Thermoluminescent Dosimeter Use for Environmental Surveillance at the Hanford Site, 1971?2005

Abstract

SummaryThe U.S. Department of Energy (DOE) requires that environmental monitoring programs be conducted at its Hanford Site in south-central Washington to protect the site's environmental and cultural resources, the public, and site workers by achieving site and contractor compliance with environmental, public health, and resource protection laws, regulations, and DOE Orders. Pacific Northwest National Laboratory (PNNL) manages Public Safety and Resource Protection Projects (PSRPP) for DOE's Richland Operations Office to monitor the Hanford environment, provide assurance that the site is operated in compliance with applicable environmental regulations, and conduct impact assessments to protect public and worker safety and Hanford's ecological and cultural resources. Under the PSRPP, the Surface Environmental Surveillance Project is responsible for measuring the concentrations of radiological and nonradiological contaminants in environmental media and for assessing the potential impacts of these materials on the environment and the public. Various media are collected onsite in the 600 Area, and offsite at perimeter, community, and distant locations. Samples of air, surface water and sediment, farm products, wildlife, and vegetation are routinely collected and analyzed for radionuclides and various chemical constituents. From 1971 through 2005, ambient external radiation was also measured at selected locations on and off the site.This report briefly describes the principles of thermoluminescent dosimetry and the various thermoluminescent dosimeter (TLD) systems that have been used at Hanford for environmental surveillance of external radiation over its operational history largely by PNNL under the so-called Hanford Environmental Surveillance TLD Program, or simply the TLD program. It presents the results of a review of the measurement of external radiation using TLDs outside of industrialized areas on the site, at locations along the river shoreline, and in areas adjacent to and distant from the Hanford Site. Quality assurance practices and independent measures of system performance are discussed, supplemented by summaries of TLD results from January 1971 through December 2005 (when the TLD program was terminated) and analysis of observed trends. Summary figures and narrative discussion of TLD readings at each surveillance location are included for both terrestrial (onsite and offsite) locations and riparian (Columbia River shoreline) locations.An apparent increase in environmental exposure rates was observed from 1985 through 1989 after a large-scale exchange of TLD chips. Part of the increase is believed to be attributable to the greater sensitivity of replacement TLD chips to low-energy photons, and possible changes in calibration practices in the TLD processing laboratory. Analysis of variance showed that there was a significant difference in TLD readings based on dosimeter type and that, historically, there was a significant difference in readings between location groupings of TLDs (i.e., onsite, perimeter, c...

Review of the thermoluminescent dosimetry method for the environmental dose monitoring

“…The TLD sys tem is com posed of TLD ma te rial, a TLD reader, a do sim e ter holder, a cal i bra tion and dose cal cu la tion method, and stor age and/or de ploy ment meth ods. If dif fer ent TLD sys tems are used over the dif fer ent mon i tor ing pe ri ods at par tic u lar lo ca tion, it is not ap pro pri ate to com pare such sys tems with out account ing for the po ten tial dif fer ences in re sponse [27].…”

“…The anal y sis of vari a tions in am bi ent dose observed dur ing the de cades re vealed that trend does not Ta ble 1. Ba sic prop er ties of TLD sys tem (adopted from [14,22,27])…”

Recent Advances and Opportunities in TLD Materials: A Review

“…LiF-based dosimeters are very sensitive not only to its impurity content but also to other treatments as well, such as thermal, mechanical and radiation treatments [71]. After exposure to 60 Co irradiations, LiF-based dosimeters are the most widely used thermoluminescence phosphors in personal radiation monitoring [72]. In a previous study, the glow curve of LiF:Mg,Ti (TLD-100) was investigated under different thermal treatments.…”