n_TOF Collaboration(Cosentino, L. et al), Domingo-Pardo, C., Tain, J. L., & Tarifeño-Saldivia, A. (2016). Experimental setup and procedure for the measurement of the Be-7(n,alpha)alpha reaction at n_TOF. Nucl. Instrum. Methods Phys. Res. A, 830, 197–205.
Abstract: The newly built second experimental area EAR2 of then n_ToF spallation neutron source at CERN allows to perform (n, charged particles) experiments on short-lived highly radioactive targets. This paper describes a detection apparatus and the experimental procedure for the determination of the cross-section of the Be-7(n,alpha)alpha reaction, which represents one of the focal points toward the solution of the cosmological Lithium abundance problem, and whose only measurement, at thermal energy, dates back to 1963. The apparently unsurmountable experimental difficulties stemming from the huge Be-7 gamma-activity, along with the lack of a suitable neutron beam facility, had so far prevented further measurements. The detection system is subject to considerable radiation damage, but is capable of disentangling the rare reaction signals from the very high background. This newly developed setup could likely be useful also to study other challenging reactions requiring the detectors to be installed directly in the neutron beam.
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Guadilla, V. et al, Algora, A., Tain, J. L., Agramunt, J., Jordan, D., Monserrate, M., et al. (2017). Characterization of a cylindrical plastic beta-detector with Monte Carlo simulations of optical photons. Nucl. Instrum. Methods Phys. Res. A, 854, 134–138.
Abstract: In this work we report on the Monte Carlo study performed to understand and reproduce experimental measurements of a new plastic beta-detector with cylindrical geometry. Since energy deposition simulations differ from the experimental measurements for such a geometry, we show how the simulation of production and transport of optical photons does allow one to obtain the shapes of the experimental spectra. Moreover, taking into account the computational effort associated with this kind of simulation, we develop a method to convert the simulations of energy deposited into light collected, depending only on the interaction point in the detector. This method represents a useful solution when extensive simulations have to be done, as in the case of the calculation of the response function of the spectrometer in a total absorption gamma-ray spectroscopy analysis.
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n_TOF Collaboration(Massimi, C. et al.), Domingo-Pardo, C., Giubrone, G., & Tain, J. L. (2017). Neutron spectroscopy of Mg-26 states: Constraining the stellar neutron source Ne-22(alpha, n)Mg-25. Phys. Lett. B, 768, 1–6.
Abstract: This work reports on accurate, high-resolution measurements of the Mg-25(n, gamma)Mg-26 and Mg-25(n, tot) cross sections in the neutron energy range from thermal to about 300 keV, leading to a significantly improved Mg-25(n, gamma)Mg-26 parametrization. The relevant resonances for n+Mg-25 were characterized from a combined R-matrix analysis of the experimental data. This resulted in an unambiguous spin/parity assignment of the corresponding excited states in Mg-26. With this information experimental upper limits of the reaction rates for Ne-22(alpha, n)Mg-25 and Ne-22(alpha, gamma)Mg-26 were established, potentially leading to a significantly higher (alpha, n)/(alpha, gamma) ratio than previously evaluated. The impact of these results has been studied for stellar models in the mass range 2 to 25 M-circle dot. (C) 2017 The Author(s). Published by Elsevier B.V.
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BRIKEN Collaboration(Tarifeño-Saldivia, A. et al), Tain, J. L., Domingo-Pardo, C., Agramunt, J., Algora, A., Morales, A. I., et al. (2017). Conceptual design of a hybrid neutron-gamma detector for study of beta-delayed neutrons at the RIB facility of RIKEN. J. Instrum., 12, P04006–22pp.
Abstract: BRIKEN is a complex detection system to be installed at the RIB-facility of the RIKEN Nishina Center. It is aimed at the detection of heavy-ion implants, β-particles, γ-rays and β-delayed neutrons. The whole detection setup involves the Advanced Implantation Detection Array (AIDA), two HPGe Clover detectors and a large set of 166 counters of 3He embedded in a high-density polyethylene matrix. This article reports on a novel methodology developed for the conceptual design and optimisation of the 3He-tubes array, aiming at the best possible performance in terms of neutron detection. The algorithm is based on a geometric representation of two selected parameters of merit, namely, average neutron detection efficiency and efficiency flatness, as a function of a reduced number of geometric variables. The response of the detection system itself, for each configuration, is obtained from a systematic MC-simulation implemented realistically in Geant4. This approach has been found to be particularly useful. On the one hand, due to the different types and large number of 3He-tubes involved and, on the other hand, due to the additional constraints introduced by the ancillary detectors for charged particles and gamma-rays. Empowered by the robustness of the algorithm, we have been able to design a versatile detection system, which can be easily re-arranged into a compact mode in order to maximize the neutron detection performance, at the cost of the gamma-ray sensitivity. In summary, we have designed a system which shows, for neutron energies up to 1(5) MeV, a rather flat and high average efficiency of 68.6%(64%) and 75.7%(71%) for the hybrid and compact modes, respectively. The performance of the BRIKEN system has been also quantified realistically by means of MC-simulations made with different neutron energy distributions.
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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(Barbagallo, M. et al), Domingo-Pardo, C., & Tain, J. L. (2018). Experimental setup and procedure for the measurement of the Be-7(n,p)Li-7 reaction at n_TOF. Nucl. Instrum. Methods Phys. Res. A, 887, 27–33.
Abstract: Following the completion of the second neutron beam line and the related experimental area (EAR2) at the n_TOF spallation neutron source at CERN, several experiments were planned and performed. The high instantaneous neutron flux available in EAR2 allows to investigate neutron induced reactions with charged particles in the exit channel even employing targets made out of small amounts of short-lived radioactive isotopes. After the successful measurement of the Be-7(n,alpha)alpha cross section, the Be-7(n,p)Li-7 reaction was studied in order to provide still missing cross section data of relevance for Big Bang Nucleosynthesis (BBN), in an attempt to find a solution to the cosmological Lithium abundance problem. This paper describes the experimental setup employed in such a measurement and its characterization.
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n_TOF Collaboration(Praena, J. et al), Domingo-Pardo, C., Giubrone, G., Tain, J. L., & Tarifeño-Saldivia, A. (2018). Preparation and characterization of S-33 samples for S-33(n,alpha)Si-30 cross-section measurements at the n_TOF facility at CERN. Nucl. Instrum. Methods Phys. Res. A, 890, 142–147.
Abstract: Thin S-33 samples for the study of the S-33(n,alpha)Si-30 cross-section at the n_TOF facility at CERN were made by thermal evaporation of S-33 powder onto a dedicated substrate made of kapton covered with thin layers of copper, chromium and titanium. This method has provided for the first time bare sulfur samples a few centimeters in diameter. The samples have shown an excellent adherence with no mass loss after few years and no sublimation in vacuum at room temperature. The determination of the mass thickness of S-33 has been performed by means of Rutherford backscattering spectrometry. The samples have been successfully tested under neutron irradiation.
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Olleros, P., Caballero, L., Domingo-Pardo, C., Babiano, V., Ladarescu, I., Calvo, D., et al. (2018). On the performance of large monolithic LaCl3(Ce) crystals coupled to pixelated silicon photosensors. J. Instrum., 13, P03014–17pp.
Abstract: We investigate the performance of large area radiation detectors, with high energy-and spatial-resolution, intended for the development of a Total Energy Detector with gamma-ray imaging capability, so-called i-TED. This new development aims for an enhancement in detection sensitivity in time-of-flight neutron capture measurements, versus the commonly used C6D6 liquid scintillation total-energy detectors. In this work, we study in detail the impact of the readout photosensor on the energy response of large area (50 x 50 mm(2)) monolithic LaCl3(Ce) crystals, in particular when replacing a conventional mono-cathode photomultiplier tube by an 8 x 8 pixelated silicon photomultiplier. Using the largest commercially available monolithic SiPM array (25 cm(2)), with a pixel size of 6 x 6 mm(2), we have measured an average energy resolution of 3.92% FWHM at 662 keV for crystal thick-nesses of 10, 20 and 30 mm. The results are confronted with detailed Monte Carlo (MC) calculations, where optical processes and properties have been included for the reliable tracking of the scintillation photons. After the experimental validation of the MC model, we use our MC code to explore the impact of a smaller photosensor segmentation on the energy resolution. Our optical MC simulations predict only a marginal deterioration of the spectroscopic performance for pixels of 3 x 3 mm(2).
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Rasco, B. C., Brewer, N. T., Yokoyama, R., Grzywacz, R., Rykaczewski, K. P., Tolosa-Delgado, A., et al. (2018). The ORNL analysis technique for extracting beta-delayed multi-neutron branching ratios with BRIKEN. Nucl. Instrum. Methods Phys. Res. A, 911, 79–86.
Abstract: Many choices are available in order to evaluate large radioactive decay networks. There are many parameters that influence the calculated beta-decay delayed single and multi-neutron emission branching fractions. We describe assumptions about the decay model, background, and other parameters and their influence on beta-decay delayed multi-neutron emission analysis. An analysis technique, the ORNL BRIKEN analysis procedure, for determining beta-delayed multi-neutron branching ratios in beta-neutron precursors produced by means of heavy-ion fragmentation is presented. The technique is based on estimating the initial activities of zero, one, and two neutrons occurring in coincidence with an ion-implant and beta trigger. The technique allows one to extract beta-delayed multi-neutron decay branching ratios measured with the He-3 BRIKEN neutron counter. As an example, two analyses of the beta-neutron emitter Cu-77 based on different a priori assumptions are presented along with comparisons to literature values.
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Guadilla, V. et al, Tain, J. L., Algora, A., Agramunt, J., Gelletly, W., Jordan, D., et al. (2018). Characterization and performance of the DTAS detector. Nucl. Instrum. Methods Phys. Res. A, 910, 79–89.
Abstract: DTAS is a segmented total absorption y-ray spectrometer developed for the DESPEC experiment at FAIR. It is composed of up to eighteen NaI(Tl) crystals. In this work we study the performance of this detector with laboratory sources and also under real experimental conditions. We present a procedure to reconstruct offline the sum of the energy deposited in all the crystals of the spectrometer, which is complicated by the effect of NaI(Tl) light-yield non-proportionality. The use of a system to correct for time variations of the gain in individual detector modules, based on a light pulse generator, is demonstrated. We describe also an event-based method to evaluate the summing-pileup electronic distortion in segmented spectrometers. All of this allows a careful characterization of the detector with Monte Carlo simulations that is needed to calculate the response function for the analysis of total absorption gamma-ray spectroscopy data. Special attention was paid to the interaction of neutrons with the spectrometer, since they are a source of contamination in studies of beta-delayed neutron emitting nuclei.
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