Estimating MDA for low-level radioactivity in a radiobioassay laboratory

To ensure a safe working enviromment and to provide occupational health and safety protection to its employees, the Intemal Dosimetry Group under the Radiation Protection Monitoring Program at Oak Ridge National Laboratory routinely collects urine samples from persons working with radioactive materials or working in areas where exposure to radiation is possible. The ORNL Radiobioassay Laboratory (RBL) analyzes these urine samples for various mdionuclides such as Americium, Uranium, Plutonium, Strontium, and many others. During 1991, RBL processed approximately 4,500 analyses, covering over 1,400 samples and a total of 18 different isotopes. The accuracy of dose assessment is extremely vital to radiation control in a laboratory, not only because the credibility of a laboratory is affected by its ability to obtain accurate measurements, but also because the health safety of those who work in the laboratory is a major concem. The ANSI N13.30: Draft American National Standardfor Performance Cilteria for Radiobioassay, published in 1989 and revised in 1992, was written for that reason. ANSI N13.30 provides guidance for sample processing and measurement control. It addresses quality control criteria and procedures to be followed by a radiobioassay laboratory. ANSI N13.30 also provides criteria for these laboratories to conduct performance testing. Such standardizedmore » methods make inter-laboratory comparisons both possible and meaningful. Also, intra-laboratory personnel exposures can be better monitored. One of the major performance testing methods standardized by ANSI N13.30 is the method for determining an instrument's Minimum Detectable Amount (MDA) of a given radionuclide.« less