Geel Electron Linear Accelerator Research Articles

Nuclear data activities at GELINA

Over the last decade, efforts were made to improve the performance of the experimental set-ups at the Geel Electron Linear Accelerator (GELINA) neutron time-of-flight facility of the European Commission Joint Research Centre (EC-JRC). These efforts, which result in an improved quality of neutroninduced cross section data for many reaction channels like elastic, inelastic, capture, fission, etc., relate to the accelerator, the measurement setups and the data reduction and analysis procedures. This paper presents a summary of the data produced in the last years at GELINA for nuclear energy applications. Most of the work has been performed as part of the EUFRAT open-access program.

The past and the future of the GAINS spectrometer @ GELINA

GAINS (Gamma Array for Inelastic Neutron Scattering), currently installed at the GELINA (Geel Electron Linear Accelerator) neutron source of the EC-JRC (European Commission-Joint Research Centre), is one of the best instruments available worldwide for measuring high resolution, low uncertainty neutron inelastic cross-section data relevant for both fundamental research and nuclear physics applications (like Generation IV facilities). It features 12 HPGe detectors coupled with a 235U fission chamber for neutron flux monitoring. The paper presents a short history of the GAINS development over the years and reviews some of the main experimental results together with plans for future experiments.

Neutron-induced inelastic γ-production cross sections on 58,60,64Ni

This paper reports partial results of a (n, n’γ) measurement on nickel. The inelastic channel was measured using the Gamma Array for Inelastic Neutron Scattering (GAINS) spectrometer at the 100-m measurement cabin of the Geel Electron Linear Accelerator (GELINA) neutron source of the European Commission’s Joint Research Centre (EC-JRC) in Geel, Belgium. Using γ spectroscopy, we were able to extract angle-integrated production cross sections for several γ rays but we report here only the results for the main transition in 58Ni. We discuss however in detail the observed discrepancy between our data and other experiments (especially the work of Voss et al.). We also shortly comment on the quality of the neutron-target optical model potential in describing the inelastic data in this mass region. The calculations were performed using the talys 1.9 code in the default settings.

Measurement of U238(n,n′γ ) cross section data and their impact on reaction models

A better knowledge of $(n,xn)$ reaction cross sections is important for both reaction modeling and energy applications. This article focuses on inelastic scattering of neutrons off $^{238}\mathrm{U}$ for which improvements are needed to better constrain evaluations and solve inconsistencies in nuclear power reactor calculations. A new precise measurement of $(n,xn\ensuremath{\gamma})$ reaction cross sections on $^{238}\mathrm{U}$ has been performed at the GELINA (Geel Electron LINear Accelerator) neutron facility operated by EC-JRC-Geel (Belgium) with the GRAPhEME (GeRmanium array for Actinides PrEcise MEasurements) setup. The prompt $\ensuremath{\gamma}$-ray spectroscopy method coupled to time-of-flight measurements is used to extract $(n,xn\ensuremath{\gamma})$ cross section values which can be further combined to infer the total neutron inelastic scattering cross section. Cross section data for 18 $\ensuremath{\gamma}$ transitions (five never measured before) are presented and compared to the data in the literature. Emphasis is especially given to the uncertainty determination to produce partial cross section data as accurate as possible. Due to intrinsic limitations of the experimental method, the use of additional nuclear structure information coupled with theoretical modeling is required to determine the total $(n,{n}^{\ensuremath{'}})$ cross section over the whole neutron energy range. We have investigated modeling aspects of the $^{238}\mathrm{U}(n,{n}^{\ensuremath{'}}\ensuremath{\gamma})$ cross sections related to the description of compound nucleus and preequilibirum mechanisms as well as the discrete part of nuclear structure. Through comparison between experimental and calculated $(n,{n}^{\ensuremath{'}}\ensuremath{\gamma})$ cross sections, we pinpoint inaccuracies in the description of specific reaction mechanisms and challenge recently implemented models. This helps improving the whole modeling of the $(n,{n}^{\ensuremath{'}})$ reaction.

Nucleon inelastic scattering cross sections on O16 and Si28

This paper reports cross-section measurements of the ($n,{n}^{\ensuremath{'}}$) and ($p,{p}^{\ensuremath{'}}$) reactions on $^{16}\mathrm{O}$ and $^{28}\mathrm{Si}$ at Geel Electron Linear Accelerator and at the 9-MV Tandem Accelerator of Horia Hulubei National Institute for Physics and Nuclear Engineering, respectively. The main purpose was to measure the neutron- and proton-induced inelastic $\ensuremath{\gamma}$-production cross sections for all observed transitions in $^{16}\mathrm{O}$ and $^{28}\mathrm{Si}$, followed by the calculation of the corresponding total inelastic cross section. The results are compared with theoretical calculations performed using the talys 1.9 code, evaluated nuclear data, and previously reported experimental data. The broader goal of this work is to study whether and to what extent the neutron-induced inelastic cross sections of these nuclei can be inferred from those obtained using suitable charged particle reactions. We show that, by making use of the formal similarities between the neutron- and the proton-target optical model potentials and isospin symmetry in mirror nuclei, one can develop a procedure that combines experimental proton-induced inelastic cross sections with theoretical calculations to infer neutron inelastic cross sections. For $^{16}\mathrm{O}$ and $^{28}\mathrm{Si}$, the precision associated with this procedure is around 10--20% for most of the incident energy range.

High precision neutron inelastic cross sections on16O

This work reports partial results of a (n, nγ) measurement on16O. Theγrays of interest from the inelastic channel were detected using the Gamma Array for Inelastic Neutron Scattering (GAINS) spectrometer at the Geel Electron Linear Accelerator (GELINA) neutron source. A very thick (32.30(4) mm) SiO2target was used. The main goal was to determine the angle-integrated γ-production cross section for the most important transitions. In this work we report the results for the main16O transition and we emphasize a consistency check aiming to ensure data reliability. Our results are compared with theoretical calculations performed using theTALYS1.8 code and with previously reported experimental data.

Neutron inelastic cross section measurements on 58,60Ni

A natural nickel sample was used at the GELINA (Geel Electron LINear Accelerator) neutron source of the European Commission, Joint Research Centre, Geel to measure the neutron inelastic cross sections. The GAINS (Gamma Array for Inelastic Neutron Scattering) spectrometer was employed to detect the emitted γ rays while a 235U fission chamber monitored the neutron flux. We report the preliminary production cross sections corresponding to the first transitions in 58,60Ni in comparison with previously reported data and with TALYS 1.9 calculations performed using the default input parameters.

Neutron inelastic cross section measurements on 54Fe

A 54Fe(n, n'γ) cross section measurement was performed at the Geel Electron LINear Accelerator of EC-JRC, Geel using the Gamma Array for Inelastic Neutron Scattering spectrometer and a 235U fission chamber for flux normalization. The experimental results are presented in comparison with talys 1.9 default and tuned calculations. The tuned calculation, implying modifications of the optical model parameters, improved significantly the description of the experimental values and led to interesting conclusions regarding the interaction of the 54Fe nucleus with neutrons. Since the results of these calculations were already presented extensively in a dedicated paper, the present article focuses on details related to the experimental particularities and data analysis procedure.

Integral Benchmark Experiments on a Large Copper Block Using the GELINA Accelerator to Validate natCu Neutron Cross Sections From Different Neutron Cross-Sectional Databases

A neutronics integral benchmark experiment on a pure copper block, aimed at testing and validating recent copper nuclear data libraries, has been performed at Geel Electron LINear Accelerator Facility (GELINA). GELINA is a powerful photoneutron source using a 75- $\mu \text{A}$ , 110-MeV electron beam impinging on a depleted U rotating target, producing a white neutron spectrum ranging from the epithermal region up to about 20 MeV with a mean energy of about 1.4 MeV and intensity up to $3.2 \times 10^{13}$ n/s. A large natCu block (dimensions $60 \times 60 \times 60$ cm3) has been positioned at 100 cm from the target. Thin activation foils were used as neutron flux probes and located inside the block in six positions at different depths with respect to the main neutron propagation direction. Materials whose activation cross section are sensitive to different neutron energy ranges were used, and the measured fluxes were compared with calculations performed using the MCNP6 neutron transport code coupled to different neutron cross-sectional databases (FENDL3.1, JEFF33_T2, and ENDF 7.1). The MCNP6 calculation also used the neutron spectrum produced by the GELINA accelerator. This is the first time that a neutronics integral experiment on copper is performed using such a white neutron spectrum and the results of our comparison could be used to validate the neutron copper cross sections in the neutron energy range covered by GELINA. The C/E results, taking into account the sources of uncertainties, are satisfactory: no large differences are observed among the result obtained using the three cross-sectional databases; however, the JEFF-3.3 seems, slightly, better predict the results.

Neutron inelastic scattering on 54Fe

A neutron inelastic scattering experiment was performed at the Geel Electron Linear Accelerator neutron source using an enriched 54Fe sample. The $\gamma$ rays produced in the reaction were detected using the Gamma Array for Inelastic Neutron Scattering spectrometer. For each observed transition we determined the $\gamma$ -production cross section for incident energies ranging from the inelastic threshold ( $\approx 1.434$ MeV) up to 18 MeV. Using these primary data we also calculated the cross section of the first excited level and the total inelastic cross section. Our experimental results are compared with previous reported values, evaluated nuclear data libraries and theoretical calculations performed with the TALYS 1.9 code. A careful tuning of the optical model parameters allowed significant improvements in the description of the experimental results leading to interesting conclusions regarding the interaction of the 54Fe nucleus with neutrons.

Cross-section measurements for theFe57(n,nγ)Fe57andFe57(n,2nγ)Fe56reactions

A neutron inelastic scattering experiment was performed on an enriched $^{57}\mathrm{Fe}$ sample at the Geel Electron Linear Accelerator neutron source using the Gamma Array for Neutron Inelastic Scattering spectrometer. Several $\ensuremath{\gamma}$-production cross sections were determined, but the first transition (14.4 keV) could not be detected owing to the steadily increased $\ensuremath{\gamma}$ background at low energies. Consequently, we use an interplay between experimental data and carefully tuned theoretical calculations to generate the total inelastic cross section.

Neutron inelastic scattering measurements on the stable isotopes of titanium

The results of a neutron inelastic scattering experiment performed at the Geel Electron Linear Accelerator pulsed white neutron source of the European Commission Joint Research Centre are reported. The neutrons with energies up to 18 MeV interacted with a $^{\mathrm{nat}}\mathrm{Ti}$ sample and the $\ensuremath{\gamma}$ rays resulting from inelastic scattering reactions on the stable isotopes were detected using the Gamma Array for Inelastic Neutron Scattering (GAINS) spectrometer. We were able to measure the $\ensuremath{\gamma}$-production cross sections for 21 transitions in the five stable Ti isotopes. From these, the level cross sections and the total inelastic cross sections were determined. Our experimental results are compared with theoretical calculations performed using the talys 1.8 code, evaluated nuclear data libraries, and also with previously reported results.

Inelastic neutron scattering cross-section measurements on 7Li and 63,65Cu

The γ-ray production cross section for the 477.6-keV transition in 7 Li following inelastic neutron scattering has been measured from the reaction threshold up to 18 MeV. This cross section is interesting as a possible standard for other inelastic scattering measurements. The experiment was conducted at the Geel Electron LINear Accelerator (GELINA) pulsed white neutron source with the Gamma Array for Inelastic Neutron Scattering (GAINS) spectrometer. Previous measurements of this cross section are reviewed and compared with our results. Recently, this cross section has also been calculated using the continuum discretized coupled-channels (CDCC) method. Experiments for studying neutrinoless double-β decay (2β0ν) or other very rare processes require greatly reducing the background radiation level (both intrinsic and external). Copper is a common shielding and structural material, used extensively in experiments such as COBRA, CUORE, EXO, GERDA, and MAJORANA. Understanding the background contribution arising from neutron interactions in Cu is important when searching for very weak experimental signals. Neutron inelastic scattering on nat Cu was investigated with GAINS. The results are compared with previous experimental data and evaluated nuclear data libraries.

Neutron nuclear data measurements for criticality safety

To support the US Department of Energy Nuclear Criticality Safety Program, neutron-induced cross section experiments were performed at the Geel Electron Linear Accelerator of the Joint Research Center Site Geel, European Union. Neutron capture and transmission measurements were carried out using metallic natural cerium and vanadium samples. Together with existing data, the measured data will be used for a new evaluation and will be submitted with covariances to the ENDF/B nuclear data library.

Neutron-induced Cross Section Measurements of Calcium

To support the US Department of Energy Nuclear Criticality Safety Program, neutron-induced cross section experiments were performed at the Geel Electron Linear Accelerator of the Institute for Reference Material and Measurements of the Joint Research Centers, European Union. Neutron capture and transmission measurements were carried out using a metallic calcium sample. The measured data will be used for a new calcium evaluation, which will be submitted with covariances to the ENDF/B nuclear data library.

Kinematics of the 6Li(n, t)4He Reaction and Experimental Scenarios for Cross-Section Measurement

An approach is presented for the measurement of the 6Li(n,t)4He reaction cross section based on complementary measurements benchmarked against kinematic simulations. Key aspects of the approach include taking advantage of the particle leaking (PL) effect, and using a one-dimensional time projection chamber (1D-TPC) and an ionization chamber to detect the reaction products from monoenergetic and white neutron beams, respectively. We have derived analytical expressions describing the PL region in both the laboratory and the center-of-mass reference systems. Two complementary 1D-TPC experiments are discussed, using 6LiF deposits onto transparent aluminum foils, in the backward and forward orientations, respectively. The 6Li(n,t)4He reaction kinematics is discussed for 2-MeV neutrons and extended to the energy range from thermal to 3 MeV to reflect the experimental capability of the Institute for Reference Materials and Measurements Van de Graaff and Geel Electron Linear Accelerator facilities.

Study of the radiation damage of Silicon Photo-Multipliers at the GELINA facility

In this paper we present a study of the neutrons-induced damage in Silicon Photo-Multipliers. Twenty-six devices, produced by AdvanSiD, Hamamatsu and SensL, have been irradiated at the Geel Electron LINear Accelerator (GELINA) in Belgium with a nearly white neutron beam. The total 1 MeV equivalent integrated dose was 6.2 × 109 neq/cm2. Photodetector performances have been measured during the whole irradiation period and a gradual worsening of the detector properties, such as dark current and charge spectra, has been observed.An extensive comparison of the performances of all the tested deviceswill be presented.

γproduction and neutron inelastic scattering cross sections for76Ge

The 2040.7-keV $\ensuremath{\gamma}$ ray from the 69th excited state of ${}^{76}$Ge was investigated in the interest of Ge-based double-$\ensuremath{\beta}$-decay experiments like the Germanium Detector Array (GERDA) experiment. The predicted transition could interfere with valid $0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$ events at 2039.0 keV, creating false signals in large-volume ${}^{76}$Ge enriched detectors. The measurement was performed with the Gamma Array for Inelastic Neutron Scattering (GAINS) at the Geel Electron Linear Accelerator (GELINA) white neutron source, using the ($n$,${n}^{\ensuremath{'}}$$\ensuremath{\gamma}$) technique and focusing on the strongest $\ensuremath{\gamma}$ rays originating from the level. Upper limits obtained for the production cross section of the 2040.7-keV $\ensuremath{\gamma}$ ray showed no possible influence on GERDA data. Additional analysis of the data yielded high-resolution cross sections for the low-lying states of ${}^{76}$Ge and related $\ensuremath{\gamma}$ rays, improving the accuracy and extending existing data for five transitions and five levels. The inelastic scattering cross section for ${}^{76}$Ge was determined for incident neutron energies up to 2.23 MeV, significantly increasing the energy range for which experimental data are available. Comparisons with model calculations using the talys code are presented indicating that accounting for the recently established asymmetric rotor structure should lead to an improved description of the data.

Measurement of235U(n,n′γ) and235U(n,2nγ) reaction cross sections

The design of generation IV nuclear reactors and the studies of new fuel cycles require knowledge of the cross sections of various nuclear reactions. Our research is focused on ($n,xn\ensuremath{\gamma}$) reactions occurring in these new reactors. The aim is to measure unknown cross sections and to reduce the uncertainty on present data for reactions and isotopes of interest for transmutation or advanced reactors. The present work studies the ${}^{235}$U($n,{n}^{\ensuremath{'}}\ensuremath{\gamma}$) and ${}^{235}$U($n,2n\ensuremath{\gamma}$) reactions in the fast neutron energy domain (up to 20 MeV). The experiments were performed with the Geel electron linear accelerator GELINA, which delivers a pulsed white neutron beam. The time characteristics enable measuring neutron energies with the time-of-flight (TOF) technique. The neutron induced reactions [in this case inelastic scattering and ($n,2n$) reactions] are identified by on-line prompt $\ensuremath{\gamma}$ spectroscopy with an experimental setup including four high-purity germanium (HPGe) detectors. A fission ionization chamber is used to monitor the incident neutron flux. The experimental setup and analysis methods are presented and the model calculations performed with the TALYS-1.2 code are discussed.

The 10B(n,α0)7Li and 10B(n,α1γ)7Li Alpha-Particle Angular Distributions for En < 1 MeV

The 10B(n,α0)7Li and 10B(n,α1γ)7Li angular distributions have been measured at the Geel Electron Linear Accelerator time-of-flight spectrometer in the incident neutron energy range from 0.1 keV to 1 MeV. A twin Frisch-grid ionization chamber has been used with two very thin 94% 10B-enriched samples mounted back-to-back on the common cathode. With this type of charged-particle detector, it is possible to measure the angular distribution of the alpha particles in a nearly 2x2π solid angle, with a clear separation of the alpha-particle yields from both reaction channels: α-emission to the 7Li ground state {α0} and to its first excited state {α1}. Hence, for the first time nearly the full solid angle at all incident neutron energies investigated has been covered. A strong angular anisotropy was observed and is discussed in the frame of the compound nucleus reaction mechanism. The alpha-particle center-of-mass angular distributions have been used to calculate the branching ratio 10B(n,α0)/10B(n,α1γ). Both data sets had a strong impact at the International Atomic Energy Agency Coordinated Research Project “Improvement of the Standard Cross Sections for Light Elements” and the corresponding evaluation of the standards data file for this reaction.