2,964 research outputs found
Calculation of the number of partitions with constraints on the fragment size
This article introduces recursive relations allowing the calculation of the
number of partitions with constraints on the minimum and/or on the maximum
fragment size
Resilient Reducibility in Nuclear Multifragmentation
The resilience to averaging over an initial energy distribution of
reducibility and thermal scaling observed in nuclear multifragmentation is
studied. Poissonian reducibility and the associated thermal scaling of the mean
are shown to be robust. Binomial reducibility and thermal scaling of the
elementary probability are robust under a broad range of conditions. The
experimental data do not show any indication of deviation due to averaging.Comment: 5 pages, 6 figures, submitted to Physical Review
Z-dependent Barriers in Multifragmentation from Poissonian Reducibility and Thermal Scaling
We explore the natural limit of binomial reducibility in nuclear
multifragmentation by constructing excitation functions for intermediate mass
fragments (IMF) of a given element Z. The resulting multiplicity distributions
for each window of transverse energy are Poissonian. Thermal scaling is
observed in the linear Arrhenius plots made from the average multiplicity of
each element. ``Emission barriers'' are extracted from the slopes of the
Arrhenius plots and their possible origin is discussed.Comment: 15 pages including 4 .ps figures. Submitted to Phys. Rev. Letters.
Also available at http://csa5.lbl.gov/moretto
The Role of Phase Space in Complex Fragment Emission from Low to Intermediate Energies
The experimental emission probabilities of complex fragments by low energy
compound nuclei and their dependence upon energy and atomic number are compared
to the transition state rates. Intermediate-mass-fragment multiplicity
distributions for a variety of reactions at intermediate energies are shown to
be binomial and thus reducible at all measured transverse energies. From these
distributions a single binary event probability can be extracted which has a
thermal dependence. A strong thermal signature is also found in the charge
distributions. The n-fold charge distributions are reducible to the 1-fold
charge distributions through a simple scaling dictated by fold number and
charge conservation.Comment: 15 pages, TeX type, psfig, also available at
http://csa5.lbl.gov/moretto/ps/brazil.ps, to appear in Proceedings of the 1st
International Conference on Nuclear Dynamics at Long and Short Distances,
April 8-12, 1996, Angra dos Reis, Brazi
The complement: a solution to liquid drop finite size effects in phase transitions
The effects of the finite size of a liquid drop undergoing a phase transition
are described in terms of the complement, the largest (but still mesoscopic)
drop representing the liquid in equilibrium with the vapor. Vapor cluster
concentrations, pressure and density from fixed mean density lattice gas
(Ising) model calculations are explained in terms of the complement. Accounting
for this finite size effect is key to determining the infinite nuclear matter
phase diagram from experimental data.Comment: Four two column pages, four figures, two tables; accepted for
publication in PR
Laser-induced electron emission from a tungsten nanotip: identifying above threshold photoemission using energy-resolved laser power dependencies
We present an experiment studying the interaction of a strongly focused 25 fs
laser pulse with a tungsten nanotip, investigating the different regimes of
laser-induced electron emission. We study the dependence of the electron yield
with respect to the static electric field applied to the tip. Photoelectron
spectra are recorded using a retarding field spectrometer and peaks separated
by the photon energy are observed with a 45 % contrast. They are a clear
signature of above threshold photoemission (ATP), and are confirmed by
extensive spectrally resolved studies of the laser power dependence.
Understanding these mechanisms opens the route to control experiment in the
strong-field regime on nanoscale objects.Comment: 9 pages, 6 figure
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
Simulation of cellular irradiation with the CENBG microbeam line using GEANT4
Light-ion microbeams provide a unique opportunity to irradiate biological
samples at the cellular level and to investigate radiobiological effects at low
doses of high LET ionising radiation. Since 1998 a single-ion irradiation
facility has been developed on the focused horizontal microbeam line of the
CENBG 3.5 MV Van de Graaff accelerator. This setup delivers in air single
protons and alpha particles of a few MeV onto cultured cells, with a spatial
resolution of a few microns, allowing subcellular targeting. In this paper, we
present results from the use of the GEANT4 toolkit to simulate cellular
irradiation with the CENBG microbeam line, from the entrance to the microprobe
up to the cellular medium.Comment: 6 pages, 8 figures, presented at the 2003 IEEE-NSS conference,
Portland, OR, USA, October 20-24, 200
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