Variability of nutrient limitation in the Archipelago Sea, SW Finland

Eutrophication is the most acute environmental problem in the Archipelago Sea, SW Finland. When analysing the factors behind this escalating eutrophication the determination of limiting nutrient at a given time is essential. Besides experimentations, nutrient limitation of plankton has been extensively studied by direct chemical analyses. We used the latter approach in this work. Nutrient limitation was studied by calculating different nutrient ratios - total nitrogen:phosphorus, inorganic nitrogen:phosphorus, and nutrient balance ratio. Results showed that phosphorus usually limited primary production only near the coast line. In the middle zone of the Archipelago Sea the limiting factor varied temporally. Outer in the open sea nitrogen limited primary production during most of the year. Phosphorus limited phytoplankton growth especially in spring and in summer and nitrogen in late summer and in autumn. Our results suggested that nitrogen is an important limiting nutrient in the Archipelago Sea. In recent years when the eutrophication has proceeded there has been a shift from.production limitation by both nutrients to limitation by nitrogen alone. But if we want to define and characterize the nutrient limitation of the entire ecosystem of the Archipelago Sea, budgets have to be calculated for both N and P and internal recycling must be taken into account as well as external supply of nutrients and loss processes.</p

Automatic material identifier

Radiation survey instruments could be used to verify the presence of radioactive material inside a container, but identification of the material would not be possible. One could imagine a very complex detector-analyzer system to analyze the radiation being emitted from a container, but it would be very large and difficult to use. At Los Alamos, a portable instrument with some limitations has been developed to identify plutonium and uranium inside a container. The instrument consists of a thin NaI crystal and an electronics package which is based on a microcomputer. The instrument uses the energy spectrum of the emitted radiation to identify the nuclear material present. The function of this instrument is to provide the user a tool for qualitative verification of nuclear materials in a container. The instrument can distinguish plutonium-239 and uranium-235 from other radioactive materials. A count rate indicator provides some measure of the quantity of material. 1 reference, 2 figures

Unique applications of tamper indicating devices

Various organizations at Los Alamos have used tamper indicating devices (TID) to help control nuclear materials for several years. During the past year a formal documented TID program has been developed to be implemented throughout the Laboratory. Special needs of all organizations have been incorporated into the program. Applications vary from waste containers to unique configurations of special nuclear materials (SNM). Several examples of these applications will be discussed

Measurement of plutonium oxalate in thermal neutron coincidence counters

A coincidence neutron counting method has been developed for assaying batches of plutonium oxalate. Using counting data from two concentric rings of /sup 3/He detectors, corrections are made for the effects that water has on the coincidence neutron count rate. Batches of plutonium oxalate varying from 750 to 1000 g of plutonium and from 34 to 54% water are assayed with an average accuracy of +-3%

Beta-gamma discriminator circuit

The major difficulty encountered in the determination of beta-ray dose in field conditions is generally the presence of a relatively high gamma-ray component. Conventional dosimetry instruments use a shield on the detector to estimate the gamma-ray component in comparison with the beta-ray component. More accurate dosimetry information can be obtained from the measured beta spectrum itself. At Los Alamos, a detector and discriminator circuit suitable for use in a portable spectrometer have been developed. This instrument will discriminate between gammas and betas in a mixed field. The portable package includes a 256-channel MCA which can be programmed to give a variety of outputs, including a spectral display, and may be programmed to read dose directly

Design impacts of safeguards and security requirements for a US MOX fuel fabrication facility

The disposition of plutonium that is no longer required for the nation`s defense is being structured to mitigate risks associated with the material`s availability. In the 1997 Record of Decision, the US Government endorsed a dual-track approach that could employ domestic commercial reactors to effect the disposition of a portion of the plutonium in the form of mixed oxide (MOX) reactor fuels. To support this decision, the Office of Materials Disposition requested preparation of a document that would review US requirements for safeguards and security and describe their impact on the design of a MOX fuel fabrication facility. The intended users are potential bidders for the construction and operation of the facility. The document emphasizes the relevant DOE Orders but also considers the Nuclear Regulatory Commission (NRC) requirements. Where they are significantly different, the authors have highlighted this difference and provided guidance on the impact to the facility design. Finally, the impacts of International Atomic Energy Agency (IAEA) safeguards on facility design are discussed. Security and materials control and accountability issues that influence facility design are emphasized in each area of discussion. This paper will discuss the prepared report and the issues associated with facility design for implementing practical, modern safeguards and security systems into a new MOX fuel fabrication facility

The Epidemiology of Lead Toxicity in Adults: Measuring Dose and Consideration of Other Methodologic Issues

We review several issues of broad relevance to the interpretation of epidemiologic evidence concerning the toxicity of lead in adults, particularly regarding cognitive function and the cardiovascular system, which are the subjects of two systematic reviews that are also part of this mini-monograph. Chief among the recent developments in methodologic advances has been the refinement of concepts and methods for measuring individual lead dose in terms of appreciating distinctions between recent versus cumulative doses and the use of biological markers to measure these parameters in epidemiologic studies of chronic disease. Attention is focused particularly on bone lead levels measured by K-shell X-ray fluorescence as a relatively new biological marker of cumulative dose that has been used in many recent epidemiologic studies to generate insights into lead’s impact on cognition and risk of hypertension, as well as the alternative method of estimating cumulative dose using available repeated measures of blood lead to calculate an individual’s cumulative blood lead index. We review the relevance and interpretation of these lead biomarkers in the context of the toxico-kinetics of lead. In addition, we also discuss methodologic challenges that arise in studies of occupationally and environmentally exposed subjects and those concerning race/ethnicity and socioeconomic status and other important covariates