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Hornillos, M. B. G., Gorlychev, V., Caballero, R., Cortes, G., Poch, A., Pretel, C., et al. (2011). Monte Carlo Simulations for the Study of a Moderated Neutron Detector. J. Korean Phys. Soc., 59(2), 1573–1576.
Abstract: This work presents the Monte Carlo simulations performed with the MCNPX and GEANT4 codes for the design of a BEta deLayEd Neutron detector, BELEN-20. This detector will be used for the study of beta delayed neutron emission and consists of a block of polyethylene with dimensions 90 x 90 x 80 cm(3) and 20 cylindrical (3)He gas counters. The results of these simulations have been validated experimentally with a (252)Cf source in the laboratory at UPC, Barcelona. Also the first experiment with this detector has been carried out in November 2009 in JYFL, Finland. In this experiment the neutron emission probability after beta decay of the fission products (88)Br, (94,95)Rb, and (138)I has been measured; this data is still under analysis. Simulations with MCNPX and GEANT4 have been performed in order to obtain the efficiency of the BELEN-20 detector for each of the above nuclei using the neutron energy distribution corresponding to each nucleus.
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n_TOF Collaboration(Mendoza, E. et al), Giubrone, G., & Tain, J. L. (2011). Improved Neutron Capture Cross Section Measurements with the n_TOF Total Absorption Calorimeter. J. Korean Phys. Soc., 59(2), 1813–1816.
Abstract: The n_TOF collaboration operates a Total Absorption Calorimeter (TAC) [1] for measuring neutron capture cross-sections of low-mass and/or radioactive samples. The results obtained with the TAC have led to a substantial improvement of the capture cross sections of (237)Np and (240)Pu [2]. The experience acquired during the first measurements has allowed us to optimize the performance of the TAC and to improve the capture signal to background ratio, thus opening the way to more complex and demanding measurements on rare radioactive materials. The new design has been reached by a series of detailed Monte Carlo simulations of complete experiments and dedicated test measurements. The new capture setup will be presented and the main achievements highlighted.
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Guerrero, C., Cano-Ott, D., Mendoza, E., Tain, J. L., Algora, A., Berthoumieux, E., et al. (2012). Monte Carlo simulation of the n_TOF Total Absorption Calorimeter. Nucl. Instrum. Methods Phys. Res. A, 671, 108–117.
Abstract: The n_TOF Total Absorption Calorimeter (TAC) is a 4 pi BaF2 segmented detector used at CERN for measuring neutron capture cross-sections of importance for the design of advanced nuclear reactors. This work presents the simulation code that has been developed in GEANT4 for the accurate determination of the detection efficiency of the TAC for neutron capture events. The code allows to calculate the efficiency of the TAC for every neutron capture state, as a function of energy, crystal multiplicity, and counting rate. The code includes all instrumental effects such as the single crystal detection threshold and energy resolution, finite size of the coincidence time window, and signal pile-up. The results from the simulation have been validated with experimental data for a large set of electromagnetic de-excitation patterns: beta-decay of well known calibration sources, neutron capture reactions in light nuclei with well known level schemes like Ti-nat, reference samples used in (n,gamma) measurements like Au-197 and experimental data from an actinide sample like Pu-240. The systematic uncertainty in the determination of the detection efficiency has been estimated for all the cases. As a representative example, the accuracy reached for the case of Au-197(n,gamma) ranges between 0.5% and 2%, depending on the experimental and analysis conditions. Such a value matches the high accuracy required for the nuclear cross-section data needed in advanced reactor design.
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Garcia, A. R., Martinez, T., Cano-Ott, D., Castilla, J., Guerrero, C., Marin, J., et al. (2012). MONSTER: a time of flight spectrometer for beta-delayed neutron emission measurements. J. Instrum., 7, C05012–12pp.
Abstract: The knowledge of the beta-decay properties of nuclei contributes decisively to our understanding of nuclear phenomena: the beta-delayed neutron emission of neutron rich nuclei plays an important role in the nucleosynthesis r-process and constitutes a probe for nuclear structure of very neutron rich nuclei providing information about the high energy part of the full beta strength (S-beta) function. In addition, beta-delayed neutrons are essential for the control and safety of nuclear reactors. In order to determine the neutron energy spectra and emission probabilities from neutron precursors a MOdular Neutron time-of-flight SpectromeTER (MONSTER) has been proposed for the DESPEC experiment at the future FAIR facility. The design of MONSTER and status of its construction are reported in this work.
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Jordan, D., Tain, J. L., Algora, A., Agramunt, J., Domingo-Pardo, C., Gomez-Hornillos, M. B., et al. (2013). Measurement of the neutron background at the Canfranc Underground Laboratory LSC. Astropart Phys., 42, 1–6.
Abstract: The energy distribution of the neutron background was measured for the first time at Hall A of the Canfranc Underground Laboratory. For this purpose we used a novel approach based on the combination of the information obtained with six large high-pressure He-3 proportional counters embedded in individual polyethylene blocks of different size. In this way not only the integral value but also the flux distribution as a function of neutron energy was determined in the range from 1 eV to 10 MeV. This information is of importance because different underground experiments show different neutron background energy dependence. The high sensitivity of the setup allowed to measure a neutron flux level which is about four orders of magnitude smaller that the neutron background at sea level. The integral value obtained is Phi(Hall A) = (3.44 +/- 0.35) x 10(-6) cm(-2) s(-1).
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n_TOF Collaboration(Mendoza, E. et al), Domingo-Pardo, C., & Tain, J. L. (2014). Measurement and analysis of the Am-243 neutron capture cross section at the n_TOF facility at CERN. Phys. Rev. C, 90(3), 034608–16pp.
Abstract: Background: The design of new nuclear reactors and transmutation devices requires to reduce the present neutron cross section uncertainties of minor actinides. Purpose: Improvement of the Am-243(n, gamma) cross section uncertainty. Method: The Am-243(n, gamma) cross section has been measured at the n_TOF facility at CERN with a BaF2 total absorption calorimeter, in the energy range between 0.7 eV and 2.5 keV. Results: The Am-243(n, gamma) cross section has been successfully measured in the mentioned energy range. The resolved resonance region has been extended from 250 eV up to 400 eV. In the unresolved resonance region our results are compatible with one of the two incompatible capture data sets available below 2.5 keV. The data available in EXFOR and in the literature have been used to perform a simple analysis above 2.5 keV. Conclusions: The results of this measurement contribute to reduce the Am-243(n, gamma) cross section uncertainty and suggest that this cross section is underestimated up to 25% in the neutron energy range between 50 eV and a few keV in the present evaluated data libraries.
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Tain, J. L., Agramunt, J., Algora, A., Aprahamian, A., Cano-Ott, D., Fraile, L. M., et al. (2015). The sensitivity of LaBr3:Ce scintillation detectors to low energy neutrons: Measurement and Monte Carlo simulation. Nucl. Instrum. Methods Phys. Res. A, 774, 17–24.
Abstract: The neutron sensitivity of a cylindrical circle minus 1.5 in x 1.5 in LaBr3:Ce scintillation detector was measured using quasi-monoenergetic neutron beams in the energy range from 40 keV to 2.5 MeV. In this energy range the detector is sensitive to gamma-rays generated in neutron inelastic and capture processes. The experimental energy response was compared with Monte Carlo simulations performed with the Geant4 simulation toolkit using the so-called High Precision Neutron Models. These models rely on relevant information stored in evaluated nuclear data libraries. The performance of the Geant4 Neutron Data Library as well as several standard nuclear data libraries was investigated. In the latter case this was made possible by the use of a conversion tool that allowed the direct use of the data from other libraries in Geant4. Overall it was found that there was good agreement with experiment for some of the neutron data bases like ENDF/B-VII.0 or JENDL-3.3 but not with the others such as ENDF/B-VI.8 or JEFF-3.1.
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Tain, J. L., Algora, A., Agramunt, J., Guadilla, V., Jordan, M. D., Montaner-Piza, A., et al. (2015). A decay total absorption spectrometer for DESPEC at FAIR. Nucl. Instrum. Methods Phys. Res. A, 803, 36–46.
Abstract: This paper presents the design of a total absorption gamma-ray spectrometer for the determination of beta-decay intensity distributions of exotic nuclear species at the focal plane of the FAIR-NUSTAR Super Fragment Separator. The spectrometer is a key instrument in the DESPEC experiment and the proposed implementation follows extensive design studies and prototype tests. Two options were contemplated, based on Nal(TI) and LaBr3:Ce inorganic scintillation crystals respectively. Monte Carlo simulations and technical considerations determined the optimal configurations consisting of sixteen 15 x 15 x 25 cm(3) crystals for the Nal(Tl) option and one hundred and twenty-eight 5.5 x 5.5 x 11 cm(3) crystals for the LaBr3:Ce option. Minimization of dead material was crucial for maximizing the spectrometer full-energy peak efficiency. Module prototypes were build to verify constructional details and characterize their performance. The measured energy and timing resolution was found to agree rather well with estimates based on simulations of scintillation light transport and collection. The neutron sensitivity of the spectrometer, important when measuring beta-delayed neutron emitters, was investigated by means of Monte Carlo simulations.
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Garcia, A. R., Mendoza, E., Cano-Ott, D., Nolte, R., Martinez, T., Algora, A., et al. (2017). New physics model in GEANT4 for the simulation of neutron interactions with organic scintillation detectors. Nucl. Instrum. Methods Phys. Res. A, 868, 73–81.
Abstract: The accurate determination of the response function of organic scintillation neutron detectors complements their experimental characterization. Monte Carlo simulations with GEANT4 can reduce the effort and cost implied, especially for complex detection systems for which the characterization is more challenging. Previous studies have reported on the inaccuracy of GEANT4 in the calculation of the neutron response of organic scintillation detectors above 6 MeV, due to an incomplete description of the neutron-induced alpha production reactions on carbon. We have improved GEANT4 in this direction by incorporating models and data from NRESP, an excellent Monte Carlo simulation tool developed at the Physikalisch-Technische Bundesanstalt (PTB), Germany, for the specific purpose of calculating the neutron response function of organic scintillation detectors. The results have been verified against simulations with NRESP and validated against Time-Of-Flight measurements with an NE213 detector at PTB. This work has potential applications beyond organic scintillation detectors, to other types of detectors where reactions induced by fast neutrons on carbon require an accurate description.
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n_TOF Collaboration(Mendoza, E. et al), Giubrone, G., Tain, J. L., & Tarifeño-Saldivia, A. (2018). Measurement and analysis of the Am-241 neutron capture cross section at the n_TOF facility at CERN. Phys. Rev. C, 97(5), 054616–21pp.
Abstract: The Am-241(n, gamma) cross section has been measured at the nTOF facility at CERN with the nTOF BaF2 Total Absorption Calorimeter in the energy range between 0.2 eV and 10 keV. Our results are analyzed as resolved resonances up to 700 eV, allowing a more detailed description of the cross section than in the current evaluations, which contain resolved resonances only up to 150-160 eV. The cross section in the unresolved resonance region is perfectly consistent with the predictions based on the average resonance parameters deduced from the resolved resonances, thus obtaining a consistent description of the cross section in the full neutron energy range under study. Below 20 eV, our results are in reasonable agreement with JEFF-3.2 as well as with the most recent direct measurements of the resonance integral, and differ up to 20-30% with other experimental data. Between 20 eV and 1 keV, the disagreement with other experimental data and evaluations gradually decreases, in general, with the neutron energy. Above 1 keV, we find compatible results with previously existing values.
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