David Hickman

Polonium metabolism in adult female baboons

The biokinetics of polonium in nonhuman primates (Papio anubis) has been studied after intravenous injection of 210Po citrate. The urinary excretion of polonium in the baboon could be described by a single exponential function with a half-time of 15.6 days. Excretion fractions of polonium were found to be markedly different from those reported for other species, including humans. Polonium-210 was found to be distributed throughout the soft tissues of the baboon with 29% of the injected polonium being deposited in liver, 7% in kidneys and 0.6% in spleen. Retention of polonium in all tissues exhibited single exponential functions; however, the biological half-times were variable, ranging from 15 to 50 days.

Reconstruction of a human skull calibration phantom using bone sections from an 241Am exposure case.

New York University Medical Centers Institute of Environmental Medicine (NYUMC/IEM) was called upon by representatives of the United States Transuranic Registry to reconstruct a human skull phantom for the purpose of producing a calibration structure to be used for determining 241Am skeletal content from in vivo measurements. The human skull represented a deposition pattern of 241Am in the bone matrix which had accumulated into the bone via natural metabolic processes after an accidental intake. Soon after death, the skull was sagittally divided and the left lateral side was analyzed radiochemically. Assuming symmetry of deposition, and based on measurements of the right lateral side of the skull performed at NYUMC/IEM as well as results of radiochemical analysis of sections of the left side, the activity content of the right side was estimated to be 307 +/- 4 Bq (8.3 +/- 0.1 nCi). The right side was subsequently paired with a blank left lateral of a control skull and embedded into tissue-equivalent material. The reconstructed skull phantom was then evaluated to determine its applicability as a calibration phantom which could be used to estimate skeletal burdens of 241Am.

Measurement of the attenuation coefficient for Livermore Thoracic Phantom lungs fabricated using contemporary materials.

The University of Cincinnati has reproduced the original formulation for the Livermore Thoracic Phantom lungs using contemporary materials and has adopted the linear attenuation coefficient as the primary quality assurance parameter for evaluating the performance capabilities of these new lung phantoms. The Livermore Thoracic Phantom was originally fabricated in 1978 to intercalibrate detector systems used to measure plutonium and other low-energy, photon emitting radionuclides deposited in the respiratory tract. The linear attenuation coefficient is a critical performance indicator for these phantom lungs since the presence of any material with a high effective atomic number (where Z > or = 20) will make a significant change in the photoelectric cross section, the predominant mode of interaction for plutonium x rays. A set of test lungs was fabricated with KCl to introduce a known quantity of 40K in the phantom and to determine, by measurement and calculations, what change would be made to the attenuation coefficient at photon energies below 100 keV as a result of the modified formulation. The KCl increased the linear attenuation coefficient below 60 keV by more than a factor of two, which would produce a substantial systematic error in any subsequent calibration measurements performed with these modified phantom lungs. These results support use of the attenuation coefficient as an important performance indicator for the Livermore Thoracic Phantom lungs and also suggest that KCl not be added to the lung tissue substitute formulation as a means to incorporate 40K in the phantom for low energy calibrations.

The Importance of Acid Digestion of Urine Prior to Spontaneous Deposition of 210po

Historically, radiochemical analysis of 210Po in urine has used spontaneous deposition of the nuclide directly from raw urine onto a suitable metal disc. Consequently, the urinary excretion fraction for Po in some current metabolic and dosimetric models is based on studies which inherently assume that metabolized (i.e., filtered out of the blood by the kidneys) 210Po is plated with the same efficiency as tracer 210Po which has been added to urine samples. Urine samples collected after intravenous administration of 210Po citrate to two species of nonhuman primates were divided and simultaneously analyzed via two methods: the historical procedure of plating 210Po from raw urine for one sample and a method which includes the addition of 208Po tracer and sample digestion with concentrated HNO3 prior to 210Po deposition for the other sample. A more significant amount of 210Po was consistently recovered when the urine was wet ashed then when it was not wet ashed. A temporal relationship was found to describe the change in the ratio of the deposition recoveries for the two methods. Possible mechanisms for this phenomenon and its dosimetric implications are discussed.

A whole body counting facility in a remote Enewetak Island setting.

The U.S. Department of Energy (DOE) has recently implemented a series of strategic initiatives to address long-term radiological surveillance needs at former U.S. test sites in the Marshall Islands. The plan is to engage local atoll communities in developing shared responsibilities for implementing radiation protection programs for resettled and resettling populations. As part of this new initiative, DOE agreed to design and construct a radiological laboratory on Enewetak Island, and help develop the necessary local resources to maintain and operate the facility. This cooperative effort was formalized in August 2000 between the DOE, the Republic of the Marshall Islands (RMI), and the Enewetak/Ujelang Local Atoll Government (EULGOV). The laboratory facility was completed in May 2001. The laboratory incorporates both a permanent whole body counting system to assess internal exposures to 137Cs, and clean living space for people providing 24-h void urine samples. DOE continues to provide on-going technical assistance, training, and data quality review while EULGOV provides manpower and infrastructure development to sustain facility operations on a full-time basis. This paper will detail the special construction, transportation and installation issues in establishing a whole body counting facility in an isolated, harsh environmental setting.

A calibration phantom for direct, in vivo measurement of 241Am in the axillary lymph nodes.

A calibration phantom was developed at the University of Cincinnati (UC) to determine detection efficiency and estimate the quantity of activity deposited in the axillary lymph nodes of a worker who had unknowingly sustained a wound contaminated with 241Am at some distant time in the past. This paper describes how the Livermore Torso Phantom was modified for calibrating direct, in vivo measurements of 241Am deposited in the axillary lymph nodes. Modifications involved milling a pair of parallel, flat bottom, cylindrical holes into the left and right shoulders (below the humeral head) of the Livermore Torso Phantom in which solid, 1.40-cm-diameter cylindrical rods were inserted. Each rod was fabricated using a muscle tissue substitute. One end of each rod contained a precisely known quantity of 241Am sealed in a 1-cm-diameter, 2.54-cm-deep well to simulate the axillary lymph nodes when inserted into the modified Livermore Torso Phantom. The fixed locations for the axillary lymph nodes in the phantom were determined according to the position of the Level I and the combined Level II + III axillary lymph nodes reported in the literature. Discrete calibration measurements for 241Am in the simulated axillary lymph nodes located in the right and left sides of the thorax were performed using pairs of high-resolution germanium detectors at UC and Lawrence Livermore National Laboratory. The percent efficiency for measuring the 59.5 keV photon from 241Am deposited in the right and left axillary lymph nodes using a pair of 3,000 mm2 detectors is 2.60 ± 0.03 counts &ggr;−1 and 5.45 ± 0.07 counts &ggr;−1, respectively. Activity deposited in the right and left axillary lymph nodes was found to contribute 12.5% and 19.7%, respectively, to a lung measurement and 1.2% and 0.2%, respectively, to a liver measurement. Thus, radioactive material mobilized from a wound in a finger or hand and deposited in the axillary lymph nodes has been shown to confound results of a direct, in vivo measurement of the lungs.

THYROID PHANTOM MEASUREMENTS IN JOINT EURADOS–LLNL INTERCOMPARISON EXERCISE

The European Radiation Dosimetry Group (EURADOS), in collaboration with Lawrence Livermore National Laboratorys (LLNLs) Thyroid Intercomparison Program (TRIP), conducted an intercomparison exercise consistent with the goals of EURADOS. In total, 35 in vivo radiobioassay facilities from 18 countries participated to evaluate the differences between the neck and thyroid phantoms specified in two standards issued by the American National Standards Institute. Radioiodine (125I and 131I) measurement results were compared to the traceable standard activity levels added to each phantom. Measurement data showed no statistically significant differences between normalized activity measurements of the thyroid phantom types (20 and 30 ml). Differences were noted between the laboratories that routinely participate in the radioiodine thyroid intercomparison program (TRIP participants) and laboratories that have not previously participated in TRIP. Evaluation of the reasons for these differences will require additional EURADOS-LLNL collaborations. Finally, the measurement data from this intercomparison was used with a designed intake scenario for intercomparison of dose evaluations. Results from the dose intercomparison will be presented in a subsequent article.

Comparative Pathway Analysis of Radiocesium in the Hudson River Estuary: Environmental Measurements and Regulatory Dose Assessment Models

This work summarizes the measurements and associated environmental dosimetry of reactor-released 137Cs and 134Cs and weapons-produced 137Cs in samples of water, shoreline sediment and fish collected from 1971 to 1980 in the Hudson River Estuary. Trends observed in annual mean concentrations and the resultant dose implications for man from each source are discussed. The human exposure pathways examined are: fish consumption, water consumption, swimming and recreational use of the shoreline. Based on environmental measurements, a maximum, adult, whole-body, 50-y committed effective dose equivalent (CEDE) of 0.79 mu Sv (79 mu rem) is estimated from fish consumption in 1971, the year of maximum reactor discharge of the radiocesiums. For comparison, during the period 1974-79, mean estimates (+/- 1 SD) of the CEDE based on environmental measurements and attributed to other pathways are as follows: consumption of indigenous fish species caught downstream of the reactor outfall, 0.05 +/- 0.02 mu Sv (5 +/- 2 mu rem); consumption of fresh water sampled upstream of the reactors, 0.02 +/- 0.03 mu Sv (2 +/- 3 mu rem); and swimming, 10(-4) +/- 10(-4) mu Sv (0.01 +/- 0.01 mu rem). In addition, external, whole-body exposure resulting from recreational use of the shoreline 1.6 km downstream of the reactors is estimated to be 1.2 X 10(-8) C kg-1 (46 +/- 11 mu R yr-1). The above dose estimates are based on consumption factors of 3.9 and 803 kg y-1 (fish and water, respectively) and on usage factors of 50 and 140 h y-1 (swimming and shoreline recreation, respectively). Differences in dose estimates obtained from these long-term environmental measurements and from assessment models currently recommended for use by the U.S. Nuclear Regulatory Commission (NRC) are discussed.

International Intercomparison Exercise for Nuclear Accident Dosimetry at the DAF Using GODIVA-IV

The Nuclear Criticality Safety Program operated under the direction of Dr. Jerry McKamy completed the first NNSA Nuclear Accident Dosimetry exercise on May 27, 2016. Participants in the exercise were from Lawrence Livermore National Laboratory (LLNL), Los Alamos National Laboratory (LANL), Sandia National Laboratory (SNL), Savanah River Site (SRS), Pacific Northwest National Laboratory (PNNL), US Navy, the Atomic Weapons Establishment (United Kingdom) under the auspices of JOWOG 30, and the Institute for Radiological Protection and Nuclear Safety (France) by special invitation and NCSP memorandum of understanding. This exercise was the culmination of a series of Integral Experiment Requests (IER) that included the establishment of the Nuclear Criticality Experimental Research Center, (NCERC) the startup of the Godiva Reactor (IER-194), the establishment of a the Nuclear Accident Dosimetry Laboratory (NAD LAB) in Mercury, NV, and the determination of reference dosimetry values for the mixed neutron and photon radiation field of Godiva within NCERC.

Historical review of lung counting efficiencies for low energy photon emitters.

AbstractThis publication reviews the measured efficiency and variability over time of a high purity planar germanium in vivo lung count system for multiple photon energies using increasingly thick overlays with the Lawrence Livermore Torso Phantom. The measured variations in efficiency are compared with the current requirement for in vivo bioassay performance as defined by the American National Standards Institute Standard in ANSI Standard N13.30.Health Phys. 106(3):000-000; 2014