In low-level radioactivity measurements, it is often important to decide whether a measurement differs from background. A traditional formula for decision level (DL) is given in numerous sources, including the recent ANSI/HPS N13.30-1996, Performance Criteria for Radiobioassay and the Multi-Agency Radiation Survey and Site Investigation Manual (MARSSIM). This formula, which we dub the N13.30 rule, does not adequately account for the discrete nature of the Poisson distribution for paired blank (equal count times for background and sample) measurements, especially at low numbers of counts. We calculate the actual false positive rates that occur using the N13.30 DL formula as a function of a priori false positive rate a and background Poisson mean mu = rhot, where rho is the underlying Poisson rate and t is the counting time. False positive rates exceed a by significant amounts for alpha < or = 0.2 and mu < 100 counts, peaking at 25% at mu approximately equal to 0.71, nearly independent of alpha. Monte Carlo simulations verified calculations. Currie's derivation of the N13.30 DL was based on knowing a good estimate of the mean and standard deviation of background, a case that does not hold for paired blanks and low background rates. We propose one new decision rule (simply add 1 to the number of background counts), and we present six additional decision rules from various sources. We evaluate the actual false positive rate for all eight decision rules as a function of a priori false positive rate and background mean. All of the seven alternative rules perform better than the N13.30 rule. Each has advantages and drawbacks. Given these results, we believe that many regulations, national standards, guidance documents, and texts should be corrected or modified to use a better decision rule.
The ever-increasing sensitivity of ICPMS continues to expand the technique's application in the field of health physics. Enhancements in sample introduction and instrument design over the last few years have resulted in improving the ICPMS detection limit from -10 ng/1 to _<0.1 ng/1. This additional sensitivity provides greater flexibility in the analysis of long-lived radionuclides in biological fluids, and requires only minimal sample preparation of urine for uranium analysis; the described 3-minute abbreviated matrix separation provides detection limits that are comparable to or better than alpha counting. For urine samples tested having concentrations that exceed the accepted administrative limit for total uranium (0.2 ~tg/day), isotopic analysis by ICPMS (e.g., determining the presence of 236U, or measuring appropriate uranium isotope ratios) provides a reliable indication of occupational exposure. Our laboratory also utilizes ICPMS in a study examining uranium dissolution rate classification of dust collected at the perimeter of a nuclear facility. Specific details regarding these and other health physics applications are featured, including our group's participation in assisting the DOE with the evaluation of ICPMS as a cost-effective alternative to fission-track analysis for the routine determination of 239pu in urine.
This document describes a project to evaluate the in-vivo counting performance criteria of draft ANSI Standard N13.30, Performance Criteria for Radiobioassay. The draft ANSI Standard provides guidance to in-vivo counting facilities regarding the precision and accuracy of measurements for certain categories of commonly assayed radionuclides and critical regions of the body. The draft ANSI Standard was evaluated by conducting an intercomparison test involving a number of whole-body counting facilities. The testing involved three types of measurements: chest counting for detection of radioactive materials in the lung, whole-body counting for detection of uniformly distributed activity, and neck counting for detection of radioactive material concentrated in the thyroid. Results of the first-round intercomparison test are presented in this report. The appropriateness of the draft Standard performance criteria was judged by the measurement results reported by participating in-vivo counting facilities. The intercomparison testing showed that some laboratories had difficulty meeting the performance criteria specified in the draft ANSI Standard Nl3.30 .
In the event of an accidental or intentional release of radionuclides into a populated area, massive numbers of people may require radiobioassay screening as triage for dose-reduction therapy or identification for longer-term follow-up. If the event released significant levels of beta- or alpha-emitting radionuclides, in vivo assays would be ineffective. Therefore, highly efficient and rapid analytical methods for radionuclide detection from submitted spot urine samples (≤50 mL) would be required. At present, the quantitative determination of alpha-emitting radionuclides from urine samples is highly labor intensive and requires significant time to prepare and analyze samples. Sorbent materials that provide effective collection and enable rapid assay could significantly streamline the radioanalytical process. The authors have demonstrated the use of magnetic nanoparticles as a novel method of extracting media for four alpha-emitting radionuclides of concern (polonium, radium, uranium and americium) from chemically-unmodified and pH-2 human urine. Herein, the initial experimental sorption results are presented along with a novel method that uses magnetic nanoparticles to extract radionuclides from unmodified human urine and then collect the magnetic field-induced particles for subsequent alpha-counting-source preparation. Additionally, a versatile human dose model is constructed that determines the detector count times required to estimate dose at specific protective-action thresholds. The model provides a means to assess a method's detection capabilities and uses fundamental health physics parameters and actual experimental data as core variables. The modeling shows that, with effective sorbent materials, rapid screening for alpha-emitters is possible with a 50-mL urine sample collected within 1 wk of exposure/intake.
Knowledge of site-specific extremity dosimetry programs is a necessary prerequisite for the identification of feasible alternatives to the upgrading of extremity dosimetry practices. Therefore, the Department of Energy (DOE), Office of Nuclear Safety (ONS) initiated a study to review the status of extremity dosimetry programs at DOE and DOE contractor facilities. The study is a result of information obtained during an earlier evaluation of the status of beta dosimetry programs.The objective of this study is to determine the adequacy of present extremity dosimetry programs and identify areas for improvement. This report is based upon the responses provided by DOE contractors throughout the United States.; ; i E. J. Vallario, Leader Health Physics Programs Office of Nuclear Safety U.S. Department of Energy • EXECUTIVE SUM~ARYA personnel dosimetry system must provide an accurate and reliable estimate of absorbed dose. Because extremity monitoring is one of the least well-defined facets of personnel dosimetry, the DOE Office of Nuclear Safety is interested in evaluating and, if necessary, upgrading extremity dosimetry. As part of the initial effort, a questionnaire on extremity dosimetry was distributed to DOE facilities along with a questionnaire on beta dosimetry. An informal telephone survey was conducted as a follow-up survey to answer a few additional questions concerning extremity monitoring practices. The responses to the questionnaire and the telephone survey are summarized in this report.Background information, developed from operational experience and a review of the current literature, is presented as a basis for understanding the information obtained by the survey and questionnaire. The information contained in the background section as well as the survey responses are used as a basis for recommendations for areas of further research and improvement. BACKGROUND INFORMATIONThe background information includes a discussion of regulations and recommendations from advisory groups, extremity dosimeter design and calibration, dosimeter use and placement, and methods used for dose assessment.The current regulations and recommendations specify dose equivalent limits to the hands, feet and forearms, which are different from the whole-body dose equivalent limit. Little guidance exists on the design or calibration of extremity dosimeters, the appropriate placement of extremity dosimeters, or methods of dose assessment.A wide variety of extremity dosimeter designs exists. Many of the extremity dosimeters in use are simple modifications of whole-body dosimeters. However, the critical tissues for radiation damage in the extremity, the composition of the tissues, and the type of damage that may occur differs from that of the whole body. The measurement of beta or neutron radiation to the extremities presents special problems. Because of the shallower penetration of beta radiation, the material above the dosimeter must be thin enough for the v beta radiation to penetrate. Further, the thickness of dosimeter material will...
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