Fragment size correlations in finite systems - application to nuclear multifragmentation

We present a new method for the calculation of fragment size correlations in a discrete finite system in which correlations explicitly due to the finite extent of the system are suppressed. To this end, we introduce a combinatorial model, which describes the fragmentation of a finite system as a sequence of independent random emissions of fragments. The sequence is accepted when the sum of the sizes is equal to the total size. The parameters of the model, which may be used to calculate all partition probabilities, are the intrinsic probabilities associated with the fragments. Any fragment size correlation function can be built by calculating the ratio between the partition probabilities in the data sample (resulting from an experiment or from a Monte Carlo simulation) and the 'independent emission' model partition probabilities. This technique is applied to charge correlations introduced by Moretto and collaborators. It is shown that the percolation and the nuclear statistical multifragmentaion model ({\sc smm}) are almost independent emission models whereas the nuclear spinodal decomposition model ({\sc bob}) shows strong correlations corresponding to the break-up of the hot dilute nucleus into nearly equal size fragments

Electronic emission of radio-sensitizing gold nanoparticles under X-ray irradiation : experiment and simulations

In this paper we present new results on electronic emission of Gold Nanoparticles (GNPs) using X-ray photoelectron spectroscopy (XPS) and compare them to the gold bulk electron emission. This subject has undergone new interest within the perspective of using GNPs as a radiotherapy enhancer. The experimental results were simulated using various models (Livermore and PENELOPE) of the Geant 4 simulation toolkit dedicated to the calculation of the transportation of particles through the matter. Our results show that the GNPs coating is a key parameter to correctly construe the experimental GNPs electronic emission after X-ray irradiation and point out some limitations of the PENELOPE model. Using XPS spectra and Geant4 Livermore simulations,we propose a method to determine precisely the coating surface density of the GNPs. We also show that the expected intrinsic nano-scale electronic emission enhancement effect - suspected to contribute to the GNPs radio-sensitizing properties - participates at most for a few percent of the global electronic emission spectra of the GNPs compared to gold bulk.Comment: Journal: Journal of Nanoparticle Research Vol. 16,4 201

Probing the Concept of Statistical Independence of Intermediate-Mass Fragment Production in Heavy-Ion Collisions

It is found that the total IMF-transverse-energy (E_t) spectra in multi-IMF events are well represented by synthetic spectra obtained by folding of the single-IMF spectrum. Using the experimental IMF multiplicity distribution, the observed trends in the IMF multiplicity distribution for fixed values of E_t are reproduced. The synthetic distributions show binomial reducibility and Arrhenius-like scaling, similar to that reported in the literature. Similar results are obtained when the above folding-type synthesis is replaced with one based on mixing events with different IMF multiplicities. For statistically independent IMF emission, the observed binomial reducibility and Arrhenius-type scaling are merely reflections of the shape of the single-IMF transverse-energy spectrum. Hence, a valid interpretation of IMF distributions in terms of a particular production scenario has to explain independently the observed shape of the single-IMF E_t spectrum.Comment: 13 pages with 8 figur

Correlations in Nuclear Arrhenius-Type Plots

Arrhenius-type plots for multifragmentation process, defined as the transverse energy dependence of the single-fragment emission-probability, -ln(p_{b}) vs 1/sqrt(E_{t}), have been studied by examining the relationship of the parameters p_{b} and E_{t} to the intermediate-mass fragment multiplicity . The linearity of these plots reflects the correlation of the fragment multiplicity with the transverse energy. These plots may not provide thermal scaling information about fragment production as previously suggested.Comment: 12 pages, Latex, 3 Postscript figures include

Travelling convection vortices in the ionosphere map to the central plasma sheet

International audienceWe investigate the magnetospheric domain responsible for the generation of ionospheric travelling convection vortices (TCV) by comparing the location of the TCV to the locations of the low-altitude particle-precipitation boundaries deduced from the DMSP satellite measurements. For three very well documented TCV events we are able to identify suitable satellite passes, in the sense that for each event we can identify two to three passes occurring close to the TCV observation in both time and space. In all three cases the comparisons place the TCV centres at or equatorward of the central plasma sheet/boundary plasma sheet precipitation boundary. Thus our results indicate that the field-aligned currents related to the TCV originate in the plasma sheet rather than at the magnetopause or in the low-latitude boundary layer, as previous studies suggest