209 research outputs found
Evaluation of Short-Period, Near-Regional M_s Scales for the Nevada Test Site
Surface wave magnitude (M_s) estimation for small events recorded at
near-regional distances will often require a magnitude scale designed for Rayleigh
waves with periods less than 10 sec. We have examined the performance of applying
two previously published M_s scales on 7-sec Rayleigh waves recorded at distances
less than 500 km. First, we modified the Marshall and Basham (1972) M_s scale,
originally defined for periods greater than 10 sec, to estimate surface wave magnitudes
for short-period Rayleigh waves from earthquakes and explosions on or near
the Nevada Test Site. We refer to this modification as ^(M+B) M_s(7), and we have used
short-period, high-quality dispersion curves to determine empirical path corrections
for the 7-sec Rayleigh waves. We have also examined the performance of the Rezapour
and Pearce (1998) formula, developed using theoretical distance corrections
and surface wave observations with periods greater than 10 sec, for 7-sec Rayleigh
waves ^(R+P) (M_S(7)) as recorded from the same dataset. The results demonstrate that both
formulas can be used to estimate M_s for nuclear explosions and earthquakes over a
wider magnitude distribution than is possible using conventional techniques developed
for 20-sec Rayleigh waves. These M_s(7) values scale consistently with other
Ms studies at regional and teleseismic distances with the variance described by a
constant offset; however, the offset for the ^(M+B) M_s(7) estimates is over one magnitude
unit nearer the teleseismic values than the ^(R+P) M_s(7) estimates. Using our technique, it
is possible to employ a near-regional single-station or sparse network to estimate
surface wave magnitudes, thus allowing quantification of the size of both small earthquakes
and explosions. Finally, we used a jackknife technique to determine the false-alarm
rates for the ^(M+B) M_s(7)-m_b discriminant for this region and found that the probability of misclassifying an earthquake as an explosion is 10%, while the probability
of classifying an explosion as an earthquake was determined to be 1.2%. The misclassification
probabilities are slightly higher for the ^(R+P) M_s(7) estimates. Our future
research will be aimed at examining the transportability of these methods
Millimeter-wave Signature of Strange Matter Stars
One of the most important questions in the study of compact objects is the
nature of pulsars, including whether they consist of neutron matter or strange
quark matter (SQM). However, few mechanisms for distinguishing between these
two possibilities have been proposed. The purpose of this paper is to show that
a strange star (one made of SQM) will have a vibratory mode with an oscillation
frequency of approximately 250 GHz (millimeter wave). This mode corresponds to
motion of the center of the expected crust of normal matter relative to the
center of the strange quark core, without distortion of either. Radiation from
currents generated in the crust at the mode frequency would be a SQM signature.
We also consider effects of stellar rotation, estimate power emission and
signal-to-noise ratio, and discuss briefly possible mechanisms for exciting the
mode.Comment: 13 pages, Latex, one figur
Seismic Search for Strange Quark Nuggets
Bounds on masses and abundances of Strange Quark Nuggets (SQNs) are inferred
from a seismic search on Earth. Potential SQN bounds from a possible seismic
search on the Moon are reviewed and compared with Earth capabilities. Bounds
are derived from the data taken by seismometers implanted on the Moon by the
Apollo astronauts. We show that the Apollo data implies that the abundance of
SQNs in the region of 10 kg to one ton must be at least an order of magnitude
less than would saturate the dark matter in the solar neighborhood.Comment: 7 pages and 4 tables, plus 3 attached figures. Revised version
responds to helpful comments of Phys. Rev. referee by adding 3 figures,
subtracting two tables and taking into account information from QC
A simple radionuclide-driven single-ion source
We describe a source capable of producing single barium ions through nuclear
recoils in radioactive decay. The source is fabricated by electroplating 148Gd
onto a silicon {\alpha}-particle detector and vapor depositing a layer of BaF2
over it. 144Sm recoils from the alpha decay of 148Gd are used to dislodge Ba+
ions from the BaF2 layer and emit them in the surrounding environment. The
simultaneous detection of an {\alpha} particle in the substrate detector allows
for tagging of the nuclear decay and of the Ba+ emission. The source is simple,
durable, and can be manipulated and used in different environments. We discuss
the fabrication process, which can be easily adapted to emit most other
chemical species, and the performance of the source
Olivine in Almahata Sitta - Curiouser and Curiouser
Almahata Sitta (hereafter Alma) is an anomalous, polymict ureilite. Anomalous features include low abundance of olivine, large compositional range of silicates, high abundance and large size of pores, crystalline pore wall linings, and overall finegrained texture. Tomography suggests the presence of foliation, which is known from other ureilites. Alma pyroxenes and their interpretation are discussed in two companion abstracts. In this abstract we discuss the composition of olivine in Alma, which is indicative of the complexity of this meteorite
Investigation of radioactivity-induced backgrounds in EXO-200
The search for neutrinoless double-beta decay (0{\nu}{\beta}{\beta}) requires
extremely low background and a good understanding of their sources and their
influence on the rate in the region of parameter space relevant to the
0{\nu}{\beta}{\beta} signal. We report on studies of various {\beta}- and
{\gamma}-backgrounds in the liquid- xenon-based EXO-200 0{\nu}{\beta}{\beta}
experiment. With this work we try to better understand the location and
strength of specific background sources and compare the conclusions to
radioassay results taken before and during detector construction. Finally, we
discuss the implications of these studies for EXO-200 as well as for the
next-generation, tonne-scale nEXO detector.Comment: 9 pages, 7 figures, 3 table
Search for Neutrinoless Double-Beta Decay in Xe with EXO-200
We report on a search for neutrinoless double-beta decay of Xe with
EXO-200. No signal is observed for an exposure of 32.5 kg-yr, with a background
of ~1.5 x 10^{-3} /(kg yr keV) in the region of interest. This
sets a lower limit on the half-life of the neutrinoless double-beta decay
(Xe) > 1.6 x 10 yr (90% CL),
corresponding to effective Majorana masses of less than 140-380 meV, depending
on the matrix element calculation
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