580 research outputs found
Abrupt changes in alpha decay systematics as a manifestation of collective nuclear modes
An abrupt change in decay systematics around the N=126 neutron shell
closure is discussed. It is explained as a sudden hindrance of the clustering
of the nucleons that eventually form the particle. This is because the
clustering induced by the pairing mode acting upon the four nucleons is
inhibited if the configuration space does not allow a proper manifestation of
the pairing collectivity.Comment: 6 pages, 3 figures, submitted to Phys. Rev. C, a few new references
adde
Mechanical Behaviour of the Short Models of LHC Main Dipole Magnets
A series of single and twin aperture 1 metre magnet models has been built and tested in the framework of the R&D program of main superconducting dipole magnets for the Large Hadron Collider project. The se models, designed for a nominal field of 8.3 T at 1.8 K, have been constructed to test the performance of SC coils and to optimise various design options for the full length 15 metre long dipoles. T he models have been extensively equipped with a specially developed mechanical instrumentation, enabling both the control of main assembly parameters - like coil azimuthal and axial pre-load, stress i n the outer shrinking cylinder - and also the monitoring of magnet behaviour during cooling and energising, under the action of electromagnetic forces. The instrumentation used, mainly based on strain gauge transducers, is described and the results of mechanical measurements obtained during power tests of the models are discussed and compared with the design predictions based on Finite Element calc ulations
State of the Short Dipole Model Program for the LHC
Superconducting single and twin aperture 1-m long dipole magnets are currently being fabricated at CERN at a rate of about one per month in the framework of the short dipole model program for the LHC. The program allows to study performance improvements coming from refinements in design, components and assembly options and to accumulate statistics based on a small-scale production. The experience thus gained provides in turn feedback into the long magnet program in industry. In recent models initial quenching fields above 9 T have been obtained and after a short training the conductor limit at 2 K is reached, resulting in a central bore field exceeding 10 T. The paper describes the features of recent single aperture models, the results obtained during cold tests and the plans to ensure the continuation of a vigorous model program providing input for the fabrication of the main LHC dipoles
Present State of the Single and Twin Aperture Short Dipole Model Program for the LHC
The LHC model program for main dipoles is based on the design, fabrication and testing at CERN of a number of single and twin aperture 1m long magnets. So far, a number of single aperture models, each with specific characteristics, were tested at 2 K at a rate of about one per month. These magnets are the main tool used to check coil performance as a function of design and assembly options in view of optimizing and finalizing choices of components and procedures. Initial quenching field levels of 8.8 T were obtained and the short sample limit of the cable at 1.9 K was reached corresponding to a central bore field of 10 T. A few twin aperture dipole models were also built and tested, using the same structural components as for the long magnets which are now being built in industry. The paper discusses the main characteristics of the models built so far, the instrumentation developed to date and the experience obtained. Finally it describes the plans aimed at continuing a vigorous program to provide input to the long magnet program in industry
Intruder bands and configuration mixing in the lead isotopes
A three-configuration mixing calculation is performed in the context of the
interacting boson model with the aim to describe recently observed collective
bands built on low-lying states in neutron-deficient lead isotopes. The
configurations that are included correspond to the regular, spherical states as
well as two-particle two-hole and four-particle four-hole excitations across
the Z=82 shell gap.Comment: 20 pages, 4 figures, accepted by PRC, reference added for section 1
in this revised versio
In-source laser spectroscopy with the laser ion source and trap: first direct study of the ground-state properties of Po-217,Po-219
D. A. Fink et al.; 15 págs.; 17 figs.; 3 tabs.; Open Access funded by Creative Commons Atribution Licence 3.0A Laser Ion Source and Trap (LIST) for a thick-target, isotope-separation on-line facility has been
implemented at CERN ISOLDE for the production of pure, laser-ionized, radioactive ion beams. It offers
two modes of operation, either as an ion guide, which performs similarly to the standard ISOLDE
resonance ionization laser ion source (RILIS), or as a more selective ion source, where surface-ionized ions
from the hot ion-source cavity are repelled by an electrode, while laser ionization is done within a radiofrequency
quadrupole ion guide. The first physics application of the LIST enables the suppression of
francium contamination in ion beams of neutron-rich polonium isotopes at ISOLDE by more than 1000
with a reduction in laser-ionization efficiency of only 20. Resonance ionization spectroscopy is performed
directly inside the LIST device, allowing the study of the hyperfine structure and isotope shift of 217Po for
the first time. Nuclear decay spectroscopy of 219Po is performed for the first time, revealing its half-life, α-
to-β-decay branching ratio, and α-particle energy. This experiment demonstrates the applicability of the
LIST at radioactive ion-beam facilities for the production and study of pure beams of exotic isotopes. Published by the American Physical SocietyThis work was supported by the Bundesministerium für Bildung und
Forschung (BMBF, Germany) within the Wolfgang-
Gentner programme as well as through the consecutive
project fundings of 06Mz9181I, 06Mz7177D, and
05P12UMCIA, by FWO-Vlaanderen (Belgium), by
GOA/2010/010 (BOF-KULeuven), by the IUAP-Belgian
State Belgian Science Policy (BRIX network P7/12), by the
U.K. Science and Technology Facilities Council (STFC),
by the European Union within FP7 (ENSAR No. 262010),
by the Slovak Research and Development Agency
(Contract No. APVV-0105-10), by the Slovak grant agency
VEGA, and the Reimei Foundation of JAEA (Contract
No. 1/0576/13). T. E. C. was supported by STFC Ernest
Rutherford Grant No. ST/J004189/1.Peer Reviewe
Early onset of ground-state deformation in the neutron-deficient polonium isotopes
In-source resonant ionization laser spectroscopy of the even- polonium
isotopes Po has been performed using the
to ( nm) transition in the polonium atom
(Po-I) at the CERN ISOLDE facility. The comparison of the measured isotope
shifts in Po with a previous data set allows to test for the first
time recent large-scale atomic calculations that are essential to extract the
changes in the mean-square charge radius of the atomic nucleus. When going to
lighter masses, a surprisingly large and early departure from sphericity is
observed, which is only partly reproduced by Beyond Mean Field calculations.Comment: As submitted to PR
Relativistic nuclear energy density functional constrained by low-energy QCD
A relativistic nuclear energy density functional is developed, guided by two
important features that establish connections with chiral dynamics and the
symmetry breaking pattern of low-energy QCD: a) strong scalar and vector fields
related to in-medium changes of QCD vacuum condensates; b) the long- and
intermediate-range interactions generated by one-and two-pion exchange, derived
from in-medium chiral perturbation theory, with explicit inclusion of
excitations. Applications are presented for binding energies,
radii of proton and neutron distributions and other observables over a wide
range of spherical and deformed nuclei from to . Isotopic
chains of and nuclei are studied as test cases for the isospin
dependence of the underlying interactions. The results are at the same level of
quantitative comparison with data as the best phenomenological relativistic
mean-field models.Comment: 48 pages, 12 figures, elsart.cls class file. Revised version,
accepted for publication in Nucl. Phys.
Beta-Delayed fission of 230Am
The exotic decay process of β-delayed fission (βDF) has been studied in the neutron-deficient isotope Am230. The Am230 nuclei were produced in the complete fusion reaction Pb207(Al27,4n)Am230 and separated by using the GARIS gas-filled recoil ion separator. A lower limit for the βDF probability PβDF(Am230)>0.30 was deduced, which so far is the highest value among all known βDF nuclei. The systematics of βDF in the region of Am230 will be discussed
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