FALSTAFF: a novel apparatus for fission fragment characterization

The study of nuclear fission and in particular the correlation between the produced fragments and the associated neutrons is encountering renewed interest since new models are available on the market and a large set of applications show a rather stringent demand on high quality nuclear data. The future Neutrons For Science installation, being presently built at GANIL (Caen, France) in the framework of the SPIRAL2 project, will produce high intensity neutron beams from hundreds of keV up to 40 MeV. In view of this opportunity, the development of an experimental setup called FALSTAFF (Four Arm cLover for the Study of Actinide Fission Fragments) has been undertaken since 2011. This novel apparatus is meant to provide a full characterization of fission fragments in terms of mass, nuclear charge and kinetic energy. Moreover, it will provide a measurement of the mass before and after neutron evaporation, leading to the determination of the neutron multiplicity as a function of the fragmentation. The FALSTAFF setup is presently in its R&D phase in order to achieve the required specifications, especially in terms of time, space and energy resolution of the different detectors

Study of (n,α) reactions of interest for nuclear reactors: the case of 19^{19}F(n,α)16^{16}N with SCALP detector

International audienceThe 19 F(n,α)16 N cross section is of great interest for the development of the next generation IV reactors that could potentially use molten fluoride salts. Significant differences (up to a factor of 3) have been observed for this nucleus regarding the (n,α) channel. In view of improving our knowledge on this (n,α) reactions, the GrACE group (Groupe Aval du Cycle Electronucl´eaire) of the LPC Caen has developed a new detector named SCALP (Scintillating ionization Chamber for ALPha particle detection in neutron induced reactions). This paper deals with the first experiment carried out with this brand new detector at the new NFS facility (GANIL, Caen, France). After discussing the needs for new measurments of the 19 F(n,α)16 N reaction, the operating procedure of the SCALP detector will be presented, as well as the experiments that have been conducted using it. Furthermore, insights into the data acquired during our experiment, as well as the ongoing data processing and associated multi-channel analysis, will be provided

Study of the excitation energy sharing and dynamics using the neutron detector DéMon in 86Kr+ 165Ho collisions at 60 A MeV *

Binary dissipative 86Kr+ 165Ho collisions are studied by investigating neutron emission using the DéMoN detector. The neutron energy spectra are measured as a function of the charge of the projectile-like-fragment, taken as a scale on the impact parameter. Equal excitation energy sharing is observed even for the most central collisions. This result is compared to the predictions of a statistical and of a participant-spectator model. An intermediate velocity source is revealed, the characteristics of which can be explained by neck emission. © 1999 Elsevier Science B.V. All rights reserved.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Monte Carlo MSM correction factors for control rod worth estimates in subcritical and near-critical fast neutron reactors

The GUINEVERE project was launched in 2006, within the 6th Euratom Framework Program IP-EUROTRANS, in order to study the feasibility of transmutation in Accelerator Driven subcritical Systems (ADS). This zero-power facility hosted at the SCK·CEN site in Mol (Belgium) couples the fast subcritical lead reactor VENUS-F with an external neutron source provided by interaction of deuterons delivered by the GENEPI-3C accelerator and a tritiated target located at the reactor core center. In order to test on-line subcriticality monitoring techniques, the reactivity of all the VENUS-F configurations used must be known beforehand to serve as benchmark values. That is why the Modified Source Multiplication Method (MSM) is under consideration to estimate the reactivity worth of the control rods when the reactor is largely subcritical as well as near-critical. The MSM method appears to be a technique well adapted to measure control rod worth over a large range of subcriticality levels. The MSM factors which are required to account for spatial effects in the reactor can be successfully calculated using a Monte Carlo neutron transport code

Spallation study with proton beams around 1 GeV: Neutron production

Experiments performed at Lab. Nat. SATURNE on neutron produced by spallation from proton beams in the range 0.8 - 1.6 GeV are presented. Experimental data compared with codes show a significant improvement of the recent intra-nuclear cascade (J. Cugnon). This is also true in the same way for the neutron production from thick targets. However the model underestimates the energetic neutrons produced in the backward direction and other quantities as residual nuclei cross sections are not accurately predicted.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Accurate measurements of delayed neutron data for reactor applications: methodology and application to 235^{235}U(nth_{th},f)

International audienceLarge inconsistencies still exist in nuclear data libraries regarding the kinetic parameters of delayed neutron (DN) precursors. As an example, there is a 17% gap between ENDF-B/VIII.0 and JEFF-3.3 on the average lifetime T$_{1/2}$ of DN precursors from thermal fission of $^{235}$U. This parameter is of major importance for reactivity predictions of nuclear reactors in nominal or accidental configurations. In this context, CEA is actively participating to the ALDEN project (Average number and Lifetime of DElayed Neutrons) which aims at providing the nuclear data community with new data sets of DN from thermal and fast neutron induced fission of various actinides. A dedicated experimental setup was designed and optimized for that purpose and is presented in this paper. It consists of a “long counter” detector containing 16 proportional counters filled with $^{3}$He, embedded in a high density polyethylene matrix. The detector surrounds a fissile target prepared in the form of a miniature fission chamber, containing a few hundreds of micro-grams of fissile material. This set-up is connected to fast and efficient neutron shutters that can produce step-irradiations of variable durations. The equations driving the DN counting following step-irradiations of the fissile target are established and discussed in the perspective of DN yield or group parameter measurement. A comprehensive analysis of the different steps of data reduction is detailed: dead time characterization, Region of Interest (ROI) determination, absolute and relative efficiency calibration, fission rate estimation, irradiation time and background determination, DN decay curve production and physical parameter fitting. Following a prototype experiment performed in 2018 at the PF1b cold neutron beam line of Institute Laue Langevin (ILL, Grenoble, France), we discuss here the analysis of two campaigns occurring in 2019 and 2021 in which significant improvements were achieved in terms of background minimization, counting statistics and fission rate determination. The achievements of this work are the measurement of the delayed neutron emission per fission for the thermal neutron induced fission of $^{235}$U, estimated at (1.625 ± 0.010) % and the group parameters leading to an estimated lifetime of ${T}_{1/2}$ = (8.87 ± 0.10) s. Those results are consistent with the values recommended by the IAEA/CRP work and they come with reduced uncertainties compared with previously published results