Half-life determination of the ground state decay of ¹¹¹Ag.

The radioactive decay half-life of the ß(-)-emitter (111)Ag has been measured using decay transitions identified using a high purity germanium γ-ray spectrometer. The time series of measurements of the net peak areas of the 96.8 keV, 245.4 keV and 342.1 keV γ-ray emissions following the ß(-) decay of (111)Ag were made over approximately 23 days, i.e. ~3 half-life periods. The measured half-life of the ground state decay of (111)Ag was determined as 7.423 (13) days which is consistent with the Evaluated Nuclear Structure Data File (ENSDF) recommended half-life of 7.45 (1) days at k=2. Utilising all available experimental half-life values, a revised recommended half-life of 7.452 (12) days has been determined.

Certified reference materials for radionuclides in Bikini Atoll sediment (IAEA-410) and Pacific Ocean sediment (IAEA-412).

The preparation and characterization of certified reference materials (CRMs) for radionuclide content in sediments collected offshore of Bikini Atoll (IAEA-410) and in the open northwest Pacific Ocean (IAEA-412) are described and the results of the certification process are presented. The certified radionuclides include: (40)K, (210)Pb ((210)Po), (226)Ra, (228)Ra, (228)Th, (232)Th, (234)U, (238)U, (239)Pu, (239+240)Pu and (241)Am for IAEA-410 and (40)K, (137)Cs, (210)Pb ((210)Po), (226)Ra, (228)Ra, (228)Th, (232)Th, (235)U, (238)U, (239)Pu, (240)Pu and (239+240)Pu for IAEA-412. The CRMs can be used for quality assurance and quality control purposes in the analysis of radionuclides in sediments, for development and validation of analytical methods and for staff training.

Certified Reference Material IAEA-446 for radionuclides in Baltic Sea seaweed.

A Certified Reference Material (CRM) for radionuclides in seaweed (Fucus vesiculosus) from the Baltic Sea (IAEA-446) is described and the results of the certification process are presented. The (40)K, (137)Cs, (234)U and (239+240)Pu radionuclides were certified for this material, and information values for 12 other radionuclides ((90)Sr, (99)Tc, (210)Pb ((210)Po), (226)Ra, (228)Ra, (228)Th, (230)Th, (232)Th, (235)U, (238)U, (239)Pu and (240)Pu) are presented. The CRM can be used for Quality Assurance/Quality Control of analysis of radionuclides in seaweed and other biota samples, as well as for development and validation of analytical methods, and for training purposes.

Characterization of the NIST seaweed Standard Reference Material.

The National Institute of Standards and Technology (NIST) Standard Reference Material (SRM) for seaweed was developed through an interlaboratory comparison with 24 participants from 16 countries. After evaluating different techniques to calculate certified values for the radionuclides, the median method was found to be the most representative technique. The certified values were provided for 13 radionuclides and information values were given for 15 more radionuclides. Results for the natural decay series showed disequilibrium in both the uranium and thorium series.

On the integrated decay and ingrowth equations used in the measurement of radioactive decay families: the general solution.

In the measurement of radioactivity, a finite measurement time is employed to collect data. Usually, this time is small with respect to the half-life of the nuclide being measured and the 'usual' decay equations can be used to decay measured activities to a given reference time. In some applications, such as neutron activation, an integrated form of the decay equation needs to be employed as the measurement time is comparable to the half-life and using the non-integrated form introduces a significant error. This correction is well known and is used widely. For radionuclide families, such as the natural decay series of uranium and thorium or simple parent--daughter systems, no such integrated form of the decay and ingrowth series appears to have been published in the open literature. This paper sets out the general solution for integrated decay and ingrowth of sequential decay and illustrates the validity of this theoretical solution by applying it to real examples.

Development of an organically bound tritium standard.

High-concentration factors between seawater and marine organisms have been observed for organically bound tritium (OBT). The absence of an available OBT standard impedes the validation of an analytical method for environmental samples. This paper describes the secondary standardisation of tritiated thymidine, which was chosen to act as an OBT standard, using liquid scintillation counting. Traceability was provided by using internal standards of tritiated water (HTO). The assumption that the counting efficiencies for tritiated thymidine and HTO were identical was tested with separate quench curves. The rate of self-decomposition for tritiated thymidine, which resulted in an activity concentration of tritiated thymidine lower than the total tritium activity concentration, was determined.

Secondary standardisation of 95mTc.

The radionuclide 95mTc, which has a half-life of 61(2)days and emits a number of gamma-rays, may be used in radiochemical analysis as a yield tracer for the long-lived fission product 99Tc. In this work, we present (i) the production of 95mTc via an (alpha, 2n) reaction with stable 93Nb (a method which does not result in the production of any 97mTc, 98Tc or 99Tc), (ii) the chemical separation of 95mTc from niobium via coprecipitation, liquid-liquid extraction and liquid chromatography, and (iii) the secondary standardisation of 95mTc with high-resolution gamma-ray spectrometry and an ionisation chamber system.

Primary standardisation of 204Tl using the efficiency tracing method.

The electron-capture and beta(-) -emitting radionuclide 204Tl has been known from previous experience to show discrepancies between different methods of standardisation. Source preparation is also difficult due to the complex chemistry of thallium. The Bureau International des Poids et Mesures (BIPM) intercomparison held in 1997, showed discrepancies of up to 10% between measurements of solid sources and liquid scintillation methods. These problems have been the subject of a BIPM CCRI(II) working group since 1999. This paper presents the results from a primary standardisation of a 204Tl solution using 4pibeta-gamma coincidence counting and liquid scintillation counting. The tracer technique was used for the 4pibeta-gamma coincidence counting, where 204Tl was traced with 134Cs and 60Co. The extrapolation to 100% beta-efficiency was performed by three different approaches: foiling, adding carrier and measuring sources of different initial masses. The results showed that tracing with 60Co and using external foiling gave the same result as obtained by liquid scintillation counting. A comparison of the results achieved by the different methods of measurement, tracers and methods for extrapolation is presented and discussed in this paper.

Thorium in the workplace: the preparation and validation of comparison samples for a European-based measurement comparison project.

The quality of any comparison exercise depends critically on the quality. accuracy and fitness for purpose of the comparison samples. The comparisons were designed to move progressively from the testing of the analysis capabilities for relatively simple. aqueous solutions through to the more complex natural matrix materials encountered in the workplace. In each case, it was imperative that the comparison samples were prepared and validated in such a way as to ensure traceability of their activity values to national and international standards of radioactivity, to enable a reasonable estimate to be made of the uncertainty on those values and to ensure homogencity both within and between samples. The processes involved are discussed.

Thorium in the workplace: results from a European-based measurement comparison project.

A Series of comparisons were conducted to test the capabilities of a range of metrological techniques and analytical laboratories engaged in the assay of thorium in the workplace. The results of these exercises are presented together with the decision criteria used to determine whether results are significantly different from the true value. The discussion highlights those aspects which warrant closer and further attention.