Speaker
Description
Micropattern gas detectors (MPGDs) have been extensively applied in high-energy Physics experiments. Other specific applications include Homeland security, medical imaging and cultural heritage. The primary ionization electrons produced by the radiation in the sensitive volume drift towards a cascade of micropatterned elements, being amplified through electron charge avalanches occurring in the gas under the high electric fields established in the micropattern elements. Imaging of the radiation interaction position is achieved either by using pixelated anode electrodes, readout by a suitable electronic signal readout and imaging systems or, else, by readout the scintillation produced in gas with photosensitive imaging systems.
The readout of the gas scintillation promoted by the primary electrons in the avalanches as a mean of the primary ionization signal amplification presents advantages over the charge readout. The mechanical and electrical decoupling of the signal readout system from the amplification region render improved immunity to high-voltage problems and to electronic noise and radiofrequency pick up. In addition, the extra gain of the photosensor allows obtaining signals with higher amplitude and reduced signal-to-noise ratio, requiring less demanding electronics for signal readout and processing, further allowing these electronics to be placed far away from the detector sensitive volume. The use of expensive and/or complex photosensors for readout gas scintillation-based imaging systems, such as PMTs, CCD or CMOS cameras, present a drawback, limiting the applications of the optical readout alternative. However, a 2D-arrays of SiPMs present a good low-cost alternative.
Nevertheless, blurring and noise are particularly significant in gaseous detectors, where the range of the photoelectron and the electron diffusion in the gas contribute to the degradation of the position resolution that can be obtained. As the ionization electrons drift towards the signal amplification region, the transverse and longitudinal diffusive spread of the electron cloud contribute to the distribution of the readout signal among different neighbour pixels. In addition, for optical readout imaging, the isotropic emission of the gas scintillation and the additional reflections of the photons from the inner surfaces of the gas chamber also creates an additional “halo” of diffuse light, contributing for image blurring. These processes combine to further optically smear the image of the scintillation signal readout, with a similar relative contribution as electron diffusion.
In this work, we present our ongoing efforts to improve the imaging quality obtained with a commercial Hamamatsu S13361-3050 SiPM unit, reading out the scintillation produced in a GEM-based MPGD. This study addressed the challenges posed by image degradation due to electron diffusion and light spread, which result in blurring and reduced spatial resolution. Systematic evaluations of grid refinement and Gaussian filtering highlighted the needed compromise between spatial resolution and noise reduction. While finer grid refinements enhanced image fidelity, careful tuning of Gaussian filters is necessary to prevent excessive resolution loss. The RL algorithm effectively mitigate image degradation caused by electron diffusion and light spread, achieving significant enhancement in spatial resolution, confirming the RL algorithm’s utility in counteracting blurring effects inherent to optical gas detectors. The findings emphasize the importance of integrating advanced image processing techniques like the RL algorithm with modern detector technologies to maximize their potential.
| Workshop topics | Imaging theory |
|---|
