Neutron capture measurement of 54Fe and 57Fe at CERN n_TOF

La medida de secciones e caces de captura neutronica (n,gamma) para dos de los isotopos del hierro, 54Fe y 57Fe, ha sido realizada en la instalaci ón n_TOF del CERN con el objetivo de una mejor comprensión del llamado proceso lento (del inglés s-process) de la nucleosíntesis estelar. Al mismo tiempo, el hierro es un constituyente fundamental para la realización y el diseño de sistemas de producción de energía asistidos por acelerador(ADS del inglés Accelerator Driven Systems). La medida de secciones e caces (n,gamma ) para los isotopos 54Fe y 57Fe en el rango de las resonancias resueltas (RRR) ha sido llevada a cabo utilizando la técnica de tiempo de vuelo. Dichas medidas han sido realizadas utilizando una adecuada con guración experimental de manera tal que las secciones e caces puedan ser determinadas con un error sistem ático despreciable debido a la sensibilidad neutrónica. La primera parte de este trabajo ha consistido en desarrollar simulaciones Monte Carlo de la función de respuesta de los detectores para calcular la correspondiente función peso. Estas funciones peso han sido aplicadas a los datos medidos para poder obtener experimentalmente la tasa de captura neutrónica. El análisis nal de la sección e caz ha sido realizado utilizando el código SAMMY. Los datos obtenidos en nuestras medidas han sido contrastados frente a experimentos realizados anteriormente en otras instalaciones de medida similares.The measurement of the (n, ) cross section of 54Fe and 57Fe isotopes was performed at the CERN n_TOF facility with the aim of better understanding the s-process stellar nucleosynthesis in the Fe-Ni region. At the same time Fe is a structural material in accelerator driven systems (ADS) and accurate neutron cross sections are required for reliable design studies, to account for the neutron balance and for assessing the related uncertainties. The accurate measurement of the (n,gamma ) cross section of 54Fe and 57Fe isotopes in the resolved resonance region (RRR) has been carried out with high resolution using the time of ight technique. These measurements were performed using the total energy detector technique. An optimized detection setup has been used, which permitted the determination of their cross sections with a minimal in uence of neutron sensitivity. First part of this work was devoted to the MC simulation of the response function to calculate the corresponding weighting functions. These weighting functions were applied to the measured data in order to obtain the capture yield, and derive the capture cross section. An R-matrix analysis of the resolved resonance region has been performed for both nuclides, deriving the total radiative capture cross section and the corresponding resonance parameters. The analysis was carried out using the R-matrix code SAMMY. The results obtained in this work are compared with previous experiments performed elsewhere and with evaluated data. The results presented in this work are important to disentangle the r and s contribution observed in the old stars and for advanced reactor concepts

Calculation of Coincidence Summing Correction Factors for an HPGe detector using GEANT4

[EN] The aim of this paper was to calculate the True Coincidence Summing Correction Factors (TSCFs) for an HPGe coaxial detector in order to correct the summing effect as a result of the presence of Y-88 and Co-60 in a multigamma source used to obtain a calibration efficiency curve. Results were obtained for three volumetric sources using the Monte Carlo toolkit, GEANT4. The first part of this paper deals with modeling the detector in order to obtain a simulated full energy peak efficiency curve. A quantitative comparison between the measured and simulated values was made across the entire energy range under study. The True Summing Correction Factors were calculated for Y-88 and Co-60 using the full peak efficiencies obtained with GEANT4. This methodology was subsequently applied to Cs-134, and presented a complex decay scheme.Giubrone, G.; Ortiz Moragón, J.; Gallardo Bermell, S.; Martorell Alsina, SS.; Bas Cerdá, MDC. (2016). Calculation of Coincidence Summing Correction Factors for an HPGe detector using GEANT4. Journal of Environmental Radioactivity. 158:114-118. doi:10.1016/j.jenvrad.2016.04.008S11411815

Measurements of neutron cross sections for advanced nuclear energy systems at n_TOF (CERN)

The n_TOF facility operates at CERN with the aim of addressing the request of high accuracy nuclear data for advanced nuclear energy systems as well as for nuclear astrophysics. Thanks to the features of the neutron beam, important results have been obtained on neutron induced fission and capture cross sections of U, Pu and minor actinides. Recently the construction of another beam line has started; the new line will be complementary to the first one, allowing to further extend the experimental program foreseen for next measurement campaigns

Neutron cross-sections for advanced nuclear systems: the n_TOF project at CERN

The study of neutron-induced reactions is of high relevance in a wide variety of fields, ranging from stellar nucleosynthesis and fundamental nuclear physics to applications of nuclear technology. In nuclear energy, high accuracy neutron data are needed for the development of Generation IV fast reactors and accelerator driven systems, these last aimed specifically at nuclear waste incineration, as well as for research on innovative fuel cycles. In this context, a high luminosity Neutron Time Of Flight facility, n_TOF, is operating at CERN since more than a decade, with the aim of providing new, high accuracy and high resolution neutron cross-sections. Thanks to the features of the neutron beam, a rich experimental program relevant to nuclear technology has been carried out so far. The program will be further expanded in the near future, thanks in particular to a new high-flux experimental area, now under construction

Neutron capture cross section measurement of 238U at the CERN n_TOF facility in the energy region from 1 eV to 700 keV

The aim of this work is to provide a precise and accurate measurement of the 238U(n,γ) reaction cross section in the energy region from 1 eV to 700 keV. This reaction is of fundamental importance for the design calculations of nuclear reactors, governing the behavior of the reactor core. In particular, fast reactors, which are experiencing a growing interest for their ability to burn radioactive waste, operate in the high energy region of the neutron spectrum. In this energy region most recent evaluations disagree due to inconsistencies in the existing measurements of up to 15%. In addition, the assessment of nuclear data uncertainty performed for innovative reactor systems shows that the uncertainty in the radiative capture cross section of 238U should be further reduced to 1–3% in the energy region from 20 eV to 25 keV. To this purpose, addressed by the Nuclear Energy Agency as a priority nuclear data need, complementary experiments, one at the GELINA and two at the n_TOF facility, were proposed and carried out within the 7th Framework Project ANDES of the European Commission. The results of one of these 238U(n,γ) measurements performed at the n_TOF CERN facility are presented in this work. The γ-ray cascade following the radiative neutron capture has been detected exploiting a setup of two C6D6 liquid scintillators. Resonance parameters obtained from this work are on average in excellent agreement with the ones reported in evaluated libraries. In the unresolved resonance region, this work yields a cross section in agreement with evaluated libraries up to 80 keV, while for higher energies our results are significantly higher

Experimental neutron capture data of 58Ni from the CERN n_TOF facility

The neutron capture cross section of 58Ni was measured at the neutron time of flight facility n_TOF at CERN, from 27 meV to 400 keV neutron energy. Special care has been taken to identify all the possible sources of background, with the so-called neutron background obtained for the first time using high-precision GEANT4 simulations. The energy range up to 122 keV was treated as the resolved resonance region, where 51 resonances were identified and analyzed by a multilevel R-matrix code SAMMY. Above 122 keV the code SESH was used in analyzing the unresolved resonance region of the capture yield. Maxwellian averaged cross sections were calculated in the temperature range of kT = 5 – 100 keV, and their astrophysical implications were investigated

238U(n, γ) reaction cross section measurement with C6D6 detectors at the n_TOF CERN facility

The radiative capture cross section of 238U is very important for the developing of new reactor technologies and the safety of existing ones. Here the preliminary results of the 238U(n,γ) cross section measurement performed at n_TOF with C6D6 scintillation detectors are presented, paying particular attention to data reduction and background subtraction

GEANT4 simulation of the neutron background of the C6D6 set-up for capture studies at n_TOF

The neutron sensitivity of the C6D6 detector setup used at n_TOF facility for capture measurements has been studied by means of detailed GEANT4 simulations. A realistic software replica of the entire n_TOF experimental hall, including the neutron beam line, sample, detector supports and the walls of the experimental area has been implemented in the simulations. The simulations have been analyzed in the same manner as experimental data, in particular by applying the Pulse Height Weighting Technique. The simulations have been validated against a measurement of the neutron background performed with a natC sample, showing an excellent agreement above 1 keV. At lower energies, an additional component in the measured natC yield has been discovered, which prevents the use of natC data for neutron background estimates at neutron energies below a few hundred eV. The origin and time structure of the neutron background have been derived from the simulations. Examples of the neutron background for two different samples are demonstrating the important role of accurate simulations of the neutron background in capture cross-section measurements

Fission fragment angular distribution measurements of 235U and 238U at CERN n_TOF facility

Neutron-induced fission cross sections of 238U and 235U are used as standards in the fast neutron region up to 200 MeV. A high accuracy of the standards is relevant to experimentally determine other neutron reaction cross sections. Therefore, the detection effciency should be corrected by using the angular distribution of the fission fragments (FFAD), which are barely known above 20 MeV. In addition, the angular distribution of the fragments produced in the fission of highly excited and deformed nuclei is an important observable to investigate the nuclear fission process. In order to measure the FFAD of neutron-induced reactions, a fission detection setup based on parallel-plate avalanche counters (PPACs) has been developed and successfully used at the CERN-n_TOF facility. In this work, we present the preliminary results on the analysis of new 235U(n,f) and 238U(n,f) data in the extended energy range up to 200 MeV compared to the existing experimental data

High accuracy 234U(n,f) cross section in the resonance energy region

New results are presented of the 234U neutron-induced fission cross section, obtained with high accuracy in the resonance region by means of two methods using the 235U(n,f) as reference. The recent evaluation of the 235U(n,f) obtained with SAMMY by L. C. Leal et al. (these Proceedings), based on previous n_TOF data [1], has been used to calculate the 234U(n,f) cross section through the 234U/235U ratio, being here compared with the results obtained by using the n_TOF neutron flux