J.M. Los Arcos

Standardization of carbon-14 by 4πβ liquid scintillation efficiency tracing with hydrogen-3

Abstract Carbon-14 in the form of [ 14 C]tartaric acid solution has been standardized by means of 4πβ liquid-scintillation efficiency tracing using the NBS [ 3 H]water standard. The method of computing the detector efficiency for a two-phototube counting system using a standard of 3 H is described. The combined uncertainty in the 14 C radioactivity concentration, which may be treated as if it were one standard deviation, is 0.20%.

The standardization and decay scheme of rhenium-186

Abstract Rhenium-186 has been standardized for activity by the CIEMAT/NIST method of 4πβ liquid-scintillation efficiency tracing with tritium, with an uncertainty (equivalent to 1 SD) of 1.61%. Half-life measurements with a pressurized ionization chamber give a T 1 2 = 89.25 ± 0.07 h . Photon emission rates were measured with semiconductor detectors, and the probability of emission of the principal γ-ray at 137 keV was found to be P7 = 0.0945 ± 0.0016.

Comparison of activity concentration measurement of 63Ni and 55Fe in the framework of the EUROMET 297 project

Abstract Eleven laboratories participated in an intercomparison of activity concentration measurements using liquid scintillation counting (LSC) for the standardization of 63Ni and 55Fe in the frame of the EUROMET project No. 297 and under the co-ordination of LPRI. The purpose of this action was to compare the main LSC activity concentration measurement methods currently used in radioactive metrology, and to exchange models and ideas on LSC. This paper presents a summary of the results reported by the participant laboratories and an overview of the measurement methods used.

41Ca standardization by the CIEMAT/NIST LSC method

Abstract A procedure for the liquid scintillation counting standardization of the electron-capture nuclide 41 Ca has been successfully developed and applied with 41 CaCl 2 and 41 Ca-(HDEHP) n samples synthesized in the laboratory from 41 CaCO 3 supplied by Oak Ridge National Laboratory. Six scintillators were tested: the organic samples were stable in toluene—alcohol, Ultima-Gold™ and HiSafe III™ for 30 d, whereas the inorganic samples were only stable in toluene—alcohol and HiSafe III™ for the same period of time. Despite of the low counting efficiencies (1%–13%) due to the very low-energy of less than 3.6 keV of the X-rays and Auger electrons of 41 Ca, the stable samples were standardized by the CIEMAT/NIST method to a combined uncertainty of 2.4% over a range of figures of merit of 1.75 to 7.25 ( 3 H equivalent efficiency of 40% to 7%).

A new digital pulse height analysis method for radiation spectroscopy

Abstract A new PHA method has been developed which analyzes the preamplifier pulses directly. This technique is based on digital sampling of the preamplifier output, followed by hard-disk storage and digital processing. Data are acquired by a dual-channel oscilloscope with 32×2 kbytes of storage memory and up to 100 Msample/s to give a time resolution of 10 ns. A personal computer is used to control the acquisition system through a standard GPIB interface; data processing is also carried out off-line on the same computer. The procedure has been applied to radiation spectra obtained with semiconductor detectors, and the results have been compared with equivalent spectra acquired by conventional PHA methods under the same experimental conditions.

LSC standardization of 54Mn in inorganic and organic samples by the CIEMAT/NIST efficiency tracing method

Abstract The standardization of 54 Mn by the CIEMAT/NIST LSC efficiency tracing method using a commercial solution of 54 MnCl 2 and three specially synthetized organic salts of the dimethyl-butyric, decanoic and palmitic acids, in six different scintillators, is described. Samples over a wide range, 1–5, of figures of merit, were used and an overall uncertainty between 0.71% and 1.3%, depending on the scintillator used, was estimated for the activity concentration o the radioactive solutions.

EBEGA — the counting efficiency of a beta-gamma emitter in liquid scintillators

Abstract A program is described which computes the counting efficiency of a beta-gamma ray emitter as function of the figure of merit in liquid scintillation systems. A Monte Carlo scheme is used to simulate the gamma-ray interaction with a toluene-based scintillator. The results are valid for systems with two photomultipliers working in coincidence.

LSC standardization of 45Ca by the CIEMAT/NIST efficiency tracing method

Abstract A commercial solution of 45 CaCl 2 and two organic compounds, 45 Ca-2-ethylhexadecanoate and 45 Ca-HDEHP complex, synthesized in the laboratory, have been used to produce appropriate sources for LSC measurements. A toluene-based scintillator and three commercial cocktails (Hisafe II, Ultima Gold and Instagel) were used for measuring the samples. Their concentration quenching, time stability, and spectral behaviour were studied over a 30-day period. The stable samples were used to standardize the radioactive solutions by the CIEMAT/NIST efficiency tracing method. Experimental quench curves for 3 H were measured with each scintillator to cover the range of figure of merit between 1 and 4, corresponding to 3 H equivalent efficiency between 52 and 12%. Experimental and computed efficiencies were in good agreement, with individual discrepancies lower than 0.6% in all cases; high efficiency values, better than 95%, were obtained with unquenched samples. A combined uncertainty of 0.4% was obtained for the activity concentration estimation of each radioactive solution.

Monte Carlo simulation of the spectral response of beta-particle emitters in LSC systems

Abstract This paper presents a new method to evaluate the counting efficiency and the effective spectra at the output of any dynodic stage, for any pure beta-particle emitter, measured in a liquid scintillation counting system with two photomultipliers working in sum-coincidence mode. The process is carried out by a Monte Carlo simulation procedure that gives the electron distribution, and consequently the counting efficiency, at any dynode, in response to the beta particles emitted, as a function of the figure of merit of the system and the dynodic gains. The spectral outputs for 3 H and 14 C have been computed and compared with experimental data obtained with two sets of quenched radioactive standards of these nuclides.

Point source preparation by polypyrrole-based conductive thin film production and radionuclide labelling

Abstract A new method for radioactive point source preparation by radiolabelling of polypyrrole-based conductive thin films is presented. First, the polypyrrole is prepared onto an ITO glass in an electrolytic cell and then the radioactive material is incorporated locally into a small area as a droplet in which electrochemically activated redox reactions are induced, resulting in a strong, chemical bond of radioactive ions to the functional groups of the prrrolic conductive surface. This procedure leads to radiolabelling yields greater than 98% and sources with very low self-absorption and 10% or 17% better energy resolution than VYNS or electrodeposited conventional sources.