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 is known that commercial dRAM cells are sensitive to alpha particles, but 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 phototransistors are also very sensitive to alpha particles. Our first development in the field of alpha-radiation detection systems has been based on our experience in the field of high-density dRAMs by improving the collecting efficiency for electron-hole pairs generated in the substrate 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 sensor cells. 1024 sensor cells, the preamplifiers, the analog memories, a fast four-bit parallel A/D converter and the address-coding system are integrated on a single chip. The chip area is 56 mm2 and the effective sensor area is 40 mm2. The energy resolution for 5 MeV alpha particles 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 systems are tested in several radiation fields (neutron, proton, alpha, beta and gamma radiation). The efficiency of the alpha-radiation detection systems in radon-monitoring systems is proved in various applications. The use of low-cost alpha-particle detection systems in radon-monitoring systems is a big advance for environmental surveys.