Pulse Shape Analysis with scintillating bolometers

Among the detectors used for rare event searches, such as neutrinoless Double Beta Decay (0$\nu$DBD) 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 ($\sim$10-500 g) built with scintillating crystals showed that it is possible to distinguish between an electron or $\gamma$-ray and an $\alpha$ particle interaction (i.e. the main source of background for 0$\nu$DBD experiments based on the bolometric technique). Results on pulse shape analysis of a CaMoO$_4$ 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

First Ex Vivo Animal Study of a Biological Heart Valve Prosthesis Sensorized with Intravalvular Impedance

IntraValvular Impedance (IVI) sensing is an innovative concept for monitoring heart valve prostheses after implant. We recently demonstrated IVI sensing feasible in vitro for biological heart valves (BHVs). In this study, for the first time, we investigate ex vivo the IVI sensing applied to a BHV when it is surrounded by biological tissue, similar to a real implant condition. A commercial model of BHV was sensorized with three miniaturized electrodes embedded in the commissures of the valve leaflets and connected to an external impedance measurement unit. To perform ex vivo animal tests, the sensorized BHV was implanted in the aortic position of an explanted porcine heart, which was connected to a cardiac BioSimulator platform. The IVI signal was recorded in different dynamic cardiac conditions reproduced with the BioSimulator, varying the cardiac cycle rate and the stroke volume. For each condition, the maximum percent variation in the IVI signal was evaluated and compared. The IVI signal was also processed to calculate its first derivative (dIVI/dt), which should reflect the rate of the valve leaflets opening/closing. The results demonstrated that the IVI signal is well detectable when the sensorized BHV is surrounded by biological tissue, maintaining the similar increasing/decreasing trend that was found during in vitro experiments. The signal can also be informative on the rate of valve opening/closing, as indicated by the changes in dIVI/dt in different dynamic cardiac conditions

Nicotinamide and calcipotriol counteract UVB-induced photoaging on primary human dermal fibroblasts

Background: Photoaging is mainly caused by ultraviolet radiations inasmuch they can damage the DNA, trigger ROS production, and activate p53/p21 pathway, which cause cell cycle arrest and senescence. The accumulationof senescent cells within the dermis contributes to tissue deregulation and skin carcinogenesis. However, the use of photoprotector molecules could reduce UV-induced damages and prevent photoaging. Therefore, the aim of this study is to evaluate whether the active forms of vitamin B3 (nicotinamide) and the analog of vitamin D3 (calcipotriol) might protect primary human dermal fibroblasts (HDFs) from UVB-induced photoaging. Methods: HDFs were isolated from a healthy adult donor and stimulated with nicotinamide (25 μM) and calcipotriol (100 nM) for 24h before UVB exposure, and then, cultured for further 24h on vitamin-supplemented media. Then, cell viability, ROS production, DNA damages, senescence markers, protein and gene expression were evaluated. Results: HDFs treated with nicotinamide and calcipotriol showed better proliferation properties and lower DNA damages due to a reduced UVB-induced ROS production. Consequently, p53/p21 pathway was less active which enhanced cell cycle progression and reduced senescence and cell death. Conclusions: Overall, our results suggest that nicotinamide and calcipotriol can counteract UVB-induced effects responsible for the onset of skin photoaging

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

TeO2_2 bolometers with Cherenkov signal tagging: towards next-generation neutrinoless double beta decay experiments

CUORE, an array of 988 TeO$_2$ 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 $\alpha$ radioactivity. A few years ago it has been pointed out that the signal from $\beta$s can be tagged by detecting the emitted Cherenkov light, which is not produced by $\alpha$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 $Q$-value of the decay. To completely reject the $\alpha$ 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$_2$ bolometric experiments able to probe the inverted hierarchy of neutrino masses.Comment: 5 pages, 4 figures. Added referee correction

New experimental limits on the alpha decays of lead isotopes

For the first time a PbWO4 crystal was grown using ancient Roman lead and it was run as a cryogenic detector. Thanks to the simultaneous and independent read-out of heat and scintillation light, the detector was able to discriminate beta/gamma interactions with respect to alpha particles down to low energies. New more stringent limits on the alpha decays of the lead isotopes are presented. In particular a limit of T_{1/2} > 1.4*10^20 y at a 90% C.L. was evaluated for the alpha decay of 204Pb to 200Hg

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

First bolometric measurement of the two neutrino double beta decay of 100^{100}Mo with a ZnMoO4_4 crystals array

The large statistics collected during the operation of a ZnMoO$_4$ array, for a total exposure of 1.3 kg $\cdot$ day of $^{100}$Mo, allowed the first bolometric observation of the two neutrino double beta decay of $^{100}$Mo. The observed spectrum of each crystal was reconstructed taking into account the different background contributions due to environmental radioactivity and internal contamination. The analysis of coincidences between the crystals allowed the assignment of constraints to the intensity of the different background sources, resulting in a reconstruction of the measured spectrum down to an energy of $\sim$300 keV. The half-life extracted from the data is T$_{1/2}^{2\nu}$= [7.15 $\pm$ 0.37 (stat) $\pm$ 0.66 (syst)] $\cdot$ 10$^{18}$ y.Comment: 6 pages, 2 figure, Accepted for publication in Journal of Physics G: Nuclear and Particle Physic