Precise determination of photon emission probabilities for the main X- and gamma-rays of 226Ra in equilibrium with daughters.

Within the context of a joint project between VNIIM (D.I. Mendeleyev Institute for Metrology) and LNHB (Laboratoire National Henri Becquerel), special 226Ra sources were prepared by VNIIM in order to determine as accurately as possible the absolute photon emission probabilities for the main X- and gamma-rays following the decay of 226Ra and daughters. The main purpose of this work was to supplement a previous joint study by Laboratorio Nacional de Metrologia das Radiaçoes Ionizantes (LNMRI) and LNHB to determine their relative values. Some specific point sources were produced for alpha-spectrometry measurements that were undertaken at VNIIM and also for gamma-ray spectrometry studies at VNIIM and LNHB. The 226Ra activity for the gamma-spectrometric sources was measured relative to the alpha-spectrometric sources by comparing the counts of the main gamma-rays. The total uncertainty of the activity for these sources was 0.2% (k = 1). Using calibrated germanium detectors, several X- and gamma-ray spectra were analyzed to determine the absolute photon emission probabilities of 226Ra in radioactive equilibrium with daughters. The results are presented and compared to other published values.

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.

Emission probabilities of the KX-rays following the decay of 237Np in equilibrium with 233Pa.

Following international EUROMET Project No. 416 and our recent measurement of the emission probabilities of the main gamma-rays of 237Np in equilibrium with 233Pa, a complementary work has been undertaken to determine the photon emission probabilities of the KX-rays associated with the decay of these nuclides. Two different analysis methods have been used: the KX-rays region was analyzed by fitting both Voigt and full response functions. Photon emission probabilities were determined with a relative uncertainty of about 2%.

A source for measurement of the absolute intensities of 226Ra gamma-radiation in equilibrium with decay products.

The design and production techniques of a gamma-ray spectrometric source of 226Ra in equilibrium with its daughter decay products have been developed. The radon emanation coefficient of the source did not exceed 0.1%. The 226Ra activity in the gamma-ray spectrometric source was measured relative to that in an alpha-particle spectrometric source by comparison of the intensities of the main gamma rays using a semiconductor gamma-ray spectrometer. The total uncertainty of the activity measurement results was 0.5% for a coverage factor of k = 2.

Study of XK and gamma photon emission following decay of 154Eu.

A joint project has been established between VNIIM (D.I. Mendeleyev Institute for Metrology) and LNHB (Laboratoire National Henri Becquerel) to determine as accurately as possible the X- and gamma-ray emission probabilities of 154Eu. Point sources were prepared by VNIIM, and absolute measurements of activity per unit mass were undertaken by both laboratories using coincidence, anti-coincidence and 4pi-gamma counting methods. Other point sources and one aliquot were also prepared for precise gamma-ray spectrometry measurements. Absolute photon emission probabilities were determined with a maximum uncertainty of 0.5% for the most intense lines, supporting the development of this nuclide as a multigamma standard.

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%.

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.