322 research outputs found
0.5V 3rd-order Tunable gm-C Filter
This paper proposes a 3rd-order gm-C filter that operates with the extremely low voltage supply of 0.5V. The employed transconductor is capable for operating in an extremely low voltage power supply environment. A benefit offered by the employed transconductor is that the filter’s cut-off frequency can be tuned, through a dc control current, for relatively large ranges. The filter structure was designed using normal threshold transistors of a triple-well 0.13μm CMOS process and is operated under a 0.5V supply voltage; its behavior has been evaluated through simulation results by utilizing the Analog Design Environment of the Cadence software
Neutron-rich rare isotope production from projectile fission of heavy beams in the energy range of 20 MeV/nucleon
We investigate the possibilities of producing neutron-rich nuclides in
projectile fission of heavy beams in the energy range of 20 MeV/nucleon
expected from low-energy facilities. We report our efforts to theoretically
describe the reaction mechanism of projectile fission following a multinucleon
transfer collision at this energy range. Our calculations are mainly based on a
two-step approach: the dynamical stage of the collision is described with
either the phenomenological Deep-Inelastic Transfer model (DIT), or with the
microscopic Constrained Molecular Dynamics model (CoMD). The
deexcitation/fission of the hot heavy projectile fragments is performed with
the Statistical Mul- tifragmentation Model (SMM). We compared our model
calculations with our previous experimental projectile-fission data of 238U (20
MeV/nucleon)+208Pb and 197Au (20 MeV/nucleon)+197Au and found an overall
reasonable agreement. Our study suggests that projectile fission following
periph- eral heavy-ion collisions at this energy range offers an effective
route to access very neutron-rich rare isotopes toward and beyond the
astrophysical r-process path
Enhanced Production of Neutron-Rich Rare Isotopes in Peripheral Collisions at Fermi Energies
A large enhancement in the production of neutron-rich projectile residues is
observed in the reactions of a 25 MeV/nucleon 86Kr beam with the neutron rich
124Sn and 64Ni targets relative to the predictions of the EPAX parametrization
of high-energy fragmentation, as well as relative to the reaction with the less
neutron-rich 112Sn target. The data demonstrate the significant effect of the
target neutron-to-proton ratio (N/Z) in peripheral collisions at Fermi
energies. A hybrid model based on a deep-inelastic transfer code (DIT) followed
by a statistical de-excitation code appears to account for part of the observed
large cross sections. The DIT simulation indicates that the production of the
neutron-rich nuclides in these reactions is associated with peripheral nucleon
exchange. In such peripheral encounters, the neutron skins of the neutron-rich
124Sn and 64Ni target nuclei may play an important role. From a practical
viewpoint, such reactions between massive neutron-rich nuclei offer a novel and
attractive synthetic avenue to access extremely neutron-rich rare isotopes
towards the neutron-drip line.Comment: 4 pages, 3 figures, submitted to Phys. Rev. Let
Symmetry energy and the isoscaling properties of the fragments produced in Ar, Ca + Fe, Ni reactions at 25 53 MeV/nucleon
The symmetry energy and the isoscaling properties of the fragments produced
in the multifragmentation of Ar, Ca + Fe, Ni
reactions at 25 - 53 MeV/nucleon were investigated within the framework of
statistical multifragmentation model. The isoscaling parameters , from
the primary (hot) and secondary (cold) fragment yield distributions, were
studied as a function of excitation energy, isospin (neutron-to-proton
asymmetry) and fragment symmetry energy. It is observed that the isoscaling
parameter decreases with increasing excitation energy and decreasing
symmetry energy. The parameter is also observed to increase with
increasing difference in the isospin of the fragmenting system. The sequential
decay of the primary fragments into secondary fragments, when studied as a
function of excitation energy and isospin of the fragmenting system, show very
little influence on the isoscaling parameter. The symmetry energy however, has
a strong influence on the isospin properties of the hot fragments. The
experimentally observed scaling parameters can be explained by symmetry energy
that is significantly lower than that for the ground state nuclei near
saturation density. The results indicate that the properties of hot nuclei at
excitation energies, densities and isospin away from the normal ground state
nuclei could be significantly different.Comment: 14 pages, 15 figure
Recent progress constraining the nuclear equation of state from astrophysics and heavy ion reactions
The quest for the nuclear equation of state (EoS) at high densities and/or
extreme isospin is one of the longstanding problems of nuclear physics. Ab
initio calculations for the nuclear many-body problem make predictions for the
density and isospin dependence of the EoS far away from the saturation point of
nuclear matter. On the other hand, in recent years substantial progress has
been mode to constrain the EoS both, from the astrophysical side and from
accelerator based experiments. Heavy ion experiments support a soft EoS at
moderate densities while recent neutron star observations require a ``stiff''
high density behavior. Both constraints are discussed and shown to be in
agreement with the predictions from many-body theory.Comment: Invited talk given at NPA III, Dresden, Germany, March 200
Nuclear expansion and symmetry energy of hot nuclei
The decrease in the symmetry energy of hot nuclei populated in Ni +
Ni, Fe + Ni and Fe + Fe reactions at beam
energies of 30, 40, and 47 MeV/nucleon, as a function of excitation energy is
studied. It is observed that this decrease is mainly a consequence of
increasing expansion or decreasing density rather than the increasing
temperature. The results are in good agreement with the recently reported
microscopic calculation based on the Thomas-Fermi approach. An empirical
relation to study the symmetry energy of finite nuclei in various mass region
is proposed.Comment: 10 pages, 2 figure
Analysis of fragment yield ratios in the nuclear phase transition
The critical phenomena of the liquid-gas phase transition has been
investigated in the reactions 78,86Kr+58,64Ni at beam energy of 35 MeV/nucleon
using the Landau free energy approach with isospin asymmetry as an order
parameter. Fits to the free energy of fragments showed three minima suggesting
the system to be in the regime of a first order phase transition. The relation
m =-{\partial}F/{\partial}H, which defines the order parameter and its
conjugate field H, has been experimentally verified from the linear dependence
of the mirror nuclei yield ratio data, on the isospin asymmetry of the source.
The slope parameter, which is a measure of the distance from a critical
temperature, showed a systematic decrease with increasing excitation energy of
the source. Within the framework of the Landau free energy approach, isoscaling
provided similar results as obtained from the analysis of mirror nuclei yield
ratio data. We show that the external field is primarily related to the minimum
of the free energy, which implies a modification of the source concentration
\Delta used in isospin studies
Neutron to proton ratios of quasiprojectile and midrapidity emission in the Zn + Zn reaction at 45 MeV/nucleon
Simultaneous measurement of both neutrons and charged particles emitted in
the reaction Zn + Zn at 45 MeV/nucleon allows comparison of the
neutron to proton ratio at midrapidity with that at projectile rapidity. The
evolution of N/Z in both rapidity regimes with increasing centrality is
examined. For the completely re-constructed midrapidity material one finds that
the neutron-to-proton ratio is above that of the overall Zn + Zn
system. In contrast, the re-constructed ratio for the quasiprojectile is below
that of the overall system. This difference provides the most complete evidence
to date of neutron enrichment of midrapidity nuclear matter at the expense of
the quasiprojectile
- …