Detectors for alpha particles and X-rays operating in ambient air in pulse counting mode or/and with gas amplification

Abstract

Ionization chambers working in ambient air in currentdetection mode are attractive due to their simplicity and low cost andare widely used in several applications such as smoke detection,dosimetry, therapeutic beam monitoring and so on. The aim of this workwas to investigate if gaseous detectors can operate in ambient air inpulse counting mode as well as with gas amplification whichpotentially offers the highest possible sensitivity in applicationslike alpha particle detection or high energy X-ray photon or electrondetection.To investigate the feasibility of this method two types of open- endgaseous detectors were build and successfully tested. The first onewas a single wire or multiwire cylindrical geometry detector operatingin pulse mode at a gas gain of one (pulse ionization chamber). Thisdetector was readout by a custom made wide -band charge sensitiveamplifier able to deal with slow induced signals generated by slowmotion of negative and positive ions. The multiwire detector was ableto detect alpha particles with an efficiency close to 22%. The secondtype of an alpha detector was an innovative GEM-like detector withresistive electrodes operating in air in avalanche mode at high gasgains (up to 104). This detector can also operate in a cascadedmode or being combined with other detectors, for example withMICROMEGAS. This detector was readout by a conventional charge-sensitive amplifier and was able to detect alpha particles with 100%efficiency. This detector could also detect X-ray photons or fastelectrons. A detailed comparison between these two detectors is givenas well as a comparison with commercially available alphadetectors. The main advantages of gaseous detectors operating in airin a pulse detection mode are their simplicity, low cost and highsensitivity. One of the possible applications of these new detectorsis alpha particle background monitors which, due to their low cost canfind wide application not only in houses, but in public areas:airports, railway station and so on.