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- Author or Editor: D. Efurd x
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Abstract
In 1944 Los Alamos National Laboratory (LANL) instituted a program for the collection and analyses of urine samples from individuals working with plutonium. This program has operated continuously for over 60 years. During that time the plutonium bioassay program incorporated advances in urine sample collection, radiochemical separation techniques, alpha-spectroscopy and thermal ionization mass spectrometry measurement techniques as well as cleanroom technology. All of these advances have produced incremental improvements in plutonium detection limits. A chronological description is given of the methodologies used in the plutonium bioassay program at Los Alamos.
Summary
We have developed cleanroom compatible techniques for processing bone samples for characterization of their uranium and plutonium content. The bone samples are dried and ashed in quartz crucibles placed inside cleanroom compatible thermal ashing furnaces. The bone ash is dissolved in ultra-pure acids prepared by sub-boiling distillation. The uranium and plutonium in the samples are isolated and purified by ion-exchange chromatography and measured by thermal ionization mass spectrometry. The technique is capable of detecting 74 picograms of 238U and 8 femtograms of 239Pu in 100 mg bone ash samples. If the ash contains larger amounts of uranium and plutonium, the technique can be used to isotopically fingerprint the material to identify potential origins.
Summary
Extensive soil and sediment sampling was conducted along the Colorado Front Range and the plains east of the Front Range at locations believed to only be exposed to global fallout. The average 240Pu/239Pu atom ratio in the samples collected in Colorado was determined to be 0.165±0.008. A limited number of samples were collected at various locations in the Arctic at approximately 70° N latitude. Analyses of these samples predict that the 240Pu/239Pu atom ratio in environmental samples collected at 70° N latitude at locations only containing fallout is 0.183±0.009. These results provide data that help to precisely define the 240Pu/239Pu atom ratios representative of global fallout at the two locations studied.
Abstract
Utilization of thermal ionization mass spectrometry as a routine analytical service provided to the Los Alamos National Laboratory Bioassay Program has evolved significantly since its implementation just over three years ago. Converting this unique research tool designed to support nuclear weapons testing to a quasi-production mode for the routine analysis of ~300 urine samples/year for ultra-low levels of plutonium has required resolution of numerous practical issues. These issues include clean-room sample preparation, adequate tracer recovery, customer specified turn-around times, throughput, water and urine blank values, statistical data reduction, and quality control and performance evaluation sample requirements.
Summary
The lung dissolution rates for PuO2 were determined using a 100 day in vitro experiment. A very small amount of the PuO2 rapidly dissolved with a half-time of approximately 10 days, while the majority of the material (>99%) dissolved with a half-time of approximately 5 . 105 days. This dissolution half time is significantly longer than what is recommended by the ICRP, and would result in higher calculated doses for inhalation intakes of PuO2 than those currently estimated by the ICRP 66 human respiratory tract model for radiological protection.
Summary
As a follow up to the initial 1998 intercomparison study, a second study was initiated in 2001 as part of the ongoing evaluation of the capabilities of various ultra-sensitive methods to analyze 239Pu in urine samples. The initial study1 was sponsored by the Department of Energy, Office of International Health Programs to evaluate and validate new technologies that may supersede the existing fission tract analysis (FTA) method for the analysis of 239Pu in urine at the µBq/l level. The ultra-sensitive techniques evaluated in the second study included accelerator mass spectrometry (AMS) by LLNL, thermal ionization mass spectrometry (TIMS) by LANL and FTA by the University of Utah. Only the results for the mass spectrometric methods will be presented. For the second study, the testing levels were approximately 4, 9, 29 and 56 µBq of 239Pu per liter of synthetic urine. Each test sample also contained 240Pu at a 240Pu/239Pu atom ratio of ~0.15 and natural uranium at a concentration of 50 µBq/ml. From the results of the two studies, it can be inferred that the best performance at the µBq level is more laboratory specific than method specific. The second study demonstrated that LANL-TIMS and LLNL-AMS had essentially the same quantification level for both isotopes. Study results for bias and precision and acceptable performance compared to ANSI N13.30 and ANSI N42.22 have been compiled.
