Safeguard

Neutron-induced Fission Cross Section of240,242Pu

A sensitivity analysis for the new generation of fast reactors [Salvatores (2008)] has shown the importance of improved cross section data for several actinides. Among them, the240,242Pu(n,f) cross sections require an accuracy improvement to 1-3% and 3-5%, respectively, from the current level of 6% and 20%. At the Van de Graaff facility of the Institute for Reference Materials and Measurements (JRC-IRMM) the fission cross section of the two isotopes was measured relative to two secondary standard reactions,237Np(n,f) and238U(n,f), using a twin Frisch-grid ionization chamber. The secondary standard reactions were benchmarked through measurements against the primary standard reaction235U(n,f) in the same geometry. Sample masses were determined by means of low-geometry alpha counting or/and a 2p Frisch-grid ionization chamber, with an uncertainty lower than 2%. The neutron flux and the impact of scattering from material between source and target was examined, the largest effect having been found in cross section ratio measurements between a fissile and a fertile isotope. Our240,242Pu(n,f) cross sections are in agreement with previous experimental results and slightly lower than present evaluations. In case of the242Pu(n,f) reaction no evidence for a resonance at En=1.1 MeV was found.Postprint (published version

Prompt fission neutron emission: Problems and challenges

This paper presents some of the challenges ahead of us even after 75 years of the discovery of the fission process and large progress made since then. The focus is on application orientation, which requires improved measurements on fission cross-sections and neutron and γ-ray multiplicities. Experimental possibilities have vastly improved the past decade leading to developments of highly sophisticated detector systems and the use of digital data acquisition and signal processing. The development of innovative fast nuclear reactor technology needs improved respective nuclear data. Advancements in theoretical modelling also require better experimental data. Theory has made progress in calculating fission fragment distributions (i.e. GEF code) as well as prompt neutron and γ-ray emission to catch up with the improved experiments.JRC.D.4-Standards for Nuclear Safety, Security and Safeguard