350 research outputs found
Spectroscopy of Po
Prompt, in-beam rays following the reaction Yb + 142 MeV
Si were measured at the ATLAS facility using 10 Compton-suppressed Ge
detectors and the Fragment Mass Analyzer. Transitions in Po were
identified and placed using -ray singles and coincidence data gated on
the mass of the evaporation residues. A level spectrum up to
J10 was established. The structure of Po is more
collective than that observed in the heavier polonium isotopes and indicates
that the structure has started to evolve towards the more collective nature
expected for deformed nuclei.Comment: 8 pages, revtex 3.0, 4 figs. available upon reques
Decay modes of 250No
The Fragment Mass Analyzer at the ATLAS facility has been used to
unambiguously identify the mass number associated with different decay modes of
the nobelium isotopes produced via 204Pb(48Ca,xn)(252-x)No reactions.
Isotopically pure (>99.7%) 204Pb targets were used to reduce background from
more favored reactions on heavier lead isotopes. Two spontaneous fission
half-lives (t_1/2 = 3.7+1.1-0.8 us and 43+22-15 us) were deduced from a total
of 158 fission events. Both decays originate from 250No rather than from
neighboring isotopes as previously suggested. The longer activity most likely
corresponds to a K-isomer in this nucleus. No conclusive evidence for an alpha
branch was observed, resulting in upper limits of 2.1% for the shorter lifetime
and 3.4% for the longer activity.Comment: RevTex4, 10 pages, 5 figures, submitted to PR
Stellar ArAr reactions and their effect on light neutron-rich nuclide synthesis
The ArAr ( = 35 d) and
ArAr (269 y) reactions were studied for the first time
with a quasi-Maxwellian ( keV) neutron flux for Maxwellian Average
Cross Section (MACS) measurements at stellar energies. Gas samples were
irradiated at the high-intensity Soreq applied research accelerator
facility-liquid-lithium target neutron source and the Ar/Ar and
Ar/Ar ratios in the activated samples were determined by
accelerator mass spectrometry at the ATLAS facility (Argonne National
Laboratory). The Ar activity was also measured by low-level counting at
the University of Bern. Experimental MACS of Ar and Ar, corrected
to the standard 30 keV thermal energy, are 1.9(3) mb and 1.3(2) mb,
respectively, differing from the theoretical and evaluated values published to
date by up to an order of magnitude. The neutron capture cross sections of
Ar are relevant to the stellar nucleosynthesis of light neutron-rich
nuclides; the two experimental values are shown to affect the calculated mass
fraction of nuclides in the region A=36-48 during the weak -process. The new
production cross sections have implications also for the use of Ar and
Ar as environmental tracers in the atmosphere and hydrosphere.Comment: 18 pages + Supp. Mat. (13 pages) Accepted for publication in Phys.
Rev. Let
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Shock compression experimental capabilities of the Atlas facility
Atlas is a high-energy pulsed-power facility under construction at Los Alamos National Laboratory. When completed in late 2000, Atlas will provide a laboratory environment to perform shock compression experiments in regimes presently unattainable by other methods. The high-energy-density environment on Atlas will be produced by the rapid ({approximately}4{micro}s) implosion of a 20--40 gram, {approximately}4cm radius, 4 cm length cylindrical aluminum or aluminum/high-Z composite liner, driven by a fast current pulse of {approximately}32 MA from a 24 MJ capacitor bank. Implosion velocities up to 20 km/s are predicted, allowing Hugoniot experiments to {approximately}20 Mbar and quasi-adiabatic compression to several Mbar. However, many issues face scientist in performing such experiments, including how to diagnose conditions inside the imploding liner, how to correct results for distortions and density gradients created by the cylindrical geometry and magnetic drive, and how to prevent geometric distortions and instabilities from degrading results. In this paper, liner performance is predicted for a shock compression experiment utilizing 1-D MHD simulations, and the effect of gradients in density, pressure, and velocity in the impactor prior to collision are discussed
Fusion-Fission of 16O+197Au at Sub-Barrier Energies
The recent discovery of heavy-ion fusion hindrance at far sub-barrier
energies has focused much attention on both experimental and theoretical
studies of this phenomenon. Most of the experimental evidence comes from
medium-heavy systems such as Ni+Ni to Zr+Zr, for which the compound system
decays primarily by charged-particle evaporation. In order to study heavier
systems, it is, however, necessary to measure also the fraction of the decay
that goes into fission fragments. In the present work we have, therefore,
measured the fission cross section of 16O+197Au down to unprecedented far
sub-barrier energies using a large position sensitive PPAC placed at backward
angles. The preliminary cross sections will be discussed and compared to
earlier studies at near-barrier energies. No conclusive evidence for
sub-barrier hindrance was found, probably because the measurements were not
extended to sufficiently low energies.Comment: Fusion06 - Intl. Conf. on Reaction Mechanisms and Nuclear Structure
at the Coulomb Barrier, San Servolo, Venezia, Italy, March 19-223, 2006 5
pages, 4 figure
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Multi-megagauss field-generation using capacitor banks
Design of a high-field (6 MG) production experiment on the Pegasus capacitor bank is presented. One and two dimensions MHD simulations are benchmarked against Alikhanov`s previous experiments and used to support the design for the Pegasus experiment. Possible extensions to the Atlas facility, where production of 20 Mg fields may be possible, are also discussed
International Standard Problem No 50 â The University of Pisa contribution
The present paper deals with the participation of the University of Pisa in the last International Standard Problem (ISP)
focused on system thermal hydraulic, which was led by the Korean Atomic Energy Research Institution (KAERI). The selected
test was a Direct Vessel Injection (DVI) line break carried out at the ATLAS facility. University of Pisa participated, together
with other eighteen institutions, in both blind and open phase of the analytical exercise pursuing its methodology for developing
and qualifying a nodalization. Qualitative and quantitative analysis of the code results have been performed for both ISP-50
phases, the latter adopting the Fast Fourier Transfer Based Method (FFTBM). The experiment has been characterized by three dimensional behavior in downcomer and core region. Even though an attempt to reproduce these phenomena, by developing a
fictitious three-dimensional nodalization has been realized, the obtained results were generally acceptable but not fully satisfactory
in replicating 3D behavio
The Relational Database Aspects of Argonne's ATLAS Control System
The Relational Database Aspects of Argonnes ATLAS Control System Argonnes
ATLAS (Argonne Tandem Linac Accelerator System) control system comprises two
separate database concepts. The first is the distributed real-time database
structure provided by the commercial product Vsystem [1]. The second is a more
static relational database archiving system designed by ATLAS personnel using
Oracle Rdb [2] and Paradox [3] software. The configuration of the ATLAS
facility has presented a unique opportunity to construct a control system
relational database that is capable of storing and retrieving complete archived
tune-up configurations for the entire accelerator. This capability has been a
major factor in allowing the facility to adhere to a rigorous operating
schedule. Most recently, a Web-based operator interface to the control systems
Oracle Rdb database has been installed. This paper explains the history of the
ATLAS database systems, how they interact with each other, the design of the
new Web-based operator interface, and future plans.Comment: ICALEPCS 2001 Conference, PSN WEAP066, 3 pages, 3 figure
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