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
Total Neutron Cross-Section of Teflon Between 0.00038-EV and 590-EV
NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, 1995
The neutron total cross section of Teflon has been measured for energies between 3.8 × 10−4 eV an... more The neutron total cross section of Teflon has been measured for energies between 3.8 × 10−4 eV and 5.9 × 102 eV by the transmission method with pulsed neutron time-of-flight techniques. In order to cover that wide energy range, two independent measurements were performed on samples with different thicknesses and employing as neutron moderator a conventional polyethylene slab for the
Physics Procedia, 2012
The determination of total cross section of a material as a function of neutron energy by means o... more The determination of total cross section of a material as a function of neutron energy by means of transmission experiments is rather easy on a pulsed neutron source. The spectrometer and associated instrumentation required may be described as relatively simple, and sound statistical data are achieved even using a small, pulsed, accelerator based neutron source. Despite its simplicity, detailed scientific and technological information can be extracted from such measurements, at the cost of fairly elaborate data analysis techniques. These features make this an attractive tool for neutron-based materials research within small research groups. Different physical properties of a material manifest over the different neutron energy ranges. At our group we have focused on the determination and analysis of the total cross section for thermal and sub-thermal neutrons, which is very sensitive to the geometric arrangement and movement of the atoms, over distances ranging from the 'first-neighbour scale' up to the microstructural level or 'grain scale'.
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.
New approach in the study of hydrogen dynamics in metal hydrides by neutron transmission experiments
Physica B: Condensed Matter, 1999
ABSTRACT We propose a new approach to the analysis of total cross-section measurements of hydroge... more ABSTRACT We propose a new approach to the analysis of total cross-section measurements of hydrogen in metal hydrides, aimed at obtaining primary information about the dynamics of hydrogen in these compounds, including the characteristic frequencies and mean-square displacement of the proton. We use a simplified model to describe the hydrogen vibrational spectra and a translational effective mass to take into account the hydrogen diffusive motion. This approach is based on the splitting of the total incoherent cross-section in two well-defined terms: a quasi-elastic contribution – depending on the translational effective mass and the mean-square displacement of hydrogen atoms – and an inelastic contribution, related to the vibrational frequency spectra. In this work we present the starting approximations and develop the formalism involved in the analysis, illustrating its application through experiments performed on zircaloy-4, magnesium and niobium hydrides.
Physica B: Condensed Matter, 1995
In this work we present two methods, based on neutronic techniques, for the non-destructive deter... more In this work we present two methods, based on neutronic techniques, for the non-destructive determination of low hydrogen content (~< 20 wt ppm) in metals. The first method is based on neutron transmission measurements over the thermal and subthermal energy ranges, and exploits the very large cross-section of hydrogen at low neutron energies. The second method is based on scattering measurements, using epithermal neutrons in combination with time-of-flight techniques and exploiting the large difference in energy-transfer in the neutron metal and neutron-H interaction processes. We will discuss the conceptual aspects of both methods, the models developed to describe those processes, the experiments performed, and the results obtained for samples of steel and Zircaloy-IV.
A neutronic method to determine low hydrogen concentrations in metals
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2007
We propose a method for the non-destructive determination of low hydrogen content in metals. The ... more We propose a method for the non-destructive determination of low hydrogen content in metals. The method is based on measurements of neutron inelastic scattering combined with cadmium filters. Determination is simple and the method would allow to construct a mobile device, to perform the analysis “in situ”. We give a brief description of the usual methods to determine low hydrogen
Neutron spectrometer for the determination of very low hydrogen content in metals
Journal of Neutron Research, 1998
Abstract The commonly available techniques for the determination of hydrogen dissolved in solids ... more Abstract The commonly available techniques for the determination of hydrogen dissolved in solids are usually destructive from the point of view of the sample. A new, nondestructive method for this kind of measurements has been developed, with the requirement of improved sensitivity for massive samples. The method is based on the use of epithermal neutrons together with time-of-flight techniques, and has been implemented through the design and construction of a spectrometer dedicated to that task. In this work we describe the basic concepts of this method, as well as the different stages of design, building, and characterization of the new spectrometer. A pulsed neutron source based on an electron LINAC has been employed to perform the measurements. Preliminary results showing the sensitivity achieved are presented.
Proposal for instruments at small and medium size neutron facilities
Journal of Physics: Conference Series, 2011
ABSTRACT The deployment of small and medium intensity regional neutron sources facilitates the av... more ABSTRACT The deployment of small and medium intensity regional neutron sources facilitates the availability of neutron techniques to a wider users community. With a minimum set of instruments it is possible to cover a variety of applications. Based on the experience gained with the use of the Bariloche Electron Linear Accelerator (Argentina), we propose a few basic instruments that are suitable to be installed at a small or medium scale neutron facility.
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
Physical Review B - PHYS REV B, 1998
We present a full set of procedures to evaluate the experimental corrections needed to derive phy... more We present a full set of procedures to evaluate the experimental corrections needed to derive physically meaningful quantities from the measured neutron intensities in inelastic neutron-scattering experiments. Multiple-scattering corrections are evaluated by means of a Monte Carlo code, in which a combination of experimental data and the Synthetic Model is used to account for neutron-molecule interactions. Multiphonon corrections are treated with an iterative scheme. To illustrate the procedure the densities of vibrational states of deuterated water and ice near room temperature are evaluated from data measured in a chopper spectrometer. ͓S0163-1829͑98͒00326-9͔
Slow neutron total cross-section of Al6061 at low temperatures
Journal of Nuclear Materials, 2000
ABSTRACT This work presents evaluations of the total cross-section and its components, correspond... more ABSTRACT This work presents evaluations of the total cross-section and its components, corresponding to the aluminum based alloy Al6061 at a few temperatures of interest, over the neutron energy range from 10−5 to 10 eV. A practical procedure for subtraction of the cold source’s vessel contribution to the measured emerging spectra is discussed, and data given for the specific cases where Al6061 is used as the vessel material.
EPL (Europhysics Letters), 2009
PACS 61.05.fd-Theories of neutron diffraction and scattering PACS 28.20.-v-Neutron physics PACS 7... more PACS 61.05.fd-Theories of neutron diffraction and scattering PACS 28.20.-v-Neutron physics PACS 78.70.Nx-Neutron inelastic scattering Abstract-A new scattering kernel to describe the interaction of slow neutrons with solid deuterium was developed. The main characteristics of that system are contained in the formalism, including the lattice's density of states, the Young-Koppel quantum treatment of the rotations, and the internal molecular vibrations. The elastic processes involving coherent and incoherent contributions are fully described, as well as the spin-correlation effects. The results from the new model are compared with the best available experimental data, showing very good agreement.
Annals of Nuclear Energy, 1997
In most neutronic calculations, either to account for the effect of lattice vibration on nuclear ... more In most neutronic calculations, either to account for the effect of lattice vibration on nuclear resonances, the contributions due to multiple scattering processes or the presence of sample container in scattering experiments, the neutron-solid interaction is represented in a rather crude way, usually through a simple gas model. In this work we introduce a synthetic scattering kernel to describe incoherent neutron scattering processes in Debye solids. The model is based on a new prescription to represent the many-phonon contribution, whereas the first three terms of the phonon expansion are explicitly included. This prescription, which contains no adjustable parameters, is given in terms of analytical functions that produce a very good approximation to the sum of multiphonon terms. We present a few selected applications of this new method, using vanadium as a case to illustrate its merits and limitations.
… in Physics Research Section B: Beam …, 2006
Total cross sections of light water ice at 115 K and benzene at 90 K were measured at the LINAC o... more Total cross sections of light water ice at 115 K and benzene at 90 K were measured at the LINAC of Centro Ató mico Bariloche. A comparison between these experiments and experimental total cross sections of benzene and light water at 300 K is presented. The capabilities of those two molecular systems as cold neutron moderators are briefly discussed.
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.
Uploads
Papers by Rolando Granada