213 research outputs found
Dispersion relation of longitudinal waves in liquid He-4 in the framework of quantum macroscopic equations derived from Bohm’s potential
No full textHe-4 is known to become superfluid at very low temperatures. This effect is now generally accepted to be connected with BEC (Bose–Einstein Condensation). The dispersion relation of pressure waves in superfluid He-4 has been determined at 1.1 °K by Yarnell et al., and exhibits a non monotonic behavior–with a maximum and a minimum–usually explained in terms of excitations called rotons, introduced by Landau. In the present work an attempt is made to describe the phenomenon within the Bohmian interpretation of QM. To this end, the effects of the intermolecular potential, taken to be essentially of the Lennard-Jones type modified to account for molecule finiteness, are included as a Vlasov-type self-consistent field. A dispersion relation is found, that is in quite good agreement with Yarnell’s curve
Bayesian inversion of coupled radiative and heat transfer models for asteroid regoliths and lakes
No full textestimation, the quantities we seek to retrieve are considered as random variables. The randomness includes the uncertainty regarding
their true values.Weintend to use this approach to perform inversion of coupled radiative and heat transfer models for asteroid regoliths and lakes. The Bayesian inversion of this kind of models allows estimating optical and thermodynamic properties of the systems considered, and also allows finding any correlation among these properties; that would be quite difficult to find with the classical approaches
New derivation of Blackshow–Murrays formula for the Doppler-broadened scattering kernel and calculation of the angular moments via Lagrange interpolation
No full textA new independent derivation of Blackshow–Murray’s classical formula for the Doppler-broadening elastic scattering kernel is given, including an extension to anisotropy of scattering in the center of mass. Also, the puzzling behavior of the secondary angular and energy neutron distribution about the lower resonances of heavy isotopes is explained by introducing an asymptotic ordering, which includes on the same foot thermal agitation and resonance effects, and by a detailed analysis for the case of collinear scattering. Finally, we use Lagrange polynomial interpolations for a fast and accurate calculations of the angular moments of the kernel. Results for 238U are presented, analyzed and compared to those in the existing literature, for both isotropic an anisotropic scattering in the center of mass
Density Distribution for the Molecules of a Liquid in a Semi-infinite Space
No full textThe Sutherland approximation to the van der Waals forces is applied to the derivation of a self-consistent Vlasov-type field in a liquid filling a half space, bordering vacuum. The ensuing Vlasov equation is then derived, and solved to predict the behavior of the density at and in the vicinity of the liquid-vacuum interface. A numerical solution to the Vlasov equation is also produced and the density profile shown and discussed
The Specific Heat of Liquid Helium
No full textStarting from the modified Lennard–Jones potential, a method is proposed to calculate the internal energy in liquids, and from this the specific heat. The method is applied to liquid helium-4 and the well-known shape of the “lambda point” is reproduced
Apparecchiatura per la produzione endogena di radioisotopi, particolarmente per diagnostica tomografica ad emissione di positroni
No full textApparecchiatura per la produzione endogena di radioisotopi, particolarmente per diagnostica tomografica ad emissione di positoni, caratterizzata dal fatto di comprendere:
- una camera da vuoto, la cui superficie interna è trattata per resistere all'implantazione ionica,
- una coppia di elettrodi posti all'interno di detta camera da vuoto,
- un banco capacitivo,
- mezzi di connessione di detto banco capacitivo a detta coppia di elettrodi per la generazione tra questi di una scarica elettrica, che provoca la formazione di plasma e crea le condizioni per lo sviluppo di reazioni nucleari che generano radioisotopi,
- un'induttanza complessiva del circuito elettrico equivalente di detta apparecchiatura non superiore a 50nH,
- mezzi comunicanti con detta camera da vuoto per la creazione di un vuoto non superiore a 10-6 torr,
- mezzi comunicanti con detta camera da vuoto per l'immissione in essa, dopo la creazione del vuoto, di almeno un gas di reazione ad una pressione in grado di garantire la formazione di plasma durante la fase di scarica ed il raggiungimento di condizioni di confinamento di detto plasma dell'ordine di 1015 keV. sec/cm3, e
- mezzi comunicanti con detta camera da vuoto per l'estrazione di gas
15th Workshop on European Collaboration in Higher Education on Radiological and Nuclear Engineering and Radiation Protection
No full textNo abstrac
Wave Propagation in an Ideal Gas: First and Second Sound
No full textPropagation of sound waves through an ideal gas is studied in the framework of kinetic theory, starting from the integral representation of the Boltzmann Equation (BE). The distribution function is calculated and used to obtain the dispersion relation of density waves. The parallel existence of temperature waves (in some contexts referred to as second sound) is also part of this investigation. Temperature waves are found to exist; the phase difference between density and temperature waves is determined
Computation of the Doppler-broadened scattering kernel and its Legendre moments
No full textA numerical computation of the Doppler convolution of the elastic scattering kernel based on the gas model is presented, without making assumptions on the variation of the cross section with energy and for a general scattering law in the center of mass system. The range of integration has been optimized employing a numerical cutoff, allowing for a faster numerical evaluation of the convolution integral. Legendre moments of the transfer kernel are subsequently obtained by direct quadrature and a numerical analysis of the convergence is presented
Assessing radiological hazards in building materials: a case study with a focus on the ceramic industry in Emilia-Romagna, Italy
No full textThe building materials industry encounters naturally occurring radioactive materials problems and elicits growing attention in radiation protection regulations. However, the availability of useful, comprehensive data on radiological hazard in building materials is unfortunately scant: data are few and far between. In the Italian region of Emilia-Romagna, there is a flourishing ceramic industry, with a vast production of building materials, particularly tiles and bricks. Our laboratory of Environmental
Chemistry and Radioactivity has collaborated with this industry since the year 2000, collecting over time a vast number of samples and processing them through high-resolution gamma spectrometry, to obtain a large dataset of radionuclide contents. This paper presents a radiation protection study based on said dataset, aimed at assessing the radiological risk associated with these materials: in particular, different indexes, internationally accepted, and dose rates are calculated in compliance with well-established EU algorithms. Statistical treatment of data is also presented
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