Papers by Rolando Granada
EPJ Web of Conferences, 2020
Cold neutrons are widely used in different fields of research such as the study of the structure ... more Cold neutrons are widely used in different fields of research such as the study of the structure and dynamics of solids and liquids, the investigation of magnetic materials, biological systems, polymer science, and a rapidly growing area of industrial applications. In a pulsed neutron source where the pulse width is an important parameter to be considered, hydrogenated materials are often used because of their high energy transfer in each collision. The preliminary scattering kernel for triphenylmethane, a material of great potential interest for cold neutron production, had been presented at the ND2016 conference. Here, a new model for the generation of the scattering kernels for this material, together with experimental results on its total cross section measured at the VESUVIO instrument (ISIS Neutron and Muon Source, United Kingdom) is presented. The thermal scattering kernel was generated by means of the NJOY Nuclear Data Processing system, using as input the vibrational modes ...
The European Physical Journal A, 2008
In this article we describe the experimental results of a methane hydrate moderator as well as as... more In this article we describe the experimental results of a methane hydrate moderator as well as as mesitylene moderator operated at a temperature around 20 K at the JESSICA (Jülich Experimental Spallation Target Setup In COSY Area) experiment at the Jülich cooler synchrotron COSY. For the first time the cold neutron spectrum of a methane hydrate moderator was experimentally investigated. A comparison with a solid methane and an ice moderator at T = 20 K will be shown. MCNPX simulations with new developed S(α, β) scattering kernels will be compared with experimental data. The applicability of mesitylene and methane hydrate as cold moderators at spallation neutron sources will be discussed. PACS. 24.10.Lx Monte Carlo simulations (including hadron and parton cascades and string breaking models)-25.40.Fq Inelastic neutron scattering-28.20.-v Neutron physics-28.20.Gd Neutron transport: diffusion and moderation
EPJ Web of Conferences, 2020
The Neutron Physics Department at Centro Atómico Bariloche developed new models for the interacti... more The Neutron Physics Department at Centro Atómico Bariloche developed new models for the interaction of thermal neutrons with water which have been validated against experimental data, including new thermal scattering experiments, and were adopted for the release of ENDF/B-VIII.0. Although the older models are, in general, good for most applications, some discrepancies had appeared in the case of heavy water, and this motivated new measurements that validated the new model. In the case of light water, the new model predicts a reduction of the total cross section around 0.025 eV when the temperature is increased from room temperature. This reduction, that is not predicted by the existing models, and potentially affects the calculation of temperature reactivity coefficients in nuclear reactors, has been traced to a shift in the vibrational frequency spectrum of liquid water. The only experimental data previously available is from an experiment performed at the Demokritos reactor in the...
Non-destructive determination of deuterium in Zircaloy-4
Exploration of the dynamics of condensed matter through neutron total cross-section measurements
Physica B: Condensed Matter, 1999
ABSTRACT We present a novel procedure to extract dynamical information from the inelastic incoher... more ABSTRACT We present a novel procedure to extract dynamical information from the inelastic incoherent part of the experimental neutron total cross section. The coherent elastic and inelastic components must be subtracted in order to isolate the incoherent inelastic part. We show how to obtain the one-phonon downscattering component from it, and use this result to evaluate its derivative with respect to the incident neutron wave vector. This provides a function, which serves as an input for the algorithm to extract the density of the states that is presented in this paper. We have applied this method in the case of three metal hydrides: zircaloy, magnesium and niobium, whose total cross sections were measured at a low-flux neutron source. Those results are in agreement with the inelastic scattering experiments performed at high-flux sources over the range from 40 to 250 meV.
Design of a cold-neutron source for the Bariloche LINAC with solid mesitylene as moderator material
Physica B: Condensed Matter, 2006
... [3] JF Briesmeister Ed., MCNP-A General Monte Carlo N-Particle Transport Code, Version 4B, Ma... more ... [3] JF Briesmeister Ed., MCNP-A General Monte Carlo N-Particle Transport Code, Version 4B, Manual, 1997. [4] F. Cantargi, L. Torres, Technical Report CNEA-CAB 420/004/04, 2004. [5] L. Torres, JR Granada, Technical Report CNEA-CAB 420/002/05, 2005. ...
UCANS VII Meeting Summary
Neutron News
Physica B+C
Recently a synthetic scattering law has been developed to describe the interaction of thermal neu... more Recently a synthetic scattering law has been developed to describe the interaction of thermal neutrons with molecular gases. Although this function does not contain a detailed description of the atomic motions in the molecular unit (nor pair correlations), the main features of the molecular dynamics are retained through the introduction of effective quantities which are directly related to the basic properties of the system. In this work we present evaluations of inelasticity corrections using the synthetic model for both reactor and pulsed neutron diffraction experiments. Predictions are made of differential cross sections (self component) for light and heavy water and these are compared with available experimental results.
Neutron measurements on (Pd-D2O) electrolytic cells under pulsed current conditions
AIP Conference Proceedings, 1991
We present in this work the results of neutron measurements performed on electrolytic cells conta... more We present in this work the results of neutron measurements performed on electrolytic cells containing deuterated Pd cathodes, using a high efficiency thermal neutron detection system in combination with a procedure involving a non-stationary current through the cell's circuit. Experiments carried-out at our laboratory over a long period revealed a low level neutron production correlated with the current pulses, giving
Thermal neutron scattering kernels for sapphire and silicon single crystals
Annals of Nuclear Energy, 2015
ABSTRACT Sapphire and silicon are materials usually employed as filters in facilities with therma... more ABSTRACT Sapphire and silicon are materials usually employed as filters in facilities with thermal neutron beams. Due to the lack of the corresponding thermal cross section libraries for those materials, necessary in calculations performed in order to optimize beams for specific applications, here we present the generation of new thermal neutron scattering kernels for those materials. The Debye model was used in both cases to represent the vibrational frequency spectra required to feed the NJOY nuclear data processing system in order to produce the corresponding libraries in ENDF and ACE format. These libraries were validated with available experimental data, some from the literature and others obtained at the pulsed neutron source at Centro Atómico Bariloche.
In this work we present scattering kernels and cross sections for a few cryogenic materials of in... more In this work we present scattering kernels and cross sections for a few cryogenic materials of interest as cold neutron moderators. These calculations are based on a Synthetic Scattering Function (SSF), developed to describe the incoherent interaction of slow neutrons with hydrogeneous materials in a simple way. The main advantages of this model reside in the analytical expressions that it produces for several physics parameters of specific interest to the field of Neutron and Reactor Physics. These parameters include double-differential cross sections, energy-transfer kernels, and total cross sections, which in turn allow the evaluation of neutron scattering and transport properties. The possibility of calculating those quantities in a fast and accurate way, permits the production of group constants for any specific material, at any temperature, any degree in the Legendre expansion, and over any required energy mesh. We have included the SSF routines into the NJOY code, in such a w...
The Synthetic Scattering Function (SSF) allows a simple description of the incoherent interaction... more The Synthetic Scattering Function (SSF) allows a simple description of the incoherent interaction of slow neutrons with hydrogenous materials. Its original formulation, essentially aimed at describing molecular gases, has been extended to include the important case of molecular solids. In any case, the main advantages of the Synthetic Model reside in the analytical expressions that it produces for double-differential cross sections and energy-transfer kernels, which in turn permit the fast evaluation of neutron scattering and transport properties. The SSF routines were integrated into the NJOY code, in such a way that the cross sections can be generated with the same format either from its standard library or from our model. We discuss in this work some aspects of the formalism developed to include the case of molecular solids in a more detailed manner, and present applications of the original and extended Synthetic Model to recent experimental results on liquid Hydrogen, Mesitylene...
Propiedades estructurales y transiciones de fases metaestables en aleaciones Ti-V
Regularidades en los parámetros estructurales y distancias interatómicas de la fase omega en el sistema Zr-Nb
Propiedades estructurales y estabilidad de fases bcc y omega en el sistema Zr-Nb: Parámetros de red, distancias interatómicas y efectos de enlace químico
On the thermal neutron scattering from polycrystalline vanadium
Nuclear Instruments and Methods in Physics Research, 1981
ABSTRACT
The bragg lineshapes in time-of-flight neutron powder spectroscopy
Nuclear Instruments and Methods in Physics Research, 1982
ABSTRACT
Physica B: Condensed Matter, 2003
In this paper we examine the standard procedure employed to obtain peak intensities from the expe... more In this paper we examine the standard procedure employed to obtain peak intensities from the experimental data of deep inelastic neutron scattering experiments. Our analysis is focussed on the hydrogen, deuterium and oxygen peaks observed in experiments on heavy water and the D 2 O=H 2 O equimolar mixture. As a result of our analysis we conclude that the usual procedure (based on a convolution formalism) introduces errors in the determination of the peak areas, and that the analysis must be based on an exact formalism, that was previously published. The present paper brings consequences on the quantitative results of recent publications.
Zeitschrift für Metallkunde
Systematic Approach to Structural Properties and Stability of the Bcc and Omega Phases in the Zr-Nb System: Assessment of Lattice Parameter Data and Neutron Diffraction Study of a Zr-10wt% Nb Alloy
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Papers by Rolando Granada