Response of TLD-albedo and nuclear track dosimeters exposed to plutonium sources

Abstract

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...

Hanford External Dosimetry Technical Basis Manual PNL-MA-842

“…Periodic field measurements have demonstrated adequate performance can be obtained with the 8816 TLD albedo neutron dosimeter. Detailed design considerations for the HCND are provided by Brackenbush, Baumgartner and Fix (1991) and Endres et al (1996). A clear plastic holder is used to retain the 8816 and 8825 TLDs , along with an optional Personnel Nuclear Accident Dosimeter (PNAD), as shown in Figure 5.16.…”

“…Knowledge of the spectrum of energies for beta, photon, and neutron radiation in Hanford facility work environments is critically important to the correct interpretation of personnel dose. Technical reports of field measurements (Fix et al 1981(Fix et al , 1982Brackenbush et al 1980Brackenbush et al , 1991Endres et al 1996;Scherpelz, Fix, and Rathbone 2000), along with numerous letter reports to HEDP files, have been prepared. Much of this work has been focused on evaluating dosimeter performance in Hanford facility work environments and the overall uncertainty in Hanford recorded dose.…”

“…HEDP staff have used one or more of these systems to measure dose on several occasions. Techniques for gamma spectroscopy are well defined in the literature (Brackenbush, Baumgartner, and Fix 1991).…”