3,861 research outputs found
On the mass formula and Wigner and curvature energy terms
The efficiency of different mass formulas derived from the liquid drop model
including or not the curvature energy, the Wigner term and different powers of
the relative neutron excess has been determined by a least square fitting
procedure to the experimental atomic masses assuming a constant
R/A ratio. The Wigner term and the curvature energy can be
used independently to improve the accuracy of the mass formula. The different
fits lead to a surface energy coefficient of around 17-18 MeV, a relative sharp
charge radius r of 1.22-1.23 fm and a proton form-factor correction to the
Coulomb energy of around 0.9 MeV
On the double and triple-humped fission barriers and half-lives of actinide elements
The deformation barriers standing in the quasi-molecular shape path have been
determined in the actinide region within a macroscopic-microscopic energy
derived from a generalized liquid drop model, the algebraic droplet model shell
corrections and analytic expressions for the pairing energies. Double and
triple-humped fission barriers appear. The second barrier corresponds to the
transition from one-body shapes to two touching ellipsoids. The third minimum
and third peak, when they exist, come from shell rearrangements in the deformed
fragment. The shape of the other almost magic one is close to the sphere. The
barrier heights agreewith the experimental results, the energy of the second
minimum being a little too high. The predicted half-lives follow the
experimental data trend
Ternary cluster decay within the liquid drop model
Longitudinal ternary and binary fission barriers of Ar, Ni and
Cf nuclei have been determined within a rotational liquid drop model
taking into account the nuclear proximity energy. For the light nuclei the
heights of the ternary fission barriers become competitive with the binary ones
at high angular momenta since the maximum lies at an outer position and has a
much higher moment of inertia.Comment: Talk presented at the 9th International Conference on Clustering
Aspects of Nuclear Structure and Dynamics (CLUSTERS'07
Coefficients and terms of the liquid drop model and mass formula
The coefficients of different combinations of terms of the liquid drop model
have been determined by a least square fitting procedure to the experimental
atomic masses. The nuclear masses can also be reproduced using a Coulomb radius
taking into account the increase of the ratio with increasing
mass, the fitted surface energy coefficient remaining around 18 MeV
On the coefficients of the liquid drop model mass formulae and nuclear radii
The coefficients of different mass formulae derived from the liquid drop
model and including or not the curvature energy, the diffuseness correction to
the Coulomb energy, the charge exchange correction term, different forms of the
Wigner term and different powers of the relative neutron excess
have been determined by a least square fitting procedure to 2027 experimental
atomic masses. The Coulomb diffuseness correction term or the charge
exchange correction term plays the main role to improve the
accuracy of the mass formula. The Wigner term and the curvature energy can also
be used separately for the same purpose. The introduction of an
dependence in the surface and volume energies improves slightly the efficiency
of the expansion and is more effective than an dependence. Different
expressions reproducing the experimental nuclear charge radius are provided.
The different fits lead to a surface energy coefficient of around 17-18 MeV and
a relative equivalent rms charge radius r of 1.22-1.23 fm.Comment: 19 pages, 1 figure, accepted for publication in Nuclear Physics
Spontaneous fission half-lives of heavy and superheavy nuclei within a generalized liquid drop model
We systematically calculate the spontaneous fission half-lives for heavy and
superheavy nuclei between U and Fl isotopes. The spontaneous fission process is
studied within the semi-empirical WKB approximation. The potential barrier is
obtained using a generalized liquid drop model, taking into account the nuclear
proximity, the mass asymmetry, the phenomenological pairing correction, and the
microscopic shell correction. Macroscopic inertial-mass function has been
employed for the calculation of the fission half-life. The results reproduce
rather well the experimental data. Relatively long half-lives are predicted for
many unknown nuclei, sufficient to detect them if synthesized in a laboratory.Comment: 20 pages, 5 figures, 2 tables, accepted version by Nucl. Phys.
Compact star clusters of the LMC HII region N11C
Based on imaging and spectroscopy obtained at the ESO NTT telescope and using
an efficient image analysis algorithm, we study the core of the LMC OB
association LH13, particularly the two compact stellar clusters Sk-6641 and HNT
in the HII, region N11C. We resolve Sk-6641 into 15 components and for the
first time the HNT cluster into 70 stars, and derive photometry for the
members. Moreover, from medium resolution spectroscopy we determine the
spectral types for sixteen stars in N11C. We compare the color-magnitude
diagrams of the clusters with that of the field stars and discuss the cluster
ages. With an age of ~100 Myr, the HNT cluster appears significantly older than
the very young (< 5 Myr) Sk-6641 starburst. We suggest that most of the `field'
O-stars in the core of N11C have actually been ejected from Sk-6641 through
dynamical interactions in the compact cluster. The properties of the Sk-6641
and HNT clusters suggest that we are viewing different star formation regions
lying at different distances along the same line of sight.Comment: 12 pages, 8 figure
Charm and Beauty in Particle Physics
The spectra of states containing charmed and beauty quarks, and their
regularities, are reviewed.Comment: 29 pages, LaTeX, 10 EPSF figures submitted separately. Presented at
CERN in September, 1994 at a symposium in honor of Andre Martin To be
submitted to Comments on Nuclear and Particle Physic
The atypical emission-line star Hen3-209
We analyse observations, spanning 15 years, dedicated to the extreme
emission-line object Hen3-209. Our photometric data indicate that the
luminosity of the star undergoes marked variations with a peak-to-peak
amplitude of 0.65mag. These variations are recurrent, with a period of
16.093+-0.005d. The spectrum of Hen3-209 is peculiar with many different lines
(HI, HeI, FeII,...) showing P Cygni profiles. The line profiles are apparently
changing in harmony with the photometry. The spectrum also contains [OIII]
lines that display a saddle profile topped by three peaks, with a maximum
separation of about 600km/s. Hen3-209 is most likely an evolved luminous object
suffering from mass ejection events and maybe belonging to a binary system.Comment: 6p, 5 fig, accepted for publication in MNRAS
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