57 research outputs found
Experimental study of a liquid Xenon PET prototype module
A detector using liquid Xenon in the scintillation mode is studied for
Positron Emission Tomography (PET). The specific design aims at taking full
advantage of the liquid Xenon properties. It does feature a promising
insensitive to any parallax effect. This work reports on the performances of
the first LXe prototype module, equipped with a position sensitive PMT
operating in the VUV range (178 nm).Comment: Proc. of the 7th International Workshops on Radiation Imaging
Detectors (IWORID-7), Grenoble, France 4-7 July 200
Photometric quality of Dome C for the winter 2008 from ASTEP South
ASTEP South is an Antarctic Search for Transiting Exo- Planets in the South
pole field, from the Concordia station, Dome C, Antarctica. The instrument
consists of a thermalized 10 cm refractor observing a fixed 3.88\degree x
3.88\degree field of view to perform photometry of several thousand stars at
visible wavelengths (700-900 nm). The first winter campaign in 2008 led to the
retrieval of nearly 1600 hours of data. We derive the fraction of photometric
nights by measuring the number of detectable stars in the field. The method is
sensitive to the presence of small cirrus clouds which are invisible to the
naked eye. The fraction of night-time for which at least 50% of the stars are
detected is 74% from June to September 2008. Most of the lost time (18.5% out
of 26%) is due to periods of bad weather conditions lasting for a few days
("white outs"). Extended periods of clear weather exist. For example, between
July 10 and August 10, 2008, the total fraction of time (day+night) for which
photometric observations were possible was 60%. This confirms the very high
quality of Dome C for nearly continuous photometric observations during the
Antarctic winter
Design and construction of a Cherenkov imager for charge measurement of nuclear cosmic rays
A proximity focusing Cherenkov imager called CHERCAM, has been built for the
charge measurement of nuclear cosmic rays with the CREAM instrument. It
consists of a silica aerogel radiator plane across from a detector plane
equipped with 1,600 1" diameter photomultipliers. The two planes are separated
by a ring expansion gap. The Cherenkov light yield is proportional to the
charge squared of the incident particle. The expected relative light collection
accuracy is in the few percents range. It leads to an expected single element
separation over the range of nuclear charge Z of main interest 1 < Z < 26.
CHERCAM is designed to fly with the CREAM balloon experiment. The design of the
instrument and the implemented technical solutions allowing its safe operation
in high altitude conditions (radiations, low pressure, cold) are presented.Comment: 24 pages, 19 figure
The secondary eclipses of WASP-19b as seen by the ASTEP 400 telescope from Antarctica
The ASTEP (Antarctica Search for Transiting ExoPlanets) program was
originally aimed at probing the quality of the Dome C, Antarctica for the
discovery and characterization of exoplanets by photometry. In the first year
of operation of the 40 cm ASTEP 400 telescope (austral winter 2010), we
targeted the known transiting planet WASP-19b in order to try to detect its
secondary transits in the visible. This is made possible by the excellent
sub-millimagnitude precision of the binned data. The WASP-19 system was
observed during 24 nights in May 2010. The photometric variability level due to
starspots is about 1.8% (peak-to-peak), in line with the SuperWASP data from
2007 (1.4%) and larger than in 2008 (0.07%). We find a rotation period of
WASP-19 of 10.7 +/- 0.5 days, in agreement with the SuperWASP determination of
10.5 +/- 0.2 days. Theoretical models show that this can only be explained if
tidal dissipation in the star is weak, i.e. the tidal dissipation factor Q'star
> 3.10^7. Separately, we find evidence for a secondary eclipse of depth 390 +/-
190 ppm with a 2.0 sigma significance, a phase consistent with a circular orbit
and a 3% false positive probability. Given the wavelength range of the
observations (420 to 950 nm), the secondary transit depth translates into a day
side brightness temperature of 2690(-220/+150) K, in line with measurements in
the z' and K bands. The day side emission observed in the visible could be due
either to thermal emission of an extremely hot day side with very little
redistribution of heat to the night side, or to direct reflection of stellar
light with a maximum geometrical albedo Ag=0.27 +/- 0.13. We also report a
low-frequency oscillation well in phase at the planet orbital period, but with
a lower-limit amplitude that could not be attributed to the planet phase alone,
and possibly contaminated with residual lightcurve trends.Comment: Accepted for publication in Astronomy and Astrophysics, 13 pages, 13
figure
ASTEP South: An Antarctic Search for Transiting ExoPlanets around the celestial South pole
ASTEP South is the first phase of the ASTEP project (Antarctic Search for
Transiting ExoPlanets). The instrument is a fixed 10 cm refractor with a 4kx4k
CCD camera in a thermalized box, pointing continuously a 3.88 degree x 3.88
degree field of view centered on the celestial South pole. ASTEP South became
fully functional in June 2008 and obtained 1592 hours of data during the 2008
Antarctic winter. The data are of good quality but the analysis has to account
for changes in the point spread function due to rapid ground seeing variations
and instrumental effects. The pointing direction is stable within 10 arcseconds
on a daily timescale and drifts by only 34 arcseconds in 50 days. A truly
continuous photometry of bright stars is possible in June (the noon sky
background peaks at a magnitude R=15 arcsec-2 on June 22), but becomes
challenging in July (the noon sky background magnitude is R=12.5 arcsec?2 on
July 20). The weather conditions are estimated from the number of stars
detected in the field. For the 2008 winter, the statistics are between 56.3 %
and 68.4 % of excellent weather, 17.9 % to 30 % of veiled weather and 13.7 % of
bad weather. Using these results in a probabilistic analysis of transit
detection, we show that the detection efficiency of transiting exoplanets in
one given field is improved at Dome C compared to a temperate site such as La
Silla. For example we estimate that a year-long campaign of 10 cm refractor
could reach an efficiency of 69 % at Dome C versus 45 % at La Silla for
detecting 2-day period giant planets around target stars from magnitude 10 to
15. This shows the high potential of Dome C for photometry and future planet
discoveries. [Short abstract
Asperities and barriers on the seismogenic zone in North Chile: state-of-the-art after the 2007 Mw 7.7 Tocopilla earthquake inferred by GPS and InSAR data
The Mw 7.7 2007 November 14 earthquake had an epicentre located close to the city of Tocopilla, at the southern end of a known seismic gap in North Chile. Through modelling of Global Positioning System (GPS) and radar interferometry (InSAR) data, we show that this event ruptured the deeper part of the seismogenic interface (30–50 km) and did not reach the surface. The earthquake initiated at the hypocentre and was arrested ~150 km south, beneath the Mejillones Peninsula, an area already identified as an important structural barrier between two segments of the Peru–Chile subduction zone. Our preferred models for the Tocopilla main shock show slip concentrated in two main asperities, consistent with previous inversions of seismological data. Slip appears to have propagated towards relatively shallow depths at its southern extremity, under the Mejillones Peninsula. Our analysis of post-seismic deformation suggests that small but still significant post-seismic slip occurred within the first 10 d after the main shock, and that it was mostly concentrated at the southern end of the rupture. The post-seismic deformation occurring in this period represents ~12–19 per cent of the coseismic deformation, of which ~30–55 per cent has been released aseismically. Post-seismic slip appears to concentrate within regions that exhibit low coseismic slip, suggesting that the afterslip distribution during the first month of the post-seismic interval complements the coseismic slip. The 2007 Tocopilla earthquake released only ~2.5 per cent of the moment deficit accumulated on the interface during the past 130 yr and may be regarded as a possible precursor of a larger subduction earthquake rupturing partially or completely the 500-km-long North Chile seismic gap
The GUINEVERE Project for Accelerator Driven System Physics
paper 9414International audienceThe GUINEVERE project is part of the EUROTRANS Integrated Project of the 6th EURATOM Framework Programme. It is mainly devoted to ADS on-line reactivity monitoring validation, sub-criticality determination and operational procedures (loading, start-up, shut-down, ...) as a follow-up of the MUSE experiments. The project consists in coupling a fast lead core, set-up in the VENUS reactor at SCK*CEN Mol (B), with a GENEPI neutron source under construction by CNRS. To accommodate the accelerator in a vertical coupling configuration, the VENUS building is being heightened. The fast core will be loaded with enriched Uranium and will be moderated and reflected with solid lead (zero power experiment). For the purpose of the experimental programme, the neutron source has to be operated not only in pulsed mode but also in continuous mode to investigate the current-to-flux reactivity indicator in representative conditions of a powerful ADS. In this latter mode it is also required to make short beam interruptions to have access to the neutron population decrease as a function of time: from this spectrum it will be possible to apply different analysis techniques such as "prompt decay" fitting techniques and "source jerk" techniques. Beam interruptions will be repeated at a programmable frequency to improve time spectra statistics. Different sub-criticality levels (keff=0.99, 0.97, 0.95, ...) will be investigated in order to obtain a full set of data points for the final overall validation of the methodology. This paper describes the status of the experimental facility assembling, and the foreseen experimental programme to be started
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