Giovanni Romanelli

We provide an updated scattering library for the simulation of thermal neutron transport in air, including the effects of rotational and vibrational modes in N2 and O2 and neutron magnetic scattering in O2, showing their significance compared to smaller effects related to water humidity. The modeling is based on the Young–Koppel treatment of thermal neutron scattering from diatomic molecules, as well as ab initio simulations of the electronic density of O2. The theoretical predictions are benchmarked against experimental measurements of the total scattering cross section of air under monitored thermophysical conditions, in the neutron energy range between 0.6 meV and 10 keV. The updated scattering library is used to calculate excess neutron scattering in air, compared to traditional approaches, where only nuclear scattering from gases of free nuclei is implemented in Monte Carlo transport codes.

We provide the modeling and experimental validation of thermal neutron cross sections, including scattering and absorption contributions, of aluminum fluoride and magnesium fluoride, as well as MgF2–AlF3 and AlF3–LiF mixtures, in the neutron energy range between 0.6 meV and 1 keV. The neutron scattering properties have been investigated as a function of temperature, between 10 and 370 K, and sample microscopic structure, focusing in particular on differences between powder and sintered samples. Concurrent measurements of neutron transmission, neutron diffraction, neutron resonance capture analysis, and neutron Compton scattering provide a comprehensive picture of scattering and transport properties of these materials. We provide crystallographic information at the atomic scale, the effect of sintering on the grain size at the nanometer scale, the related occurrence of small angle scattering, and the impact of fluorine zero-point nuclear energy at different temperatures, requiring the use of an effective temperature to model its scattering within the impulse approximation. Finally, combining this self-consistent experimental information, we discuss the application of the uncertainty principle to the fluorine single-particle potential.

We provide a beam shape characterization of the VESUVIO spectrometer, at the ISIS Neutron and Muon Source, employing CR-39 solid-state nuclear track detectors and combining techniques including optical and electron microscopy, as well as Monte Carlo transport simulations. In particular, we show, through comparison with irradiation with 14 MeV neutrons at the NILE Facility at ISIS, that the majority of defects on the etched surface of the dosimeters irradiated on VESUVIO were induced by neutrons with energies between 100 keV and 10 MeV. Our results were compared to previous characterizations of the VESUVIO beam shape performed in either the thermal or fast energy ranges, and we conclude that the VESUVIO beam has a constant shape from thermal-neutron energies up to 10 MeV, composed of an umbra (intensity above 90% of the maximum) with radius 1.1 cm, and surrounded by a penumbra (intensity above 1% of the maximum) that extends up to 2.5 cm.

In view of wide-ranging application to the biomedical field, this work investigates the mechanical and electrical properties of a composite made of Single Wall Carbon Nanotubes (SWCNT) bundles self-grafted onto a poly-dimethyl-siloxane (PDMS) elastomer, particularly Sylgard 184, that has well assessed biocompatible properties and is commonly used in prosthetics. Due to the potential risks associated with the use of carbon nanostructures in implanted devices, we also assess the viability of cells directly grown on such composite substrates. Furthermore, as the stability of conductive, stretchable devices made of such composite is also crucial to their use in the medical field, we investigate, by different experimental techniques, the grafting of SWCNT bundles deep into PDMS films. Our findings prove that penetration of SWCNT bundles into the polymer bulk depends on heating time and carbon nanotubes can be seen beyond 150 μm from the surface. This is confirmed by direct electron microscopy observation of large bundles as deep as about 20 μm. The composites exhibit reliable mechanical and electrical responses that are more suitable to large and repeated deformation of the polymer with respect to thermoplastic based composites, suggesting a wide potential for their application to stretchable biomedical devices. Aiming at the proposed application of artificial bladders, a bladder prototype made of poly-dimethyl siloxane endowed with a printed SWCNT-based strain sensor was developed.

Phantom materials are used to design radiation safety and protection strategies by means of numerical dose calculation. In the case of thermal neutrons, the radiation transport in the phantom relies on mass attenuation coefficients and total cross sections which are dependent on the physical and chemical properties of the material. Specifically for medical applications, such as neutron capture therapy, the neutron-induced dose is mainly related to the neutron absorption by hydrogen and nitrogen in the human tissue and body. Here, we investigate the use of poly(2-hydroxyethyl methacrylate) as a phantom material by experimental measurement and modeling of its total neutron scattering cross section and mass attenuation coefficient. We show that by varying the hydration level from 10 to 40 w%, one can obtain a neutron attenuation coefficient similar to polymethyl methacrylate or more representative of the human body, respectively. By benchmarking our phenomenological model on the experimental data, we provide a new example of how to use the average functional group approximation to accurately model total neutron cross sections in the framework of personalized medicine approaches.

We provide a concurrent measurement of the hydrogen and oxygen nuclear kinetic energies in the water molecule across melting at 270 K in the solid phase and 276 K in the liquid phase. Experimental values are obtained by analyzing the neutron Compton profiles of each atomic species in a deep inelastic neutron scattering experiment. The concurrent measurement of the atom kinetic energy of both hydrogen and oxygen allows the estimate of the total kinetic energy per molecule due to the motion of nuclei, specifically 35.3 ± 0.8 and 34.8 ± 0.8 kJ/mol for the solid and liquid phases, respectively. Such a small difference supports results from ab initio simulations and phenomenological models from the literature on the mechanism of competing quantum effects across the phase change. Despite the experimental uncertainties, the results are consistent with the trend from state-of-the-art computer simulations, whereby the atom and molecule kinetic energies in the liquid phase would be slightly lower than in the solid phase. Moreover, the small change of nuclear kinetic energy across melting can be used to simplify the calculation of neutron-related environmental dose in complex locations, such as high altitude or polar neutron radiation research stations where liquid water and ice are both present: for neutron energies between hundreds of meV and tens of keV, the total scattering cross section per molecule in the two phases can be considered the same, with the macroscopic cross section only depending upon the density changes of water near the melting point.

This work provides a current, critical view of the application of MAss-selective Neutron SpEctroscopy (MANSE) to nanocomposite materials. MANSE is a unique technique made possible owing to the existence of the pulsed neutron sources. At present, the only operating MANSE spectrometer in the world, VESUVIO, is located at the ISIS Neutron and Muon Source in the UK. We start by providing a brief description of the neutron Compton scattering, the anatomy of a mass-selective neutron spectrometer, and the experimental data treatment. We continue by briefly outlining the main quantum mechanical concepts, models and approximations relevant both to the ab initio prediction and experimental measurement of main MANSE observables. Next, we present several recent exemplars chosen to highlight the use of MANSE in the field of nanocomposites. Our examples include, in chronological order, encapsulated nanoparticles in amorphous silica gel, bioactive glass-ionomer cement, Cu-Ti-C composites, and sodium carboxymethyl starch-based binders in the presence of a mineral matrix. We close by providing our view of the ongoing and future challenges and opportunities in the mass-selective neutron investigation of NQEs in nanocomposite materials.