A Segmented Total Energy Detector (sTED) optimized for (n, γ) cross-section measurements at n_TOF EAR2

The neutron time-of-flight facility n_TOF at CERN is a spallation source dedicated to measurements of neutroninduced reaction cross-sections of interest in nuclear technologies, astrophysics, and other applications. Since 2014, Experimental ARea 2 (EAR2) is operational and delivers a neutron fluence of ∼ 4 ⋅ 107 neutrons per nominal proton pulse, which is ∼50 times higher than the one of Experimental ARea 1 (EAR1) of ∼ 8 ⋅ 105 neutrons per pulse. The high neutron flux at EAR2 results in high counting rates in the detectors that challenged the previously existing capture detection systems. For this reason, a Segmented Total Energy Detector (sTED) has been developed to overcome the limitations in the detector’s response, by reducing the active volume per module and by using a photo-multiplier (PMT) optimized for high counting rates. This paper presents the main characteristics of the sTED, including energy and time resolution, response to γ-rays, and provides as well details of the use of the Pulse Height Weighting Technique (PHWT) with this detector. The sTED has been validated to perform neutron-capture cross-section measurements in EAR2 in the neutron energy range from thermal up to at least 400 keV. The detector has already been successfully used in several measurements at n_TOF EAR2.I+D+i grant PGC2018- 096717-B-C21 funded by MCIN/AEI/10.13039/501100011033, by the European Commission H2020 Framework Programme project SANDA (Grant agreement ID: 847552)Funding agencies of the n_TOF participating institution

EARMO: An Energy-Aware Refactoring Approach for Mobile Apps

The energy consumption of mobile apps is a trending topic and researchers are actively investigating the role of coding practices on energy consumption. Recent studies suggest that design choices can conflict with energy consumption. Therefore, it is important to take into account energy consumption when evolving the design of a mobile app. In this paper, we analyze the impact of eight type of anti-patterns on a testbed of 20 android apps extracted from F-Droid. We propose EARMO, a novel anti-pattern correction approach that accounts for energy consumption when refactoring mobile anti-patterns. We evaluate EARMO using three multiobjective search-based algorithms. The obtained results show that EARMO can generate refactoring recommendations in less than a minute, and remove a median of 84% of anti-patterns. Moreover, EARMO extended the battery life of a mobile phone by up to 29 minutes when running in isolation a refactored multimedia app with default settings (no WiFi, no location services, and minimum screen brightness). Finally, we conducted a qualitative study with developers of our studied apps, to assess the refactoring recommendations made by EARMO. Developers found 68% of refactorings suggested by EARMO to be very relevant.This work has been supported by the Natural Sciences and Engineering Research Council of Canada (NSERC) and Consejo Nacional de Ciencia y Tecnología, México (CONACyT)

New detection systems for an enhanced sensitivity in key stellar (n,γ) measurements

Neutron capture cross-section measurements are fundamental in the study of astrophysical phenomena, such as the slow neutron capture (s-) process of nucleosynthesis operating in red-giant and massive stars. However, neutron capture measurements via the time-of-flight (TOF) technique on key s-process nuclei are often challenging. Difficulties arise from the limited mass (∼mg) available and the high sample-related background in the case of the unstable s-process branching points. Measurements on neutron magic nuclei, that act as s-process bottlenecks, are affected by low (n,γ) cross sections and a dominant neutron scattering background. Overcoming these experimental challenges requires the combination of facilities with high instantaneous flux, such as n_TOFEAR2, with detection systems with an enhanced detection sensitivity and high counting rate capabilities. This contribution reviews some of the latest detector developments in detection systems for (n,γ) measurements at n_TOF, such as i-TED, an innovative detection system which exploits the Compton imaging technique to reduce the dominant neutron scattering background and s-TED, a highly segmented total energy detector intended for high flux facilities. The discussion will be illustrated with results of the first measurement of key the s-process branching-point reaction 79Se(n,γ).European Research Council (ERC)European Union’s Horizon 2020 research and innovation programme (ERC Consolidator Grant project HYMNS, with grant agreement No. 681740)FJC2020-044688-IICJ220-045122-I funded by MCIN/AEI/ 10.13039/501100011033European Union NextGenerationEU/PRTRSpanish Ministerio de Ciencia e Innovación under grants PID2019- 104714GB-C21FPA2017-83946-C2-1-P, FIS2015-71688-ERCPIE-201750I26CERN policy in matters of scientific publications, the n_TOF Collaboratio

First measurement of the 94Nb(n,γ) cross section at the CERN n_TOF facility

One of the crucial ingredients for the improvement of stellar models is the accurate knowledge of neutron capture cross-sections for the different isotopes involved in the s-,r- and i- processes. These measurements can shed light on existing discrepancies between observed and predicted isotopic abundances and help to constrain the physical conditions where these reactions take place along different stages of stellar evolution. In the particular case of the radioactive 94Nb, the 94Nb(n,γ) cross-section could play a role in the determination of the s-process production of 94Mo in AGB stars, which presently cannot be reproduced by state-of-the-art stellar models. There are no previous 94Nb(n,γ) experimental data for the resolved and unresolved resonance regions mainly due to the difficulties in producing highquality samples and also due to limitations in conventional detection systems commonly used in time-of-flight experiments. Motivated by this situation, a first measurement of the 94Nb(n,γ) reaction was carried out at CERN n_TOF, thereby exploiting the high luminosity of the EAR2 area in combination with a new detection system of small-volume C6D6-detectors and a high quality 94Nb-sample. The latter was based on hyper-pure 93Nb material activated at the high-flux reactor of ILL-Grenoble. An innovative ring-configuration detection system in close geometry around the capture sample allowed us to significantly enhance the signal-to-background ratio. This set-up was supplemented with two conventional C6D6-detectors and a highresolution LaCl3(Ce)-detector, which will be employed for addressing reliably systematic effects and uncertainties. At the current status of the data analysis, 18 resonance in 94Nb+n have been observed for the first time in the neutron energy range from thermal up to 10 keV.European Research Council (ERC)European Union’s Horizon 2020 research and innovation programme (ERC Consolidator Grant project HYMNS, with grant agreement No. 681740)ICJ220-045122-IMCIN/AEI/ 10.13039/501100011033European Union NextGenerationEU/PRTRSpanish Ministerio de Ciencia e Innovación under grants PID2019-104714GB-C21, FPA2017-83946-C2-1-P, FIS2015-71688-ERCCSICPIE-201750I2

Measurement of the 160Gd(n, γ) cross section at n_TOF and its medical implications

Neutron-capture reactions on gadolinium isotopes play an important role in several fields of physics, in particular in nuclear Astrophysics for the understanding of the nucleosynthesis of heavy elements (beyond iron) in stars via the s- and r-processes [1] and in nuclear technology. Another important application of gadolinium is linked to the production of terbium, that offers a set of clinically interesting isotopes for theranostics, characterized by complementary physical decay characteristics. In particular, the low -energy beta(-) emitter terbium-161 is very similar to lutetium-177 in terms of half-life (6.89 d), beta(-) - energy and chemical properties. Being a significant emitter of conversion/Auger electrons, greater therapeutic effect can therefore be expected in comparison to Lu-177 [2, 3]. For this reason, in the last decade, the study of the neutron capture reaction Gd-160(n,,gamma)(161) Gd and the subsequent beta(-) - decay in terbium-161 is getting particular attention. As the nuclear data on the Gd-160 neutron capture reaction are quite scarce and inconsistent, a new measurement of the capture cross section of Gd-160 at the CERN neutron Time -Of-Flight facilty was performed in order to provide high resolution, high -accuracy data on this important reaction, in the energy range from thermal to hundreds of keV. In this contribution, the preliminary results of the n_TOF measurement are presented

The n_TOF facility at CERN

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

Overview of the dissemination of n_TOF experimental data and resonance parameters

The n_TOF neutron time-of-flight facility at CERN is used for nuclear data measurements. The n_TOF Collaboration works closely with the Nuclear Reaction Data Centres (NRDC) network to disseminate the experimental data through the international EXFOR library. In addition, the Collaboration helps integrate the results in the evaluated library projects. The present contribution describes the dissemination status of n_TOF results, their impact on evaluated libraries and ongoing efforts to provide n_TOF resonance parameters in ENDF-6 format for further use by evaluation projects

The neutron time-of-flight facility n TOF at CERN. Recent facility upgrades and detector developments

Part of this work has been carried out in the framework of a project funded by the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (ERC Consolidator Grant project HYMNS, with grant agreement No. 681740). The authors acknowledge support from the Spanish Ministerio de Ciencia e Innovaci´on under grants PID2019-104714GB-C21, FPA2017-83946-C2-1-P and FIS2015-71688-ERC. In line with the principles that apply to scientific publishing and the CERN policy in matters of scientific publications, the n TOF Collaboration recognises the work of V. Furman and Y. Kopatch (JINR, Russia), who have contributed to the experiment used to obtain the results described in this paper.Based on an idea by Carlo Rubbia, the n_TOF facility at CERN has been operating for over 20 years. It is a neutron spallation source, driven by the 20 GeV/c proton beam from the CERN PS accelerator. Neutrons in a very wide energy range (from GeV, down to sub-eV kinetic energy) are generated by a massive Lead spallation target feeding two experimental areas. EAR1, horizonal with respect to the proton beam direction is set at 185 meters from the spallation target. EAR2, on the vertical line from the spallation source, is placed at 20 m. Neutron energies for experiments are selected by the time-of-flight technique (hence the name n_TOF), while the long flight paths ensure a very good energy resolution. Over one hundred experiments have been performed by the n_TOF Collaboration at CERN, with applications ranging from nuclear astrophysics (synthesis of the heavy elements in stars, big bang nucleosynthesis, nuclear cosmo-chronology), to advanced nuclear technologies (nuclear data for applications, nuclear safety), as well as for basic nuclear science (reaction mechanisms, structure and decay of highly excited compound states). During the planned shutdown of the CERN accelerator complex between 2019 and 2021, the facility went through a substantial upgrade with a new target-moderator assembly, refurbishing of the neutron beam lines and experimental areas. An additional measuring and irradiation station (the NEAR Station) has been envisaged and its capabilities for performing material test studies and new physics opportunities are presently explored. An overview of the facility and of the activities performed at CERN is presented in this contribution, with a particular emphasis on the most relevant experiments for nuclear astrophysics.European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (ERC Consolidator Grant project HYMNS, with grant agreement No. 681740)Spanish Ministerio de Ciencia e Innovación under grants PID2019-104714GB-C21, FPA2017-83946-C2-1-P and FIS2015-71688-ERC

Compton imaging for enhanced sensitivity (n,γ) cross section TOF experiments: Status and prospects

This work has been carried out in the framework of a project funded by the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (ERC Consolidator Grant project HYMNS, with grant agreement No. 681740). The authors acknowledge support from the Spanish Ministerio de Ciencia e Innovacion under grants PID2019-104714GB-C21, FPA2017-83946C2-1-P, FIS2015-71688-ERC, CSIC for funding PIE201750I26. In line with the principles that apply to scientific publishing and the CERN policy in matters of scientific publications, the n_TOF Collaboration recognises the work of V. Furman and Y. Kopatch (JINR, Russia), who have contributed to the experiment used to obtain the results described in this paper.Radiative neutron-capture cross sections are of pivotal importance in many fields such as nucle-osynthesis studies or innovative reactor technologies. A large number of isotopes have been measured with high accuracy, but there are still a large number of relevant isotopes whose cross sections could not be experimentally determined yet, at least with sufficient accuracy and completeness, owing to limitations in detection techniques, sample production methods or in the facilities themselves. In the context of the HYMNS (High-sensitivitY Measurements of key stellar Nucleo-Synthesis reactions) project over the last six years we have developed a novel detection technique aimed at background suppression in radiative neutron-capture time-of-flight measurements. This new technique utilizes a complex detection set-up based on position-sensitive radiation-detectors deployed in a Compton-camera array configuration. The latter enables to implement gamma-ray imaging techniques, which help to disentangle true capture events arising from the sample under study and contaminant background events from the surroundings. A summary on the main developments is given in this contribution together with an update on recent experiments at CERN n_TOF and an outlook on future steps.European Research Council (ERC)European Union’s Horizon 2020 research and innovation programme HYMNS 681740Spanish Ministerio de Ciencia e Innovación under grants PID2019-104714GB-C21, FPA2017-83946-C2-1-P, FIS2015-71688-ERCCSIC for funding PIE-201750I2

New perspectives for neutron capture measurements in the upgraded CERN-n_TOF Facility

This work has been carried out in the framework of a project funded by the European Research Council (ERC) under the European Union ' s Horizon 2020 research and innovation programme (ERC Consolidator Grant project HYMNS, with grant agreement No. 681740). This work was supported by grant FJC2020-044688-I funded by MCIN/AEI/10.13039/501100011033 and by European Union NextGenerationEU/PRTR. The authors acknowledge support from the Spanish Ministerio de Ciencia e Innovacion under grants PID2019-104714GB-C21, FPA2017-83946-C2-1-P, FIS2015-71688-ERC, CSIC for funding PIE-201750I26.The n_TOF facility has just undergone in 2021 a major upgrade with the installation of its third generation spallation target that has been designed to optimize the performance of the two n_TOF time-of-flight lines. This contribution describes the key features and limitations for capture measurements in the two beam lines prior to the target upgrade and presents first results of (n,gamma) measurements carried out as part of the commissioning of the upgraded facility. In particular, the energy resolution, a key factor for both increasing the signal-to background ratio and obtaining accurate resonance parameters, has been clearly improved for the 20 m long vertical beam-line with the new target design while keeping the remarkably high resolution of the long beamline n_TOF-EAR1. The improvements in the n_TOF neutron beam-lines need to be accompanied by improvements in the instrumentation. A review is given on recent detector R&D projects aimed at tackling the existing challenges and further improving the capabilities of this facility.European Research Council (ERC)European Union's Horizon 2020 research and innovation programme HYMNS 681740MCIN/AEI FJC2020-044688-IEuropean Union (EU)Instituto de Salud Carlos III Spanish Government PID2019-104714GB-C21, FPA2017-83946-C2-1-P, FIS2015-71688-ERCCSIC PIE-201750I2