311 research outputs found
HST color-magnitude diagrams of 74 galactic globular clusters in the HST F439W and F555W bands
We present the complete photometric database and the color-magnitude diagrams
for 74 Galactic globular clusters observed with the HST/WFPC2 camera in the
F439W and F555W bands. A detailed discussion of the various reduction steps is
also presented, and of the procedures to transform instrumental magnitudes into
both the HST F439W and F555W flight system and the standard Johnson B and V
systems. We also describe the artificial star experiments which have been
performed to derive the star count completeness in all the relevant branches of
the color magnitude diagram. The entire photometric database and the
completeness function will be made available on the Web immediately after the
publication of the present paper.Comment: 21 pages, 77 figures. High resolution version of this paper can be
retrived at http://dipastro.pd.astro.it/globular
An experimental survey of the production of alpha decaying heavy elements in the reactions of U +Th at 7.5-6.1 MeV/nucleon
The production of alpha particle decaying heavy nuclei in reactions of
7.5-6.1 MeV/nucleon U +Th has been explored using an in-beam
detection array composed of YAP scintillators and gas ionization chamber-Si
telescopes. Comparisons of alpha energies and half-lives for the observed
products with those of the previously known isotopes and with theoretically
predicted values indicate the observation of a number of previously unreported
alpha emitters. Alpha particle decay energies reaching as high as 12 MeV are
observed. Many of these are expected to be from decay of previously unseen
relatively neutron rich products. While the contributions of isomeric states
require further exploration and specific isotope identifications need to be
made, the production of heavy isotopes with quite high atomic numbers is
suggested by the data.Comment: 12 pages, 12 figure
Elements Discrimination in the Study of Super-Heavy Elements using an Ionization Chamber
Dedicated ionization chamber was built and installed to measure the energy
loss of very heavy nuclei at 2.7 MeV/u produced in fusion reactions in inverse
kinematics (beam of 208Pb). After going through the ionization chamber,
products of reactions on 12C, 18O targets are implanted in a Si detector. Their
identification through their alpha decay chain is ambiguous when their
half-life is short. After calibration with Pb and Th nuclei, the ionization
chamber signal allowed us to resolve these ambiguities. In the search for rare
super-heavy nuclei produced in fusion reactions in inverse or symmetric
kinematics, such a chamber will provide direct information on the nuclear
charge of each implanted nucleus.Comment: submitted to NIMA, 10 pages+4 figures, Latex, uses elsart.cls and
grahpic
Site-Dilution in quasi one-dimensional antiferromagnet Sr2(Cu1-xPdx)O3: reduction of Neel Temperature and spatial distribution of ordered moment sizes
We investigate the Neel temperature of Sr2CuO3 as a function of the site
dilution at the Cu (S=1/2) sites with Pd (S=0), utilizing the muon spin
relaxation (muSR) technique. The Neel temperature, which is Tn=5.4K for the
undoped system, becomes significantly reduced for less than one percent of
doping Pd, giving a support for the previous proposal for the good
one-dimensionality. The Pd concentration dependence of the Neel temperature is
compared with a recent theoretical study (S. Eggert, I. Affleck and M.D.P.
Horton, Phys. Rev. Lett. 89, 47202 (2002)) of weakly coupled one-dimensional
antiferromagnetic chains of S=1/2 spins, and a quantitative agreement is found.
The inhomogeneity of the ordered moment sizes is characterized by the muSR time
spectra. We propose a model that the ordered moment size recovers away from the
dopant S=0 sites with a recovery length of \xi = 150-200 sites. The origin of
the finite recovery length \xi for the gapless S=1/2 antiferromagnetic chain is
compared to the estimate based on the effective staggered magnetic field from
the neighboring chains.Comment: 10 pages, 9 figures, submitted to PR
KATANA - a charge-sensitive triggering system for the SRIT experiment
KATANA - the Krakow Array for Triggering with Amplitude discrimiNAtion - has
been built and used as a trigger and veto detector for the SRIT TPC at
RIKEN. Its construction allows operating in magnetic field and providing fast
response for ionizing particles, giving the approximate forward multiplicity
and charge information. Depending on this information, trigger and veto signals
are generated. The article presents performance of the detector and details of
its construction. A simple phenomenological parametrization of the number of
emitted scintillation photons in plastic scintillator is proposed. The effect
of the light output deterioration in the plastic scintillator due to the
in-beam irradiation is discussed.Comment: 14 pages, 11 figure
Investigation of thermal and magnetic properties of defects in a spin-gap compound NaV2O5
The specific heat, magnetic susceptibility and ESR signals of a Na-deficient
vanadate Na_xV_2O_5 (x=1.00 - 0.90) were studied in the temperature range 0.07
- 10 K, well below the transition point to a spin-gap state. The contribution
of defects provided by sodium vacancies to the specific heat was observed. It
has a low temperature part which does not tend to zero till at least 0.3 K and
a high temperature power-like tail appears above 2 K. Such dependence may
correspond to the existence of local modes and correlations between defects in
V-O layers. The magnetic measurements and ESR data reveal S=1/2 degrees of
freedom for the defects, with their effective number increasing in temperature
and under magnetic field. The latter results in the nonsaturating magnetization
at low temperature. No long-range magnetic ordering in the system of defects
was found. A model for the defects based on electron jumps near vacancies is
proposed to explain the observed effects. The concept of a frustrated
two-dimensional correlated magnet induced by the defects is considered to be
responsible for the absence of magnetic ordering.Comment: 6 pages, 8 figure
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