Studies on iridium and platinum determination in metallic rhodium by NAA and CPAA

The determination of Ir and Pt in rhodium neutron monitors was investigated via¹⁹²Ir and¹⁹⁹Au after neutron activation, via¹⁹¹Pt and¹⁹⁴Au–¹⁹⁶Au after proton activation. Ir was determined by instrumental NAA. A chemical separation of gold, with a yield measurement method by a radioactive tracer, was developed for platinum determination after neutron or proton irradiation.     

Relationship between the cervical uterine cancer evolution and selenium concentration in urine determied by NAA

Neutron activation analysis of Se in urine reaches an optimum sensitivity (few ppb) and precision (±12%) when the traces are complexed without using a carrier by ammonium pryrrolidindithiocarbamate (APDC) at pH 1.5–2 and adsorbed on activated carbon filters. In this way the selenium traces analysis have been carried out through^77mSe in 45 urine samples on a pre-separation basis by cyclic activation ofthe carbon filters. The selenium concentration in our blanks is virtually zero, because APDC proved to be selnium free and selenium mass in 50 mg of activated carbon used as a filter is 20 times below our qualitative detection limit and 144 times below our quantitative detection limit. The samples were first of day urine from healthy and ill women suffering cervical uterine cancer, at different evolution stages: incipient, intemediate and advanced, with no treatment, and surgery, radiotherapy, chemotherapy, or a combined treatment. The results show a consistent tred to increase the selenium trace concentration during the intemediate stage, whereas it is the same than nomal for incipient cases, and it decreases to the lowest concentrations for advanced cases.     

Further study on parametric standardization in reactor NAA

A post-K_o study of parametric reactor NAA is described including the determination and applications of working K_oS for non-1/V reactions¹⁵¹Eu(n,)¹⁵²Eu and¹⁷⁶Lu(n,)¹⁷⁷Lu; parametric corrections for²³⁵U fission, threshold reaction and -spectral interferences; and parametric normalizations for different counting geometries. The analytical significance, the principles, the experimental confirmations, and the application examples of these methods are briefly introduced.     

Determination of concentration of iodine in grass and cow milk by NAA methods using reactor neutrons

Instrumental and preconcentration methods of neutron activation analysis (NAA) have been standardized for the determination of concentration of iodine in grass and cow milk samples, respectively. To study the transfer of iodine from grass to milk, known quantity of grass spiked with potassium iodide solution was fed to a cow. The spiked grass samples and milk samples, obtained from the cow after the ingestion of spiked grass, were collected. Iodine was separated from the milk samples chemically using Dowex 1X8 anion exchange resin. Spiked grass and ion exchange resin samples were neutron irradiated and radioactive assay was carried out using a 45?% relative efficiency HPGe detector coupled to an 8k channel analyzer. Iodine concentrations in spiked grass samples were found to be in the range of 1,487?C2,002?mg?kg^?1. Concentration of iodine in milk after 12?h of feeding the cow with spiked grass was 871?±?56???g?L^?1 which was reduced to 334?±?32???g?L^?1 after 48?h.     

A comparative study of the bonding in different halides of iridium

X-ray photoelectron spectroscopy and multiple scattering Xα calculations have been applied to a series of iridium halide complexes in order to corroborate the nature of the bondings inherent in this class of compounds. Our results seem to substantiate contentiously that higher oxidation states of iridium favor the formation of covalent bonds. This conclusion is based on the observation that (1) successive bombardment of the iridium species by Ar ions almost definitely leads to a configuration in which iridium is bound to at most one halide ion, and (2) the theoretical charge per ligand ion approaches systematically a value of {1?} in the limit as the formal oxidation state of iridium approaches {1+}. The theoretical results are further arthenticated by the fact that the experimental ionization energy of the Ir(4f) level in the different iridium halide complexes studied is seen to decrease as a result of exposure to Ar ions.     

A relationship between network chain concentration and time dependence of rupture for SBR vulcanizates

The failure properties of crosslinked elastomers are influenced by variables such as the test rate, test temperature, chemical nature of the elastomers, degree of crosslinking, etc. For an elastomer with a fixed degree of crosslinkingthe time dependence of both the stress- and strain-at-break, when determined as a function of the test rate and test speed, can be correlated using a time–temperature shift such as the WLF a_T shift factor. When a similar study is carried out with a sample having a different degree of crosslinking, the time dependence of both the stress- and strain-at-break is shifted along the time scale. It is demonstrated here that the time dependence of failure obtained as a function of the degree of crosslinking can be superposed on a master curve by the use of a time shift factor whose value depends directly on the degree of crosslinking.     

Further study on NAA in characterizations of reference materials

A program was initiated at Chalk River Laboratories (CRL) to determine the physical, chemical and radiological properties of wastes intended for disposal in IRUS (Intrusion Resistant Underground Structure), a below ground vault to be constructed at CRL. One of the most restrictive radionuclides for IRUS is¹²⁹I, which has been assigned a maximum activity concentration in waste of 10⁶ Bq/m³. The limit of detection for radionuclides in waste has been set at 1% of the approximate maximum activity concentration, or 10⁴ Bq/m³ for¹²⁹I. A radiochemical instrumental neutron activation analysis method has been developed to determine¹²⁹I in two waste streams, incinerator ash and liquid feed to a bituminizer. Solid samples are spiked with¹²⁵I tracer, fused at 960°C with Li₂B₄O₇ in a platinum boat in a flowing oxygen stream inside a three zone tube furnace, and the volatilized I₂ is trapped on in-line charcoal filters. The charcoal filters are irradiated together with a filter containing a spiked¹²⁵I/¹²⁹I standard, in the NRU reactor, and then subjected to post-irradiation chemistry to remove⁸²Br interference. The¹²⁹I concentration in the sample is determined by comparing the activity of the activated¹³⁰I in the sample with that of the standard, and the chemical recovery for¹²⁹I is determined from the activity of¹²⁵I tracer. Limits of detection for¹²⁹I in solids are typically 0.005 Bq/g, based on a 4 hour counting period on a 10% efficient HPGe gamma-spectrometer at a source to detector distance of approximately 12 cm. This paper presents a summary of the method and the results from analysis of two waste streams.     

A NAA collaborative study in white rice performed in seven Asian countries

Since 2000, collaborative studies for applying NAA have been performed through the Forum for Nuclear Cooperation in Asia (FNCA) sponsored by the Japanese Government. White rice is a main food for Asians and thus was selected as a common target sample for a collaborative study in 2008. Seven Asian countries including China, Indonesia, Japan, Korea, Malaysia, Philippines and Thailand, are greatly concerned about the composition of arsenic, heavy metals, and essential trace elements and took part in this study. Rice samples were purchased and prepared by following a protocol that had been proposed for this study. Samples were analyzed by their own NAA systems. In each country, more than 10 elements were examined and the results were compared. These data will be very useful in the monitoring of the levels of food contamination and to evaluate the nutritional status for people living in Asia.     

A DFT study on the electronic structure for iridium nitride under high pressure

We present density functionary theory (DFT) calculations on the structural parameters and electronic structure for iridium nitride by using the generalized gradient approximation (GGA) and the Perdew–Burke–Ernserhof (PBE) exchange-correlation functional. The lattice parameters and bulk modulus (B ₀) for the ground state are obtained, and the energy band structure and electron densities of states (DOS) of IrN₂ are presented. It is found that IrN₂ has a very close indirect energy gap. There is a strong covalent bond between the two nearest N atoms. This gives rise to a very high elastic modulus of IrN₂ and reveals the quasimolecular nature of the N₂ in IrN₂ crystal. Lattice parameters, bulk modulus, and the electronic structure of IrN₂ under high pressure have also been investigated based on DFT. The compressibility along three cell vectors is very close to each other. The band gap increases a little with the pressure even when the pressure is up to 100 Gpa.     

ROMOS: A new computer code for nuclide identification and concentration calculation in NAA using the k0-concept

The program ROMOS and the assisting program RECAL are presented. These programs were designed to facilitate nuclide identification and concentration calculation in NAA using the k₀-concept. For nuclide identification classical tests (energy match, decay factor) are complemented with a test of the saturation factor including the sensitivity of neutron acctivation analysis for the candidate nuclide. For nuclides emitting more than one gamma-energy the intensity of the observed peaks in the spectrum are compared. Thereby full account is taken of relative detection efficiency and true coincidence effects. Practical experience in using the interactive code shows that it is a convenient and time-saving working aid for an experienced experimenter.     

The relationship between the drug concentration profiles in plasma and the drug doses in the colon

After the dosing of an extended-release (ER) formulation, compounds may exist in solutions at various concentrations in the colon because the drugs are released at various speeds from the ER dosage form. The aim of this study was to investigate the relationship between the drug concentration profiles in plasma and the drug doses in the colon. Several drug solutions of different concentrations were directly administered into the ascending colon of dogs using a lubricated endoscope, and the effects of the drug dose on colonic absorption were estimated. As a result, dose-dependency of colonic absorption varied from compound to compound. Although the relative bioavailability of colonic administration of diclofenac, metformin and cevimeline compared to oral administration was similar regardless of the drug doses in the colon, colonic absorption of diltiazem varied according to the doses. From the results of the co-administration of verapamil and fexofenadine, it was clear that diltiazem underwent extensive hepatic and gastrointestinal first-pass metabolism, resulting in a low area under the curves (AUC) at a low drug dose. During the design of oral ER delivery systems, a colonic absorption study of candidate compounds should be carried out at several solutions of different drug concentrations and assessed carefully.     

Determination of iridium concentration in sedimentary rocks and in the geochemical standard PCC-1 by radiochemical neutron activation analysis

A radiochemical neutron activation analysis procedure is described for the determination of concentration levels of iridium in sedimentary rocks and in the geochemical standard PCC-1. After irradiation, the powdered rock samples and standard are dissolved with a mixture of HF, HNO₃ and HClO₄ in a teflon bomb. The final solution obtained, in dilute HCl, is passed through a column containing the cationic resin Bio Rad AG 50W-X8. The interfening radionuclides are sorbed by the resin. The effluent solution containing iridium is concentrated for counting by evaporation. Experiments with radioactive tracer for checking radiochemical separation yield are carried out. The accuracy of the method is evaluated by means of analysis of the USGS “standard rock” peridotite, PCC-1. The precision is about 25% in the ppb range. The method is used for the determination of iridium in 16 samples of sedimentary rocks collected at different depths in the “Campos” basin-RJ (BRAZIL).     

Investigation of Quantitative Relationship between Adsorbed Amount of Solute and Solvent Concentration at Relatively High Solute Con－centration by Frontal Analysis in RPLC

In previous paper a new adsorption isotherm which relates the amount of solute absorbed to the solvent concentration is pro-posed and simplified, and it only can be used at lower solute concentration. In this article the scope of the new adsorption isotherm is extended and the expressions with three and four parameters are obtained. The equations with multi-parameters are valid when the adsorbed mounts are larger and show non-linear logarithmic relationships. Tests with a homologue of are-matic alcohols by frontal analysis in reversed phase liquid chro-matography demonstrate that the experimental results fit those equations well. In addition, the predicted values by the multi-parameters were found to fit the experimental values well also. The parameters have physical meaning only for the two-param-eter equation for the aromatic alcohols.     

Investigation on the relationship between analytical precision and concentration with iteratively reweighted least-squares linear regression method

It is very important to investigate the relationship between analytical precision and concentration for quality control and assessment of analytical results. A set of analytical data of trace elements in soil and water deposits (Chinese certified reference materials) was studied for the relationship between the analytical precision of collaboration trials (i.e. reproducibility) and the concentration of the analytes. Iteratively reweighted least-squares (IRLS) linear regression, a robust method, was employed in this study. The linear relationship between the standard deviation and concentration was successfully established. On comparison with the conventional least-squares (LS) method , the results of IRLS linear regression are superior to those of LS.     

The relationship between the mercury concentration in fish muscles and scales/fins and its significance

The determination of mercury in fish typically involves analysis of muscles. For predicting the concentration of mercury in fish muscle on the basis of the analysis of fish scales or fins, the relationship between total mercury concentrations in fish muscles and in fish scales and fins was studied. Mercury content in fish muscles, scales and fins was determined by atomic absorption spectrometry with thermal decomposition of the sample in a flow of oxygen. A number of scale treatments were applied in order to remove impurities and to enhance the prediction quality. For scale treatment, 40 min of washing with DI water in an ultrasonic bath is recommended. A coefficient of determination r²= 0.93 for the relationship between Hg concentrations in muscles and scales was achieved for 40 fish among the different fish species tested (European bream, perch, roach) from the Hamry Reservoir, Czech Republic. With respect to fin sampling, the coefficient of determination r² for these fish was 0.86. The analysis of fish scales and caudal fins is a useful screening tool for assessing the relative mercury contamination of monitored fish. The method of sampling scales is not suitable for fish species with small scales such as brown trout.      

Robustness in NAA evaluated by the Youden and Steiner test

The chemistry laboratory at the Peruvian Institute of Nuclear Energy (IPEN) has carried out a validation method for the samples of siliceous composition. At least seven variables affecting the robustness of the results were initially identified, which may interact simultaneously or individually. Conventional evaluation hereof would imply a massive number of analyses and a far more effective approach for assessment of the robustness for these effects was found in the Youden-Steiner test, which provides the necessary information by only eight analyses for each sample type. Three reference materials were used for evaluating the effects of variations in sample mass, irradiation duration, standard mass, neutron flux, decay time, counting time and counting distance.     

A study on radiation sterilization of SPF animal feed

SPF animal feed could be infected with various microorganisms in the crushing or granulating process. Fumigation with chemicals is generally employed for sterilization of feeds, but owing to low permeability of the chemicals, this sterilization method is not very good, and there may be residual chemicals in the feed. Research results of sterilization by radiation show that irradiation by ⁶⁰Co gamma rays will reduce infections for SPF animals. 8 kGy can kill microoganisms in the feed with satisfactory efficiency. After the irradiation treatment with different doses, the changes of nutrient components in the feeds, such as crude fats, coarse fibres, calcium, phosphorus, salts and amino acids, were not found to change in our tests.