NEW ALPHA-RADIATION DETECTION SYSTEMS FOR ENVIRONMENTAL SURVEYS

We report on the development of low-cost alpha-particle sensor systems for radon and radon daughter monitoring and dosimetry (E(alpha) = 5.5 -7.9 MeV) and on the first application for environmental surveys. It i s known that commercial dRAM cells are sensitive to alpha particles, b ut their efficiency is at most 20%, resulting in an unstable operating range (U(cc)<4 V). Furthermore it is known that p-n diodes and photot ransistors are also very sensitive to alpha particles. Our first devel opment in the field of alpha-radiation detection systems has been base d on our experience in the field of high-density dRAMs by improving th e collecting efficiency for electron-hole pairs generated in the subst rate by the incidence of alpha particles. Using the experience of the MEGARAD-microsystem we have developed an alpha-particle spectroscopic sensor array with special PMOS transistors in a floating n-well as sen sor cells. 1024 sensor cells, the preamplifiers, the analog memories, a fast four-bit parallel A/D converter and the address-coding system a re integrated on a single chip. The chip area is 56 mm2 and the effect ive sensor area is 40 mm2. The energy resolution for 5 MeV alpha parti cles is better than 300 keV. The dead time is smaller than 10% for up to 10(6) alpha particles per second and per square centimetre. The sys tems are tested in several radiation fields (neutron, proton, alpha, b eta and gamma radiation). The efficiency of the alpha-radiation detect ion systems in radon-monitoring systems is proved in various applicati ons. The use of low-cost alpha-particle detection systems in radon-mon itoring systems is a big advance for environmental surveys.