Measurement uncertainty is an important quality index in gamma spectrometry related to the level of bias and precision involved in the measuring procedure. Quality control measurements during the commissioning of a 16-input whole body counter showed substantial deviations between the experimentally determined precision and the theoretical estimation, indicating either equipment malfunction or lack of reproducibility of the experimental setup. In this study, the role of the magnitude and variability of airborne background radiation present in the counting room and the human body in the deterioration of the precision of counters employing NaI(Tl) detectors was investigated. Correction methods and actions based on case-specific background features were developed and applied. The experimental observations were benchmarked using a mathematical model of the counter. The efficacy of the developed methods was tested by measurements, and updated precision values were obtained. Quasi-equilibrium between the gamma-emitters Bi and Pb in the counting room and the human body is a prerequisite for accurate direct low-level radioactivity measurements in the human body.
A prototype shadow-shield whole body counter is used at the University of Ioannina Medical Physics Laboratory as a tool in radiation protection and in biomedical research. In this study the effect of natural airborne radioactivity on the measurement quality features was investigated and performance improvements were developed. Radon air concentration in the counting room was assessed using electret and track detectors over short and long time periods, respectively under various ventilation conditions. A method based on the assessment of the 214Bi 1.76 MeV spectral region was developed to correct for the interference of the radon products to the lower energies of the spectrum. Moreover airborne radioactivity in the counting room was controlled by forced ventilation. Double measurements were carried out in anthropomorphic phantoms and in adult volunteers to assess the impact of the room ventilation module in the measurement precision. Radon control coupled with corrections for the interference of its decay products improved substantially the counter performance characteristics.
A prototype shadow-shield whole body counter was designed, constructed and tested as a radiation protection, medical and research tool, such as in in vivo human body composition and in occupational exposure studies. In the present study potential fields of application of a prototype whole body counter were investigated carrying out measurements in groups of adult volunteers. Among others, the naturally occurring 40 K and 214 Bi whole body radioactivity was assessed. The activity of the former was correlated with the amount of the total body potassium, a quantity related to both cell mass and lean mass in the human body. Increased 214 Bi levels found in two subjects was attributed to radium intake by ingestion. Patients were found contaminated with long lived radionuclides after administration of radiopharmaceutical of short half-life, administered for either diagnosis or treatment. Among the radiation workers monitored for internal occupational exposure, two were found contaminated with small amounts of 99m Tc.
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