Absolute Efficiency Curve Research Articles

Preparation of 134Cs sealed source based on WO3 adsorbent for radiometric calibration purposes

Cesium-134 artylon sealed source based on inorganic adsorbent (as a core) was easily prepared. The sealed source was in the form of a disk constituted of two halves; base and top. Cesium-134 was adsorbed by equilibration of 134CsCl solution with WO3 inorganic adsorbent at pH 4 for 24 h at 25±1°C. Then, the liquid phase was decanted and checked for the remaining activity. Thereafter, the 134Cs-loaded WO3 was dried at 100 °C for 24 h. A definite weight the 134Cs-loaded WO3 adsorbent was placed in the central cavity of the base half-disk. Then the two half-disks were assembled using a commercial epoxy adhesive. The activity values of the sealed source were 7.81×10-2 and 7.70×10-2 Ci, calculated by using the absolute efficiency curve and DETEFF software were found to be closest at a 5 cm source-detector distance; respectively. After radiometric standardization and encapsulation, the sealed source was checked radiometrically before release to the local market for calibration purposes of radiation measurement and identification instruments.

Use of mathematical modeling to extend the scope of application for the procedure of measuring the mass of 235U in solid radioactive waste

The known dependence of absolute efficiency on energy and space for particular measurement conditions is used to determine the mass (activity) of 235U in solid radioactive waste by gamma-spectrometric method. The ISOCS system makes it possible to avoid laborious and time-consuming calibration measurements using standard samples to obtain the absolute efficiency curve due to using the so-called characterized detector having a file with a set of efficiencies for various measurement geometries. In many cases, the establishment of standard samples with parameters covering the 235U mass measurement range in the variation intervals of influencing factors, including density, non-uniformity, isotopic composition, geometry, etc., is very expensive and, most often, not feasible. With regard for this, a computational and experimental approach is used based on results obtained by Monte Carlo method using the MCNP code with variation of the key influencing parameters in a broad range. Calculations were performed for detector-recorded spectra of gamma quanta from casks containing waste differing in the density of the cask content (the density was calculated with regard for the uranium contained in waste) – from 0.016 to 1 g/cm3, in the mass of uranium in waste – from 0.64 g to 2 kg, and in the matrix material – graphite, cellulose, quartz, cellulose with 20 % of iron dust. Applicability boundaries have been defined for the developed procedure to measure uranium-containing waste in terms of the material matrix (~ 2.2 %) and its density (~ 10 %) and the contribution of the uranium mass uncertainty in the cask (5 % for nonporous matrices, 10 % for porous matrices) to the obtained result has been estimated.

Production of 152,154Eu mixed sources for calibrations of gamma-ray spectrometers

Mixed gamma-ray point sources consisting of 152Eu and 154Eu were prepared from a solution of EuCl3 containing both isotopes. Gamma-rays emitted from these isotopes were used to establish the relative efficiency curves of HPGe detector, which were converted to absolute ones using gamma-ray sources of well-known activities. Gamma-ray attenuation correction factors were taken into account. Accuracies of activity measurements of the prepared sources were checked by measuring other sources of well-known activities and confirmed by simulating the absolute efficiency curve at distance of 15 cm from the detector window using the DETEFF software. The prepared sources were then submitted to quality control tests.

239Pu, 240Pu, and 241Am Determination in Hot Particles by Low Level Gamma-Spectrometry

A nondestructive method based on low-energy, high-resolution photon spectrometry is presented which allows accurate determination of (239)Pu, (240)Pu, and (241)Am (as a daughter of (241)Pu) activities in radioactive particles containing relatively high levels of plutonium isotopes. The proposed method requires only one measurement for the establishment of an absolute efficiency curve. Since the density and composition of the radioactive particles of interest may vary, a self-absorption correction is required for the accurate determination of isotopic activities and ratios. This correction is carried out for each individual particle using the convenient gamma-ray emissions of (241)Am.

Experimental Method to Determine the Absolute Efficiency Curve of a Wavelength Dispersive Spectrometer

A method for the experimental determination of the absolute efficiency of wavelength dispersive spectrometers was developed, based on the comparison of spectra measured with a wavelength dispersive system and with an energy dispersive spectrometer. The aim of studying this parameter arises because its knowledge is necessary to perform standardless analysis. A simple analytical expression was obtained for the efficiency curve for three crystals (TAP, PET, and LiF) of the spectrometer used, within an energy range from 0.77 to 10.83 keV. Although this expression is particular for the system used in this work, the method may be extended to other spectrometers and crystals for electron probe microanalysis and X-ray fluorescence.

Specific activity and hazards of granite samples collected from the Eastern Desert of Egypt

Fifty granitic rock samples were collected from different plutons in the central part of the Eastern Desert of Egypt and were analyzed for specific concentrations of 238U, 232Th and 40K radionuclei. The measurements were carried out using a high performance and stability Nomad Plus spectroscopy system attached to a 1.7 keV (FWHM) HPGe detector. The spectra were analyzed using the direct gamma counting comparison method as well as the traditional absolute efficiency curve method. The highest average value of 238U concentration (1184 Bq kg −1) was observed at EI Misikat region whereas the highest average values of 40K and 232Th concentration (2301.8 and 162.5 Bq kg −1 respectively), were detected at Gabal Homret Waggat area. The radium equivalent activity (Ra eq), the absorbed dose rate ( D), the external hazard index ( H ex) and the annual gonadal dose equivalent were also calculated and compared to the international recommended values. Radon exhalation rate from the rock samples were measured using the activated charcoal canister method. The average value of radon exhalation varies from 0.052 to 0.69 Bq m −2 h −1 and depends on the specific concentration of uranium.

Production of Co-60 sources for high-accuracy efficiency calibrations of gamma-ray spectrometers

Activity determination by gamma-ray spectrometry is a valuable aid which is widely used where radioactive sources are applied. For the construction of an efficiency curve vs. energy in a standard geometry, the accuracy is limited not only by the uncertainty of peak area determination and the knowledge of the relevant emission probabilities but also by the uncertainties of the activity values applied to efficiency calibration with standard sources. Recently, a method to determine a relative efficiency function using selected radionuclides with gamma cascades of well known emission probabilities has been developed which yields very accurate efficiency values. Such a curve has to be converted into an absolute efficiency curve by calibration of the detector system with at least one source of very well known activity. Especially for this purpose, a set of Co-60 gamma-ray spectrometer sources was produced at the PTB. The activity values (10–45 kBq) were measured by the 4 πβ-γ coincidence technique with a standard uncertainty of less than 0.1%. Production and measurement of these sources are described in the present paper. Special care was taken to include all contributions to the standard uncertainty of the activity value when establishing the uncertainty budget for the activity of each of these sources. The activity ratio of two of these sources, as obtained by the absolute measurements, was checked by independent gamma-ray counting at two other laboratories, where the precision achieved was less than 0.2%. The procedure described is considered to be a step towards more accurately determined efficiency functions in gamma-ray spectrometry.

Rapid monitoring of gaseous fission products released from nuclear power stations

Rapid, in situ measurements were used for quantitative monitoring of gaseous fission products around the nuclear power stations in Taiwan. A portable high-resolution germanium detector with portable multichannel analyzer was used in the field monitoring work. The detecting unit was calibrated using activated Ar, Kr, and Xe isotopes dispersed in a large chamber to obtain absolute efficiency curve in terms of γ-counts per m3 versus gamma-ray energy. The calibrated detecting unit was brought to the nuclear power plants for in situ monitoring for both normal operation and nuclear accidental exercise. In a typical four-hour measurement, the detection limits for most Kr and Xe fission product isotopes were 0.0028%≈0.98% of the derived air concentration (DAC) imposed by the local authority. The dose rate caused by gaseous radioisotopes released from nuclear power stations and dispersed to the surroundings can be quantitatively monitored in a short period using this portable unit.

On a high-purity Ge EDS detector I. Determination of detector efficiency

The absolute efficiency curve for an ultra-thin window (UTW) high-purity (intrinsic) germanium (HPGe) EDS detector was determined by comparing EDS spectra from a set of standard specimens with spectra from the same compounds taken with a UTW Si(Li) detector, and with systematic computer simulations. The efficiencies of the two detectors are comparable, except at energies between the Ge-L 3 and Si-K absorption edges, where the efficiency of the HPGe detector is ~ 20% lower. The methodology employed allows important features of both detectors, particularly their dead layer thicknesses, to be determined.

A single detector method for the determination of PK 1 in 133Ba

A method is described for determining P K 1 ω K ε K for 133Ba utilizing X-ray-γ-ray summing in a single high resolution intrinsic Ge detector. The absolute efficiency curve for the Ge detector is established, and a value of P K 1 = 0.747 ± 0.096 is determined for 133Ba. The result is compared to earlier measurements and the factors limiting the accuracy of the measurement are discussed.