DEVELOPMENT OF ON-LINE HYBRID ELECTRONIC RADIATION DOSIMETER FOR A MOBILE ROBOT USING COMMERCIAL POWER pMOSFET AND PIN DIODE

摘要

The electronics of a robot working in a nuclear power plant needs to survive in its radiation environment. To know how much radiation the robot has been encountered to replace sensitive electronic parts, a dosimeter to measure total accumulated dose is necessary. Among many radiation dosimeters or detectors, semiconductor radiation sensors have advantages in terms of power requirements and their sizes over conventional detectors. Among such sensors, a metal oxide field effect transistor (MOSFET) can be used as a dosimeter that measures total accumulated radiation dose for a measurement period and a diode as a dose-rate sensor for radiation survey. This paper describes the use of the radiation-induced threshold voltage change ofa commercial power pMOSFET as an accumulated radiation dose monitoring meanand that of the photo-current of a commercial PIN Diode as a dose-rate measurement mean. Commercial p-type power MOSFETs and PIN Diodes were tested in Co-60 gamma irradiation facilities to see their capabilities as radiation sensors. We found an inexpensive commercial power pMOSFET that shows good linearity in their threshold voltage shift with radiation dose and a PIN diodethat shows good linearity in its photo-current change with dose-rate. According to these findings, a radiation hardened hybrid electronic radiation dosimeter for nuclear robots has been developed for the first time. This small hybrid dosimeter has also an advantage in terms of reliability improvement by using diversity concept. No such small and simple semiconductor electronic dosimeter with these extended ranges of dose (～ 100 krad) and dose-rate (50 rad/hr ～ 8 krad/hr) capability and with these levels of redundancy and diversity has ever been found.