83 research outputs found
Calibration of the ASTRI SST-2M Prototype using Muon Ring Images
The study of ring images generated from high-energy muons is a very useful
tool for the performance monitoring and calibration of any Imaging Atmosphere
Cherenkov Telescope. Isolated muons travelling towards the telescope light
collector system produce characteristic Cherenkov ring images in the focal
plane camera. Since the geometry and the distribution of light deployed onto
the camera can be easily reconstructed analytically for a muon of given energy
and direction, muon rings are a powerful tool for monitoring the behaviour of
crucial properties of an imaging telescope such as the point-spread-function
and the overall light collection efficiency. In this contribution we present
the possibility of using the analysis of muon ring images as calibrator for the
ASTRI SST-2M prototype point spread function.Comment: In Proceedings of the 33rd International Cosmic Ray Conference
(ICRC2013), Rio de Janeiro (Brazil). All ASTRI contributions at
arXiv:1307.463
Volcanoes muon imaging using Cherenkov telescopes
A detailed understanding of a volcano inner structure is one of the
key-points for the volcanic hazards evaluation. To this aim, in the last
decade, geophysical radiography techniques using cosmic muon particles have
been proposed. By measuring the differential attenuation of the muon flux as a
function of the amount of rock crossed along different directions, it is
possible to determine the density distribution of the interior of a volcano. Up
to now, a number of experiments have been based on the detection of the muon
tracks crossing hodoscopes, made up of scintillators or nuclear emulsion
planes. Using telescopes based on the atmospheric Cherenkov imaging technique,
we propose a new approach to study the interior of volcanoes detecting the
Cherenkov light produced by relativistic cosmic-ray muons that survive after
crossing the volcano. The Cherenkov light produced along the muon path is
imaged as a typical annular pattern containing all the essential information to
reconstruct particle direction and energy. Our new approach offers the
advantage of a negligible background and an improved spatial resolution. To
test the feasibility of our new method, we have carried out simulations with a
toy-model based on the geometrical parameters of ASTRI SST-2M, i.e. the imaging
atmospheric Cherenkov telescope currently under installation onto the Etna
volcano. Comparing the results of our simulations with previous experiments
based on particle detectors, we gain at least a factor of 10 in sensitivity.
The result of this study shows that we resolve an empty cylinder with a radius
of about 100 m located inside a volcano in less than 4 days, which implies a
limit on the magma velocity of 5 m/h.Comment: 21 pages, 21 figures, in press on Nuclear Inst. and Methods in
Physics Research, A. Final version published online: 3-NOV-201
Effective pointing of the ASTRI-Horn telescope using the Cherenkov camera with the Variance method
Cherenkov telescope cameras are not suitable to perform astrometrical
pointing calibration since they are not designed to produce images of the sky,
but rather to detect nanosecond atmospheric flashes due to very high-energy
cosmic radiation. Indeed, these instruments show only a moderate angular
resolution (fractions of degrees) and are almost blind to the steady or
slow-varying optical signal of starlight. For this reason, auxiliary optical
instruments are typically adopted to calibrate the telescope pointing. However,
secondary instruments are possible sources of systematic errors. Furthermore,
the Cherenkov camera is the only one framing exactly the portion of the sky
under study, and hence its exploitation for pointing calibration purposes would
be desirable. In this contribution, we present a procedure to assess the
pointing accuracy of the ASTRI-Horn telescope by means of its innovative
Cherenkov camera. This instrument is endowed with a statistical method, the
so-called Variance method, implemented in the logic board and able to provide
images of the night sky background light as ancillary output. Taking into
account the convolution between the optical point spread function and the pixel
distribution, Variance images can be used to evaluate the position of stars
with sub-pixel precision. In addition, the rotation of the field of view during
observations can be exploited to verify the alignment of the Cherenkov camera
with the optical axis of the telescope, with a precision of a few arcminutes,
as upper limit. This information is essential to evaluate the effective
pointing of the telescope, enhancing the scientific accuracy of the system.Comment: 7 pages, 5 figures, Proceedings of the 37th International Cosmic Ray
Conference (ICRC 2021), Berlin, German
Use of the Peak-Detector mode for gain calibration of SiPM sensors with ASIC CITIROC read-out
The Cherenkov Imaging Telescope Integrated Read Out Chip (CITIROC) is a
32-channel fully analogue front-end ASIC dedicated to the read-out of silicon
photo-multiplier (SiPM) sensors that can be used in a variety of experiments
with different applications: nuclear physics, medical imaging, astrophysics,
etc. It has been adopted as front-end for the focal plane detectors of the
ASTRI-Horn Cherenkov telescope and, in this context, it was modified
implementing the peak detector reading mode to satisfy the instrument
requirements. For each channel, two parallel AC coupled voltage preamplifiers,
one for the high gain and one for the low gain, ensure the read-out of the
charge from 160 fC to 320 pC (i.e. from 1 to 2000 photo-electrons with SiPM
gain = 10, with a photo-electron to noise ratio of 10). The signal in
each of the two preamplifier chains is shaped and the maximum value is captured
by activating the peak detector for an adjustable time interval. In this work,
we illustrate the peak detector operation mode and, in particular, how this can
be used to calibrate the SiPM gain without the need of external light sources.
To demonstrate the validity of the method, we also present and discuss some
laboratory measurements.Comment: 11 pages, 9 figures, 15th Topical Seminar on Innovative Particle and
Radiation Detectors (IPRD19) 14-17 October 2019 Siena, Italy (Submitted to
JINST peer review on 05 January 2020
Geant4 simulations of soft proton scattering in X-ray optics. A tentative validation using laboratory measurements
Low energy protons (< 300 keV) can enter the field of view of X-ray space
telescopes, scatter at small incident angles, and deposit energy on the
detector, causing intense background flares at the focal plane or in the most
extreme cases, damaging the X-ray detector. A correct modelization of the
physics process responsible for the grazing angle scattering processes is
mandatory to evaluate the impact of such events on the performance of future
X-ray telescopes as the ESA ATHENA mission. For the first time the Remizovich
model, in the approximation of no energy losses, is implemented top of the
Geant4 release 10.2. Both the new scattering physics and the built-in Coulomb
scattering are used to reproduce the latest experimental results on grazing
angle proton scattering. At 250 keV multiple scattering delivers large proton
angles and it is not consistent with the observation. Among the tested models,
the single scattering seems to better reproduce the scattering efficiency at
the three energies but energy loss obtained at small scattering angles is
significantly lower than the experimental values. In general, the energy losses
obtained in the experiment are higher than what obtained by the simulation. The
experimental data are not completely representative of the soft proton
scattering experienced by current X-ray telescopes because of the lack of
measurements at low energies (< 200 keV) and small reflection angles, so we are
not able to address any of the tested models as the one that can certainly
reproduce the scattering behavior of low energy protons expected for the ATHENA
mission. We can, however, discard multiple scattering as the model able to
reproduce soft proton funneling, and affirm that Coulomb single scattering can
represent, until further measurements, the best approximation of the proton
scattered angular distribution at the exit of X-ray optics.Comment: submitted to Experimental Astronom
Updates on the background estimates for the X-IFU instrument onboard of the ATHENA mission
ATHENA, with a launch foreseen in 2028 towards the L2 orbit, addresses the
science theme "The Hot and Energetic Universe", coupling a high-performance
X-ray Telescope with two complementary focal-plane instruments. One of these,
the X-ray Integral Field Unit (X-IFU) is a TES based kilo-pixel array providing
spatially resolved high-resolution spectroscopy (2.5 eV at 6 keV) over a 5
arcmin FoV. The background for this kind of detectors accounts for several
components: the diffuse Cosmic X-ray Background, the low energy particles
(<~100 keV) focalized by the mirrors and reaching the detector from inside the
field of view, and the high energy particles (>~100 MeV) crossing the
spacecraft and reaching the focal plane from every direction. Each one of these
components is under study to reduce their impact on the instrumental
performances. This task is particularly challenging, given the lack of data on
the background of X-ray detectors in L2, the uncertainties on the particle
environment to be expected in such orbit, and the reliability of the models
used in the Monte Carlo background computations. As a consequence, the
activities addressed by the group range from the reanalysis of the data of
previous missions like XMM-Newton, to the characterization of the L2
environment by data analysis of the particle monitors onboard of satellites
present in the Earth magnetotail, to the characterization of solar events and
their occurrence, and to the validation of the physical models involved in the
Monte Carlo simulations. All these activities will allow to develop a set of
reliable simulations to predict, analyze and find effective solutions to reduce
the particle background experienced by the X-IFU, ultimately satisfying the
scientific requirement that enables the science of ATHENA. While the activities
are still ongoing, we present here some preliminary results already obtained by
the group
An XMM-Newton proton response matrix
Soft protons constitute an important source of background in focusing X-ray telescopes, as Chandra and XMM-Newton experience has shown. The optics in fact transmit them to the focal plane with efficiency similar to the X-ray photon one. This effect is a good opportunity to study the environment of the Earth magnetosphere crossed by the X-ray satellite orbits, provided that we can link the spectra detected by the instruments with the ones impacting on the optics. For X-ray photons this link has the form of the so-called response matrix that includes the optics effective area and the energy redistribution in the detectors. Here we present a first attempt to produce a proton response matrix exploiting ray-tracing and GEANT4 simulations with the final aim to be able to analyse XMM-Newton soft proton data and link them to the external environment. If the procedure is found to be reliable, it can be applied to any future X-ray missions to predict the soft particles spectra impacting on the focal plane instruments
Intermittent theta-burst stimulation rescues dopamine-dependent corticostriatal synaptic plasticity and motor behavior in experimental parkinsonism. Possible role of glial activity.
Background: Recent studies support the therapeutic utility of repetitive transcranial magnetic stimulation in Parkinson's disease (PD), whose progression is correlated with loss of corticostriatal long-term potentiation and long-term depression. Glial cell activation is also a feature of PD that is gaining increasing attention in the field because astrocytes play a role in chronic neuroinflammatory responses but are also able to manage dopamine (DA) levels.
Methods: Intermittent theta-burst stimulation protocol was applied to study the effect of therapeutic neuromodulation on striatal DA levels measured by means of in vivo microdialysis in 6-hydroxydopamine-hemilesioned rats. Effects on corticostriatal synaptic plasticity were studied through in vitro intracellular and whole-cell patch clamp recordings while stepping test and CatWalk were used to test motor behavior. Immunohistochemical analyses were performed to analyze morphological changes in neurons and glial cells.
Results: Acute theta-burst stimulation induced an increase in striatal DA levels in hemiparkinsonian rats, 80 minutes post-treatment, correlated with full recovery of plasticity and amelioration of motor performances. With the same timing, immediate early gene activation was restricted to striatal spiny neurons. Intense astrocytic and microglial responses were also significantly reduced 80 minutes following theta-burst stimulation.
Conclusion: Taken together, these results provide a first glimpse on physiological adaptations that occur in the parkinsonian striatum following intermittent theta-burst stimulation and may help to disclose the real potential of this technique in treating PD and preventing DA replacement therapy-associated disturbances
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