245 research outputs found
IDeF-X ASIC for Cd(Zn)Te spectro-imaging systems
Joint progresses in Cd(Zn)Te detectors, microelectronics and interconnection
technologies open the way for a new generation of instruments for physics and
astrophysics applications in the energy range from 1 to 1000 keV. Even working
between -20 and 20 degrees Celsius, these instruments will offer high spatial
resolution (pixel size ranging from 300 x 300 square micrometers to few square
millimeters), high spectral response and high detection efficiency. To reach
these goals, reliable, highly integrated, low noise and low power consumption
electronics is mandatory. Our group is currently developing a new ASIC detector
front-end named IDeF-X, for modular spectro-imaging system based on the use of
Cd(Zn)Te detectors. We present here the first version of IDeF-X which consists
in a set of ten low noise charge sensitive preamplifiers (CSA). It has been
processed with the standard AMS 0.35 micrometer CMOS technology. The CSA are
designed to be DC coupled to detectors having a low dark current at room
temperature. The various preamps implemented are optimized for detector
capacitances ranging from 0.5 up to 30 pF.Comment: 8 pages, 11 figures, IEEE NSS-MIC conference in Rome 2004, submitted
to IEEE TNS, correction in unit of figure
Hard X-ray polarimetry with Caliste, a high performance CdTe based imaging spectrometer
Since the initial exploration of soft gamma-ray sky in the 60's, high-energy
celestial sources have been mainly characterized through imaging, spectroscopy
and timing analysis. Despite tremendous progress in the field, the radiation
mechanisms at work in sources such as neutrons stars and black holes are still
unclear. The polarization state of the radiation is an observational parameter
which brings key additional information about the physical process. This is why
most of the projects for the next generation of space missions covering the
tens of keV to the MeV region require a polarization measurement capability. A
key element enabling this capability is a detector system allowing the
identification and characterization of Compton interactions as they are the
main process at play. The hard X-ray imaging spectrometer module, developed in
CEA with the generic name of Caliste module, is such a detector. In this paper,
we present experimental results for two types of Caliste-256 modules, one based
on a CdTe crystal, the other one on a CdZnTe crystal, which have been exposed
to linearly polarized beams at the European Synchrotron Radiation Facility.
These results, obtained at 200-300 keV, demonstrate their capability to give an
accurate determination of the polarization parameters (polarization angle and
fraction) of the incoming beam. Applying a selection to our data set,
equivalent to select 90 degrees Compton scattered interactions in the detector
plane, we find a modulation factor Q of 0.78. The polarization angle and
fraction are derived with accuracies of approximately 1 degree and 5%. The
modulation factor remains larger than 0.4 when essentially no selection is made
at all on the data. These results prove that the Caliste-256 modules have
performances allowing them to be excellent candidates as detectors with
polarimetric capabilities, in particular for future space missions.Comment: 17 pages, 14 figures, 2 tables in Experimental Astronomy, 201
The Microchannel X-ray Telescope on Board the SVOM Satellite
We present the Micro-channel X-ray Telescope (MXT), a new narrow-field (about
1{\deg}) telescope that will be flying on the Sino-French SVOM mission
dedicated to Gamma-Ray Burst science, scheduled for launch in 2021. MXT is
based on square micro pore optics (MPOs), coupled with a low noise CCD. The
optics are based on a "Lobster Eye" design, while the CCD is a focal plane
detector similar to the type developed for the seven eROSITA telescopes. MXT is
a compact and light (<35 kg) telescope with a 1 m focal length, and it will
provide an effective area of about 45 cmsq on axis at 1 keV. The MXT PSF is
expected to be better than 4.2 arc min (FWHM) ensuring a localization accuracy
of the afterglows of the SVOM GRBs to better than 1 arc min (90\% c.l. with no
systematics) provided MXT data are collected within 5 minutes after the
trigger. The MXT sensitivity will be adequate to detect the afterglows for
almost all the SVOM GRBs as well as to perform observations of non-GRB
astrophysical objects. These performances are fully adapted to the SVOM science
goals, and prove that small and light telescopes can be used for future small
X-ray missions.Comment: 6 pages, 6 figures, proceedings of the conference "Swift: 10 years of
Discovery", Rome, December 2-5, 2014. To be published by Po
Fast, broad-band magnetic resonance spectroscopy with diamond widefield relaxometry
We present an alternative to conventional Electron Paramagnetic Resonance
spectroscopy equipment. Avoiding the use of bulky magnets and magnetron
equipment, we use the photoluminescence of an ensemble of Nitrogen-Vacancy
centers at the surface of a diamond. Monitoring their relaxation time (or T1),
we detected their cross-relaxation with the compound of interest. In addition,
the EPR spectra is encoded through a localized magnetic field gradient. While
12 minutes was necessary to record each data point of the spectrum with
previous individual NV center's technics, we are able to reconstruct a full
spectrum at once in 3 seconds, over a range from 3 to 11 gauss. In term of
sensitivity, only 0.5 microliter of a hexaaquacopper (II) ion solution with 1
micromole per liter concentration was necessary.Comment: Main text (15 pages, 6 Figures) + Supplementary (6 Pages, 7 Figures
A photon calorimeter using lead tungstate crystals for the CEBAF Hall A Compton polarimeter
The performances of the calorimeter of the Jlab Hall A Compton Polarimeter
have been measured using the Mainz tagged photon beam.Comment: 13 page
Fast-neutron induced background in LaBr3:Ce detectors
The response of a scintillation detector with a cylindrical 1.5-inch LaBr3:Ce
crystal to incident neutrons has been measured in the energy range En = 2-12
MeV. Neutrons were produced by proton irradiation of a Li target at Ep = 5-14.6
MeV with pulsed proton beams. Using the time-of-flight information between
target and detector, energy spectra of the LaBr3:Ce detector resulting from
fast neutron interactions have been obtained at 4 different neutron energies.
Neutron-induced gamma rays emitted by the LaBr3:Ce crystal were also measured
in a nearby Ge detector at the lowest proton beam energy. In addition, we
obtained data for neutron irradiation of a large-volume high-purity Ge detector
and of a NE-213 liquid scintillator detector, both serving as monitor detectors
in the experiment. Monte-Carlo type simulations for neutron interactions in the
liquid scintillator, the Ge and LaBr3:Ce crystals have been performed and
compared with measured data. Good agreement being obtained with the data, we
present the results of simulations to predict the response of LaBr3:Ce
detectors for a range of crystal sizes to neutron irradiation in the energy
range En = 0.5-10 MeVComment: 28 pages, 10 figures, 4 Table
Unusual consequences of status epilepticus in Dravet syndrome
AbstractAlthough status epilepticus (SE) affects the course of Dravet syndrome (DS), it rarely alters dramatically psychomotor outcome. We report an unusual pattern in 3 patients who following refractory SE lasting respectively 2, 7 and 12h experienced persistent and severe cognitive and motor deterioration. We compared these patients to published data and to personal experience in Necker hospital, to find links between severe outcome and clinical features such as treatment or duration of refractory SE. The key point was that anoxoischemic-like lesions appeared on MRI although cardiovascular function had remained stable. Therefore, neither hemodynamic failure, nor abnormalities of cardiac rhythm could explain the lesions and neurological worsening. For theoretical reasons the responsibility of therapy common for the 3 patients, e.g., barbiturates was suspected
Quantum monitoring of cellular metabolic activities in single mitochondria
Free radicals play a vital role in all kinds of biological processes including immune responses. However, free radicals have short lifetimes and are highly reactive, making them difficult to measure using current methods. Here, we demonstrate that relaxometry measurement, or T1, inherited from the field of diamond magnetometry can be used to detect free radicals in living cells with subcellular resolution. This quantum sensing technique is based on defects in diamond, which convert a magnetic signal into an optical signal, allowing nanoscale magnetic resonance measurements. We functionalized fluorescent nanodiamonds (FNDs) to target single mitochondria within macrophage cells to detect the metabolic activity. In addition, we performed measurements on single isolated mitochondria. We were able to detect free radicals generated by individual mitochondria in either living cells or isolated mitochondria after stimulation or inhibition
The interaction of fluorescent nanodiamond probes with cellular media
Fluorescent nanodiamonds (FNDs) are promising tools to image cells, bioanalytes and physical quantities such as temperature, pressure, and electric or magnetic fields with nanometer resolution. To exploit their potential for intracellular applications, the FNDs have to be brought into contact with cell culture media. The interactions between the medium and the diamonds crucially influence sensitivity as well as the ability to enter cells. The authors demonstrate that certain proteins and salts spontaneously adhere to the FNDs and may cause aggregation. This is a first investigation on the fundamental questions on how (a) FNDs interact with the medium, and (b) which proteins and salts are being attracted. A differentiation between strongly binding and weakly binding proteins is made. Not all proteins participate in the formation of FND aggregates. Surprisingly, some main components in the medium seem to play no role in aggregation. Simple strategies to prevent aggregation are discussed. These include adding the proteins, which are naturally present in the cell culture to the diamonds first and then inserting them in the full medium. Graphical abstractSchematic of the interaction of nanodiamonds with cell culture medium. Certain proteins and salts adhere to the diamond surface and lead to aggregation or to formation of a protein corona
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