Characterization of the energy resolution and the tracking capabilities of a hybrid pixel detector with CdTe-sensor layer for a possible use in a neutrinoless double beta decay experiment

Abstract

Many different experiments are being developed to explore the existence of the neutrinoless double beta decay (0νββ) since it would imply fundamental consequences for particle physics. In this work we present results on the evaluation of Timepix detectors with cadmium-telluride sensor material to search for 0νββ in 116 Cd. This work was carried out with the COBRA collaboration and the Medipix collaboration. Due to the relatively small pixel dimension of 110 × 110 × 1000 µm 3 the energy deposited by particles typically extends over several detector pixels leading to a track in the pixel matrix. We investigated the separation power regarding different event-types like α-particles, atmospheric muons, single electrons and electron-positron pairs produced at a single vertex. We achieved excellent classification power for α-particles and muons. In addition, we achieved good separation power between single electron and electron-positron pair production events. These separation abilities indicate a very good background reduction for the 0νββ search. Further, in order to distinguish between 2νββ and 0νββ, the energy resolution is of particular importance. We carried out simulations which demonstrate that an energy resolution of 0.43 % is achievable at the Q-value for 0νββ of 116 Cd at 2.814 MeV. We measured an energy resolution of 1.6 % at a nominal energy of 1589 keV for electron-positron tracks which is about two times worse that predicted by our simulations. This deviation is probably due to the problem of detector calibration at energies above 122 keV which is discussed in this paper as well. a

The Potential of Hybrid Pixel Detectors in the Search for the Neutrinoless Double-Beta Decay of116Cd

“…It has already been demonstrated that 1 mm thick CdTe layers can be assembled with the Timepix ASIC [19,20]. Other hybrid pixel detectors like the HEXITEC detector already have been successfully contacted to even 3 mm thick CdZnTe sensors with 80 × 80 pixels at 250 m pixel pitch [21].…”

“…Electron-positron tracks were generated by pair production. The experiment and the results were presented by Filipenko et al [20] in more detail. A 1 mm thick CdTe sensor layer with ohmic contacts (Pt) biased continuously at −500 V was exposed from the side to 2.614 MeV photons from the decay of 208 Tl.…”

Implementation of an imaging spectrometer for localization and identification of radioactive sources

“…As a first step, we plan the global calibration of the Timepix chip. Improvements of the energy resolution of a factor between two and four are reported by [26] with a pixel by pixel calibration and this approach will be considered as a second step. Test of a 1 mm thick, 110 µm pixel side Timepix chip is also expected.…”

“…The Ikrum current both controls falling times of pulses generated by charge preamplifiers and compensates leakage currents (within the limit of Ikrum/2). All parameters were finally set to their default value, except Ikrum which was set to the DAC code value 2 corresponding to a falling time in the order of 1 µs [26]. It is important to notice that the pile-up is limited with such a value.…”

In-situ CdS/CdTe heterojuntions deposited by pulsed laser deposition

“…Ma et al reported multilayers of CdTe quantum dots as formaldehyde gases sensors. [10] Filipenko et al and Murphy et al also reported the use of single crystal and thin films CdTe as particle detectors for -particles, single electrons, and thermal neutrons [11,12]. An additional advantage of thin film CdTe is that it can be deposited using a wide variety of methods including sputtering, close-spaced sublimation, pulsed laser deposition, physical vapor deposition, among others [2,13,14].…”