6,361 research outputs found
Three-nucleon forces and spectroscopy of neutron-rich calcium isotopes
We study excited-state properties of neutron-rich calcium isotopes based on
chiral two- and three-nucleon interactions. We first discuss the details of our
many-body framework, investigate convergence properties, and for two-nucleon
interactions benchmark against coupled-cluster calculations. We then focus on
the spectroscopy of 47-56Ca, finding that with both 3N forces and an extended
pfg9/2 valence space, we obtain a good level of agreement with experiment. We
also study electromagnetic transitions and find that experimental data are well
described by our calculations. In addition, we provide predictions for
unexplored properties of neutron-rich calcium isotopes.Comment: 15 pages, 22 figures, published versio
Exploring sd-shell nuclei from two- and three-nucleon interactions with realistic saturation properties
We study ground- and excited-state properties of all sd-shell nuclei with
neutron and proton numbers 8 <= N,Z <= 20, based on a set of low-resolution
two- and three-nucleon interactions that predict realistic saturation
properties of nuclear matter. We focus on estimating the theoretical
uncertainties due to variation of the resolution scale, the low-energy
couplings, as well as from the many-body method. The experimental two-neutron
and two-proton separation energies are reasonably well reproduced, with an
uncertainty range of about 5 MeV. The first excited 2+ energies also show
overall agreement, with a more narrow uncertainty range of about 500 keV. In
most cases, this range is dominated by the uncertainties in the Hamiltonian.Comment: 6 pages, 4 figure
Saturation with chiral interactions and consequences for finite nuclei
We explore the impact of nuclear matter saturation on the properties and
systematics of finite nuclei across the nuclear chart. Using the ab initio
in-medium similarity renormalization group (IM-SRG), we study ground-state
energies and charge radii of closed-shell nuclei from He to Ni,
based on a set of low-resolution two- and three-nucleon interactions that
predict realistic saturation properties. We first investigate in detail the
convergence properties of these Hamiltonians with respect to model-space
truncations for both two- and three-body interactions. We find one particular
interaction that reproduces well the ground-state energies of all closed-shell
nuclei studied. As expected from their saturation points relative to this
interaction, the other Hamiltonians underbind nuclei, but lead to a remarkably
similar systematics of ground-state energies. Extending our calculations to
complete isotopic chains in the and shells with the valence-space
IM-SRG, the same interaction reproduces not only experimental ground states but
two-neutron-separation energies and first excited states. We also
calculate radii with the valence-space IM-SRG for the first time. Since this
particular interaction saturates at too high density, charge radii are still
too small compared with experiment. Except for this underprediction, the radii
systematics is, however, well reproduced. Our results highlight the importance
of nuclear matter as a theoretical benchmark for the development of
next-generation chiral interactions.Comment: 11 pages, 15 figures, 1 tabl
Structure of the lightest tin isotopes
We link the structure of nuclei around Sn, the heaviest doubly magic
nucleus with equal neutron and proton numbers (), to nucleon-nucleon
() and three-nucleon () forces constrained by data of few-nucleon
systems. Our results indicate that Sn is doubly magic, and we predict
its quadrupole collectivity. We present precise computations of Sn
based on three-particle--two-hole excitations of Sn, and reproduce the
small splitting between the lowest and states. Our
results are consistent with the sparse available data.Comment: 8 pages, 4 figure
The potential and challenges of monitoring-supported energy efficiency improvement strategies in existing buildings
The ongoing EU-supported CAMPUS 21 explores the energy efficiency potential of integrated security, control, and building management software. The main objective of the project is to compare the energy and indoor-environmental performance of a number of existing facilities before and after real or virtual implementation of monitoring-based control improvement measures
Construction and Performance of a Micro-Pattern Stereo Detector with Two Gas Electron Multipliers
The construction of a micro-pattern gas detector of dimensions 40x10 cm**2 is
described. Two gas electron multiplier foils (GEM) provide the internal
amplification stages. A two-layer readout structure was used, manufactured in
the same technology as the GEM foils. The strips of each layer cross at an
effective crossing angle of 6.7 degrees and have a 406 um pitch. The
performance of the detector has been evaluated in a muon beam at CERN using a
silicon telescope as reference system. The position resolutions of two
orthogonal coordinates are measured to be 50 um and 1 mm, respectively. The
muon detection efficiency for two-dimensional space points reaches 96%.Comment: 21 pages, 17 figure
Ground-State Electromagnetic Moments of Calcium Isotopes
High-resolution bunched-beam collinear laser spectroscopy was used to measure
the optical hyperfine spectra of the Ca isotopes. The ground state
magnetic moments of Ca and quadrupole moments of Ca were
measured for the first time, and the Ca ground state spin was
determined in a model-independent way. Our results provide a critical test of
modern nuclear theories based on shell-model calculations using
phenomenological as well as microscopic interactions. The results for the
neutron-rich isotopes are in excellent agreement with predictions using
interactions derived from chiral effective field theory including three-nucleon
forces, while lighter isotopes illustrate the presence of particle-hole
excitations of the Ca core in their ground state.Comment: Accepted as a Rapid Communication in Physical Review
Breakdown of the Isobaric Multiplet Mass Equation for the A = 20 and 21 Multiplets
Using the Penning trap mass spectrometer TITAN, we performed the first direct
mass measurements of 20,21Mg, isotopes that are the most proton-rich members of
the A = 20 and A = 21 isospin multiplets. These measurements were possible
through the use of a unique ion-guide laser ion source, a development that
suppressed isobaric contamination by six orders of magnitude. Compared to the
latest atomic mass evaluation, we find that the mass of 21Mg is in good
agreement but that the mass of 20Mg deviates by 3{\sigma}. These measurements
reduce the uncertainties in the masses of 20,21Mg by 15 and 22 times,
respectively, resulting in a significant departure from the expected behavior
of the isobaric multiplet mass equation in both the A = 20 and A = 21
multiplets. This presents a challenge to shell model calculations using either
the isospin non-conserving USDA/B Hamiltonians or isospin non-conserving
interactions based on chiral two- and three-nucleon forces.Comment: 5 pages, 2 figure
Modeling of the Radiation Doses during Dismantling of RBMK-1500 Reactor Pressurized Tanks from Emergency Core Cooling System
Decommissioning of the Ignalina Nuclear Power Plant involves multiple problems. One of them is personnel radiation safety during the performance of dismantling activities. In this paper, modeling results of radiation doses during the dismantling of the pressurized tank from the emergency core cooling system (ECCS PT) of RBMK-1500 reactor are presented. The radiological surveys indicate that the inner surface of the ECCS PT is contaminated with radioactive products of corrosion and sediments due to the radioactive water. The effective doses to the workers have been modeled for different strategies of ECCS PT dismantling. In order to select the optimal personnel radiation safety, the modeling has been performed by the means of computer code “VISIPLAN 3D ALARA Planning tool” developed by SCK CEN (Belgium). The impacts of dismantling tools, shielding types, and extract ventilation flow rate on effective doses during the dismantling of ECCS PT have been analyzed. The total effective personnel doses have been obtained by summarizing the effective personnel doses from various sources of exposure, that is, direct radiation from radioactive equipment, internal radiation due to inhalation of radioactive aerosols, and direct radiation from radioactive aerosols arising during hot cutting in premises. The uncertainty of the collective doses is also presented in this paper
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