Past radioactive particle contamination in the Columbia river at the Hanford site, USA.

One closed-loop and eight single-pass plutonium production reactors originally operated on the Columbia river. During the 26 years of single-pass reactor operations, small amounts of radioactive particles were released in liquid discharges to the Columbia river and were deposited in sediment and cobble along the shoreline and on islands in the river. Islands located adjacent to D island and immediately downstream of D island had the greatest density of particles. In 1979, the small particles contained between 63 and 890 kBq of cobalt-60 activity. Dose rates emanating from those particles ranged from 1 to 14 microGy h(-1). Because of the short half-life of cobalt-60 (5.3 y), the hot-particle problem at Hanford has taken care of itself through radiological decay. Some scientists have proposed that it is economically and environmentally advantageous to manage isolated low-level contaminated sites with institutional controls until the activity decays and the sites can be released rather than to pursue expensive clean-up options.

Public participation in radiological surveillance.

In 1989, Pacific Northwest National Laboratory developed a program, for the U.S. Department of Energy, to involve local citizens in environmental surveillance at the Hanford Site. The Community-Operated Environmental Surveillance Program was patterned after similar community-involvement efforts at the Nevada Test Site and the Three Mile Island nuclear facility. Its purpose is to increase the flow of information to the public, thereby enhancing the public's awareness and understanding of surveillance activities. The program consists of two components: radiological air monitoring at nine offsite locations and agricultural product sampling at selected locations near the site. At each air-monitoring station, two local school teachers collect air particulate samples and operate equipment to monitor ambient radiation levels. Atmospheric tritium samples (as water vapor) are also collected at some locations. Four of the air-monitoring stations include large, colorful informational displays for public viewing. These displays provide details on station equipment, sample types, and sampling purposes. Instruments in the displays also monitor, record, and show real-time ambient radiation readings (measured with a pressurized ionization chamber) and meteorological conditions. Agricultural products, grown primarily by middle-school-aged students, are obtained from areas downwind of the site. Following analysis of these samples, environmental surveillance staff visit the schools to discuss the results with the students and their teachers. The data collected by these air and agricultural sampling efforts are summarized with other routinely collected sitewide surveillance data and reported annually in the Hanford Site environmental report.

The Brain Bench: virtual tools for stereotactic frame neurosurgery.

We present a suite of neurosurgery supporting tools developed around (i) the Virtual Workbench, a productive environment for the control of 3-D data, in which delicate work can be performed for hours on end without strain, and (ii) the Electronic Brain Atlas, integrating the major print brain atlases in day-to-day clinical use. We describe in detail the Brain Bench, a surgical planning system for stereotactic frame neurosurgery. Its objective is to prepare faster plans; have a better and more accurate choice of target points; improve the avoidance of sensitive structures; have fewer sub-optimal frame attachments and speedier, more effective planning and training. If validated by a clinical study now under way, this will improve medical efficacy and reduce costs.

Short-term bioconcentration studies of Np in freshwater biota.

Short-term laboratory exposures were conducted to determine the potential accumulation of Np in aquatic organisms. Concentration factors were highest in green algae. Daphnia magna, a filter-feeding crustacean, accumulated Np at levels one order of magnitude greater than the amphipod Gammarus sp., an omnivorous substrate feeder. Accumulation of Np in juvenile rainbow trout (Oncorhynchus mykiss) was highest in carcass (generally greater than 78% of the total body burden) and lowest in fillets. Recommended concentration factors for Np, based on fresh weight, were 300 for green algae, 100 for filter-feeding invertebrates, for nonfilter-feeding invertebrates, 10 for whole fish, and one for fish flesh.

Concentration factors used in the assessment of radiation dose to consumers of fish: a review of 27 radionuclides.

Concentration factors (CFs) for 27 radionuclides in marine and freshwater fish were reviewed, as were factors that may influence the dose commitment to man resulting from the consumption of fish. These factors include environmental partitioning, ecological trophic level discrimination and specific tissue accumulation (tropism). Our recommendations are based first on field data for radioisotopes of each element; second, on data for stable elements for which data on radioisotopes are lacking; and third, on the potential for bioaccumulation, which is influenced most by the established biological significance of the element or its chemical similarity to biologically active elements in the same chemical group. Only radionuclides of elements with known biological functions or their analogues accumulate to significant levels in fish tissue. The environmental data that exist for Cs, Sr, Co, Fe, Mn, I, P, Am, Cm, Np and Pu were used for adjusting CFs based on water quality or trophic status of fish. Separate CFs have been listed for particular groups of fish that showed a high propensity for certain radionuclides to accumulate in tissue at higher specific activity than that found in water.

Nonlinear modeling of multistable perception.

Multistable figures show that the stimulus-percept relation is not a single valued function. We therefore propose a tentative nonlinear model on the hypothesis that the graph of this relation is the equilibrium set of a dynamic system. For simplicity and to obtain testable predictions, we consider a system whose bifurcations are gradient-like and thus generically described by the elementary catastrophes. We motivate this general model, and then show how, in conjunction with the principle of minimal singularity, it implies cusp catastrophe geometry in a specific perceptual example. Indeed, we argue for canonical cusp geometry in this case. The model incorporates naturally certain observed features of multistable perception, such as hysteresis and bias effects. Despite being a continuum model it is naturally compatible with the subjective dichotomy of bistable perception. The model makes testable predictions which may easily be extended to other specific examples of multistable perception.