128 research outputs found
Nonextensive Interpretation Of Radiative Recombination In Electron Cooling
An interest for the low-energy range of the nonextensive distribution
function arises from the study of radiative recombination in electron cooling
devices in particle accelerators, whose experimentally measured reaction rates
are much above the theoretical prediction. The use of generalized
distributions, that differ from the Maxwellian in the low energy part (due to
subdiffusion between electron and ion bunches), may account for the observed
rate enhancement. In this work, we consider the isotropic distribution function
and we propose a possible experiment for verifying the existence of a cut-off
in the generalized momentum distribution, by measuring the spectrum of the
X-rays emitted from radiative recombination reactions.Comment: 8 pages, 2 figures, Submitted for publication in the Proceedings of
the 3rd International Conference NEXT-SigmaPhi, 2005, Cret
Temperature dependence of modified CNO nuclear reaction rates in dense stellar plasmas
We study the dependence of the CNO nuclear reaction rates on temperature, in
the range of K, the typical range of temperature evolution from
a Sun-like star towards a white dwarf. We show that the temperature dependence
of the CNO nuclear reaction rates is strongly affected by the presence of
non-extensive statistical effects in the dense stellar core. A very small
deviation from the Maxwell-Boltzmann particle distribution implies a relevant
enhancement of the CNO reaction rate and could explain the presence of heavier
elements (e.g. Fe, Mg) in the final composition of a white dwarf core. Such a
behavior is consistent with the recent experimental upper limit to the fraction
of energy that the Sun produces via the CNO fusion cycle.Comment: Presented at NEXT2003 (Second International Conference on "News and
Expectations in Thermostatistics"), Villasimius (Cagliari)- Italy in 21-28
September 2003. 7 pages including 3 figure
Modified Debye-Huckel Electron Shielding and Penetration Factor
Screened potential, modified by non standard electron cloud distributions
responsible for the shielding effect on fusion of reacting nuclei in
astrophysical plasmas, is derived. The case of clouds with depleted tails in
space coordinates is discussed. The modified screened potential is obtained
both from statistical mechanics arguments based on fluctuations of the inverse
of the Debye-Huckel radius and from the solution of a Bernoulli equation used
in generalized statistical mechanics. Plots and tables useful in evaluating
penetration probability at any energy are provided.Comment: 9 pages, 3 figures, 3 table
Metastable and stable equilibrium states of stellar electron-nuclear plasmas
By minimizing free energy density, we show that the stellar core of a
hydrogen burning star is not in a global thermodynamical equilibrium unless
density, temperature, mass and composition assume given values. The core (as
the solar interior) may be viewed more appropriately as a metastable state with
very long lifetime. Slightly non-extensive distribution function could be the
natural distribution for a weakly non-ideal plasma like a stellar core and
represents a more appropriate approximation to this system than a Maxwellian
distribution, without affecting bulk properties of stars.Comment: 14 pages, to appear in Phys. Lett.
An inexpensive spectroscopic beam monitor for hard X-ray synchrotron applications
We describe an inexpensive beam monitor for hard X-ray synchrotron applications which has good spectroscopic abilities and can operate without cooling. The device is centred on an inexpensive, commercial off-the-shelf, large area (1.2 Ă— 1.2 mm2) Si photodiode operated in single counting mode. Measurements carried out at the HASYLAB synchrotron research facility have shown that it is fully spectroscopic across the energy range 8 keV to 100 keV with a measured energy resolution of ~ 1.2 keV FWHM at room temperature. The measured resolutions were found to be the same under pencil-beam and full-area illumination, indicating uniform crystallinity and stoichiometry of the bulk. The low cost, simplicity and performance of the detector make it suitable for a wider range of applications, e.g., in undergraduate laboratory experiments
Characterization of Large Volume 3.5 x 8 inches LaBr3:Ce Detectors
The properties of large volume cylindrical 3.5 x 8 inches (89 mm x 203 mm)
LaBr3:Ce scintillation detectors coupled to the Hamamatsu R10233-100SEL
photo-multiplier tube were investigated. These crystals are among the largest
ones ever produced and still need to be fully characterized to determine how
these detectors can be utilized and in which applications. We tested the
detectors using monochromatic gamma-ray sources and in-beam reactions producing
gamma rays up to 22.6 MeV; we acquired PMT signal pulses and calculated
detector energy resolution and response linearity as a function of gamma-ray
energy. Two different voltage dividers were coupled to the Hamamatsu
R10233-100SEL PMT: the Hamamatsu E1198-26, based on straightforward resistive
network design, and the LABRVD, specifically designed for our large volume
LaBr3:Ce scintillation detectors, which also includes active semiconductor
devices. Because of the extremely high light yield of LaBr3:Ce crystals we
observed that, depending on the choice of PMT, voltage divider and applied
voltage, some significant deviation from the ideally proportional response of
the detector and some pulse shape deformation appear. In addition, crystal
non-homogeneities and PMT gain drifts affect the (measured) energy resolution
especially in case of high-energy gamma rays. We also measured the time
resolution of detectors with different sizes (from 1x1 inches up to 3.5x8
inches), correlating the results with both the intrinsic properties of PMTs and
GEANT simulations of the scintillation light collection process. The detector
absolute full energy efficiency was measured and simulated up to gamma-rays of
30 Me
- …