1,826 research outputs found
Fragment Formation in Central Heavy Ion Collisions at Relativistic Energies
We perform a systematic study of the fragmentation path of excited nuclear
matter in central heavy ion collisions at the intermediate energy of . The theoretical calculations are based on a Relativistic
Boltzmann-Uehling-Uhlenbeck () transport equation including stochastic
effects. A Relativistic Mean Field () approach is used, based on a
non-linear Lagrangian, with coupling constants tuned to reproduce the high
density results of calculations with correlations.
At variance with the case at Fermi energies, a new fast clusterization
mechanism is revealed in the early compression stage of the reaction dynamics.
Fragments appear directly produced from phase-space fluctuations due to
two-body correlations. In-medium effects of the elastic nucleon-nucleon cross
sections on the fragmentation dynamics are particularly discussed. The
subsequent evolution of the primordial clusters is treated using a simple
phenomenological phase space coalescence algorithm.
The reliability of the approach, formation and recognition, is investigated
in detail by comparing fragment momentum space distributions {\it and
simultaneously} their yields with recent experimental data of the
collaboration by varying the system size of the colliding system, i.e. its
compressional energy (pressure, radial flow). We find an excellent agreement
between theory and experiment in almost all the cases and, on the other hand,
some limitations of the simple coalescence model. Furthermore, the temporal
evolution of the fragment structure is explored with a clear evidence of an
earlier formation of the heavier clusters, that will appear as interesting
of the high density phase of the nuclear Equation of State ().Comment: 21 pages, 8 figures, Latex Elsart Style, minor corrections in p.7,
two refs. added, Nucl.Phys.A, accepte
Wave Speed Measurements in Non-Ideal Compressible Flows Using the Flexible Asymmetric Shock Tube (FAST)
Non-ideal compressible fluid dynamics (NICFD) are defined as compressible fluid flows occurring in the dense vapour, dense vapour-liquid equilibrium or supercritical thermodynamic region. This type of flow can occur in expanders of organic Rankine cycle power plants. In order to study NICFD, a Ludwieg tube-type facility has been designed and constructed at Delft University of Technology. A large variety of fluids can be employed in the facility, but for this study D6 siloxane is chosen as working fluid due to its high thermal stability and the possibility of encountering non-classical gasdynamic phenomena. This compound belongs to the siloxane class, which are also used as working fluids in ORC power systems. Gasdynamic experiments within the NICFD region are presented from which the wave speed and speed of sound can be inferred using the time-of-flight technique. These data can be used to improve and validate thermodynamic models
Tectonic setting of the kenya rift in the nakuru area, based on geophysical prospecting
In this paper, we present results of tectonic and geophysical investigations in the Kenya Rift valley, in the Nakuru area. We compiled a detailed geological map of the area based on published earlier works, well data and satellite imagery. The map was then integrated with original fieldwork and cross sections were constructed. In key areas, we then performed geophysical survey using Electrical Resistivity Tomography (ERT), Hybrid Source AudioMagnetoTelluric (HSAMT), and single station passive seismic measurements (HVSR). In the study area, a volcano-sedimentary succession of the Neogene-Quaternary age characterized by basalts, trachytes, pyroclastic rocks, and tephra with intercalated lacustrine and fluvial deposits crops out. Faulting linked with rift development is evident and occurs throughout the area crosscutting all rock units. We show a rotation of the extension in this portion of the Kenya rift with the NE-SW extension direction of a Neogene-Middle Pleistocene age, followed by the E-Wextension direction of anUpper Pleistocene-Present age. Geophysical investigations allowed to outline main lithostratigraphic units and tectonic features at depth and were also useful to infer main cataclasites and fractured rock bodies, the primary paths for water flow in rocks. These investigations are integrated in a larger EU H2020 Programme aimed to produce a geological and hydrogeological model of the area to develop a sustainable water management system
A new FSA approach for in situ -ray spectroscopy
An increasing demand of environmental radioactivity monitoring comes both
from the scientific community and from the society. This requires accurate,
reliable and fast response preferably from portable radiation detectors. Thanks
to recent improvements in the technology, -spectroscopy with sodium
iodide scintillators has been proved to be an excellent tool for in-situ
measurements for the identification and quantitative determination of
-ray emitting radioisotopes, reducing time and costs. Both for
geological and civil purposes not only K, U, and Th have
to be measured, but there is also a growing interest to determine the
abundances of anthropic elements, like Cs and I, which are used
to monitor the effect of nuclear accidents or other human activities.
The Full Spectrum Analysis (FSA) approach has been chosen to analyze the
-spectra. The Non Negative Least Square (NNLS) and the energy
calibration adjustment have been implemented in this method for the first time
in order to correct the intrinsic problem related with the
minimization which could lead to artifacts and non physical results in the
analysis.
A new calibration procedure has been developed for the FSA method by using in
situ -spectra instead of calibration pad spectra. Finally, the new
method has been validated by acquiring -spectra with a 10.16 cm x 10.16
cm sodium iodide detector in 80 different sites in the Ombrone basin, in
Tuscany. The results from the FSA method have been compared with the laboratory
measurements by using HPGe detectors on soil samples collected in the different
sites, showing a satisfactory agreement between them. In particular, the
Cs isotopes has been implemented in the analysis since it has been
found not negligible during the in-situ measurements.Comment: accepted by Science of Total Environment: 8 pages, 10 figures, 3
table
Correlations between isospin dynamics and Intermediate Mass Fragments emission time scales: a probe for the symmetry energy in asymmetric nuclear matter
We show new data from the Ni+Sn and Ni+Sn
reactions studied in direct kinematics with the CHIMERA detector at INFN-LNS
and compared with the reverse kinematics reactions at the same incident beam
energy (35 A MeV). Analyzing the data with the method of relative velocity
correlations, fragments coming from statistical decay of an excited
projectile-like (PLF) or target-like (TLF) fragments are discriminated from the
ones coming from dynamical emission in the early stages of the reaction. By
comparing data of the reverse kinematics experiment with a stochastic mean
field (SMF) + GEMINI calculations our results show that observables from neck
fragmentation mechanism add valuable constraints on the density dependence of
symmetry energy. An indication is found for a moderately stiff symmetry energy
potential term of EOS.Comment: Talk given by E. De Filippo at the 11th International Conference on
Nucleus-Nucleus Collisions (NN2012), San Antonio, Texas, USA, May 27-June 1,
2012. To appear in the NN2012 Proceedings in Journal of Physics: Conference
Series (JPCS
Preliminary results for the characterization of the radiological levels of rocks in Tuscany Region.
The environmental background levels of natural
radiation due to the nuclides in rocks vary in significant
amounts that depend on the geological and geomorphological
features of a territory. The main source of terrestrial
gamma-ray radiation exposure to humans is from 238U,
232Th decay chains and 40K decay.
This paper reports a part of the results of the Research
Project “Measurement of natural radioactivity and
mapping of the radioisotope abundances of Tuscany
Region”, which started at August 2008 and it is supported
by founds of Tuscany Region. The aim of this project is to
realize the thematic maps of radioactivity content and in
particular of the abundances of eU1, eTh1 and 40K. These
goals will be achieved by integrating the information from
measurements on samples in laboratory with in-situ
investigations and airborne surveys. The Legnaro National
Laboratory (LNL) is the national leader for the design and
realization of high-resolution gamma-ray spectrometers,
portable and massive NaI(Tl) detectors.
The MCA_Rad gamma-ray spectrometry system was
designed and built up at LNL for measuring large amount
of samples with a minimum attendance: these features fit
perfectly with the requirements of this project. This system
is able to measure any type of materials (solid, liquid, gas),
and due to the high efficiency and its geometric symmetry,
absolute activity measurements are possible with systematic
errors below 5%. http://www.fe.infn.it/u/mantovani/CV/Proceedings/Bezzon_10b.pd
Analisi dei cambiamenti di uso del suolo nell’area montuosa e collinare dell’Emilia-Romagna nel periodo 1954-1994
Lo scopo di questo studio è stato la realizzazione di una banca dati multitemporale di uso del suolo per i territori montuosi e collinari della Regione Emilia-Romagna, relativa al periodo 1954-1994. Tale banca dati riporta gli attributi relativi all’uso del suolo del 1954-55 e 1994 e consente di analizzare i cambiamenti di estensione, tipologia e localizzazione delle classi di uso del suolo. I dati più recenti sono quelli relativi alla banca dati vettoriale di uso del suolo del 1994 già pubblicata
dalla Regione Emilia-Romagna. I dati del 1954 sono stati ottenuti dall’interpretazione e delineazione visuale di ortofoto ottenute da foto aeree pancromatiche del volo G.A.I. del 1954- 1955. È stata utilizzata una nomenclatura di uso del suolo a priori gerarchica a due livelli comparabile con quella della banca dati del 1994. I risultati dimostrano che in quaranta anni, l’area indagata ha subito una significativa evoluzione di uso del suolo. Le aree a seminativo ed a foresta sono aumentate, a scapito delle aree a coltivazione parcellizzata e specializzata e di cespuglieto
Preliminary results for the characterization of the radiological levels of rocks in Tuscany Region
http://www.fe.infn.it/u/mantovani/CV/Proceedings/Bezzon_10a.pd
Investigation of Zero-Sound Dispersion Equation in the Complex Plane of Frequency
The known solutions to the zero-sound dispersion equation are considered as
placed on the physical and unphysical sheets in the complex plane of frequency.Comment: 15 pages, 7 figure
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