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Register a new userNovel position-sensitive gaseous detectors with solid photo-cathodes
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Currently a revolution is happening in the development of gaseous detectors of photons and particles. Recently developed gaseous detectors with solid photocathodes are now replacing photosensitive wire chambers, which dominated for years in high energy and space flight experiments. We will review the main developments in this field as well as their applications in high-energy physics, medicine, industry and plasma diagnostics. New results on solid photocathodes coupled with gaseous micropattern/wire detectors will also be presented.
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Position sensitive detectors based on gaseous scintillation proportional counters with Anger-type readout are being used in several research areas such as neutron detection, search for dark matter and neutrinoless double beta decay. Design and optimization of such detectors are complex and time consuming tasks. Simulations, while being a powerful tool, strongly depend on the light transport models and demand accurate knowledge of many parameters, which are often not available. Here we describe an alternative approach based on the experimental evaluation of a detector using an isotropic point-like light source with precisely controllable light emission properties, installed on a 3D positioning system. The results obtained with the developed setup at validation conditions, when the scattered light is strongly suppressed, show good agreement with simulations.
Migdal effect is attracting interests because of the potential to enhance the sensitivities of direct dark matter searches to the low mass region. In spite of its great importance, the Migdal effect has not been experimentally observed yet. A realistic experimental approach towards the first observation of the Migdal effect in the neutron scattering was studied with Monte Carlo simulations. In this study, potential background rate was studied together with the event rate of the Migdal effect by a neutron source. It was found that a table-top sized $sim (30rm cm )^3$ position-sensitive gaseous detector filled with argon or xenon target gas can detect characteristic signatures of the Migdal effect with sufficient rates (O($10^2sim10^3$) events/day). A simulation result of a simple experimental set-up showed two significant background sources, namely the intrinsic neutrons and the neutron induced gamma-rays. These background rates were found to be much higher than those of the Migdal effect in the neutron scattering. As a consequence of this study, it is concluded that the experimental observation of the Migdal effect in the neutron scattering can be realized with a good understanding and reduction of the background.
Recent developments in photo-detectors and photo-detector systems are reviewed. The main emphasis is made on Silicon Photo-Multipliers (SiPM) - novel and very attractive photo-detectors. Their main features are described. Properties of detectors manufactured by different producers are compared. Different applications are discussed including calorimeters, muon detection, tracking, Cherenkov light detection, and time of flight measurements.
We have demonstrated experimentally that the main breakdown-triggering mechanism in most gaseous detectors, including micropattern gaseous detectors, is sporadic electron jets from the cathode surfaces. Depending on conditions, each jet contains randomly from a few primary electrons up to 10^5, emitted in a time interval ranging between 0.1 microsecond to milliseconds. After the emission, these primary electrons experience a full gas multiplication in the detector and create spurious pulses. The rate of these jets increases with applied voltage and very sharply at voltages close to the breakdown limit. We found that these jets are in our measurements responsible for the breakdown-triggering at any counting rate between 10^(-2) Hz/mm^2 and 10^8 Hz/mm^2. We demonstrated on a few detectors that an optimized cathode-geometry, a high electrode surface quality and a proper choice of the gas mixture, considerably improve the performance characteristics and provide the highest possible gains.
There are several applications and fundamental research areas which require the detection of VUV light at cryogenic temperatures. For these applications we have developed and successfully tested special designs of gaseous detectors with solid photocathodes able to operate at low temperatures: sealed gaseous detectors with MgF2 windows and windowless detectors. We have experimentally demonstrated, that both primary and secondary (due to the avalanche multiplication inside liquids) scintillation lights could be recorded by photosensitive gaseous detectors. The results of this work may allow one to significantly improve the operation of some noble liquid gas TPCs.
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