Neutron capture cross section measurements for 197Au from 3.5 to 84 keV at GELINA

Cross section measurements have been performed at the time-of-flight facility GELINA to determine the average capture cross section for 197Au in the energy region between 3.5 keV and 84 keV. Prompt gamma-rays, originating from neutron induced capture events, were detected by two C6D6 liquid scintillators. The sample was placed at about 13 m distance from the neutron source. The total energy detection principle in combination with the pulse height weighting technique was applied. The energy dependence of the neutron flux was measured with a double Frisch-gridded ionization chamber based on the 10B(n,alpha)reaction. The data have been normalized to the well-isolated and saturated 197Au resonance at 4.9 eV. Special care was taken to reduce bias effects due to the weighting function, normalization, dead time and background corrections. The total uncertainty due to normalization, neutron flux and weighting function is 1.0%. An additional uncertainty of 0.5% results from the correction for self-shielding and multiple interaction events. Fluctuations due to resonance structures have been studied by complementary measurements at a 30 m flight path station. The results reported in this work deviate systematically by more than 5% from the cross section that is recommended as a reference for astrophysical applications. They are about 2% lower compared to an evaluation of the 197Au(n,gamma) cross section, which was based on a least squares fit of experimental data available in the literature prior to this work. The average capture cross section as a function of neutron energy has been parameterized in terms of average resonance parameters. Maxwellian average cross sections at different temperatures have been calculated.JRC.D.4-Standards for Nuclear Safety, Security and Safeguard

Μελέτη των χαρακτηριστικών της δέσμης νετρονίων και προσδιορισμός παραμέτρων συντονισμού της σύλληψης νετρονίων στο 234U με την μέθοδο της ολικής απορρόφησης, στην πειραματική διάταξη n_TOF του CERN

At an international level several issues accompany the long-term development of nuclear science and its applications: nuclear waste management, new reactor design, increasingly safety requirements, public acceptance etc. This has triggered many sophisticated R&D activities, such as Accelerator Driven Systems or next generation reactor concepts and enhanced the ongoing effort to expand and improve the existing nuclear data. Among other measurements of special interest, is the neutron capture cross section determination for several isotopes related to the nuclear fuel cycle. This text mainly presents the obtained results from the (n,γ) cross section measurement of 234U that was performed at n_TOF facility (CERN). In detail we describe the main features of the facility, the TAC (Total Absorption Calorimeter) detection arrangement and its performance under specific experimental conditions. Results in the form of R-matrix resonance parameters and cross sections are discussed in parallel with the existing ENDF data

Neutralino-neutralino annihilation and production of a photon and a Z particle

On the first part the one loop computation of the process xixj→γz has been performed at an arbitrary c.m. energy for any pair of MSSM neutralinos. As an application suitable for Dark matter searches; the neutralino-neutralino annihilation is studied at the limiting case of vanishing relative velocity, describing the present DM distribution in the galactic halo; and at a relative velocity of about 0.5., determining the neutralino relic density contribution. The most useful situation is obviously for ι=j=1 but the case of non-identical neutralinos may also be useful in some corners of the parameter space. Our results are contained in the FORTRAN code PLATONdmZ, applying to any set of real MSSM parameters. Numerical results are also presented for a sample of 6 MSSM models; describing the various possible neutralino properties. A comparison with other existing works is also made. On the second part, the code, gamgamZZ is presented, which may be used to calculate all possible observations related to the process γγ→ΖΖ, in either the Standard Model (SM), or the Minimal Supersnumetric Standard Model (MSSM) with real parameters.Στο πρώτο μέρος επιτυγχάνεται στη μελέτη αυτή, ο υπολογισμός ενός βρόχου της διαδικασίας xixj→γz για οποιοδήποτε ενέργεια του ζεύγους νιουτραλίνο του ελάχιστου υπερσυμμετρικού μοντέλου (MSSM). Ως εφαρμογή κατάλληλη για την αναζήτηση της σκοτεινής ύλης (Dark matter) γίνεται μελέτη της νιουτραλίνο-νιουτραλίνο αλληλοαναίρεσης στην οριακή περίπτωση που η σχετική τους ταχύτητα τείνει στο μηδέν, περιγράφοντας την παρούσα κατανομή της σκοτεινής ύλης στην γαλαξιακή άλω, καθώς επίσης και για σχετική ταχύτητα 0.5. Παρουσιάζονται αποτελέσματα για 6 διαφορετικά MSSM πρότυπα, περιγράφοντας της διάφορες πιθανές ιδιότητες των νιουτραλίνο. Γίνονται συγκρίσεις με προηγούμενες εργασίες. Η πιο χρήσιμη περίπτωση είναι αυτή της αλληλοαναίρεσης ταυτόσημων νιουτραλίνο αλλά και οι άλλες περιπτώσεις μπορούν να φανούν χρήσιμες σε ειδικές καταστάσεις. Στο δεύτερο μέρος παρουσιάζεται ο κώδικας gangamZZ, ο οποίος υπολογίζει όλα τα πιθανά αποτελέσματα που σχετίζονται με τη διαδικασία γγ→ΖΖ τόσο για το καθιερωμένο μοντέλο όσο και για το MSSM. Διάφορα παραδείγματα μοντέλων εξετάζονται και γίνονται συγκρίσεις μεταξύ αυτών

Neutron beam characteristics study and determination of the neutron resonance parameters for 234U, using the total adsorption technique, at the n-TOF facility (CERN)

At an international level several issues accompany the long-term development of nuclear science and its applications: nuclear waste management, new reactor design, increasingly safety requirements, public acceptance etc. This has triggered many sophisticated R&D activities, such as Accelerator Driven Systems or next generation reactor concepts and enhanced the ongoing effort to expand and improve the existing nuclear data. Among other measurements of special interest, is the neutron capture cross section determination for several isotopes related to the nuclear fuel cycle. This text mainly presents the obtained results from the (n,γ) cross section measurement of 234U that was performed at n_TOF facility (CERN). In detail we describe the main features of the facility, the TAC (Total Absorption Calorimeter) detection arrangement and its performance under specific experimental conditions. Results in the form of R-matrix resonance parameters and cross sections are discussed in parallel with the existing ENDF data.Ο κλάδος της πυρηνικής φυσικής και πιο συγκεκριμένα οι εφαρμογές της, συνοδεύονται σε διεθνές επίπεδο από διάφορα ζητήματα, όπως: η διαχείριση των πυρηνικών αποβλήτων, ο σχεδιασμός νέων πυρηνικών αντιδραστήρων, η θέσπιση νέων κανόνων ασφαλείας κλπ. Τα παραπάνω δημιούργησαν την ανάγκη κατασκευής εξελιγμένων συστημάτων και ενίσχυσαν την προσπάθεια επέκτασης και βελτίωσης των βιβλιοθηκών δεδομένων πυρηνικής φυσικής, όπως για παράδειγμα αυτά που σχετίζονται με τις αντιδράσεις σύλληψης νετρονίων σε διάφορα ισότοπα που συμμετέχουν στον κύκλο του Θορίου. Το παρόν περιλαμβάνει και παρουσιάζει τα αποτελέσματα των μετρήσεων της αντίδρασης (n,γ) στο 234U, που πραγματοποιήθηκαν στην πειραματική διάταξη n_TOF του CERN. Περιγράφεται με λεπτομέρεια η διάταξη και το βασικό σύστημα ανίχνευσης, ενώ τα αποτελέσματα δίνονται στη μορφή παραμέτρων συντονισμού της θεωρίας R – matrix και συγκρίνονται με τις υπάρχουσες βιβλιοθήκες δεδομένων

Database for Time-of-Flight Spectra Including Covariances

A data format for time-of-flight spectra (transmission, reaction and self-indication yields) and their covariance matrices based on the AGS (Analysis of Geel Spectra) format is discussed in collaboration between EC-JRC IRMM and IAEA-NDS for the EXFOR library. Experimentalists are encouraged to consider the uncertainty propagation following the AGS principle and submission of their data to the International Networks Nuclear Reaction Data Centres (NRDC) for EXFOR compilation using a proposed template.JRC.D.5-Nuclear physic

New Evaluation of Neutron Resonance Parameters of Tungsten

The importance of tungsten in criticality safety calculation motivated a new evaluation of neutron resonance parameters for the most abundant isotopes 182, 183, 184, 186W. The new evaluation is mainly based on a combined analysis of experimental data already present in the literature (i.e. Camarda et al. and Macklin et al.), together with results of transmission measurements performed at the Geel Electron LINear Accelerator (GELINA) facility on natW.JRC.D.4 - Standards for Nuclear Safety, Security and Safeguard

Neutron Total and Capture Cross Section of Tungsten Isotopes

A new set of measurements for the total and capture cross section determination of W isotopes was done using GELINA (GEel LINear Accelerator), a neutron Time-Of-Flight facility at the Institute for Reference Materials and Measurements (IRMM). Measuring stations at diferent ight path lengths were used in order to cover a broad neutron energy range with high resolution demands. Experimental techniques adopted for both transmission and capture measurements are well established using a 6Li glass detector and C6D6 scintillation arrays as detections systems respectively. As target samples highly enriched 182,183,184,186W metallic discs were used.JRC.DG.D.5-Nuclear physic

Experimental determination of the 41Ca(n,α)38Ar reaction cross section up to 80 keV and calculation of the Maxwellian averaged cross section at stellar temperature

The (41)Ca(n,alpha)(38)Ar reaction cross section was studied at the linear accelerator GELINA of the Institute for Reference Materials and Measurements in Geel (Belgium) and was determined up to a neutron energy of about 80 keV using the time-of-flight technique. In this energy region, 15 resonances were observed, whereas none were identified before. For some of them, resonance parameters such as resonance energy, total width, area, and spin could be determined. From the obtained cross-section data, Maxwellian averaged cross sections have been calculated at various stellar temperatures for further use in stellar models

Neutron Resonance Spectroscopy at GELINA

The neutron time-of-flight facility GELINA installed at the JRC-IRMM Geel (B) has been designed to produce cross section data for neutron induced reactions in the resonance region. It is a multi-user facility, providing a pulsed white neutron source, with a neutron energy range between 10 meV and 20 MeV and a time resolution of 1 ns. The research program concentrates on cross section data needs for nuclear energy applications. In this contribution efforts to improve the quality of cross section data in the resonance region are discussed. These efforts include the implementation of self-indication measurements and improved data reduction and resonance analysis procedures. Due to these efforts accurate neutron-induced cross section data and resonance parameters together with their covariance information can be obtained from thermal up to the unresolved resonance region.JRC.DG.D.5-Nuclear physic

Neutron Resonance Parameters of 197Au from Transmission, Capture and Self-Indication Measurements at GELINA

Transmission, capture and self-indication measurements on 197Au have been performed at the neutron time-of-flight facility GELINA, operated by the European Commission, at EU-JRC-IRMM in Belgium. Part of this work was performed within the framework of the EFNUDAT project, with the objective to improve resonance parameters for the 197Au(n, gamma) cross section. Resonance parameters, i.e. energy, spin, parity, neutron and radiation width, have been deduced in the energy domain up to 200 eV. A comparison with results of measurements performed at RPI and at n_TOF shows a good agreement between the data sets. In particular the nuclear resonance parameters, of the first s-wave resonance at 4.9 eV, extracted at RPI are in very good agreement with the results of the present work.JRC.DG.D.5 - Nuclear physic