The presented thesis is dedicated to particle identification in COMPASS RICH-1 experiment which is located in European Organization for Nuclear Research (CERN). For particle identification Cherenkov radiation is used, which is described in the thesis together with detection principles. Current aim in detector upgrade is replacing a part of Multi Wire Proportional Chambers (MWPC) in peripheral regions of the detection surface by a suitable photon detector so as to guarantee one-photon detection. For this purpose the hybrid photon detector based on THGEM and MicroMegas technologies was developed. The hybrid detector test results are presented in the thesis.

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Neutron imaging is a non-destructive technique with many applications in diverse fields such as industrial quality assurance, archaeology, and border security. However with the high cost of the standard fill gas 3He and the high cost of scaling conventional digital imaging systems to large areas its applications are limited. Here is presented the proof of concept for a gaseous neutron imaging system utilizing a 10B4C solid state converter and THGEM technology and 2D passive delay line readout. THGEMs used for signal amplification can be produced cost effectively and in large areas by PCB manufacturers. This combined with the reduced channel processing requirements of delay lines over individual pixel readouts results in a cost-effective and scalable system when compared to similar designs using solid state multipliers such as silicon photomultipliers. Here is presented a proof of concept of this imaging system with data acquisition accomplished by digitization and offline image reconstruction achieving mean X and Y resolution of <sigma_x> = (1.37+-0.24) mm and <sigma_y> = (1.15+-0.13) mm respectively. Studied in parallel with this system is the effectiveness of gadolinium oxide based paint as a thermal neutron shield and image contrast agent. / Thesis / Doctor of Philosophy (PhD) / In this work is presented the development process of a novel and cost-effective neutron imaging system capable of imaging soft biological and dense materials that X-rays are unable to penetrate. Such a system may be scaled to large areas for many applications including the study of large archeological objects or employed as a security measure to monitor border checkpoints for transportation of controlled radioactive materials.

<p>Position sensitive detectors represent a class of particle detectors widely used in high-energy physics, astrophysics, biophysics and medicine for imaging the spatial distribution of various radioactive sources. In recent years, a new class of gas based detectors, so-called micropattern gas detectors (MPGDs), has emerged. While modern MPGDs rival solid state detectors in terms of spatial and temporal resolution, their cost of production is significantly lower. A Thick Gaseous Electron Multiplier (THGEM) imaging detector, with a two-dimensional delay line readout, has been constructed as a concept for a large area imaging detector with reasonable spatial resolution. The delay line based THGEM imaging detector is robust, easy to manufacture and cost effective alternative to direct readout techniques which frequently employ a large number of channels. Featuring an active area of 40 x 40 mm<strong>2</strong>, the prototype has been constructed using two 0.4 mm THGEMs and successfully operated in a low pressure, propane based, gas mixture. Two sets of orthogonal electrodes, connected to individual delay lines, serve as a two-dimensional anode readout. Adjacent electrodes are separated by approximately 3.4 ns of time delay and allow the interaction position to be calculated by measuring the time difference between delay line output signals corresponding to a common axis. Using modern field programmable gate arrays (FPGAs), a time-to-digital (TDC) data acquisition (DAQ) system has been developed. The TDC DAQ performs the position reconstruction algorithm and is capable of continuous event rates up to 1.8 MHz. The imaging capabilities of the detector have been assessed using a collimated alpha source and a wide X-ray beam. Under these aforementioned conditions, the detector was able to successfully resolve 1 mm diameter holes spaced 3 mm apart. With higher operating pressures, and using Xenon based gas mixture, it is expected the imaging detector should achieve sub-mm spatial resolution. The investigations presented in this thesis serve as a framework for the development of future THGEM imaging detectors.</p> / Doctor of Philosophy (PhD)

The THick Gas Electron Multiplier (THGEM) based tissue-equivalent proportional counter (TEPC) has been proven to be useful for microdosimetry due to its flexibility in varying the gaseous sensitive volume and achieving high multiplication gain. Aiming at measuring the spatial distribution of radiation dose for mixed neutron-gamma fields, an advanced two-dimensional (2D) THGEM TEPC was designed and constructed at McMaster University which will enable us to overcome the operational limitation of the classical TEPCs, particularly for high dose rate fields. Compared to the traditional TEPCs, anode wire electrodes were replaced by THGEM layer, which not only enhances the gas multiplication gain but also offers a flexible and convenient fabrication or building 2D detectors. The 2D THGEM TEPC consists of an array of 3×3 sensitive volumes, equivalent to 9 individual TEPCs, each of which has a dimension of 5 mm diameter and length. Taking the overall cost, size and flexibility into account, to process 9 detectors signals simultaneously, a multi-input digital pulse processing system was developed by using modern microcontrollers, each of which is coupled to a 12-bit sampling ADC with a sampling rate of 42 Msps. The signal processing system was tested using a NaI(Tl) detector, which has proven that is it faster than a traditional analogue system and a commercial digital system. Using the McMaster Tandetron 7Li(p,n) accelerator neutron source, both fundamental detector performance, as well as neutron dosimetric response of the 2D THGEM TEPC, has been extensively investigated and compared to the data acquired by a spherical TEPC. It was shown that the microdosimetric response and the measured absorbed dose rate of the 2D THGEM detector developed in this study are comparable to the standard 1/2" TEPC which is commercially available. / Thesis / Doctor of Philosophy (PhD)

Radiations can be classified as either ionizing or non-ionizing according to whether it ionizes or does not ionize the medium through which they propagate. X-rays photons and gamma rays are the typical examples of ionizing radiations whereas radiowave, heat or visible light are examples of non ionizing radiations. UV photons have some features of both ionizing and non-ionizing radiation. Both ionizing and non-ionizing radiation can be harmful to living organisms and to the natural environment. Hence the detection and measurement of radiation is very important for the well being of living organisms as well as the natural environment. Not only for safety reasons, have radiation detectors found their applications in various fields including medical physics, nuclear and particle physics, astronomy and homeland security. Industrial sectors that use radiation detection include medical imaging, security and baggage scanning, the nuclear power industry and defense. Gas electron multiplier (GEM) is one of the most successful representatives of gaseous detectors used for UV photon and X-ray photon detection. Recently there is a growing demand for large area photon detectors with sensitivity reaching to the level of single photon. They are used in spectroscopy and imaging in astronomy high energy physics experiments etc. Thick GEM (THGEM) is a mechanical expansion of standard GEM. It has all the necessary requirements needed for large area detector and offers a multiplication factor that permits efficient detection of light. Hence, the development and performance study of THGEM based radiation detector is chosen as the topic of study in the present thesis. The initial part of the thesis contains simulation studies carried out for the understanding the working of the detector and the effect of various design parameters of THGEM for the above said applications. Different steps for the fabrication of THGEM and the technical challenges faced during the process are discussed. In the view of application of the fabricated THGEM for UV photon detection, cesium iodide photocathode is prepared using thin film technology and characterized. The performance of the photocathode under various operating conditions is studied in terms of its photoemission property. The effect of vacuum treatment on the photoemission property of the photocathode exposed to moist air is studied in detail. A major portion of this thesis focuses on maximizing the detection efficiency of the UV photon detector realized using the fabricated THGEM coupled with the cesium iodide photocathode. Simulations are used at different stages to interpret the experimental observations. The electron spectrum obtained from the detector under study was analyzed. The dependence of secondary effect like photon feedback on the operating parameters is also discussed. The last portion of the thesis deals with the application of THGEM as an X-ray detector. The performance is evaluated in terms of the gain and energy resolution achieved. The thesis is organized as follows: Chapter 1 is divided into two sections. Section A gives a general introduction to different types of radiation detectors found in the present day and their working principles. This is followed by discussion about gas ionization based detector and its working principle in detail. A brief literature survey of the different types of micropattern gas detectors is also given in this section. In Section B of this chapter GEM and THGEM are introduced with discussion about their working principle and areas of application. Chapter 2 deals with the simulation study of THGEM undertaken to have a clear understanding of the detector’s working. Section A of this chapter gives an overview of the simulation tools used for the present thesis in particular ANSYS and GARFIELD. Section B presents the results of the simulation study highlighting the effects of different geometrical and operating parameters on the electric field distribution in and around the THGEM aperture. The relevance of the study to the detectors performance is discussed vividly for all the cases. In Chapter 3, the details of the different steps involved in THGEM fabrication are given. Design aspects involved, fabrication of the THGEM using standard PCB technology coupled with photolithography technique are discussed in this chapter. This is followed by an elaborate description of the test setup used for all the performance study. Preface In the view of application of THGEM as a UV photon detector, cesium iodide photocathode was prepared and characterized. Chapter 4 discusses about the CsI photocathode preparation and its characterization for the above said application. Photoemission property of the photocathode was analyzed under various operating parameters. The effect of vacuum treatment on the photocathode performance is a new aspect of this thesis. Its correlation with the microstructure of the film is reported for the first time. Chapter 5 deals with the application of THGEM as a UV photon detector. The study mainly focuses on the improvement of the detection efficiency of the detector. The effect of drift parameters on the electron transfer efficiency and hence on the detection efficiency of the detector is a major contribution of this thesis. There are no literature available which discusses this aspect of a UV photon detector. The experimental study has been supported with simulation results. In addition to the study on detection efficiency, electron spectrum has also been acquired from the UV photon detector. The spectrum has been analyzed under various operating conditions. Discussions about secondary effects like photon feedback prevailing in the detector output are also present in this chapter. Chapter 6 presents the results of THGEM as an X-ray detector. The performance of the detector has been evaluated in terms of the effective gain and energy resolution achieved under different operating conditions. The gain instability with time and its uniformity across the THGEM area are also studied. The effect of drift field on the energy resolution and its correlation with ETE is a new aspect of this work. Chapter 7 summarizes the salient features of the work presented in this thesis. Also the scope of future work based on this thesis is discussed at the end of the chapter.