Development of a system to assay radioactive waste at Radiation Medicine Centre

Full text: Assay of radioactive waste is mandatory before its disposal. For assay of gamma ray emitting radio nuclides, gamma spectrometry techniques are conventionally used. In case of a laboratory handling only a few types of gamma emitters, the laboratory waste is well segregated. Simple dose rate measured using GM based instrument with suitable scaling factor can give the activity contents in the waste packets. A microcontroller based system developed for this purpose is inexpensive and simple and is described in this paper. This system is developed specifically to assay radioactive waste generated at Radiation Medicine Centre (RMC). The most extensively used isotopes at this center are 99mTc and 131I. At present, waste packet monitoring is carried out manually by measuring the maximum surface dose rate of the packet using a GM survey meter. In this system, waste packet to be monitored is kept in a rotating drum to simulate a homogeneous distribution of the radiation field. Five detectors are placed along the height of the drum to scan the entire volume of the drum. The versatile software built into the system arrives at the activity content in the waste packet from measured dose rate using dose rate to activity conversion methods used for standard isotopic contents. An audio visual alarm is also generated if the activity content or surface dose rate exceeds preset limits. This system minimizes radiation dose to health physicist involved in the manual monitoring of the waste and also estimates the net activity content, which is mandatory for disposal of the waste