v>EPA INTRODUCTION United States Environmental Protection Agency Environmental Monitoring Systems Laboratory P.O. Box 93478 Las Vegas NV 89193-3478 June 1991 lijft fchY',1 i A. OFFICE OF RESEARCH AND DEVELOPMENT TECHNOLOGY SUPPORT PROJECT Internal Dosimetry for Radionuclides in Humans Monitoring human exposure to radionuclides is an integral component of EPA's mission to protect the health of the public. State-of-the-science equipment and a rigorous quality assurance program provide scientists with accurate information. Whole body counting is an internal dosimetry method that uses gamma spectrom- etry to identify radionuclides and to measure their concen- tration and distribution in a human body. Lung counting detects inhaled radionuclides which are deposited in the lungs. Counting of areas of the body such as the skull, the liver, or other organs where specific radionuclides may concen- trate provides additional information necessary to calculate internal radiation dose. The germanium detectors used in both the whole body and lung counter are passive devices, i.e., they detect emitted radiation but do not emit any radiation themselves. Bioassay for tritium, stron- tium, and other radionuclides which are not detectable with gamma spectroscopy is performed, when necessary. The Environmental Monitor- ing Systems Laboratory-Las Vegas (EMSL-LV) has maintained a whole body counting facility since 1966. THE FACILITY AND EQUIPMENT Two counting vaults, shielded with 6-inch thick, pre-World War II steel walls, provide a low background area for counting. One vault, used for whole body counting, is equipped with a high purity germanium detector posi- tioned over an adjustable chair in which the subject reclines during the count. High energy gamma-emitting radionuclides, with energies ranging from 60 keV to 2.0 MeV (such as cesium and cobalt) can be identified and measured with this system. The second vault contains an adjustable chair with six state-of-the-art, high-purity germanium semi-planar detectors mounted above it. These detectors, fitted with very thin "windows" to admit very low energy radiations, are designed for detection of low energy gamma and X-ray emitting radionuclides (such as americium and plutonium). Detected energies range from 10 to 300 keV. Lung, liver, skull, and other specific organ or bone counting is done here. Both counting vaults have anticlaustrophobial mea- sures. One wall of each vault is covered with a mural to provide a less institutional feeling, and the subject may watch TV or read. Data acquisition and process- ing equipment includes a gamma spectroscopy system which detects the radiation, amplifies and shapes the detector signals, stores and displays data, and analyzes the data to identify radionu- clides. A fully-integrated computer/multichannel analyzer system is used, and the software, including data acquisition and analysis, data base management, word processing, and statistical analysis, is tailored for whole body counting needs. C333t. X 9 • ------- QUALITY ASSURANCE The efficiency of the detec- tion system is determined by comparing the amount of radiation measured by the counting system to the known amount in a sample - in this case, a polyethylene bottle "phantom" called the "BOMAB." Its shape and volume is equal to a "stan- dard man." Lung and thyroid phantoms are also used for efficiency calibration. An energy calibration is done daily to correct for the inherent drift properties of detectors. Calibration results are tracked with a quality assur- ance software package. Daily and monthly quality assurance reports and plots are generated. Internal and external audits are routinely conducted, and permanent records are kept of quality assurance and personnel counting data. This facility participates in intercalibration studies with other whole body counting facilities in the United States to check on both efficiency and energy calibration status. COUNTING PROGRAM Civilian government, Depart- ment of Defense, commercial power plant, fuel fabrication plant, and contractor person- nel who have a potential for exposure to radionuclides are counted routinely. Any person who feels they may have been exposed to radionuclides may make an appointment for a count. A program to assess levels of radionuclides in members of some of the families residing in communities and ranches surrounding the Nevada Test Site was initiated in Decem- ber 1970. The Community Monitoring Station Network, a joint endeavor among Department of Energy, Environmental Protection Agency, and the Desert Research Institute of the University of Nevada, was established in 1981. The station managers of this network, who are generally science teachers in their communities, and their families, entered the counting program at this time. The families who participate in this program are located in Nevada, California, and Utah. SUMMARY The internal dosimetry program and the networks maintained by EMSL-LV around the Nevada Test Site and in the states west of the Mississippi River provide for the monitoring of human exposure to radionuclides. Whole body counting is provided free of charge, by appointment only, to EPA Regional personnel and their contractors who are involved with radioactive or mixed waste cleanup programs and other work involving expo- sure to radionuclides. FOR FURTHER INFORMATION For further information on whole body counting, contact: Ms. Anita Mullen Health Physicist Nuclear Radiation Division U.S. Environmental Protection Agency P.O. Box 93478 Las Vegas, NV 89193-3478 (702) 798-2597 FTS 545-2597 O z o >VPPQrt o % echnology "2* d f-'roject £ \, ^ Q.QGY For Technology Support Center information, contact: Mr. Ken Brown, Manager Technology Support Center U.S. Environmental Protection Agency P.O. Box 93478 Las Vegas, NV 89193-3478 (702) 798-2270 FTS 545-2270 The Technology Support Center fact sheet series is developed and written by Clare L. Gerlach, Lockheed Engineering & Sciences Company, Las Vegas. ------- |