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.
A method for determining half value layers (HVLs) of inverter-type X-ray equipment using a computed radiography (CR) systems was developed. This method is similar to the traditional method, where the air kerma (K) is measured using an ionization based dosimeter and increasing aluminum (Al) absorber thickness, but utilized an imaging plate (IP) and the sensitivity index (S number) of the CR system as the dosimeter and the dosimeter reading, respectively. The IP and the S number were calibrated using an ionization chamber having traceability to the National Standard Ionization Chamber. A modified version of the S number definition equation K=a × S(-b) was used to translate the S number to K values for X-ray beams produced using tube voltages ranging from 50 to 120 kV and additional Al filtration up to 2.5mm. The coefficient 'a' varied depending on the beam quality, while the coefficient 'b' showed a constant value of 0.991. The HVLs in the range from 1.8 to 5.5mm Al that were obtained with this method were in good agreement with those obtained with the traditional method, as uncertainties were between -7 and 4%. This method can be used to determine the HVLs of inverter-type X-ray equipment within an acceptable accuracy.
Dosimetry using an imaging plate (IP) of computed radiography (CR) systems was developed for quality control of output of the x-ray equipment. Sensitivity index, or the S number, of the CR systems was used for estimating exposure dose under the routine condition: exposure dose from 1.0 to 1.0 x 10(2) microC kg(-1), tube voltages from 50 to 120 kV, and added filtration from 0 to 4.0 mm Al. The IP was calibrated by using a 6 cc ionization chamber having traceability to the National Standard Ionization Chamber. The uncertainty concerning the fading effect was suppressed less than 1.9% by reading the latent image 4 min+/-5 s after irradiation at the room temperature 25.9+/-1.0 degrees C. The S number decreased linearly on the logarithmic graph regardless of the beam quality as exposure dose increased. The relationship between the exposure dose (E) and the S number was fitted by the equation E=a' X S(-b). The coefficient a' decreased when the added filtration and the tube voltage were increased. The coefficient b was 0.977+/-0.007 in all beam qualities. The dosimetry using the IP and the equation can estimate the exposure dose in a range from 9.0 x 10(-2) to 5.0 microC kg(-1) within an uncertainty of +/-5% required by the Japanese Industry Standard. This dose range partially included the doses under routine condition. The doses between 1.0 and 1.0 x 10(2) microC kg(-1) under the routine condition can be shifted to the 5% region by using an absorber. The IP dosimetry is applicable to the quality control of the CR systems.
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