Eduardo García-Toraño

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 of plutonium-241 and nickel-63

Abstract Solutions of the low-energy beta-particle emitters 241 Pu and 63 Ni have been standardized using the method of 4πβ liquid scintillation (LS) efficiency tracing with 3 H. The 241 Pu has also been standardized by the method of 4 πα (LS)- γ coincidence and anticoincidence counting of the 241 Am daughter to follow its ingrowth in a separated sample. The 63 Ni solution was previously standardized at NIST by calorimetry. The uncertainties in the radioactivity concentrations obtained using these methods are discussed.

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.

α-particle emission probabilities in the decay of 235U

235U decays by α-particle emission to 231Th. The decay scheme of this nuclide is very complex, with more than 20 alpha branches. Recommended values for Pα of this nuclide are based on measurements carried out in 1975. This work presents the results of new measurements made with Si detectors and sources of enriched uranium in the frame of the EUROMET 591 cooperation project. The use of improved measurement techniques and numerical analysis of spectra allowed a new set of Pα values for 13 lines with improved uncertainties to be obtained.

Backscattering and self-absorption corrections in the measurement of alpha-emitters in 2π geometry

Abstract Monte Carlo simulation has been developed to model the slowing down and scattering of alpha particles in amorphous media so that corrections for backscattered and absorbed particles can be determined for 2π geometry measurements. These calculations are based on the total stopping powers and the Rutherford scattering law, and the resulting energy spectra are in good agreement with experimental measurements.

Alpha-particle emission probabilities in the decay of 240Pu

Sources of enriched (240)Pu were prepared by vacuum evaporation on quartz substrates. High-resolution alpha-particle spectrometry of (240)Pu was performed with high statistical accuracy using silicon detectors and with low statistical accuracy using a bolometer. The alpha-particle emission probabilities of six transitions were derived from the spectra and compared with literature values. Additionally, some alpha-particle emission probabilities were derived from gamma-ray intensity measurements with a high-purity germanium detector. The alpha-particle emission probabilities of the three main transitions at 5168.1, 5123.6 and 5021.2 keV were derived from seven aggregate spectra analysed with five different fit functions and the results were compatible with evaluated data. Two additional weak peaks at 4863.5 and 4492.0 keV were fitted separately, using the exponential of a polynomial function to represent the underlying tailing of the larger peaks. The peak at 4655 keV could not be detected by alpha-particle spectrometry, while gamma-ray spectrometry confirms that its intensity is much lower than expected from literature.

THE 1997 IAEA INTERCOMPARISON OF COMMERCIALLY AVAILABLE PC-BASED SOFTWARE FOR ALPHA-PARTICLE SPECTROMETRY

Abstract Four commercially available, PC-based analysis programs for alpha-particle spectrometry were compared using the 1997 IAEA test spectra, i.e. AlphaVision 1.20 (EG&G Ortec, USA), Alps 4.21 (Westmeier GmbH, Germany), Winner Alpha 4.0f5 (Eurisys Mesures, France) and Genie-2000 (Canberra Industries Inc., USA). A systematic statistical study of the analysis results was performed based on z -scores. The results indicate that the four programs leave room for substantial improvement.

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.

Application of ion transport simulation to the backscattering in α-particle sources

Abstract The standardization of α-particle emitting sources with 2π detectors requires corrections for backscattering from the backing material. The Monte Carlo computer code SRIM, developed to simulate the transport of ions in matter, was applied to the study of the backscattering of α-particles in different materials. Simulations of 5.3 MeV α-particles from 210 Po were performed for various backing materials with atomic numbers ranging from 13 to 79. In addition, some experiments using a 2π detector and a well-defined low solid angle chamber with a silicon detector were also performed. The experimental backscattering coefficients for 241 Am α-particle sources in Pt and Ag supports and for 239 Pu αs in stainless steel and quartz backing materials were determined. There was reasonable agreement between calculations and experimental results (carried out by us and by other laboratories). This work shows that Monte Carlo simulation of the transport of ions can be a very useful tool to evaluate the backscattering corrections in the standardization of α-particle sources.

A model shape for the analysis of alpha-particle spectra

A simple line-shape model is proposed to represent the experimental behaviour of alpha peaks in spectra measured with Si detectors. The model depends on a reduced number of parameters, which makes it suitable for the analysis of alpha-particle spectra in routine analysis. Its advantages and limitations are described.