Counting yield calibration of NaI(Tl) detectors for complex geometry samples by use of californium-252

The counting yield for large volume, complex geometry samples such as solutions in Marinelli beakers as counted on a large NaI(Tl) detector can be calibrated using radionuclides activated by neutrons form a²⁵²Cf source. Calibration may be done by using either a known neutron flux facility or by cross calibration of the activated material as a point source vs. sealed gamma-standard sources. The point source of activated material is dissolved after cross calibration to produce the large volume distributed source.     

Efficiency calibration of an HPGe detector in the 0.1–2.5 MeV energy range for Am-Be neutron source-based PGAA applications

A 740 GBq ²⁴¹Am-Be neutron source based prompt gamma-ray activation analysis (PGAA) setup in combination with a typical coaxial n-type HPGe detector (REGe) system was used to analyze light elements like H, B, C, N, etc. The absolute full energy peak (FEP) efficiencies of the shielded REGe detector for irradiation and counting geometries and for sources with different sizes (point, ampoule and cylindrical) were measured in the 0.1–2.5 MeV energy range by utilizing calibrated sources (point, liquid and solid). 4th order polynomials were fitted to the experimental data. Efficiencies in far irradiation and counting geometries are compared.     

Volume efficiency correction factor determination for gamma spectrometry using <Superscript>82</Superscript>Br

An easy experimental method for volume efficiency correction factor determination in gamma spectrometry was evolved in this work using ⁸²Br volume samples. The ⁸²Br point sample was diluted successively to form cylindrical samples of different volumes. The gamma spectra of these samples were measured before and after dilution for different sample—detector spacing. The theoretical basis of this method is simple. The volume efficiency dependence on the radius and height was determined.     

Assessment of the suitability of Monte Carlo simulation for activity measurements of extended sources

Monte Carlo simulations can be a powerful tool in calibrating high-resolution gamma-ray spectrometry based on high pure germanium (HPGe) detectors. The purpose of this work is to examine the applicability of Monte Carlo simulations for the computation of the efficiency transfer in various measurement geometries on the basis of the detected efficiency for point source geometry. For this, GEANT4 code was applied for the computation of the detection efficiency for incident gamma energy of radionuclide placed at different distances from HPGe detector from 50 to 2,000 keV in addition for volume sources of different compositions and densities. The experimental efficiency curves were compared with the prediction of the GEANT4 code. Efficiency is computed at discrete values of point and volume sources in different distances to derive new efficiencies values for other distances.     

A semi-empirical method for calculation of true coincidence corrections for the case of a close-in detection in γ-ray spectrometry

In this paper, a semi-empirical method is proposed to determine true coincidence-summing (TCS) correction factors for high resolution γ-ray spectrometry. It needs the knowledge of both full energy peak (FEP) efficiency and total-to-peak (TTP) efficiency curves. The TTP efficiency curve is established from the measurements with a set of coincidence-free point sources. Whereas for a volume source, the coincidence-free FEP efficiency curve is obtained iteratively by using the peaks from almost the coincidence-free nuclides and those from the coincident nuclides in the mixed standard sources. Then the fitting parameters obtained for both TTP and FEP efficiency curves are combined in a freely-available TCS calculation program called TrueCoinc, which yields the TCS correction factors required for any nuclide. As an application, the TCS correction factors were determined for the particular peaks of ²³⁸U, ²²⁶Ra and ²³²Th in the reference materials, measured in the case of a close-in detection geometry using a well-type Ge detector. The present TCS correction method can be applied without difficulty to all Ge detectors for any coincident nuclide.     

Gas spherical ionization chamber

A pressurized ionization chamber detector able to measure radioactive sources in internal 2π or 4π geometry was built in order to characterize alpha and beta radioactive sources, i.e. to calibrate these sources by a relative method, and to test the behavior of gas mixtures in pressurized-gas radiation detectors. The detector we made is of spherical shape and works by collecting in a quasi-uniform electric field the ionization charges resulting from the interaction of ionizing radiation with gas in the sensitive volume of the chamber. An ionizing current proportional to the activity of the radioactive source to be measured is obtained. Pressure inside the detector in standard conditions is maximum 6 × 10⁵ Pa at 22 °C and the maximum allowed voltage is 3000 V. It is presented as a spherical ionization chamber with gas under pressure, geometrical shape, dimensions and structural characteristics, functional and technical parameters and preliminary experimental results obtained from radiation measurements in the laboratory SALMROM of the IFIN-HH.     

Crystal detector calibration for large sample counting

A useful method for crystal detector calibration by using point sources is presented. The method is applied to determine the total efficiency of a 80×80 mm NaI/Tl/ crystal in an energy window suitable for¹³⁴Cs+¹³⁷Cs activity evaluation in a sample of 750 cm³.     

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.     

A thin-layer contactless conductivity cell for detection in flowing liquids

The design is described of a thin-layer contactless conductivity detector suitable for liquid chromatography and flow-injection analysis. Its principal analytical parameters have been determined using a potassium chloride solution: the linear dynamic range extends from 7.5 × 10⁻⁶ to 1.5 × 10⁻² S m⁻¹, corresponding to the KCl concentration range from 0.5 to 1000 μM, the limit of detection equals 3.5 × 10⁻⁶ S m⁻¹ (0.2 μM KCl), the detection repeatability, expressed in terms of the relative standard deviation, amounts to 1.13% and the detection volume is 0.6 μL. The detector was applied to detection of ionic compounds, benzoic, lactic and octanesulfonic acids, and sodium capronate, after their separation by liquid chromatography in a Biospher PSI 100C 18 columns using a 60% aqueous acetonitrile mobile phase. The frequency characteristics of the detector are reasonably theoretically described on the basis of a simple model which is commonly used in the field of contactless impedance detectors.     

A simple isocratic LC method for quantification of trace-level inorganic degradation impurities (ferricyanide,ferrocyanide, nitrite,and nitrate) in sodium nitroprusside injection and robustness by quality using design approach

This study developed and validated a trace-level quantification inorganic impurities method using reversed-phase HPLC and performed the robustness check using quality-by-design approach by varying the multiple factors simultaneously. This method is economical and simple and exhibits its stability-indicating nature [for the determination of ferrocyanide ([Fe(CN)₆]^4–), ferricyanide ([Fe(CN)₆]³⁻), nitrate (NO₃^–), and nitrite (NO₂^–)] in sodium nitroprusside (SNP) drug substance and liquid dosage form. Chromatographic separation was achieved using a USP L43 column (ACE PFP, 150 × 4.6 mm, 3 μm) with a simple isocratic elution. The buffer consists of potassium dihydrogen phosphate (50 mM), tetrabutylammonium hydrogen sulfate (9 mM), and tetrabutylammonium hydroxide (25 mM). The buffer pH was adjusted to 7.2 with tetrabutylammonium hydroxide. The mobile phase was mixed with the buffer and acetonitrile (68:32 v/v). The flow rate was 0.8 mL/min, column temperature was maintained at 30°C, and injection volume was 5.0 μL. The SNP impurities were monitored at 225 nm using a UV detector. Further, the method was validated per the International Council for Harmonisation (ICH) guidelines, and forced degradation studies were carried out under different stress conditions. The detector responses were plotted against concentrations, and correlation was linear (r > 0.999) over the range of 0.8–7.5 μg/mL for ferricyanide; 1.0–37.5 μg/mL for SNP; and 0.2–7.5 μg/mL for ferrocyanide, nitrite, and nitrate. The method repeatability was established for all the impurities with relative standard deviation (%), and the results were found to be less than 2.0.     

True coincidence summing corrections in point and extended sources

The true coincidence summing (TCS) effect on the full energy peak (FEP) efficiency calibration of an HPGe detector has been studied as a function of sample-to-detector distance using multi-gamma sources. Analytical method has been used to calculate coincidence correction factors for ¹⁵²Eu, ¹³³Ba, ¹³⁴Cs and ⁶⁰Co for point and extended source geometry at close sample-to-detector distance. Peak and total efficiencies required for this method have been obtained by using MCNP code by using the optimized detector geometry. The correction factors have also been obtained experimentally. The analytical and the experimental correction factors have been found to match within 1–5%. The method has been applied to obtain the activity of the radionuclides (¹⁰⁶Ru, ¹²⁵Sb, ¹³⁴Cs and ¹⁴⁴Ce) present in a fission product sample.     

Preparation and Pharmacokinetic Evaluation of Iodine-125 Labeled Alphamethyl-L-Tyrosine

A prompt gamma-ray neutron activation analysis (PGNAA) system was used to calibrate and validate a Monte Carlo model as a proof of principle for the quantification of chlorine in soil. First, the response of an n-type HPGe detector to point sources of ⁶⁰Co and ¹⁵²Eu was determined experimentally and used to calibrate an MCNP4a model of the detector. The refined MCNP4a detector model can predict the absolute peak detection efficiency within 12% in the energy range of 120–1400 keV. Second, a PGNAA system consisting of a light-water moderated ²⁵²Cf (1.06 g) neutron source, and the shielded and collimated HPGe detector was used to collect prompt gamma-ray spectra from Savannah River Site (SRS) soil spiked with chlorine. The spectra were used to calculate the minimum detectable concentration (MDC) of chlorine and the prompt gamma-ray detection probability. Using the ²⁵²Cf based PGNAA system, the MDC for Cl in the SRS soil is 4400 g/g for an 1800-second irradiation based on the analysis of the 6110 keV prompt gamma-ray. MCNP4a was used to predict the PGNAA detection probability, which was accomplished by modeling the neutron and gamma-ray transport components separately. In the energy range of 788 to 6110 keV, the MCNP4a predictions of the prompt gamma-ray detection probability were generally within 60% of the experimental value, thus validating the Monte Carlo model.     

EDXRF versus INAA in a pollution control of soil

Summary Elemental concentrations of soil samples collected in the vicinity of a Romanian fertilizer plant were determined by EDXRF and long half-life INAA. Lower limits of detection, obtained for various elements in soil by EDXRF technique with radioactive excitation sources (²³⁸Pu and ²⁴¹Am) and a HPGe detector are presented. Spurious effects characteristic for Ge detector X-ray spectrometry are evaluated and discussed, and methods to overcome this drawback are suggested. Special care was taken to subtract from the spectra the Ge Ka     

Monte Carlo and experimental efficiency calibration of gamma-spectrometers for non-destructive analysis of large volume samples of irregular shapes

A comparison of efficiency calibration of a HPGe gamma-ray spectrometer applied for non-destructive analysis of gamma-ray emitters in large volume samples of irregular shape is presented. The detector efficiency calibration was carried out during the analysis of cosmogenic radionuclides (⁶⁰Co, ⁵⁴Mn, ²²Na and ²⁶Al) in fragments of the Ko?ice meteorite. Fourteen meteorite fragments were available for the analysis with masses from 27 to 2,163 g. A reasonable agreement in the estimation of the HPGe detector efficiency was obtained using the Monte Carlo simulation GEANT 3 code, and the experimental calibration using radioactive standards mixed with iron–silica–copper powder housed in mock-ups of similar shapes as the original samples. The differences in the efficiency estimation obtained by both methods were within 10 %. It is recommended that the Monte Carlo simulation of the detector efficiency can be applied in routine analysis of gamma-ray emitters in large volume samples of regular or irregular shapes.     

An argon-ion laser fluorometer optimal for concentration detection of 5-bromomethyl fluorescein derivatized carboxylic acids

A continuous wave, argon ion laser-induced fluorescence detector was designed for use with conventional high performance liquid chromatography. Palmitic acid was selected as a model analyte to evaluate the performance of the detector. Using the intense 488.0 nm emission line, a concentration detection limit of 7.5 × 10^–10 M (38 femtomoles on-column) was established for palmitic acid at a signal to noise ratio of three. The linear dynamic range extended over two orders of magnitude with a correlation coefficient of 0.9998. The contribution of scattered radiation to the analytical signal was minimal. The concentration detection limit achieved with the constructed laser fluorometer was superior to other reports for fatty acids.     

Alpha-particle energy distributions from thin sources measured with small solid angles

The energy distribution of the alpha particles emitted from a source is in general complex. Only under particular circumstances, as in the case of very thin sources measured at large distances from the detector, can the energy distribution be approximated theoretically. In this work, we used the well-known code SRIM to simulate the interaction of alpha particles within a thin radioactive source and within the entrance window of a typical Si semiconductor detector. We considered several thin alpha particle sources measured at a large source-to-detector distance (small solid angle), in order to compare the distributions obtained by simulation with those determined by the theoretical model applied to this case. The study was performed for a variety of realistic alpha particle sources: UF₄, UO₂, U₃O₈, Gd₂O₃, and BaSO₄, considering as alpha emitters ²³⁵U, ²³³U, ¹⁴⁸Gd and ²²⁶Ra. For all these cases, we obtained the distributions due to the source and due to the entrance window of the detector, and also the final distribution given by the convolution of these two distributions. All the energy distributions obtained by simulation showed, in general, good agreement with the predictions given by the theoretical model, which includes corrections for Bohr straggling.     

The effect of the housing material on the NaI(Tl) detector response function

In this study, a Monte Carlo program has been developed to simulate the response function of the NaI(Tl) detector with all features for ⁶⁰Co and ¹³⁷Cs and to investigate the effects of detector housing material on response function. The pulse height spectra in a 2???×?2?? NaI(Tl) detector due to these gamma ray sources have been measured. Comparison of the experimentally obtained and simulated spectra shows that there is good agreement between both spectra. Energy distributions of gamma photons that generate the backscattering peak in the response function were obtained and the contribution of single, double and multiple Compton scattering events to these distributions was investigated.     

A computer program for calculating Ge(Li) detector counting efficiencies for Marinelli beakers

A novel computing method has been developed to calculate the absolute photopeak efficiency of a Ge(Li) detector for Marinelli beakers of different heights and diameters and with variable density. For each point in the cylindrical sample the detection efficiency is calculated taking into account the distance from the detector and gamma-ray attenuation and the efficiency is integrated numerically over the volume of the sample. The detector is approximated as a point detector with an experimentally determined effective interaction depth. It is necessary to measure the absolute efficiency for a point source located on the detector axis and on a line beside the detector parallel to the axis. The computer program calculates the absolute counting efficiency for Marinelli beakers of any geometry and for any density. The measured and calculated values for three different densities give a good (–2.2%) overall agreement.     

Radial efficiency gradients in Ge(Li) gamma detectors

Counting of radioactive sources in contact with the vacuum container of a Ge(Li) detector may lead to errors because of large efficiency gradients. In order to explore the radial dimension of this problem, several point sources were stepped across in contact with the cap of several detectors, and curves of absolute efficiency against radius were measured. The insensitive core of an open-end coaxial detector reduced the central point-source efficiency at 122 keV at the cap to 20% less than a comparable closed-end detector. In compensation, however, there was a reduction in the radial efficiency gradient. The radial efficiency gradient was approximately proportional to the radius, with the central flattening for the open-end detector superimposed on the trend.     

THE SPATIAL DISTRIBUTION OF LIGHT EMISSION FROM LIQUID PHASE BIO- AND CHEMILUMINESCENCE: VARIATIONS WITH CONTAINER TYPES, TURBIDITY AND CONTAINER FROSTING

Abstract— The spatial distribution of emitted light from liquid phase bioluminescence and chemiluminescent sources in three common types of containers has been evaluated. These sources, while theoretically isotropic, exhibit considerable anisotropy due to reflection and refraction effects at the interfaces between the solution, the container and the surrounding air. This anisotropy represents a considerable systematic error (>25%) in some values of quantum yields reported in the literature. The degree of asymmetry in spatial distribution depends on the solution volume, the refractive index, and the degree of light scattering in the solution. Quantitative evaluation of the projected image of these sources using a video camera system indicates that a major contribution to this asymmetry is due to reflection at the meniscus. Since container frosting removes the variability due to scattering, volume changes, refractive index differences and even, to some extent, use of different types of containers, it is recommended that quantum yields and comparative measurements be determined using frosted containers and point source geometry. The container of choice is a frosted, 1 ± 7.5 cm test tube.