Uranium determination by133Xe in mineral separates from igneous rocks comparative study with fission track and thermal release characters of133Xe

Samples of an andesite (Asama-yama, Japan) and a basalt (Kilauea, Hawaii) were finely fractioned by density and the U distributions among the separates were determined by homogenized fission track method. Groundmass was found to be enriched with U; one half of the andesite U and almost all of the basalt U are accounted for by the groundmass U. Cerium and other REE are correlated with U. In the andesite separates Na is accompanied by these elements, but Fe and Co are rather anticorrelated. Uranium concentrations in the bulk samples and some of the separates were then compared with those determined by¹³³Xe extracted by heating at 1600°C. Fissiogenic¹³³Xe seems to become labile in groundmass, especially of the andesite, during reactor irradiations for 5 h or more. Stepwise heating experiments suggested that¹³³Xe in U-rich groundmass tends to escape at low temperatures and the remaining¹³³Xe is mostly retained in highly refractory sites in phenocryst rather poor in U.     

Concentration independent calibration of β–γ coincidence detector using 131mXe and 133Xe

Absolute efficiency calibration of radiometric detectors is frequently difficult and requires careful detector modeling and accurate knowledge of the radioactive source used. In the past we have calibrated the β–γ coincidence detector of the Automated Radioxenon Sampler/Analyzer (ARSA) using a variety of sources and techniques which have proven to be less than desirable (Reeder et al., J Radioanal Nucl Chem, 235, 1989). A superior technique has been developed that uses the conversion-electron (CE) and X-ray coincidence of ^131mXe to provide a more accurate absolute gamma efficiency of the detector. The ^131mXe is injected directly into the beta cell of the coincident counting system and no knowledge of absolute source strength is required. In addition, ¹³³Xe is used to provide a second independent means to obtain the absolute efficiency calibration. These two data points provide the necessary information for calculating the detector efficiency and can be used in conjunction with other noble gas isotopes to completely characterize and calibrate the ARSA nuclear detector. In this paper we discuss the techniques and results that we have obtained.     

Uranium determination by133Xe in meteorites; comparative study with fission track and/or239Np methods and thermal release character of133Xe

Uranium concentrations in three types of inclusions of the Allende (C III), a bulk sample of the Plainview (H5), and a bulk and 5 to 15 density separates of the Huckitta pallasite were determined and discussed by comparing the results from homogenized fission track and/or²³⁹Np analyses with the¹³³Xe results. Stepwise heating experiment revealed that the¹³³Xe release from the Plainview is bimordal and incomplete by a simple heating at 1600 °C, and that the¹³³Xe releases in the Huckitta bulk and metallic samples are multitudinous but can be extracted rather completely at 1600–1700 °C. In the Huckitta, uranium-rich phase (∼100 ppb) was in the lightest density fraction of d=2.9–3.3, but the bulk uranium was found to be mostly from the heavy metal-rich fraction of d>4.2.     

Evaluation of gamma camera collimator for regional cerebral blood flow measurements using a 133Xe inhalation method

In the measurements of regional cerebral blood flow (rCBF) using inhalation of 133Xe gas, the activity present is generally limited in lower levels than those of usual brain scintigraphy. Measurements with low count-rate are usually resulted in diminishing the accuracies of results obtained. Therefore, it is necessary to make measurements using a high sensitive collimator for getting as much count-rate as possible when a gamma camera is used. The relationships among sensitivity and structures of multi-parallel collimator were mathematically analyzed. The results of analysis suggested that sensitivity usually increased by using a collimator with holes of reduced height and diameter. A prototype multi-parallel collimator with holes of low height and small diameter was made in our laboratory for testing sensitivity and resolution. The collimator possessing 1141 holes of 6 mm phi in hole diameter, 1.5 cm is hole height and septal thickness of 1 mm lead showed 24 times more sensitive than those of a general all purpose collimator supplied by the manufacturer. However, resolution measured in FWHM was of 9 to 14 mm at the collimator face and of 29 to 38 mm at 5 cm from the face. The results indicated that this collimator was useful enough in rCBF measurements with 133Xe inhalation using a gamma camera. The mathematical analysis however, suggested that optimum collimator for rCBF measurements was approximate 4.5 mm phi in hole diameter and 1.0 cm in hole height.     

Measurement of regional cerebral blood flow by 133Xe inhalation method in patients with ruptured aneurysm

Regional cerebral blood flow (rCBF) was measured in 20 patients with ruptured aneurysm. rCBF images are obtained by 133Xe inhalation method using a ring type gamma camera (SET-020, Shimazu Co.) with high sensitivity collimator. Examinations are performed at acute stage (1-7 days after onset) and at subacute stage (8-14 days after onset). In acute stage, rCBF in the affected cerebral hemisphere has tendency to be low in 12 patients with angiospasm after the aneurysmal rupture comparing to those in patients without angiospasm. Low rCBF areas in cerebral hemisphere at acute stage were apt to become normal in subacute stage. rCBF measurement by 133Xe inhalation method seemed to be an useful method to evaluate rCBF in patients with ruptured aneurysm.     

SDAT: analysis of <Superscript>131m</Superscript>Xe with <Superscript>133</Superscript>Xe interference

The Spectral Deconvolution Analysis Tool (SDAT) software was developed at The University of Texas at Austin. SDAT utilizes a standard spectrum technique for the analysis of β–γ coincidence spectra. Testing was performed on the software to compare the standard spectrum analysis technique with a region of interest (ROI) analysis technique. Experimentally produced standard spectra and sample data were produced at the Nuclear Engineering Teaching Laboratory (NETL) TRIGA reactor. The results of the testing showed that the standard spectrum technique had lower errors than the ROI analysis technique for samples with low counting statistics. In contrast, the ROI analysis technique outperformed the standard spectrum technique in high counting statistics samples. It was also shown that the standard spectrum technique benefitted from a compression of the number of channels within the spectra.     

A new scaled crossover parametric equation of state for water

In the present work, the asymmetric nature of water coexistence curve has been studied by investigating a new scaled crossover parametric equation of state. To do so, the concept of complete scaling [Fisher and Orkoulas, Phys Rev Lett 696, 85 (2000)] has been applied and the critical amplitudes near and far from the critical point have been derived. Also two mixing parameters $ a_{3} $ and $ b_{2} $ in the definition of scaling fields in terms of physical fields have been obtained for water. We have shown that mixing of the complete scaling theory and parametric equation of state can explain this nature quite carefully.     

A new sorption model with a dynamic correction for the determination of diffusion coefficients

This paper describes an improvement to the method used for the calculation of diffusion coefficients from data obtained by the measurement of vapor sorption kinetics in a flat, non-porous polymeric membrane. The advantage of our corrected model is that it can be applied to systems displaying both fast and slow sorption kinetics, as is demonstrated using cellulose myristate – hexane and cellulose acetovalerate – ethanol systems at a temperature of 298 K. Experiments were conducted on a specially developed sorption apparatus equipped with McBain’s spiral quartz balances. Sorption kinetics are generally described by the solution of Fick’s second law, the solution of which assumes relative pressure in the form of the unit step function. Our correction involves modifying this solution so that a more realistic relative pressure increase is assumed in terms of the Laplace transform.     

Ion pair chromatography: A new approach to dynamic equilibrium

Summary This work describes the dynamic equilibrium of an ionpair, reverse-phase liquid chromatography system. A given adsorbed quantity of an anionic surfactant can lead to different capacity factors and selectivity for anionic solutes.This paper was presented as a poster-communication at the 7^th International Symposium on Column Liquid Chromatography, Baden-Baden, May 3–6, 1983.     

A new approach to dynamic deactivation in capillary zone electrophoresis

This paper describes a simple means of obtaining high resolution separations of basic proteins at a pH below their pl. Small amounts of a cationic fluorosurfactant are added to the running buffer. A positively charged wall is thereby obtained which will repel positively charged proteins. The particular chemistry of fluorosurfactants is believed to enhance the efficiency of the deactivation. Examples are presented of the separation of some model proteins, including a human insulin-like growth factor (IGF-I), and a misfolded by-product of the growth factor.     

A new dynamic electrochemical transduction mechanism for interdigitated array microelectrodes

A dynamic electrochemical transduction mechanism for interdigitated array microelectrodes using an electrical charge pumping method is presented in this paper. In this dynamic transduction mechanism, a charged external capacitor is used as the charge supplier for the electrochemical reaction of the reversible redox species at the interdigitated array electrodes. The charges stored in the capacitor are consumed as the electrochemical reaction current, which causes the capacitor potential decay. The theoretical analysis has shown that the species concentration has a decisive effect on the capacitor potential decay, and therefore the characteristics of the capacitor potential decay are recorded and analyzed to evaluate the concentration of redox species. The new transduction mechanism has the advantages of achieving high sensitivity with small sensor area and simplifying the measurement instrumentation. As a demonstration device, interdigitated array microelectrodes (approximately 0.2 mm(2) electrode surface area) have been fabricated and successfully characterized using p-aminophenol as the redox species under this dynamic mechanism. The detection limit of p-aminophenol was calculated to be approximately 4 x 10(-7) M for the sensor with the new dynamic transduction mechanism.     

A guided-ion beam study of the reactions of Xe(+) and Xe(2+) with NH(3) at hyperthermal collision energies

We have measured the absolute cross sections for reactions of Xe(+) and Xe(2+) with NH(3) at collision energies in the range from near-thermal to ～34 and ～69?eV, respectively. For Xe(+), the cross section for charge transfer, the only exothermic channel, decreases from ～200A?(2) below 0.1 eV to ～12A?(2) at the highest energies studied. The production of NH(3) (+) is the only channel observed below 5 eV, above which a small amount of NH(2) (+) is also formed. In Xe(2+) reactions, the main products observed are NH(3) (+) and NH(2) (+). The charge transfer cross section decreases monotonically from ～80 to ～6A?(2) over the studied energy range. The NH(2) (+) cross section is similar to the charge transfer cross section at the lowest energies, and exhibits a second component above 0.4 eV, with a maximum of 65A?(2) at 0.7 eV, above which the cross section decreases to ～30A?(2) at the highest energies studied. At energies above 10 eV, a small amount of NH(+) is also observed in Xe(2+) collisions. Product recoil velocity distributions were determined at selected collision energies, using guided-ion beam time-of-flight methods.     

A new total antioxidant potential measurements using RP-HPLC assay with fluorescence detection

In this paper, an improved total antioxidant potential (TAP) estimation using high-performance liquid chromatographic (HPLC) assay with fluorometric detection has been described. The principle of this method is based on the hydroxyl radicals generated in the Fenton-like reaction and subsequently detected using hydroxyterephthalic acid (HTPA), which is a reaction product of hydroxyl radicals and terephthalic acid (TPA), working as a sensing compound. HTPA quantity in the samples was measured by fluorescence detector working at excitation and emission wavelengths equal to 312 and 428 nm, respectively. A number of key experimental conditions including the influence of the reaction (incubation) time on the surface areas of HTPA peaks, concentration of Fe(II) ions as well as the influence of concentration of TPA on the surface area of the chromatographic peak of HTPA were optimized to the characteristic feature of TAP measurements. The elaborated assay has been used to evaluate TAP values of selected low-molecular mass compounds like pyrogallol, tryptamine, and n-alcohols (methanol, ethanol, and n-propanol) as well as chlorogenic and ascorbic acids and benzoic acid derivatives, which are commonly present in the food samples.     

A new oxidation system using nitrite oxidants

The oxidative reactions using alkyl nitrites (RONO) as oxidant have been developed by Ube Industries, Ltd. The substrates such as CO and/or unsaturated-and/or carbonyl-compounds are oxidized by RONO over the palladium catalyst with no contact of molecular oxygen. Dialkyl carbonates, dialkyl oxalates and other useful chemicals are synthesized efficiently under moderate conditions by this alkyl nitrite technology.     

A method for dynamic system characterization using hydraulic series resistance

The pressure required to drive flow through a microfluidic device is an important characteristic of that device. We present a method to measure the flow rate through microfluidic components and systems, including micropumps and microvalves. The measurement platform is composed of two pressure sensors and a glass tube, which provides series resistance. The principle of the measurement is the fluid dynamical equivalent of Ohm's law, which defines the relationship between current, resistance, and voltage that are analogues to flow rate, hydraulic resistance, and pressure drop, respectively. Once the series resistance is known, it is possible to compute the flow rate through a device based on pressure alone. In addition, the dynamic system characteristics of the device-resistance and capacitance-can be computed. The benefits of this method are its simple configuration, capability of measuring flow rate accurately from the more easily measured pressure, and the ability to predict the dynamic response of microfluidic devices.