Measurement of the neutron-induced fission cross section of Th 230 at the CERN n_TOF facility

The neutron-induced fission cross section of 230 Th has been measured at the neutron time-of-flight facility n_TOF located at CERN. The experiment was performed at the experimental area EAR-1 with a neutron flight path of 185 m, using Micromegas detectors for the detection of the fission fragments. The 230 Th(n, f ) cross section was determined relative to the 235 U(n, f ) one, covering the energy range from the fission threshold up to 400 MeV. The results from the present work are compared with existing cross-section datasets and the observed discrepancies are discussed and analyzed. Finally, using the code EMPIRE 3.2.3 a theoretical study, based on the statistical model, was performed leading to a satisfactory reproduction of the experimental results with the proper tuning of the respective parameters, while for incident neutron energy beyond 200 MeV the fission of 230 Th was described by Monte Carlo simulations.This project received funding from the Euratom “Support safe operation of nuclear systems” program 2014–2018 under Grant Agreement No. 847552 (SANDA) and by the funding agencies of the participating institutes. This research is imple- mented through the IKY scholarships program and cofinanced by the European Union (European Social Fund ’ESF) and Greek national funds through the action entitled “Reinforce- ment of Postdoctoral Researchers - 2nd call (MIS 5033021)”, in the framework of the Operational Programme “Human Resources Development Program, Education and Lifelong Learning” of the National Strategic Reference Framework.Article signat per 137 autors/es: V. Michalopoulou, A. Stamatopoulos, M. Diakaki, A. Tsinganis, R. Vlastou, M. Kokkoris, N. Patronis, Z. Eleme, D. Macina, L. Tassan-Got, N. Colonna, E. Chiaveri, A. Ventura, P. Schillebeeckx, J. Heyse, G. Sibbens, G. Alaerts, A. Borella, A. Moens, D. Vanleeuw, O. Aberle, V. Alcayne, S. Amaducci, J. Andrzejewski, L. Audouin, V. Babiano-Suarez, M. Bacak, M. Barbagallo, S. Bennett, E. Berthoumieux, J. Billowes, D. Bosnar, A. Brown, M. Busso, M. Caamaño, L. Caballero, F. Calviño, M. Calviani, D. Cano-Ott, A. Casanovas, F. Cerutti, G. Cortés, M. A. Cortés-Giraldo, L. Cosentino, S. Cristallo, L. A. Damone, P. J. Davies, M. Dietz, C. Domingo-Pardo, R. Dressler, Q. Ducasse, E. Dupont, I. Durán, B. Fernández-Domínguez, A. Ferrari, P. Finocchiaro, V. Furman, K. Göbel, R. Garg, A. Gawlik-Ramiega, S. Gilardoni, I. F. Gonçalves, E. González-Romero, C. Guerrero, F. Gunsing, H. Harada, S. Heinitz, D. G. Jenkins, A. Junghans, F. Käppeler, Y. Kadi, A. Kimura, I. Knapová, Y. Kopatch, M. Krticka, D. Kurtulgil, I. Ladarescu, C. Lederer-Woods, H. Leeb, J. Lerendegui-Marco, S. J. Lonsdale, A. Manna, T. Martínez, A. Masi, C. Massimi, P. Mastinu, M. Mastromarco, E. A. Maugeri, A. Mazzone, E. Mendoza, A. Mengoni, P. M. Milazzo, F. Mingrone, J. Moreno-Soto, A. Musumarra, A. Negret, R. Nolte, F. Ogállar, A. Oprea, A. Pavlik, J. Perkowski, C. Petrone, L. Piersanti, E. Pirovano, I. Porras, J. Praena, J. M. Quesada, D. Ramos-Doval, T. Rauscher, R. Reifarth, D. Rochman, Y. Romanets, C. Rubbia, M. Sabaté-Gilarte, A. Saxena, D. Schumann, A. Sekhar, A. G. Smith, N. V. Sosnin, P. Sprung, G. Tagliente, J. L. Tain, A. Tarifeño-Saldivia, Th. Thomas, P. Torres-Sánchez, J. Ulrich, S. Urlass, S. Valenta, G. Vannini, V. Variale, P. Vaz, D. Vescovi, V. Vlachoudis, A. Wallner, P. J. Woods, T. Wright, and P. Žugec.Postprint (published version

NEAR at n_TOF/CERN: Preparing the first multi-foil activation measurement

The n_TOF facility at CERN is a neutron Time-Of-Flight facility based on a spallation neutron source. During the Second Long Shutdown (LS2) , a new experimental zone was designed and delivered. This new experimental area -the NEAR station - is located very close to the lead spallation target, at a distance of just ~3m. In this way, the high luminosity of the n_TOF neutron spallation source can be fully exploited. Towards the characterization of the new experimental area as well for the benchmarking of the performed simulations, the multi-foil activation measurement will be implemented. Eleven threshold and seven capture reference reactions will be utilized for the unfolding of the NEAR neutron beam energy spectrum that stretches from the meV to the GeV region

First Results of the 140^{140}Ce(n,γ)141^{141}Ce Cross-Section Measurement at n_TOF

An accurate measurement of the $^{140}$Ce(n,γ) energy-dependent cross-section was performed at the n_TOF facility at CERN. This cross-section is of great importance because it represents a bottleneck for the s-process nucleosynthesis and determines to a large extent the cerium abundance in stars. The measurement was motivated by the significant difference between the cerium abundance measured in globular clusters and the value predicted by theoretical stellar models. This discrepancy can be ascribed to an overestimation of the $^{140}$Ce capture cross-section due to a lack of accurate nuclear data. For this measurement, we used a sample of cerium oxide enriched in $^{140}$Ce to 99.4%. The experimental apparatus consisted of four deuterated benzene liquid scintillator detectors, which allowed us to overcome the difficulties present in the previous measurements, thanks to their very low neutron sensitivity. The accurate analysis of the p-wave resonances and the calculation of their average parameters are fundamental to improve the evaluation of the $^{140}$Ce Maxwellian-averaged cross-section

First Results of the 140^{140}Ce(n,γ)141^{141}Ce Cross-Section Measurement at n_TOF

An accurate measurement of the $^{140}$Ce(n,γ) energy-dependent cross-section was performed at the n_TOF facility at CERN. This cross-section is of great importance because it represents a bottleneck for the s-process nucleosynthesis and determines to a large extent the cerium abundance in stars. The measurement was motivated by the significant difference between the cerium abundance measured in globular clusters and the value predicted by theoretical stellar models. This discrepancy can be ascribed to an overestimation of the $^{140}$Ce capture cross-section due to a lack of accurate nuclear data. For this measurement, we used a sample of cerium oxide enriched in $^{140}$Ce to 99.4%. The experimental apparatus consisted of four deuterated benzene liquid scintillator detectors, which allowed us to overcome the difficulties present in the previous measurements, thanks to their very low neutron sensitivity. The accurate analysis of the p-wave resonances and the calculation of their average parameters are fundamental to improve the evaluation of the $^{140}$Ce Maxwellian-averaged cross-section

Μελέτη της αντίδρασης 241Am(n,f) στις εγκαταστάσεις n_TOF του CERN

High accuracy cross section data of neutron-induced reactions of minor actinides, are needed over a wide energy range for the feasibility, design and sensitivity studies on innovative nuclear reactors (Accelerator Driven Systems -ADS and Generation IV Fast Neutron Reactors). The concept of these systems is to incinerate/transmutate the existing actinides found in high-level nuclear waste. With the incineration/transmutation, both the half-life of the radioactive isotopes can be reduced as well as the volume of these pollutants or their wastes, so that the final nuclear waste from the reactor material that should be stored is less hazardous. Representing almost 1.8 % of the actinide mass in spent PWR UOX fuel, the 241Am isotope (T1/2 = 433 y) is considered one of the possible candidates for incineration/transmutation. On top of that, its production rate increases within the spent fuel through the β-decay of 241Pu (T1/2 = 14.3 y). Consequently, the accurate determination of the fission reaction rate of 241Am over an extended energy range is of prime importance. In the present thesis, the 241Am(n,f) reaction cross section was measured with Μicromegas detectors at the vertical experimental area (EAR-2) of the n_TOF facility at CERN, taking advantage of the high instantaneous neutron flux and using the time-of-flight technique. For the measurement, six targets of 241Am were used with a total activity of 0.1 GBq, whereas two targets of 235U and two targets of 238U were employed as reference and served as neutron flux monitors. In this work, a detailed description of the experimental set-up is given along with the data analysis procedure that was followed. The resulting nuclear cross section data, covering a broad spectrum from the meV up to the MeV neutron energy region, are presented and compared with previous data and nuclear data evaluations. Finally, the experimental results are framed with theoretical calculations that were performed using the TALYS-1.95 code.Για τις μελέτες σκοπιμότητας, σχεδιασμού και ευαισθησίας σε καινοτόμους πυρηνικούς αντιδραστήρες (Επιταχυντικά Συστήματα Ενισχυτών Ενέργειας -ADS και 4ης Γενιάς Αντιδραστήρες Ταχέων Νετρονίων), απαιτούνται υψηλής ακρίβειας πυρηνικά δεδομένα ενεργών διατομών, κυρίως για αντιδράσεις νετρονίων με ελάσσονες ακτινίδες. Οι νέοι αυτοί αντιδραστήρες ταχέων νετρονίων επιτρέπουν την αποτέφρωση/μεταστοιχείωση των υπαρχόντων ακτινίδων σε πυρηνικά απόβλητα υψηλής ραδιολογικής και χημικής τοξικότητας. Με την αποτέφρωση/μεταστοιχείωση, μπορεί να μειωθεί τόσο ο χρόνος ημιζωής των ραδιενεργών ισοτόπων όσο και ο όγκος αυτών των ρύπων ή των αποβλήτων τους, έτσι ώστε τα τελικά πυρηνικά απόβλητα από το υλικό των αντιδραστήρων που πρέπει να αποθηκευτούν να είναι λιγότερο επιβλαβή για το περιβάλλον. Αντιπροσωπεύοντας περίπου το 1.8 % σε αναλωμένο καύσιμο πυρηνικών αντιδραστήρων PWR UOX, το ισότοπο 241Am (T1/2 = 433 y) θεωρείται ένα από τα υποψήφια ισότοπα για αποτέφρωση/μεταστοιχείωση. Επιπλέον, ο ρυθμός παραγωγής του αυξάνεται εντός του αναλωμένου καυσίμου μέσω της β-αποδιέγερσης του 241Pu (T1/2 = 14.3 y). Κατά συνέπεια, ο ακριβής προσδιορισμός του ρυθμού αντίδρασης σχάσης του ισοτόπου 241Am σε ένα εκτεταμένο εύρος ενέργειας είναι πρωταρχικής σημασίας. Στην παρούσα διατριβή, η ενεργός διατομή της αντίδρασης 241Am(n,f) μετρήθηκε με ανιχνευτές Μicromegas στην κατακόρυφη πειραματική περιοχή (EAR-2) της εγκατάστασης n_TOF στο CERN, λαμβάνοντας ωφέλεια από την υψηλή στιγμιαία ροή νετρονίων και χρησιμοποιώντας την τεχνική του χρόνου πτήσης. Για τη μέτρηση χρησιμοποιήθηκαν έξι στόχοι 241Am με συνολική ενεργότητα 0.1 GBq, ενώ δύο στόχοι 235U και δύο στόχοι 238U χρησιμοποιήθηκαν ως στόχοι αναφοράς και χρησίμευσαν στην καταγραφή της ροής των νετρονίων. Σε αυτή την εργασία δίνεται μια λεπτομερής περιγραφή της πειραματικής διάταξης καθώς και της διαδικασίας ανάλυσης δεδομένων που ακολουθήθηκε. Τα πυρηνικά δεδομένα ενεργών διατομών που προέκυψαν, καλύπτοντας ένα ευρύ φάσμα από την meV έως την MeV ενεργειακή περιοχή νετρονίων, παρουσιάζονται και συγκρίνονται με προηγούμενα δεδομένα και αξιολογήσεις πυρηνικών δεδομένων. Τέλος, τα πειραματικά αποτελέσματα πλαισιώνονται με θεωρητικούς υπολογισμούς που πραγματοποιήθηκαν χρησιμοποιώντας τον κώδικα TALYS-1.95

First Results of the 140Ce(n,g)141Ce Cross-Section Measurement at n_TOF

The cerium oxide material for this measurement was provided by T. Katabuchi of the Tokyo Institute of Technology.An accurate measurement of the 140Ce(n,g) energy-dependent cross-section was performed at the n_TOF facility at CERN. This cross-section is of great importance because it represents a bottleneck for the s-process nucleosynthesis and determines to a large extent the cerium abundance in stars. The measurement was motivated by the significant difference between the cerium abundance measured in globular clusters and the value predicted by theoretical stellar models. This discrepancy can be ascribed to an overestimation of the 140Ce capture cross-section due to a lack of accurate nuclear data. For this measurement, we used a sample of cerium oxide enriched in 140Ce to 99.4%. The experimental apparatus consisted of four deuterated benzene liquid scintillator detectors, which allowed us to overcome the difficulties present in the previous measurements, thanks to their very low neutron sensitivity. The accurate analysis of the p-wave resonances and the calculation of their average parameters are fundamental to improve the evaluation of the 140Ce Maxwellian-averaged cross-section

Measurement of the 14N(n,p)14C cross section at the CERN n_TOF facility from sub-thermal energy to 800 keV

The 14N(n,p)14C 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 14N 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: Measuring the 14N(n,p)14C cross section from thermal to the resonance region in a single measurement for the first time, including characterization of the first resonances, and providing calculations of Maxwellian averaged cross sections (MACS). Method: Time-of-flight technique. Experimental Area 2 (EAR-2) of the neutron time-of-flight (n_TOF) facility at CERN. 10B(n,α)7Li and 235U(n,f) reactions as references. Two detection systems running simultaneously, one on-beam and another off-beam. Description of the resonances with the R-matrix code sammy. Results: The cross section has been measured from sub-thermal energy to 800 keV resolving the two first resonances (at 492.7 and 644 keV). A thermal cross-section (1.809±0.045 b) 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 has been obtained. A 1/v energy dependence of the cross section has been 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 to determine the 14N(n,p) cross-section over a wide energy range for the first time. We have obtained cross-sections with high accuracy (2.5 %) from sub-thermal energy to 800 keV and used these data to calculate the MACS for kT = 5 to kT = 100 keV

Measurement of the 14^{14}N(n,p)14^{14}C cross section at the CERN n_TOF facility from sub-thermal energy to 800 keV

Background: The $^{14}$N(n,p)$^{14}$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 14N 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: Measuring the 14N(n,p)14C cross section from thermal to the resonance region in a single measurement for the first time, including characterization of the first resonances, and providing calculations of Maxwellian averaged cross sections (MACS). Method: Time-of-flight technique. Experimental Area 2 (EAR-2) of the neutron time-of-flight (n_TOF) facility at CERN. $^{10}$B(n,${\alpha}$)$^7$Li and $^{235}$U(n,f) reactions as references. Two detection systems running simultaneously, one on-beam and another off-beam. Description of the resonances with the R-matrix code sammy. Results: The cross section has been measured from sub-thermal energy to 800 keV resolving the two first resonances (at 492.7 and 644 keV). A thermal cross-section (1.809$\pm$0.045 b) 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 has been obtained. A 1/v energy dependence of the cross section has been 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 to determine the $^{14}$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 sub-thermal energy to 800 keV and used these data to calculate the MACS for kT = 5 to kT = 100 keV