Standardization of 65Zn.

Two absolute methods were used for standardizing the 65Zn solution received within the framework of the 2002-2003 full-scale BIPM comparison. The first method was the 4piPC-gamma-coincidence with efficiency extrapolation. The measurement conditions were adjusted so that the slope of the extrapolation curve was absent, which ensured that the measurement result did not depend on the positron branch intensity. When using the second method, the KX-gamma-coincidence counting with two NaI(Tl) scintillation crystals of different thicknesses, extrapolation was not needed, but a correction for the positron branch was necessary. It is shown that the 4piPC-gamma-coincidence method has a significantly larger uncertainty, and it is necessary to pay attention to the uncertainty component connected with setting the gamma-channel mode, which is characteristic for 65Zn only.

Standardization of 204Tl and 89Sr at VNIIM.

D.I. Mendeleyev Institute for Metrology (VNIIM) participated in two international comparisons of 204Tl and 89Sr solutions organized by the BIPM. The activity concentration was measured using the 4pi PC beta-counting method. Special attention was paid for investigating the dependence of the result on the inner diameter of the source support ring. For thin Al rings (100-200 microm), no dependence was detected. The beta-impurities in the 89Sr solution were determined using a scintillation plastic spectrometer. The combined standard uncertainty of the standardization of the 89Sr solution is 0.2%, and that for 204Tl is 0.4%.

[Prevention of arrhythmogenic and contractile effects of excessive Ca2+ on the heart through adaptation to stress by increasing the activity of sarcoplasmic reticulum]. / Preduprezhdenie s pomo'shchiu adaptatsii k stressovym vozdeistviam aritmogennogo i kontrakturnogo vliianiia izbytka Ca2+ na serdtse za schet povysheniia aktivnosti sarkoplazmaticheskogo retukuluma.

The experiments with rat isolated hearts and papillary muscles showed that adaptation to short-term stresses increased myocardial resistance to arrhythmogenic and contractile effects of excessive Ca2+. Adaptation caused a three- and fivefold reduction in the contracture and premature beats, respectively, while Ca2+ levels were increased from 1.36 to 10 mM. In the experiments with papillary muscles, the adaptation showed a 6.5-fold decrease in the contracture and significantly limited resting potential depression resulted from lower Na+ concentrations (up to 9 mM) in the perfusion solution. The adaptation to stresses was found to restrict depression of cardiomyocyte electrophysiological parameters that was due to high Ca2+ levels and high heart rate. With the factors, the resting potential in adaptation proved to be significantly higher than in controls and the time of action potential was twice as such as in controls. Biochemical studies demonstrated that Ca2+ transport rates in the sarcoplasmic reticulum, cardiomyocytes of adapted animals were increased by more than 30% whereas the sarcoplasmic reticulum of the heart was more resistant to the effects of endogenous factors of degradation. The authors also discuss a possible mechanism of the cardioprotective effects of adaptation to stress undamaging exposures, which is associated with limited depression of electrophysiological parameters on pathological exposures and with increased Ca2+-transporting capacity of the sarcoplasmic reticulum.

Methods of producing radionuclides for spectrometric gamma-ray sources and their standardization--2. Europium-152.

The radionuclide 152Eu was produced by irradiating 151Eu2O3 or 151EuCl3 enriched to 98.9% with thermal neutrons. 152Eu was separated from rare-earth impurities by extraction chromatography on a column using 0.6 M nitric acid eluent. The specific activity of the 152Eu was 1-10 Ci/g of Eu. The impurity of the 154Eu did not exceed 0.1%. The activity standardization of 152Eu was carried out by extrapolation of 4 pi (beta, e, x)-gamma coincidences. The relative gamma-ray intensities for 28 gamma-ray energies emitted in 152Eu decay have been measured.