Development of a portable system for checking radioactive sources using long wave radio frequency identification

A portable system for automatically checking radioactive sources stored in lead containers at low temperatures was developed in order to prevent the discharging of orphan sources and contaminated materials from a controlled area to the general public. A radio frequency identification (RFID) system using a long wave in a frequency range of 125 kHz was composed of identification tags, a reader, a notebook computer, and software. ID tags without batteries were devised by using integrated circuits with an electrically erasable programmable read-only memory of 250 bytes and antennas. This software consisted of operating and maintenance functions. The read range of the ID tags was adjusted to around 5 cm in order to avoid accidental contamination and for discriminating the multiple sources. A water layer of 6.9 cm had no influence on communication between the ID tags and the reader. The data of the ID tags stored at +4, -20, and -80 degrees C were precisely read 4 mo later. The influence of lead was completely removed by separating the ID tags more than 1.6 cm from the lead. A reader can exactly identify the data of the ID tags within 6.0 cm at a velocity less than 9.0 cm s(-1). Performance of the software was verified using mock data. Nine lists concerning registered, disposed, and missing sources, etc., were displayed on the computer monitor and printed out. An RFID system using long waves proved to be applicable for routinely checking radioactive sources.

In vivo thyroid 131I monitoring system using an imaging plate

The counting efficiency and detection limit of an in vivo thyroid 131I monitoring system using an imaging plate (IP) were estimated using an anthropomorphic thyroid neck phantom. The counting efficiency of the IP system was approximately constant for thyroid volumes between 11.7 and 20 ml and neck diameters between 10 and 14 cm. The detection limits were distributed from 288 to 451 Bq depending on the combination of neck diameter, thyroid volume and tissue thickness. The IP monitoring system gives a reliable counting efficiency notwithstanding the variation of thyroid volume and neck diameter. The IP system is a new option for thyroid 131I monitoring.

Feasibility of in vivo thyroid 131I monitoring with an imaging plate

A new in vivo thyroid 131I monitoring method was devised by using an imaging plate (IP). A thyroid image obtained with a realistic neck-thyroid phantom showed a unique shape characteristic of the thyroid gland. A 131I thyroid imaging allows visual confirmation of thyroid accumulation of 131I. The detection limit of the IP system of 290 Bq was about 1/100 of the screening level of 30 kBq in cases of public emergencies. The IP system is applicable for thyroid 131I monitoring.

In-vivo thyroid 125I monitoring method using imaging plate

A new in vivo thyroid monitoring system was devised with radioluminography using an imaging plate. The counting features of the system were investigated by using a neck-thyroid phantom. A clear thyroid image was obtained at thin prethyroid tissue thicknesses and short distances between IP and neck surface. The characteristic 125I thyroid image made it possible to visually confirm that the thyroid definitely accumulated 125I. The counting efficiency in 100xcps Bq(-1) of the imaging plate system was determined by setting a region of interest on the thyroid image resulting in a maximum efficiency of 0.5%. The higher efficiency was obtained for thinner tissue thickness overlaying the thyroid, smaller thyroids, and shorter distances between the imaging plate and neck surface. The imaging plate thyroid monitoring system was sensitive to thyroid 125I. Its minimum detection limit of 23 Bq for a 10-min measurement was considerably lower than the annual thyroid burden limit of 300 kBq.