X-γ ray spectroscopy with a CdTe pixel detector and SIRIO preamplifier at deep sub-microsecond signal processing time

Advanced scientific and industrial applications based on X- and $\gamma $ -ray spectroscopic imaging need systems able to handle high incoming radiation flux (>1 Mcount/s) and, therefore, requiring processing of radiation detector signals in less than $1~\mu \text{s}$ . The design and realization of very fast systems with high spatial and energy resolution still presents a complex challenge and it is the objective of the most recent research worldwide. Since room-temperature operation and high absorption efficiency (up to 100 keV of photon energy) are required for many applications, in addition to high energy resolution, cadmium telluride (CdTe) or CdZnTe detectors are the main choice for the task. In this framework, we have developed a research-grade spectroscopic system based on a pixel CdTe detector coupled to an ultralow noise custom charge preamplifier. The detector is 1 mm thick with 0.75 mm $\times0.75$ mm pixels with Schottky junction; the front-end electronics is SIRIO-6, a CMOS charge preamplifier specifically designed to have ultralow noise and fast response. The goal of this work is to study the spectroscopic capability of a CdTe pixel detector, suitable for spectroscopic imaging, at very short signal-processing times. Deep submicrosecond X– $\gamma $ -ray spectroscopy has been successfully accomplished using a trapezoidal pulse shaping with a 50-ns flat top and peaking times ranging from $1~\mu \text{s}$ down to 50 ns. At room temperature, intrinsic energy resolutions [pulser full-width at half-maximum (FWHM)] from 205 eV (19.6 electrons rms) at $1~\mu \text{s}$ to 392 eV (37.6 electrons rms) at 50 ns have been obtained and the FWHMs of the 241Am 59.54 keV line from 472 eV at 1 $\mu \text{s}$ to 617 eV at 50 ns peaking time have been measured, and, therefore, verifying the system capability to reach high energy resolution even at such short signal-processing times. The effects of very short signal-processing times on the electronic noise, ballistic deficit, and system linearity have been measured and discussed.