Robert B. Hayes

Electron Paramagnetic Resonance Dosimetry of Dentine Following Removal of Organic Material

The feasibility of using dentine from surgically extracted human teeth as in vivo dosimeters was investigated. The organic fraction of human dentine was removed by Soxhlet extraction with diethylenetriamine. The specimens were then crushed and 75 to 250 microns granules were given doses of gamma radiation ranging from 50 mGy to 8 Gy. Following irradiation, electron paramagnetic resonance spectra were collected. Signals were detected with Lande factors of g = 2.0018, line width = 0.903 mT; and g = 1.9961, line width = 0.444 mT. These signals have both been reported for hydroxyapatite of bone and enamel. Several other signals were also seen but not characterized. It was concluded that doses of 500 mGy or less may be resolved with prior removal of the organic component of dentine.

Alpha CAM alarm set points in a salt dust environment.

While considering the regulatory and site specific requirements for Continuous Air Monitor responses in the Waste Isolation Pilot Plant underground (which is a salt mine), a number of issues relating to the buildup of salt (NaCl) on the filters must be considered when determining the alarm set points. As the Waste Isolation Pilot Plant is a Department of Energy facility, alarm set point determination must be made in light of the regulatory drivers and physical limitations found when monitoring for airborne contamination in an underground salt mine. The use of dual alarm set points is also exploited to implement a graded approach to alarm responses.

False CAM alarms from radon fluctuations.

The root cause of many false continuous air monitor (CAM) alarms is revealed for CAMs that use constant spectral shape assumptions in transuranic (TRU) alpha activity determination algorithms. This paper shows that when atmospheric radon levels continually decrease and bottom out at a minimum level, reduced false TRU count rates are not only expected but measured. Similarly, when the radon levels continually increase to a maximum level, elevated false TRU count rates were measured as predicted. The basis for expecting this dependence on changes in radon levels is discussed.

An EPR dosimetry method for rapid scanning of children following a radiation accident using deciduous teeth

Electron paramagnetic resonance dosimetry may be applied to whole deciduous teeth of children. This makes it feasible to make direct measurement of absorbed gamma ray dose in the days and weeks following a nuclear accident, particularly if used in conjunction with a public awareness program. The technique reported here requires little sample preparation and has resulted in precision of approximately 30 mGy (1 sigma) for a deciduous incisor. Under conditions for rapid screening procedures, the methodology is estimated to provide 0.5 Gy accuracy. The largest error in the process is the determination of an appropriate background native signal for subtraction from the whole tooth spectrum. The native signal is superimposed on the radiation-induced signal, and the subtraction requires knowledge of a samples relative content of enamel and dentin along with their relative native signal intensities. Using a composite background standard, an equivalent absorbed dose of 70+/-38 mGy (1 sigma) was determined. The lower detection limit of the technique was achieved by the elimination of anisotropic effects through rotation of the sample during measurement, together with subtraction of the standard native background signal and empty tube background spectra from the sample spectra.

Curve fitting air sample filter decay curves to estimate transuranic content

Abstract— By testing industry standard techniques for radon progeny evaluation on air sample filters, a new technique is developed to evaluate transuranic activity on air filters by curve fitting the decay curves. The industry method modified here is simply the use of filter activity measurements at different times to estimate the air concentrations of radon progeny. The primary modification was to not look for specific radon progeny values but rather transuranic activity. By using a method that will provide reasonably conservative estimates of the transuranic activity present on a filter, some credit for the decay curve shape can then be taken. By carrying out rigorous statistical analysis of the curve fits to over 65 samples having no transuranic activity taken over a 10-mo period, an optimization of the fitting function and quality tests for this purpose was attained.

Preliminary evaluation of real time false CAM alarm prediction through continuous radon monitoring.

The outputs of two real-time radon monitors were compared with the output from a continuous air monitor (CAM) to evaluate the potential of predicting false CAM alarms. From the results obtained, it appears that the radon monitor will be able to indicate when large rapid changes in radon levels are occurring before the effect on a CAM has taken place.

Consequence Assessment of the WIPP Radiological Release from February 2014.

AbstractOn 14 February 2014, a continuous air monitor (CAM) alarm at the exit of panel 7 in the Waste Isolation Pilot Plant (WIPP) underground facility caused the mine ventilation to shift from unfiltered air over to HEPA filtration for its effluent. Subsequent measurements of the effluent at both pre- and post-HEPA filtration using representative sampling demonstrated that a release had occurred. Using modeling based on measured effluent activity, onsite dose estimates were calculated and later measured via bioassay to be less than 0,1 mSv from intakes of radioactivity. The maximum offsite dose potential to nearby dwellings was modeled to be 1 µSv or less, which was consistent with air samples being taken at those dwellings during the release, demonstrating impressive accuracy and precision. No worker or public dose limits have been exceeded, and the release was substantially below the annual release limits for the WIPP site.

Using isotopic ratios for discrimination of environmental anthropogenic radioactivity.

AbstractWhen air is pulled into the WIPP repository for ventilation purposes, this air is unfiltered and contains all the components of ubiquitous anthropogenic radionuclides from global nuclear fallout (including 137Cs and Pu isotopes). Although the NORM in aeolian sand and dust contribute to the gross alpha beta activity on effluent air filters, there remains a need to discriminate effluent TRU generated in the disposal process at WIPP from TRU being pulled into the repository with the unfiltered surface air. This is only evaluated using ratios of Cs and Pu activity found through radioassay of air filters taken from the mine effluent. By characterizing both the credible range of 137Cs/239,240Pu ratios from the environment and those known to exist in the waste, a rigorous test criteria is attained. The use of HPGE to assay 137Cs in the intake dust plated out in the mine allowed a gross assay of total TRU radioactivity pulled into the mine over time from global fallout. Radiochemistry of samples from deposition in the mine’s air intake shaft was also carried out. The use of net activity ratios at background levels is also shown to follow a Cauchy distribution in terms of their expected statistical distributions.

Preliminary Benchmarking Efforts and MCNP Simulation Results for Homeland Security

Abstract It is shown that basic measurements made from well-defined source detector configurations can be readily converted into benchmark quality results by which Monte Carlo N-Particle (MCNP) input stacks can be validated. Specifically, a recent measurement made in support of national security at the Nevada Test Site is described with sufficient detail to be submitted to the American Nuclear Society’s Joint Benchmark Committee for consideration as a radiation measurement benchmark. From this very basic measurement, MCNP input stacks are generated and validated both in predicted signal amplitude and spectral shape. Not modeled at this time are those perturbations from the more recent pulse-height-light tally feature, although what spectral deviations are seen can be partially attributed to not including this small correction. The value of this work is as a proof-of-concept demonstration that well-documented historical testing can be converted into formal radiation measurement benchmarks. This provides evidentiary support that validated virtual testing could eventually be carried out for various detection system technologies including algorithms, new detector designs, constructions, and arbitrary source and shielding assemblies.

A new technique for preliminary estimates of tru activity on air sample filters and radiological smears

In most nuclear facilities, fixed air samplers and sometimes portable air samplers are used where some probability of a release exists but is not expected, and so the added expense and effort of using a continuous air monitor is not deemed justified. When a release is suspected, naturally occurring radioactive material buildup on the filter typically prevents any quantitative measurements within the first day or so. Likewise, outdoor air measurements suffer from the same limitations (such as those taken during the Los Alamos fires) and so any rapid quantifiable measurements of fixed air sampler/portable air sampler filters which are technically defendable (even though conservative) are of use. The technique presented here is only intended for use in routine health physics survey applications and does not presently appear to be appropriate for sub pico Curie activity determinations. This study evaluates the utility of using a portable continuous air monitor as an alpha spectrometer to make transuranic activity determinations of samples using both the built in algorithm for air monitoring and a simple region of interest analysis. All samples evaluated were from air sample filters taken using a portable air sampler. Samples were taken over many months to quantify effects from natural variation in radon progeny activity distributions.