T h i s report documents response characteristics and the development of dose algorithms for the Hanford Combination Neutron Dosimeter (HCND) implemented on January 1, 1995. The HCND was accredited under the U.S. Department o f Energy (DOE) Laboratory Accreditation Program (DOELAP) during 1994. The HCND employs two neutron dose components consisting o f 1) an albedo thermoluminescent dosimeter (TLD) , and 2) a track-etch dosimeter (TED). Response characteristics of these two dosimeter components were measured under the low-scatter conditions of the Hanford 318 Building Calibration Laboratory, and under the high-scatter conditions in the workplace a t the Plutonium Finishing Plant (PFP). The majority of personnel neutron dose a t Hanford (currently and historically) occurs a t the PFP. National Institute of Standards and Techno1 ogy (NIST) 'traceable sources were used t o characterize dosimeter response i n the laboratory. A t the PFP, neutron spectra and dose-measuring instruments, including a mu1 tisphere spectrometer, tissue equivalent proportional counters, and specially calibrated rem meters, were used t o determine the neutron dose under several configurations from three different plutonium sources: 1) plutonium tetrafluoride, 2) plutonium metal , and 3) plutonium oxide. In addition,
Neutron dosimetry has been extensivelystudied at Hanford since the g inception of operationsin the mid-J940s (Wilson et al. 1990). At the present r, time, Hanford contractorsuse thermoluminescentdosimeter (TLD)-albedo , dosimeters to record the neutron dose equivalentreceived by workers. The energy dependenceof the TLD-albedodosimeter has been recognizedand documented since introducedat Hanford in 1964, and numerous studies have been performed to help assure the accuracy of dosimetersused in the work place. Historically,the largest pe,'_onnel neutron exposures occurred at the fluorinatorglove boxes used for processingplutonium. In the past, the Hanford MultipurposeDosimeterwas calibratedto accuratelyrecord doses from this source. This has resulted in conservativeassessments for many other neutron sources. With the recent change in Hanford'smission, there has been a significant decrease in the handling of plutoniumtetrafluoride,and an increase in the handling of plutonium metal and plutonium oxide sources. Also, the introduction of U.S. Departmentof Energy LaboratoryAccreditationProgram (DOELAP) requires the dosimeter to accuratelyassess the dose equivalentfrom 2SZCf sources under the low scatter conditionsof the calibration laboratory. This study was initiated to document the performanceof the current Hanford TLD-albedodosimeter under the low scatter conditions of the callbration laboratoryand under the high scatter conditions in the work place under carefully controlledconditionsat the Plutonium Finishing Plant (PFP). The neutron fields at the PFP facility were measured using a variety of instruments,includinga multispherespectrometer,tissue equivalentproportional counters,and specially calibratedrem meters. The dose equivalent rates from plutonium fluoride, plutoniumoxide, and plutoniummetal sources were determinedusing these instruments. The plutonium tetrafluoridesource is of 'importance because it is the same source that was used to calibrate o instrumentsand neutron dosimeters at Hanford from 1964 to 1981. The dosimeter results from the plutonium tetrafluorideexposures may be useful in interpretingpast dosimeter records. A variety of neutron dosimeterswere iii exposed on an acrylic plastic phantom (the same phantoms used in DOELAP accreditation) in these measured fields. Measurements were also performed with selected thickness of acrylic plastic positioned between the neutron source and the detectors to simulate glove boxes and neutron shielding windows. Various algorithms were used to evaluate the TLD-albedo dosimeters, and q the results are given in Section 7 of this report. Using current algorithms, the dose equivalents evaluated for bare sources and sources with less than 2.5 cm (1 in.) of acrylic plastic shielding in high scatter conditions typical of glove box operations are reasonably accurate, as expected. But the TLDalbedo dosimeters significantly overestimate the dose equivalent when exposed to moderated neutrons from sources with 5 cm to 15 cm (2 in. to 6 in.) of acrylic plastic shielding. The re...
PNL-3213 UC-41 NOTICE This report was prepared as an account of work sponsored by the United States Government. Neither the United States nor the Department of Energy, nor any of their employees, nor any of their contractors, subcontractors, or their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness or usefulness of any information, apparatus, product or proce~s disclosed, or represents that its use would not infringe privately owned rights. The views, opinions and conclusions contained in this report are those of the contractor and do not necessarily represent those of the United Sta'tes Government or the United States Department of Energy.
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