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Abstract  

Neutron activation analysis and atomic absorption spectrometry (graphite furnace) methods for the analysis of selenium in human tissue are described. The sensitivity (10–30 ng/sample), accuracy and precision are of the same order for both techniques and the choice can only be made on grounds of urgency or convenience. AAS should be chosen for the analysis of wet tissue or the urgent analysis of small numbers of dry tissue. NAA should be chosen for the analysis of large numbers of dry tissue samples where time is not important. The selenium concentration of human liver is shown to be in the region of 1 to 2 ppm (dry weight). Selenium may be lost from tissue during freeze drying if the samples are not maintained at −35°C.

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Abstract

Few contemporary inventions have influenced academic publishing as much as journal impact factors. On the other hand, debates and discussion on the potential limitations of, and appropriate uses for, journal performance indicators are almost as long as the history of the measures themselves. Given that scientometrics is often undertaken using bibliometric techniques, the history of the former is inextricably linked to the latter. As with any controversy it is difficult to separate an invention from its history, and for these reasons, the current article provides an overview of some key historical events of relevance to the impact factor. When he first proposed the concept over half a century ago, Garfield did not realise that impact factors would one day become the subject of such widespread controversy. As the current Special Issue of Scientometrics suggests, this debate continues today.

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The recent discovery of the migration of plutonium in groundwater away from underground nuclear tests at the Nevada Test Site has spawned considerable interest in the mechanisms by which plutonium may be released to the environment by a nuclear explosion. A suite of solid debris samples was collected during drilling through an expended test cavity and the overlying collapse chimney. Uranium and plutonium were analyzed for isotope ratios and concentrations using high precision magnetic sector inductively coupled mass spectrometry. The data unequivocally shows that plutonium may be dispersed throughout the cavity and chimney environment at the time of the detonation. The 239Pu/240Pu ratios are also fractionated relative to initial plutonium isotope ratio for the test device. Fractionation is the result of the volatilization of uranium and production of 239Pu by the reaction 238U(n,γ). We conclude that for the test under consideration plutonium was deposited outside of the confines of the cavity by dynamic processes in early-time and it is this plutonium that is most likely transferred to the groundwater regime.

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This paper examines the process of making a decision on the optimum technique for the measurement of low concentrations of226Ra in environmental materials. The available counting techniques are alpha spectrometry, high resolution gamma spectrometry and liquid scintillation counting. The properties of the analytical technique; sensitivity, lower limit of detection (LLD) and precision are considered. Method selection is also restricted by the available sample size and activity. The influence of procedure backgrounds, geometric efficiency, chemical recovery, counting time, sample size and activity on the precision and LLD are investigated. The process of method selection, applicable to a wide range of samples, is illustrated by reference to sediments, waters and tissues.

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Breakfast wheat-flake materials of different composition have been reconstituted as barshaped test pieces to reduce geometry and structure effects and allow better comparison of the matrix mechanical properties. The ground flakes comprised a control formulation and others in which components had been subtracted or substituted. The aim was to compare the mechanical properties of pressed specimens of multiple-component systems with those published for simpler one- and two-component materials. Sucrose or fructose, present in the ratio sugar∶wheat 1∶5.9–6.1, lowered the modulus of wheat-flake material, but by progressively lesser extent with decreasing water content below 22% (wet-weight basis, w.w.b), the difference becoming negligible at water contents of 7 to 10% (w.w.b). However, the energy to break wheat-flake samples and their fracture toughness were reduced more by fructose than sucrose addition to a control formulation sample at these water contents. The energy to break and fracture toughness increased markedly with increasing water content for all formulations.

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Abstract  

Nearly all natural materials contain trace quantities of uranium (U) and thorium (Th) and their daughter nuclides, many of which emit α-particles in their decay. Lead, at the end of the U-decay chain, typically contains some radioactive210Pb which is chemically inseparable from the other Pb isotopes. α-particle emission from these decays can affect sensitive electronic components, such as memory chips or processors. Measurement of α-particle emitters can be accomplished by direct detection of the α-particles (which typically provides no positive identification of the emitting isotope because of energy loss in the sample) or by low-background γ-ray spectroscopy (which does provide positive identification via characteristic γ-rays.) The latter is by far the best method for screening kg-sized samples of materials like ceramics, aluminum, iron or copper. The difference between α counting and γ-ray spectroscopy is less for measuring210Pb in Pb since the 46.5 keV characteristic γ-rays directly following the210Pb decay are strongly absorbed and both methods are limited to thin layers. This paper discusses these two cases and concludes that a large n-type germanium γ-ray spectrometer is probably the best overall system for both measurements.

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Abstract  

High-level radioactive wastes can be transformed to low-level wastes by removing137Cs through selective ion exchange processes. Since the short-lived daughter,137inBa produces the 662-keV gamma-ray normally attributed to137Cs, equilibrium may be broken, and observation of the 662-keV gamma-ray cannot be used to detect cesium breakthrough. Two detectors viewing the output line, but separated sufficiently to measure the137mBa decay between them, are used to detect137Cs breakthrough based on deviation from the normal137mBa decay. Detection evaluated for the process separation time, counting time, fractional breakthrough detectable, and accuracy and confidence of the measurements are discussed.

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Abstract  

Instrumental Neutron Activation Analysis (INAA) is a common method of trace element analysis whose sensitivity is limited either by interference from other trace elements in the sample or by interference from ambient background radiation in the detection system. In at least two cases, a true low-background facility, such as that at Lawrence Berkeley National Laboratory, substantially enhances senitivity: (1) Ultra-pure silicon, such as that used in semiconductor fabrication. Even after prolonged exposure within a nuclear reactor, minimal observable gamma-ray emitting activities are produced in the silicon. Extrapolated from our 7 gram sample size experiments, parts-per-quadrillion (1.E-15) sensitivity to 23 elements should be obtainable for 400 gram sample sizes. (2) Similarly, the life elements H, C, N, O are effectively inert within the reactor, and this enhances sensitivity to trace elements in, for example, bacteria. Data will be presented for these two cases.

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Abstract  

As part of a program to surley low levels of radioactivity in the marine environment of the southern hemisphere, we have studied the distribution and uptake of131I found in the subtidal kelp Ecklonia radiata, on the west coast of Australia. Concentrations of 5 to 75 fCi/g of131I exist in this species over a considerable distance along the coast. We have characterized the principal source of the131I and found a general temporal correlation between the amount of radioiodine discharged from sewer outfalls and its concentration in kelp. Transplant experiments have enabled us to estimate uptake and depuration rates, and our results are consistent with laboratory measurements made by others.

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