2,481 research outputs found
Gamow-Teller strength distributions for double-beta-decaying nuclei within continuum-QRPA
A version of the pn-continuum-QRPA is outlined and applied to describe the
Gamow-Teller strength distributions for -decaying open-shell
nuclei. The calculation results obtained for the pairs of nuclei Cd-Sn
and Te-Xe are compared with available experimental data.Comment: 8 pages, 3 figures, To appear in the proceedings of "Nucleus-2007:
Fundamental problems of nuclear physics, atomic power engineering and nuclear
technologies" Voronezh, Russia, June 25-29, 200
Charge-exchange reaction cross sections and the Gamow-Teller strength for double beta decay
The proportionality between single charge-exchange reaction cross sections in
the forward direction as found, for example from and He, and
from and He) reactions, and the Gamow-Teller (GT) strength into
the same final nuclear states has been studied and/or assumed often in the
past. Using the most physically justified theory we have at our disposal and
for the specific example of the Ge-Se system that may undergo
double beta-decay, we demonstrate that the proportionality is a relative good
assumption for reactions changing a neutron into a proton, i.e.
GeAs. In this channel, the main contribution to the GT
strengths comes from the removal of a neutron from an occupied single-particle
(SP) state and putting a proton into an unoccupied SP state having either the
same state quantum numbers or those of the spin-orbit partner. In contrast to
this, in the second leg of the double beta decay a single proton must be taken
from an occupied SP state and a neutron placed in an unoccupied one. This
second process often is Pauli forbidden in medium-heavy nuclei and only can be
effected if the Fermi surface is smeared out. Such is the case for
SeAs. Our results suggest that one may not always assume
a proportionality between the forward-angle cross sections of the
charge-exchange reactions and the GT strength in any such medium-heavy nuclei.
The discrepancy originates from a pronounced effect of the radial dependence of
the nucleon-nucleon () interaction in connection with the Pauli principle
on the cross sections in the reaction channel. Such a radial dependence
is completely absent in the GT transition operator.Comment: 14 p., 7 fig
Uncertainty in the 0νββ decay nuclear matrix elements
The nuclear matrix elements M0nu of the neutrinoless double-beta decay (0nubetabeta) are evaluated for 76Ge,100Mo,130Te, and 136Xe within the renormalized quasiparticle random phase approximation (RQRPA) and the simple QRPA. Three sets of single particle level schemes are used, ranging in size from 9 to 23 orbits. When the strength of the particle-particle interaction is adjusted so that the 2nubetabeta decay rate is correctly reproduced, the resulting M0nu values become essentially independent of the size of the basis, and of the form of different realistic nucleon-nucleon potentials. Thus, one of the main reasons for variability of the calculated M0nu within these methods is eliminated
Seasonal Water "Pump" in the Atmosphere of Mars: Vertical Transport to the Thermosphere
We present results of simulations with the Max Planck Institute general
circulation model (MPI-MGCM) implementing a hydrological cycle scheme. The
simulations reveal a seasonal water "pump" mechanism responsible for the upward
transport of water vapor. This mechanism occurs in high latitudes above
60 of the southern hemisphere at perihelion, when the upward branch of
the meridional circulation is particularly strong. A combination of the mean
vertical flux with variations induced by solar tides facilitates penetration of
water across the "bottleneck" at approximately 60 km. The meridional
circulation then transports water across the globe to the northern hemisphere.
Since the intensity of the meridional cell is tightly controlled by airborne
dust, the water abundance in the thermosphere strongly increases during dust
storms.Comment: 15 pages, 4 figure
On the nuclear symmetry energy and the neutron skin in neutron-rich nuclei
The symmetry energy for nuclear matter and its relation to the neutron skin
in finite nuclei is discussed. The symmetry energy as a function of density
obtained in a self-consistent Green function approach is presented and compared
to the results of other recent theoretical approaches. A partial explanation of
the linear relation between the symmetry energy and the neutron skin is
proposed. The potential of several experimental methods to extract the neutron
skin is examined.Comment: to appear in Phys. Rev.
Double Beta Decay, Nuclear Structure and Physics beyond the Standard Model
Neutrinoless Double Beta Decay () is presently the only known
experiment to distinguisch between Dirac neutrinos, different from their
antiparticles, and Majorana neutrinos, identical with their antiparticles. In
addition allows to determine the absolute scale of the
neutrino masses. This is not possible with neutrino oscillations. To determine
the neutrino masses one must assume, that the light Majorana neutrino exchange
is the leading mechanism for and that the matrix element of
this transition can ba calculated reliably. The experimental
transition amplitude in this mechanism is a product of the light left handed
effective Majorana neutrino mass and of this transition matrix element. The
different methods, Quasi-particle Random Phase Approximation (QRPA), Shell
Model (SM), Projected Hartree-Fock-Bogoliubov (PHFB) and Interacting Boson
Model (IBM2) used in the literature and the reliability of the matrix elements
in these approaches are reviewed. In the second part it is investigated how one
can determine the leading mechanism or mechanisms from the data of the
decay in different nuclei. Explicite expressions are given for
the transition matrix elements. is shown, that possible interference terms
allow to test CP (Charge and Parity conjugation) violation.Comment: Contribution to the EPS conference in Eilath: "Nuclear Physics in
Astrophysics 5." April 3rd to 8th. 201
Search for a massless dark photon in Λc+ →pγ′ decay
A search for a massless dark photon γ′ is conducted using 4.5 fb-1 of e+e- collision data collected at center-of-mass energies between 4.600 and 4.699 GeV with the BESIII detector at BEPCII. No significant signal is observed, and the upper limit on the branching fraction B(Λc+→pγ′) is determined to be 8.0×10-5 at 90% confidence level
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