Faculty Bibliography

An imaging Mueller matrix polarimeter, named the red-green-blue (RGB)950, takes images of medium-sized (tens of centimeters) objects by using a very bright source, large polarization state generator, and high-quality camera. Its broadband extended light source switches between red, green, blue, and near-infrared light to allow taking polarimetric images for comparison with RGB camera images. The large diffuse source makes shadow transitions gradual and spreads out the specular reflected spot into a larger less conspicuous area.

Since 2000, National Institute for Occupational Safety and Health (NIOSH) has used dose conversion coefficients published by the International Commission on Radiation Protection in report 74 (ICRP 74) to determine organ dose from external radiation sources. In 2010, the ICRP issued publication 116 using more realistic phantoms than ICRP 74. NIOSH has developed a Monte Carlo method to sample the energy-organ-specific distribution of the ICRP 116 conversion coefficients to determine the organ dose and the associated uncertainty. Using Monte Carlo methods, irradiation geometry factors (IGFs) were developed to convert the measured dosemeter dose on the front of the body to values that are compatible with ICRP 116 organ dose conversion coefficients. Specific IGFs were developed for (1) both neutrons and photon exposures, (2) to male and female workers and (3) for rotational and isotropic exposure geometries. The computed mean organ dose and the associated uncertainty are used in the probability of causation calculation for compensation.

External doses reconstructed under Part B of the Energy Employees Occupational Illness Compensation Program Act include not only those that were recorded by personal dosimeters, but also those that were not recorded. Recorded doses may require corrections to account for measurement bias or limitations in the dosimeters' capabilities. Unrecorded doses that have been reconstructed include (1) those missed due to limits of detection associated with personal dosimeters, (2) external ambient doses that may have been inadvertently omitted from the monitoring results (or were not monitored altogether in the case of nonradiation workers), and (3) doses incurred as a result of medical x-ray examinations required by employers. Additionally, some workers were not monitored (or their dosimetry data are not available) even though there was a potential for exposure; doses to such workers are typically assigned based on the records of coworkers who performed the same, or similar, tasks. Additional issues that complicate the dose reconstruction process include the requirements that (1) all external doses must be partitioned according to radiation type and energy, and (2) the accompanying doses to specific body organs must be estimated. Since the external dose reconstruction process typically incorporates many claimant-favorable methodologies, parameters, and assumptions, the doses assigned do not necessarily reflect either realistic or actual estimates of the doses received, and external doses assigned to workers under the Act often are substantially higher than those contained in the dosimetry records.

There are many claimant-favorable factors inherent in both the reconstruction of radiation dose and the calculation of probability of causation under Part B of the Energy Employees Occupational Illness Compensation Program Act of 2000. These factors result in an approximate 30% compensation rate for claims filed under EEOICPA, which is roughly an order of magnitude greater than the likely incidence of increased cancers as predicted by epidemiology studies and risk models. Additionally, there is essentially no chance that a claim that is denied compensation actually involves a radiation-induced cancer. The claimant-favorable nature of the Part B program is often misunderstood or ignored when the merits of the program are reported and debated. This paper provides details on how the technical aspects of the EEOICPA program that favor the claimants are being implemented.

Theoretical models predict that selection on reaction norms should depend on the relative frequency of environmental states experienced by a population. We report a laboratory experimental test of this prediction for thermal performance curves of larval growth rate in Pieris rapae in relation to their thermal environment. We measured short-term relative growth rate (RGR) for each individual at a series of five temperatures, and then we assigned individuals randomly to warm or cool selection treatments, which differ in the frequency distributions of environmental temperatures. Selection gradient analyses of two independent experiments demonstrated significant positive selection for increasing RGR, primarily through its effects on survival to adulthood and on development rate. In both the warm and cool selection treatments, the magnitude of directional selection on RGR was consistently greater at lower (suboptimal) temperatures than at higher temperatures; differences in selection between the treatments did not match model predictions. The temporal order and duration of environmental conditions may affect patterns of selection on thermal performance curves and other continuous reaction norms, complicating the connections between variation in environment, phenotype, and fitness.

The dual-rotating-retarder configuration is one of the most common forms of the Mueller matrix polarimeter. I perform an optimization of this polarimeter configuration by minimizing the condition number of the system data reduction matrix. I find the optimum retardance for the rotating retarders to be 127 degrees. If exactly 16 intensity measurements are used for a Mueller matrix calculation, a complex relationship exists between the condition number and the sizes of the angular increments of the two retarders. If many intensity measurements are made, thus overspecifying the calculation, I find broad optimal ranges of angular increments of the two retarders that yield essentially equal performance. Experimental results are given.