587 research outputs found
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
ZnMoO4: a promising bolometer for neutrinoless double beta decay searches
We investigate the performances of two ZnMoO4 scintillating crystals operated
as bolometers, in view of a next generation experiment to search the
neutrinoless double beta decay of Mo-100. We present the results of the alpha
vs beta/gamma discrimination, obtained through the scintillation light as well
as through the study of the shape of the thermal signal alone. The
discrimination capability obtained at the 2615 keV line of Tl-208 is 8 sigma,
using the heat-light scatter plot, while it exceeds 20 sigma using the shape of
the thermal pulse alone. The achieved FWHM energy resolution ranges from 2.4
keV (at 238 keV) to 5.7 keV (at 2615 keV). The internal radioactive
contaminations of the ZnMoO4 crystals were evaluated through a 407 hours
background measurement. The obtained limit is < 32 microBq/kg for Th-228 and
Ra-226. These values were used for a Monte Carlo simulation aimed at evaluating
the achievable background level of a possible, future array of enriched ZnMoO4
crystals.Comment: 9 pages, 8 figure
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
Performance of a large TeO2 crystal as a cryogenic bolometer in searching for neutrinoless double beta decay
Bolometers are ideal devices in the search for neutrinoless Double Beta
Decay. Enlarging the mass of individual detectors would simplify the
construction of a large experiment, but would also decrease the background per
unit mass induced by alpha-emitters located close to the surfaces and
background arising from external and internal gamma's. We present the very
promising results obtained with a 2.13 kg TeO2 crystal. This bolometer, cooled
down to a temperature of 10.5 mK in a dilution refrigerator located deep
underground in the Gran Sasso National Laboratories, represents the largest
thermal detector ever operated. The detector exhibited an energy resolution
spanning a range from 3.9 keV (at 145 keV) to 7.8 keV (at the 2615 gamma-line
of 208Tl) FWHM. We discuss the decrease in the background per unit mass that
can be achieved increasing the mass of a bolometer.Comment: 6 pages, 6 figure
Evaluation of corneal distortion characteristics in different eyes using Scheimpflug camera device
Objective. To study the correlations between corneal distortion and morphological features in different kinds of eyes such as healthy ones (HE), ones previously undergone myopic PRK (PRKE), ones affected by keratoconus (KCE) and keratoconus eyes previously undergone corneal collagen crosslinking (CCCE). Materials and Methods. In this retrospective comparative study, a total of 106 HE of 106 patients, 58 PRKE of 58 patients, 33 KCE of 33 patients, 28 CCCE of 28 patients were included. A complete examination of all eyes was followed by tomographic (Pentacam, Oculus, Wetzlar, Germany) and biomechanical (Corvis ST, Oculus, Wetzlar, Germany) evaluation. Differences among Corvis ST (CST) parameters in the different groups have been analyzed. Linear regressions between central corneal thickness (CCT), intraocular pressure (IOP) and anterior corneal curvature measured with Simulated Keratometry (SK), versus corneal deformation parameters measured with Corvis ST in the different groups, have been run using SPSS software version 18.0. Results, HE showed a significant correlation between main curvature power of the cornea within the central 3 mm expressed in Diopters (KM) and 6 CST parameters; between CCT and 4 CST parameters and between IOP and 5 CST parameters. PRKE showed a significant correlation between KM and 3 CST parameters; between IOP and 4 CST parameters and none between CCT and CST parameters. KCE showed a significant correlation between SK and 3 CST parameters; between IOP and 3 CST parameters and none between CCT and CST parameters. CCCE showed a significant correlation between KM and 5 CST parameters; between CCT and 1 CST parameters and between IOP and 5 CST parameters. Discussion. Data of this study suggest that both corneal curvature and IOP could have a greater influence on the corneal deformation, compared to central corneal thickness (CCT). These results should be taken into account by further studies aiming to assess biomechanical corneal characteristics
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
TeO bolometers with Cherenkov signal tagging: towards next-generation neutrinoless double beta decay experiments
CUORE, an array of 988 TeO bolometers, is about to be one of the most
sensitive experiments searching for neutrinoless double-beta decay. Its
sensitivity could be further improved by removing the background from
radioactivity. A few years ago it has been pointed out that the signal from
s can be tagged by detecting the emitted Cherenkov light, which is not
produced by s. In this paper we confirm this possibility. For the first
time we measured the Cherenkov light emitted by a CUORE crystal, and found it
to be 100 eV at the -value of the decay. To completely reject the
background, we compute that one needs light detectors with baseline noise below
20 eV RMS, a value which is 3-4 times smaller than the average noise of the
bolometric light detectors we are using. We point out that an improved light
detector technology must be developed to obtain TeO bolometric experiments
able to probe the inverted hierarchy of neutrino masses.Comment: 5 pages, 4 figures. Added referee correction
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