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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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n_TOF Collaboration(Guerrero, C. et al), Domingo-Pardo, C., & Tain, J. L. (2011). Study of Photon Strength Function of Actinides: the Case of (235)U, (238)Np and (241)Pu. J. Korean Phys. Soc., 59(2), 1510–1513.
Abstract: The decay from excited levels in medium and heavy nuclei can be described in a statistical approach by means of Photon Strength Functions and Level Density distributions. The study of electromagnetic cascades following neutron capture based on the use of high efficiency detectors has been shown to be well suited for probing the properties of the Photon Strength Function of heavy (high level density) and/or radioactive (high background) nuclei. In this work we have investigated for the first time the validity of the recommended PSF of actinides, in particular (235)U, (238)Np and (241)Pu. Our study includes the search for resonance structures in the PSF below S(n) and draws conclusions regarding their existence and their characteristics in terms of energy, width and electromagnetic nature.
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n_TOF Collaboration(Guerrero, C. et al), Giubrone, G., & Tain, J. L. (2011). Characterization of the New n_TOF Neutron Beam: Fluence, Profile and Resolution. J. Korean Phys. Soc., 59(2), 1624–1627.
Abstract: After a halt of four years, the nTOF spallation neutron facility at CERN has resumed operation in November 2008 with a new spallation target characterized by an improved safety and engineering design, resulting in a more robust overall performance and efficient cooling. The first measurement during the 2009 run has aimed at the full characterization of the neutron beam. Several detectors, such as calibrated fission chambers, the nTOF Silicon Monitor, a MicroMegas detector with (10)B and (235)U samples, as well as liquid and solid scintillators have been used in order to characterize the properties of the neutron fluence. The spatial profile of the beam has been studied with a specially designed “X-Y” MicroMegas which provided a 2D image of the beam as a function of neutron energy. Both properties have been compared with simulations performed. with the FLUKA code. The characterization of the resolution function is based on results from simulations which have been verified by the study of narrow capture resonances. of (56)Fe, which were measured as part of a new campaign of (n,gamma) measurements on Fe and Ni isotopes.
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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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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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