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

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

Photofission fragment characteristics of 234, 238U and 232Th in the barrier region

The bremstrahlung induced fission of 234, 238U and 232Th has been studied at the superconducting Darmstadt linear accelerator (SDALINAC) in the excitation energy region close to the fission barrier. In this contribution results on the fission fragment mass, total kinetic energy (TKE) and angular distributions will be presented. Fission fragment mass and TKE distributions from 234U were studied for the first time in this energy region. The results have been analyzed in terms of fission modes and a dominant yield of the mass asymmetric standard-2 mode was found in all studied nuclei. No strong dependence of the fission mode weights on the excitation energy of the compound nucleus were found. Correlations between mass, TKE and angular distributions have been investigated in 234U and 232Th. A correlation in form of an increased anisotropy for far-asymmetric masses and low TKE were found in both fissioning systems. A possible interpretation of this correlation in terms of fission modes is discussed

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

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

Parameterisation of the residual temperature distribution based on the modelling of successive emission of prompt neutrons

A new deterministic modelling taking into account the successive emission of prompt neutrons from initial fragments of a fragmentation range {A, Z, TKE} constructed as in the Point-by-Point (PbP) treatment is described. The good agreement of different prompt emission quantities obtained from this modelling (e.g. v(A), v(TKE), E-γ(A), E-γ(TKE), etc.) with the experimental data and the results of the PbP model and other Monte-Carlo models validates the present modelling of sequential emission. The distributions of different residual quantities, including the residual temperature distributions P(T) of light and heavy fragments allow to obtain a new parameterisation of P(T) which can be used in the PbP model and the Los Alamos model