787 research outputs found
Characterization of ZnSe scintillating bolometers for Double Beta Decay
ZnSe scintillating bolometers are good candidates for future Double Beta
Decay searches, because of the 82Se high Q-value and thanks to the possibility
of alpha background rejection on the basis of the scintillation signal. In this
paper we report the characteristics and the anomalies observed in an extensive
study of these devices. Among them, an unexpected high emission from alpha
particles, accompanied with an unusual pattern of the light vs. heat scatter
plot. The perspectives for the application of this kind of detectors to search
for the Neutrinoless Double Beta Decay of 82Se are presented.Comment: 12 pages, 10 figure
Pulse Shape Analysis with scintillating bolometers
Among the detectors used for rare event searches, such as neutrinoless Double
Beta Decay (0DBD) and Dark Matter experiments, bolometers are very
promising because of their favorable properties (excellent energy resolution,
high detector efficiency, a wide choice of different materials used as
absorber, ...). However, up to now, the actual interesting possibility to
identify the interacting particle, and thus to greatly reduce the background,
can be fulfilled only with a double read-out (i.e. the simultaneous and
independent read out of heat and scintillation light or heat and ionization).
This double read-out could greatly complicate the assembly of a huge,
multi-detector array, such as CUORE and EURECA. The possibility to recognize
the interacting particle through the shape of the thermal pulse is then clearly
a very interesting opportunity.
While detailed analyses of the signal time development in purely thermal
detectors have not produced so far interesting results, similar analyses on
macro-bolometers (10-500 g) built with scintillating crystals showed that
it is possible to distinguish between an electron or -ray and an
particle interaction (i.e. the main source of background for 0DBD
experiments based on the bolometric technique). Results on pulse shape analysis
of a CaMoO crystal operated as bolometer is reported as an example. An
explanation of this behavior, based on the energy partition in the heat and
scintillation channels, is also presented.Comment: Presented at the 14th International Workshop on Low Temperature
Detectors, proceedings to be published in the Journal of Low Temperature
Physic
The high voltage distribution system for the hybrid photodetector arrays of RICH1 and RICH2 at LHCb
CdWO4 scintillating bolometer for Double Beta Decay: Light and Heat anticorrelation, light yield and quenching factors
We report the performances of a 0.51 kg CdWO4 scintillating bolometer to be
used for future Double Beta Decay Experiments. The simultaneous read-out of the
heat and the scintillation light allows to discriminate between different
interacting particles aiming at the disentanglement and the reduction of
background contribution, key issue for next generation experiments. We will
describe the observed anticorrelation between the heat and the light signal and
we will show how this feature can be used in order to increase the energy
resolution of the bolometer over the entire energy spectrum, improving up to a
factor 2.6 on the 2615 keV line of 208Tl. The detector was tested in a 433 h
background measurement that permitted to estimate extremely low internal trace
contaminations of 232Th and 238U. The light yield of gamma/beta, alpha and
neutrons is presented. Furthermore we developed a method in order to correctly
evaluate the absolute thermal quenching factor of alpha particles in
scintillating bolometers.Comment: 8 pages 7 figure
Isolated Star Formation: A Compact HII Region in the Virgo Cluster
We report on the discovery of an isolated, compact HII region in the Virgo
cluster. The object is located in the diffuse outer halo of NGC 4388, or could
possibly be in intracluster space. Star formation can thus take place far
outside the main star forming regions of galaxies. This object is powered by a
small starburst with an estimated mass of \sim 400\msun and age of \sim
3\myr. From a total sample of 17 HII region candidates, the present rate of
isolated star formation estimated in our Virgo field is small, \sim 10^{-6}
Msun arcmin}^{-2} yr^{-1}. However, this mode of star formation might have
been more important at higher redshifts and be responsible for a fraction of
the observed intracluster stars and total cluster metal production. This object
is relevant also for distance determinations with the planetary nebula
luminosity function from emission line surveys, for high-velocity clouds and
the in situ origin of B stars in the Galactic halo, and for local enrichment of
the intracluster gas by Type II supernovae.Comment: 5 pages, LaTeX, 1 figure. ApJ Letters, in press (scheduled Dec 1,
2002
Monte Carlo evaluation of the external gamma, neutron and muon induced background sources in the CUORE experiment
CUORE is a 1 ton scale cryogenic experiment aiming at the measurement of the
Majorana mass of the electron neutrino. The detector is an array of 988 TeO2
bolometers used for a calorimetric detection of the two electrons emitted in
the BB0n of 130Te. The sensitivity of the experiment to the lowest Majorana
mass is determined by the rate of background events that can mimic a BB0n. In
this paper we investigate the contribution of external sources i.e.
environmental gammas, neutrons and cosmic ray muons to the CUORE background and
show that the shielding setup designed for CUORE guarantees a reduction of this
external background down to a level <1.0E-02 c/keV/kg/y at the Q-value, as
required by the physical goal of the experiment.Comment: 14 pages, 7 figure
A very high performance stabilization system for large mass bolometerexperiments
Abstract CUORE is a large mass bolometric experiment, composed of 988 crystals, under construction in Hall A of the Gran Sasso Underground Laboratories (LNGS). Its main aim is the study of neutrinoless double beta decay of 130Te. Each bolometer is a 760 g crystal of Tellurium dioxide on which a Nuclear Transmutation Doped Ge thermistor, Ge NTD, is glued with proper thermal contact. The stability of the system is mandatory over many years of data taking. To accomplish this requirement a heating resistor is glued on each detector across which a voltage pulse can be injected at will, to develop a known calibrated heating power. We present the design solution for a pulse generator system to be used for the injection of such a small and short voltage pulse across the heaters. This system is composed by different custom PCB boards each of them having multi-channel independent outputs completely remotely programmable from the acquisition system, in pulse width and amplitude, through an on-board ARM7 microcontroller. Pulse amplitudes must be selectable, in order to handle each detector on its full dynamic range. The resolution of the output voltage is 12 bits over 10 V range. An additional 4 steps programmable voltage attenuator is added at every output. The width of any pulse can range from 100 μ s to 25.5 ms. The main features of the final system are: stability and precision in pulses generation (at the level of less than a ppm/°C), low cost (thanks to the use of commercial components) and compact implementation
The planetary nebula population in the halo of M87
We investigate the diffuse light in the outer regions of the nearby
elliptical galaxy M87 in the Virgo cluster, using planetary nebulas (PNs) as
tracers. The surveyed areas (0.43 squared degrees) cover M87 up to a radial
distance of 150 kpc, in the ransition region between galaxy halo and
intracluster light (ICL). All PNs are identified through the on-off band
technique using automatic selection criteria based on the distribution of the
detected sources in the colour-magnitude diagram and the properties of their
point-spread function. We extract a catalogue of 688 objects down to
m_5007=28.4, with an estimated residual contamination from foreground stars and
background Lyalpha galaxies, which amounts to ~35% of the sample. This is one
of the largest extragalactic PN samples in number of candidates, magnitude
depth, and radial extent, which allows us to carry out an unprecedented
photometric study of the PN population in the outer regions of M87. We find
that the logarithmic density profile of the PN distribution is shallower than
the surface brightness profile at large radii. This behaviour is consistent
with the superposition of two components associated with the halo of M87 and
with the ICL, which have different luminosity specific PN numbers, the ICL
contributing three times more PNs per unit light. Because of the depth of this
survey we are also able to study the shape of the PN luminosity function (PNLF)
in the outer regions of M87. We find a slope for the PNLF that is steeper at
fainter magnitudes than the standard analytical PNLF formula and adopt a
generalised model that treats the slope as a free parameter. Comparing the PNLF
of M87 and the M31 bulge, both normalised by the sampled luminosity, the M87
PNLF contains fewer bright PNs and has a steeper slope towards fainter
magnitudes.Comment: 16 pages, 13 figures, 5 tables, accepted for publication in A&
An ultra fast, low power readout chain for single photon sensitivity with multi-anode photomultiplier tubes for the RICH upgrade at LHCb
Abstract An upgrade proposal for the LHCb RICH detectors at the Large Hadron Collider at CERN is being developed at the INFN section of Milano Bicocca, based on multi-anode photomultiplier tubes. The application requires the fast readout of Cherenkov rings of photons, with single photon sensitivity, at an event rate up to 40 MHz. The proposed readout chain is tailored for the R7600 multi-anode photomultiplier tubes from Hamamatsu, which proved to fit the single photon sensitivity requirement. The readout electronics for each pixel will be composed of an analog pulse shaper, a binary discriminator and additional digital circuitry to count the pulses. A prototype of the analog shaper was built with commercial discrete transistors in Silicon–Germanium (SiGe) Heterojunction technology. The tradeoff between response speed and power dissipation was investigated; and power as low as a few mW per channel could be achieved with response times of the order of one nanosecond. Furthermore, noise and jitter were evaluated, showing very good performances of the prototype
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