Direct and precise determination of environmental radionuclides in solid materials using a modified Marinelli beaker and a HPGe detector

A simple but precise detection method was studied for the determination of natural radionuclides using a conventional HPGe detector. A new aluminium beaker instead of a plastic Marinelli beaker was constructed and examined to reach radioactive equilibrium conditions between radon and its daughter elements without the escape of gaseous radon. Using this beaker fifteen natural radionuclides from three natural decay series could be determined by direct γ-ray measurement and sixteen radionuclides could be determined indirectly after radioactive equilibrium had been reached. Analytical results from ground water were compared with those from conventional α spectroscopy and the results agreed well within 12% difference. Nitrogen gas purge was used to replace the surrounding air of the detector to obtain a stable background and reducing the interference of radon daughter nuclides in the atmosphere. The use of nitrogen purging and the aluminium Marinelli beaker results in an approximately tenfold increase of sensitivity and a decrease of the detection limit of ²²⁶Ra to about 0.74 Bq kg^–1 in soil samples. Received: 12 October 2000 / Revised: 12 December 2000 / Accepted: 13 December 2000     

Direct and precise determination of environmental radionuclides in solid materials using a modified Marinelli beaker and a HPGe detector.

A simple but precise detection method was studied for the determination of natural radionuclides using a conventional HPGe detector. A new aluminium beaker instead of a plastic Marinelli beaker was constructed and examined to reach radioactive equilibrium conditions between radon and its daughter elements without the escape of gaseous radon. Using this beaker fifteen natural radionuclides from three natural decay series could be determined by direct gamma-ray measurement and sixteen radionuclides could be determined indirectly after radioactive equilibrium had been reached. Analytical results from ground water were compared with those from conventional alpha spectroscopy and the results agreed well within 12% difference. Nitrogen gas purge was used to replace the surrounding air of the detector to obtain a stable background and reducing the interference of radon daughter nuclides in the atmosphere. The use of nitrogen purging and the aluminium Marinelli beaker results in an approximately tenfold increase of sensitivity and a decrease of the detection limit of 226Ra to about 0.74 Bq kg(-1) in soil samples.     

A method for self-attenuation and sample-height correction for counting efficiency of HPGe using Marinelli beaker geometry

A procedure for self-attenuation and sample height correction in HPGe gamma spectrometry efficiency has been presented. An MCNP model of an HPGe detector was used to calculate the full energy peak efficiency (FEPE) for a group of different samples with different heights in Marinelli beaker geometry. A proper function has been fitted to the simulation results to obtain the correction function. The function has been used to calculate the FEPE of a spiked soil sample in different sample heights by considering the experimentally known FEPE of another standard solution source. A good agreement between the experiments and calculations have been shown.     

Relative efficiency calibration of Ge(Li) detector in low energy region

The relative gamma-ray intensities in the energy region between 122 and 411 keV in the decay of¹⁵²Eu were measured by using a Ge(Li) detector. Its efficiency calibration was carried out with the radioactive sources of²⁴¹Am,⁵⁷Co,²⁰³Hg,¹³⁷Cs,¹³³Ba,⁷⁵Se,¹⁶⁹Yb and¹⁹²Ir.     

Optimisation design of cylindrical containers for improving the detection efficiency of a high-purity germanium detector using the LabSOCS

The LabSOCS software was used to optimise the geometric dimensions of cylindrical containers and improve the detection efficiency of a high-purity germanium detector for the measurement of environmental radioactivity samples. The optimum ratio of diameter and height for different sample volumes were determined. In addition, the degrees of influence of the sample volume and density when the amount of sample was fixed were compared. Results show that the effect of sample volume on detection efficiency was significantly greater than that of sample density for a given sample amount.     

Light-scattering detection with a fluorimetric detector in high-performance liquid chromatography

Non-fluorescence compounds were detected by a fluorescence detector based on scattering light. The fluorescence detector was used without any modification, and the scattering light was observed at the wavelength twice as long as the excitation wavelength. Actually the wavelength of the observed scattering light was the same as that of the excitation light. The maximum signal was achieved at around 280 nm. The signal was increased with increasing molecular weight or size of analytes. Colloidal silica with nanometer sizes, ethylene glycol oligomers, saccharides and cyclodextrins could be visualized by the present detection method. The detection limit at S/N=3 for colloidal silica with 78 nm was 39 pg for 20-microL injection.     

Variation of counting efficiency in determination of 131I activity in the thyroid gland as a result of its position relative to the detector

The appropriate determination of the ¹³¹I which was absorbed into the human body, especially by thyroid, depends not only on individual features of each measurement subjects but also on reproducibility of their position or the thyroid’s position in the human neck. Possible uncertainties caused by changes of the thyroid position relative to detector were studied in a series of measurements. The research has shown that the dispersion of the results can reach up even to the level of 50 %.     

An automatic sample changer for alpha spectroscopy with a surface barrier detector

Semiconductor particle detectors are ideal for alpha spectroscopy due to their compact size, low noise, and high resolution. This paper describes the construction and testing of an automatic sample changer for use with such a detector. The changer was constructed from locally available services and materials. It holds up to 24 samples of alpha emitting material deposited on 22 mm stainless steel counting planchets. The vacuum chamber can be evacuated to less than 10 μm mercury in 10 to 15 minutes. Once the chamber has been evacuated and detector bias has been applied, any sample in the chamber may be selected for analysis, either automatically or manually. Continuous automatic analysis of up to 24 samples is possible. Variation in efficiency from position to position was found to be 3.25% at the detector-sample spacing of 4.8 mm, and 2.31% at 27 mm. Shielding between the adjacent samples not under analysis and the detector was acceptable. Published with the approval of the Director of the Arkansas Agric. Exp. Stn., Fayetteville. This project was supported in part by grants from ERDA and Arkansas Power and Light Co. and is gratefully acknowledged. Received June 18, 1979. Use of trade name does not imply endorsement or guarantee of that product to the exclusion of other products of similar nature.     

Comparison of a coaxial Ge(Li) and a planar Ge detector in instrumental neutron activation analysis of geologic materials

Instrumental neutron activation analysis was made on three different rock samples and on mineral separates of plagioclase, pyroxene and magnetite. γ-spectra were recorded using both a coaxial and a planar Ge detector. Counting errors were compared for those elements that could be determined with both detectors. In nearly all cases, analyses using the planar detector yielded smaller errors. The use of this detector in instrumental analysis is of particular advantage, where only contents of rare earth elements are to be determined.     

A new improved expression for gamma-ray detection efficiency of Ge(Li) detectors

In the present paper, a new improved expression for -ray detection efficiency of Ge(Li) detectors, ⁰ , is given. It is represented as a continuous function of x (viz. E ^–1) with a maximum and decreases very rapidly to a small positive value as -ray energy, E, drops to 40 keV or lower, but slowly as E rises to 1.7 MeV or higher. Since it can well represent the whole physical process of the -ray detection, this expression may be one of the simplest and most precise representations, for ⁰ at the present time.     

Fourier transform infrared spectroscopy with a sample deposition interface as a quantitative detector in size-exclusion chromatography

Micellar electrokinetic capillary chromatography was developed to analyze plant hormones including gibberellic acid, abscisic acid, indole-3-acetic acid, alpha-naphthaleneacetic acid, 2,4-dichlorophenoxyacetic acid, kinetin-6-furfurylaminopurine and N6-benzyladenine. The influences of some crucial parameters including buffer concentration, pH value, micelle concentration and applied voltage on electrophoretic separation were investigated. Under optimum conditions (50 mM borate as the running buffer containing 50 mM sodium dodecylsulfate, pH 8.0; separation voltage: -15 kV; injection: hydrodynamic injection, 5 s at 50 mbar; temperature: 25 degrees C), a complete separation of seven plant hormones was accomplished within 30 min. Emphasis was placed on improving detection sensitivity in order to detect small amounts of hormones in plant tissue. Multiple wavelength detection and expanded bubble cell capillary were used with enrichment factors of 2 and 3, respectively. In addition, an on-line concentration method of large volume sample stacking was designed. Enrichment factors of up to approximately 10-600 were achieved for these hormones with detection limits down to 0.306 ng/ml. The method was successfully applied to analyzing abscisic acid in flowers of transgenic tobacco.     

Effect of cascade coincidences on the efficiency calibration of a gamma-X detector

The sensitivity on n-type gamma-X detectors for low-energy X- and -rays calls for coincidence corrections in the efficiency calibration that do not apply to the calibration of p-type detectors. Corrections were calculated for the effect of cascade coincidences between -rays, X-rays, annihilation radiation, and bremsstrahlung, for 15 radionuclides frequently used for efficiency calibration. Experimental results are presented for a -X detector with 37% relative efficiency at distances from 0.9 to 17.5 cm. After coincidence correction smooth efficiency curves were found for the energy range 12 to 2750 keV, even for the position closest to the detector.     

Determining the efficiency of a broad-energy HPGe detector using Monte Carlo simulations

Broad-energy HPGe detectors have a useful range of 3 keV to 3 MeV, making them ideal for the assay of environmental samples. Such measurements however, are hindered by variations in the sample matrix, summing effects, and the Compton continuum. Detectors may be characterised by proprietary software in such a situation, however Monte-Carlo modelling is a useful, inexpensive alternative that also provides greater flexibility when determining the detector response and efficiency during a measurement. In the current work, a full GEANT4 model of a broad-energy HPGe detector is presented, and simulations of various samples are compared to experimental data. These are found to be accurate within 3 % at a confidence level of 95 % for energies from 30 to 3,000 keV, with greater variations below 100 keV due to an increased sensitivity to geometrical inaccuracies.     

Use of the Pearson IV function to describe the dependence of detection efficiency of Ge detectors on gamma-ray energy

2000 analytical functions were fitted to the measured gamma-ray detection efficiencies of a Ge detector for a small irradiation vial located at the closest distance from the detector. Among these, the Pearson IV function, gave the best fit. The measured and calculated efficiencies were compared for 50 determinations (for energies which varied between 61 and 2754 keV) and a relative standard deviation of 8.3% was obtained.     

Development of a two-color laser fluorescence detector. On-line detection of internal standards and unknowns by capillary electrophoresis within the same sample

A two-laser, two-color detector has been developed for the simultaneous detection of naturally occurring and recombinant (internal standards) cytokines within the same biological sample. The internal standards were labeled with Bimane and detected with a 408 nm laser while the natural cytokines were labeled with AlexaFluor633 and detected with a 633 nm laser. The two resulting electropherograms were plotted as overlaid traces and quantification of the natural materials determined by comparison with the standards. Using this system, recovery of all four cytokine standards was greater than 94% in both saline and cytokine-depleted plasma. These recoveries could be achieved with intra- and inter-assay coefficients of variance (c.v.) of less than 4.5 and 5.6, respectively. Application of this system to the examination of clinical samples demonstrated that measurement of the four pro-inflammatory cytokines could distinguish between normals, sub-clinical and clinical inflammation. An advantage of this approach is that direct calculation of unknowns by comparison to identical internal standards can shorten analytical time by eliminating the need for additional standard or calibration runs.