The miniBELEN detector is a moderated neutron counter based on the use of 3\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$<^>3$$\end{document}He tubes and high-density polyethylene as moderator. The detector has been designed to have a neutron detection efficiency that is nearly independent from the initial neutron energy for (alpha,n\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\alpha ,n$$\end{document}) reactions with alpha-particle energies up to 15 MeV. In order to achieve that an innovative design methodology based on the use of cadmium neutron filters has been used. Monte Carlo calculations of the detector response have been validated using a 252\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$<^>{252}$$\end{document}Cf fission source. Measurements of the relatively well-known (alpha,n\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\alpha ,n$$\end{document}) thick target yields on aluminum have been found to be consistent with data from previous works. A method has been developed to correlate the counting rate ring ratios with the mean neutron energy and validated using previous time-of-flight measurements of the aluminum (alpha,n\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\alpha ,n$$\end{document}) spectra and with a 252\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$<^>{252}$$\end{document}Cf fission source.

The 35Cl(n, p)35S reaction plays a key role in neutron dosimetry for Boron Neutron Capture Therapy, in the synthesis of the isotope 36S, whose astrophysical origin remains unresolved, and in the design of next-generation molten-salt reactors. Its relevance has motivated its inclusion in the High Priority Request List (HPRL) of NEA. The goal of this work is to determine the 35Cl(n, p)35S cross-section from thermal energy to 120 keV for the first time ever in a single measurement, thus reducing systematic uncertainties related to the normalization to the thermal value. This had been a subject of concern in previous evaluations of this reaction. We made use of the Time-of-Flight technique with microMEGAS detectors at Experimental Area 2 (EAR-2) of n_TOF facility at CERN. The 10B (n, α ) 7Li and 235U(n, f) reactions were used as references. Rutherford Back-scattering Spectrometry was performed at Centro Nacional de Aceleradores (CNA) in Sevilla, in order to accurately determine the masses of the irradiated samples. We obtained a thermal cross-section of 0.470 ± 0.009 barns. The 1/v energy dependence of the cross-section is observed up to the first resonance at 0.398 keV, the resonances up to 120 keV are analyzed and resonance parameters extracted using SAMMY. Maxwellian Averaged Cross-Section (MACS) was calculated for k_B T from 1 to 100 keV, and lower values compared to estimations from ENDF were found, e.g., 1.07 ± 0.20 mb at k_BT=30 keV. The thermal cross-section and first two resonances are in agreement with the latest evaluation in ENDF/B-VIII.1, while remarkably lower resonance strengths were found for high energy resonances.

Neutron capture reactions provide essential nuclear physics input for modeling the synthesis of heavy elements in stars. The growing precision of stellar spectroscopy and isotopic measurements in presolar SiC grains now demands cross sections with improved accuracy over the full energy range, and access to unstable nuclei relevant to slow (s-) process branchings and the intermediate (i-) process. This article reviews recent progress in direct neutron capture measurements, focusing on time-of-flight (TOF) experiments at CERN n_TOF and complementary activation techniques. Substantial advances have been achieved for stable s-only and bottleneck isotopes, significantly improving constraints on s-process models. In parallel, the combination of high instantaneous neutron fluxes and advanced detector systems has facilitated first-time neutron capture measurements on several radioactive branching-point nuclei. Feasibility studies, however, reveal current limitations related to sample availability, background conditions, and restricted energy coverage. In this context, the complementarity between TOF and activation emerges as a central strategy. Future developments, including high-flux facilities and novel inverse kinematics experiments in ion storage rings, are expected to extend the boundaries of neutron capture measurements, overcoming current limitations and helping unlock new frontiers in our understanding of stellar nucleosynthesis.

The neutron capture cross section of 64Ni is an important parameter in nuclear astrophysics that is needed to accurately simulate stellar nucleosynthesis and validate stellar models. 64Ni is among the seeds of the s-process and its capture cross section has been found to have an important effect on the predicted abundances of many nuclei synthesized in Asymptotic Giant Branch (AGB) and massive stars. Despite its relevance, the measurements of the 64Ni(n,γ) available in the literature are scarce and discrepant. For this reason, a new accurate time-of-flight measurement has been performed at the n_TOF facility at CERN, taking advantage of its high instantaneous neutron flux, and using a highly enriched 64Ni sample. The first preliminary results show important discrepancies with respect to the cross sections recommended in the most recent releases of the evaluated nuclear data libraries. In particular, a large resonance reported at 9.52 keV is not observed. As a consequence, a significant reduction in the Maxwellian-Averaged Cross Section (MACS) obtained from evaluated data libraries in the 5–25 keV thermal energy region is expected.

The miniBELEN detector is a moderated neutron counter based on the use of ^3 He tubes and high-density polyethylene as moderator. The detector has been designed to have a neutron detection efficiency that is nearly independent from the initial neutron energy for ( α ,n ) reactions with alpha-particle energies up to 15 MeV. In order to achieve that an innovative design methodology based on the use of cadmium neutron filters has been used. Monte Carlo calculations of the detector response have been validated using a ^252 Cf fission source. Measurements of the relatively well-known ( α ,n ) thick target yields on aluminum have been found to be consistent with data from previous works. A method has been developed to correlate the counting rate ring ratios with the mean neutron energy and validated using previous time-of-flight measurements of the aluminum ( α ,n ) spectra and with a ^252 Cf fission source.

An innovative method is proposed to generate a realistic functional neutron and gamma pulses model for a liquid scintillator-based detector. This approach analyzed neutron and gamma pulse shapes, electronic noise, and fit the model parameters that include the intrinsic properties of the scintillator and standard deviation of the transit time of the photomultiplier tube (PMT). The synthetic data are generated using Monte-Carlo (MC)-based statistical methods from the modeled functions, energy distributions of neutrons, gammas, and electronic noise. This work emulates realistic pulses that can be used to calibrate and test scintillation detectors used in nuclear physics experiments. This synthetic data library provides realistic labeled neutron and gamma pulses for liquid scintillators and PMTs, which may be used for improving radiation detection through supervised machine learning. This study provides a comprehensive framework for neutron-gamma discrimination, synthetic data generation, and data validation.

Nuclear research reactors ( RR ) are essential facilities in countries implementing nuclear power plants and are used for experiments necessary for commercial reactor development, training and education programs, and many other applications not related to nuclear energy production (e.g., isotope production, neutron sources, materials science). Europe has a broad and very diverse landscape of RRs, many of which have been in operation for 30-60 years, are well maintained and regularly modernized. However, financial pressures caused by a combination of declining interest and the lack of a sound financial model have led to the closure of many of them (e.g. OSIRIS in Saclay, JEEP II research reactor at IFE Kjeller and BER2 in Berlin). These negative trends called for coordinated European action to assess the impact of the declining number of RRs. The Towards Optimized Use of Research Reactors (TOURR) project was a response to this challenge. Its main objective was to assess the status of the EU RR fleet and to develop a strategy for the refurbishment and construction of new RR in Europe. The assessment was based on analysed data obtained through extensive questionnaires sent to all operating European RR. The analysis revealed gaps in terms of lack of long-term funding, lack of manpower and lack of communication between RRs and their customers. It also showed threats of further European RR closures. Regarding the long-term EU RR strategy, the main recommendations of the TOURR project are to build (at least) two RRs, a medium-flux multipurpose reactor and a flexible zero-power facility. Both reactor cores could be part of a single facility built at the European level and accessible to all EU Member States.

Background: The ^35Cl(n, p)^35S reaction is of special interest in three different applications. First, in Boron Neutron Capture Therapy due to the presence of ^35Cl in brain and skin tissue. Second, it is involved in the creation of ^36S, whose astrophysical origin remains unresolved. Third, in the designing of fast nuclear reactors of new generation based on molten salts. Purpose: To measure the ^35Cl(n, p)^35S cross-section from thermal energy to 120 keV, determine the resonance parameters in this range and Maxwellian Averaged Cross-Section (MACS). Method: We made use of the Time-of-Flight technique with microMEGAS detectors at Experimental Area 2 (EAR-2) of n_TOF facility at CERN. The ^10B(n, α)^7Li and ^235U(n, f) reactions were used as references. Rutherford Back-scattering Spectrometry technique was performed at Centro Nacional de Aceleradores (CNA) in Sevilla, in order to accurately determine the masses of the irradiated samples. Results: We obtain a thermal cross-section of 0.470 ± 0.009 barns. The 1/v energy dependence of the cross-section is observed up to the first resonance at 0.398 keV, the resonances up to 120 keV are analyzed and MACS calculated for k_B T from 1 to 100 keV. Conclusions: The ^35Cl(n, p)^35S cross-section has been obtained over a wide energy range for the first time, with high accuracy across the aforementioned range. The thermal cross-section and first two resonances are in agreement with latest evaluation in ENDF/B-VIII.1, while lower resonance strength was found for high energy resonances. These data are used to calculate the MACS for different k_B T.

Nuclear research reactors ( RR ) are essential facilities in countries implementing nuclear power plants and are used for experiments necessary for commercial reactor development, training and education programs, and many other applications not related to nuclear energy production (e.g., isotope production, neutron sources, materials science). Europe has a broad and very diverse landscape of RRs, many of which have been in operation for 30-60 years, are well maintained and regularly modernized. However, financial pressures caused by a combination of declining interest and the lack of a sound financial model have led to the closure of many of them (e.g. OSIRIS in Saclay, JEEP II research reactor at IFE Kjeller and BER2 in Berlin). These negative trends called for coordinated European action to assess the impact of the declining number of RRs. The Towards Optimized Use of Research Reactors (TOURR) project was a response to this challenge. Its main objective was to assess the status of the EU RR fleet and to develop a strategy for the refurbishment and construction of new RR in Europe. The assessment was based on analysed data obtained through extensive questionnaires sent to all operating European RR. The analysis revealed gaps in terms of lack of long-term funding, lack of manpower and lack of communication between RRs and their customers. It also showed threats of further European RR closures. Regarding the long-term EU RR strategy, the main recommendations of the TOURR project are to build (at least) two RRs, a medium-flux multipurpose reactor and a flexible zero-power facility. Both reactor cores could be part of a single facility built at the European level and accessible to all EU Member States.

The average energy and multiplicity of prompt γ -rays from slow neutron-induced fission of ^235 U have been measured using the STEFF spectrometer at the neutron time-of-flight facility n_TOF. The individual responses from 11 NaI scintillators were corrected for multiple γ -ray interactions, prompt fission neutrons and background counts before being deconvolved to estimate the emitted spectrum of prompt fission γ -rays. The results give an average γ -ray energy E̅_γ of 1.71(5) MeV and multiplicity ν̅_γ of 2.66(18) considering γ -rays emitted within the energy range 0.8–6.8 MeV. The n_TOF data has a slightly larger E̅_γ and smaller ν̅_γ than other recent measurements, however the product of the two is in agreement within quoted uncertainties.

The neutron Time-of-Flight facility (n_TOF) is an innovative facility operative since 2001 at CERN, with three experimental areas. In this paper the n_TOF facility will be described, together with the upgrade of the facility during the Long Shutdown 2 at CERN. The main features of the detectors used for capture fission cross section measurements will be presented with perspectives for the future measurements.

The BC501A sensor is a liquid scintillator frequently used in nuclear physics for detecting fast neutrons. This paper describes a hardware implementation of digital pulse shape analysis (DPSA) for real-time analysis. DPSA is an algorithm that extracts the physically relevant parameters from the detected BC501A signals. The hardware solution is implemented in a MicroTCA system that provides the physical, mechanical, electrical, and cooling support for an AMC board (NAMC-ZYNQ-FMC) with a Xilinx ZYNQ Ultrascale-MP SoC. The Xilinx FPGA programmable logic implements a JESD204B interface to high-speed ADCs. The physical and datalink JESD204B layers are implemented using hardware description language (HDL), while the Xilinx high-level synthesis language (HLS) is used for the transport and application layers. The DPSA algorithm is a JESD204B application layer that includes a FIR filter and a constant fraction discriminator (CFD) function, a baseline calculation function, a peak detection function, and an energy calculation function. This architecture achieves an analysis mean time of less than 100 µs per signal with an FPGA resource utilization of about 50% of its most used resources. This paper presents a high-performance DPSA embedded system that interfaces with a 1 GS/s ADC and performs accurate calculations with relatively low latency.

The experimental setup of the new measurement of 239Pu fission and capture cross-section in the n_TOF time-of-flight facility at CERN is presented. The measurement aims to address the needs and demands of nuclear data users. The experiment incorporates an innovative fast Fission Fragment Detector and the n_TOF Total Absorption Calorimeter, enabling the implementation of the fission tagging technique. Preliminary results exhibit the robust performance of the detector systems, along with the high quality of the new 239Pu samples. These samples were exclusively produced for this measurement by the European Commission’s Joint Research Centre in Geel.

This paper summarized the efforts performed to understand decay heat estimation from existing spent nuclear fuel (SNF), under the auspices of the Working Party on Nuclear Criticality Safety (WPNCS) of the OECD Nuclear Energy Agency. Needs for precise estimations are related to safety, cost, and optimization of SNF handling, storage, and repository. The physical origins of decay heat (a more correct denomination would be decay power) are then introduced, to identify its main contributors (fission products and actinides) and time-dependent evolution. Due to limited absolute prediction capabilities, experimental information is crucial; measurement facilities and methods are then presented, highlighting both their relevance and our need for maintaining the unique current full-scale facility and developing new ones. The third part of this report is dedicated to the computational aspect of the decay heat estimation: calculation methods, codes, and validation. Different approaches and implementations currently exist for these three aspects, directly impacting our capabilities to predict decay heat and to inform decision-makers. Finally, recommendations from the expert community are proposed, potentially guiding future experimental and computational developments. One of the most important outcomes of this work is the consensus among participants on the need to reduce biases and uncertainties for the estimated SNF decay heat. If it is agreed that uncertainties (being one standard deviation) are on average small (less than a few percent), they still substantially impact various applications when one needs to consider up to three standard deviations, thus covering more than 95% of cases. The second main finding is the need of new decay heat measurements and validation for cases corresponding to more modern fuel characteristics: higher initial enrichment, higher average burnup, as well as shorter and longer cooling time. Similar needs exist for fuel types without public experimental data, such as MOX, VVER, or CANDU fuels. A third outcome is related to SNF assemblies for which no direct validation can be performed, representing the vast majority of cases (due to the large number of SNF assemblies currently stored, or too short or too long cooling periods of interest). A few solutions are possible, depending on the application. For the final repository, systematic measurements of quantities related to decay heat can be performed, such as neutron or gamma emission. This would provide indications of the SNF decay heat at the time of encapsulation. For other applications (short- or long-term cooling), the community would benefit from applying consistent and accepted recommendations on calculation methods, for both decay heat and uncertainties. This would improve the understanding of the results and make comparisons easier.

The cross section of the ^89 Y(n, γ ) reaction has important implications in nuclear astrophysics and for advanced nuclear technology. Given its neutron magic number N = 50 and a consequent small neutron capture cross section, ^89 Y represents one of the key nuclides for the stellar s-process. It acts as a bottleneck in the neutron capture chain between the Fe seed and the heavier elements. Moreover, it is located at the overlapping region, where both the weak and main s-process components take place. ^89 Y, the only stable yttrium isotope, is also used in innovative nuclear reactors. Neutron capture and transmission measurements were performed at the time-of-flight facilities n_TOF at CERN and GELINA at JRC-Geel. Resonance parameters of individual resonances were extracted from a resonance analysis of the experimental transmission and capture yields, up to a neutron incident energy of 95 keV. Even though a comparison with results reported in the literature shows differences in resonance parameters, the present data are consistent with the Maxwellian averaged cross section suggested by the astrophysical database KADoNiS.

Several international agencies recommend the study of new routes and new facilities for producing radioisotopes with application to nuclear medicine. 177Lu is a versatile radioisotope used for therapy and diagnosis (theranostics) of cancer with good success in neuroendocrine tumours that is being studied to be applied to a wider range of tumours. 177Lu is produced in few nuclear reactors mainly by the neutron capture on 176Lu. However, it could be produced at high-intensity celeratorbased neutron facilities. The energy of the neutrons in accelerator-based neutron facilities is higher than in thermal reactors.Thus, experimental data on the 176Yb(n,γ) cross-section in the eV and keV region are mandatory to calculate accurately the production of 177Yb, which beta decays to 177Lu. At present, there are not experimental data available from thermal to 3 keV of the 176Yb(n,γ) cross-section. In addition, there is no data in the resolved resonance region (RRR). This contribution shows the first results of the 176Yb capture measurement performed at the n_TOF facility at CERN.

A good data analysis of neutron cross section measurements is necessary for generating high quality and reliable nuclear databases. Artificial intelligence techniques, and in particular deep learning, have proven to be very useful for pattern recognition and data analysis, and thus may be used in the field of experimental nuclear physics. In this publication, we train a neural network in order to improve the capture-to-background ratio of neutron capture data of measurements performed in the time-of-flight facility n_TOF at CERN with the so-called Total Absorption Calorimeter. The evaluation of this deep learning-based method on accurate Monte Carlo simulated measurements with 197 Au and 239 Pu samples suggests that the capture-to-background ratio can be increased 5 times above the standard method.

During the second long shutdown period of the CERN accelerator complex (LS2, 2019-2021), several upgrade activities took place at the n_TOF facility. The most important have been the replacement of the spallation target with a next generation nitrogen-cooled lead target. Additionally, a new experimental area, at a very short distance from the target assembly (the NEAR Station) was established. In this paper, the core commissioning actions of the new installations are described. The improvement in the n_TOF infrastructure was accompanied by several detector development projects. All these upgrade actions are discussed, focusing mostly on the future perspectives of the n_TOF facility. Furthermore, some indicative current and future measurements are briefly reported.

Background: The $^{14}\mathrm{N}(n,p)^{14}\mathrm{C}$ reaction is of interest in neutron capture therapy, where nitrogen-related dose is the main component due to low-energy neutrons, and in astrophysics, where $^{14}\mathrm{N}$ acts as a neutron poison in the $s$ process. Several discrepancies remain between the existing data obtained in partial energy ranges: thermal energy, keV region, and resonance region.Purpose: We aim to measure the $^{14}\mathrm{N}(n,p)^{14}\mathrm{C}$ cross section from thermal to the resonance region in a single measurement for the first time, including characterization of the first resonances, and provide calculations of Maxwellian averaged cross sections (MACS).Method: We apply the time-of-flight technique at Experimental Area 2 (EAR-2) of the neutron time-of-flight (n_TOF) facility at CERN. $^{10}\mathrm{B}(\mathrm{n},\ensuremath{\alpha})^{7}\mathrm{Li}$ and $^{235}\mathrm{U}(n,f)$ reactions are used as references. Two detection systems are run simultaneously, one on beam and another off beam. Resonances are described with the $R$-matrix code sammy.Results: The cross section was measured from subthermal energy to 800 keV, resolving the first two resonances (at 492.7 and 644 keV). A thermal cross section was obtained ($1.809\ifmmode\pm\else\textpm\fi{}0.045$ b) that is lower than the two most recent measurements by slightly more than one standard deviation, but in line with the ENDF/B-VIII.0 and JEFF-3.3 evaluations. A 1/$v$ energy dependence of the cross section was confirmed up to tens of keV neutron energy. The low energy tail of the first resonance at 492.7 keV is lower than suggested by evaluated values, while the overall resonance strength agrees with evaluations.Conclusions: Our measurement has allowed determination of the $^{14}\mathrm{N}(n,p)$ cross section over a wide energy range for the first time. We have obtained cross sections with high accuracy (2.5%) from subthermal energy to 800 keV and used these data to calculate the MACS for $kT=5$ to $kT=100$ keV.