3,284 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
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
New Wrinkles on an Old Model: Correlation Between Liquid Drop Parameters and Curvature Term
The relationship between the volume and surface energy coefficients in the
liquid drop A^{-1/3} expansion of nuclear masses is discussed. The volume and
surface coefficients in the liquid drop expansion share the same physical
origin and their physical connection is used to extend the expansion with a
curvature term. A possible generalization of the Wigner term is also suggested.
This connection between coefficients is used to fit the experimental nuclear
masses. The excellent fit obtained with a smaller number of parameters
validates the assumed physical connection.Comment: 6 pages, 2 figure
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
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A Statistical Treatment of Angular Momentum Fractionation in Heavy Ion Reactions
Scaling Laws and Transient Times in 3He Induced Nuclear Fission
Fission excitation functions of compound nuclei in a mass region where shell
effects are expected to be very strong are shown to scale exactly according to
the transition state prediction once these shell effects are accounted for. The
fact that no deviations from the transition state method have been observed
within the experimentally investigated excitation energy regime allows one to
assign an upper limit for the transient time of 10 zs.Comment: 7 pages, TeX type, psfig, submitted to Phys. Rev. C, also available
at http://csa5.lbl.gov/moretto/ps/he3_paper.p
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
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