Net Peak Area Research Articles

Determination of lanthanides by source excited energy dispersive X-ray fluorescence (EDXRF) method after preconcentration with ammonium pyrrolidine dithiocarbamate (APDC)

A new analytical procedure for determination of lanthanides in environmental samples after chemical separation from major matrix elements on DOWEX 50W-X8 resin followed by preconcentration with chelating agent ammonium pyrrolidine dithiocarbamate (APDC) and analyses of thin targets by energy dispersive X-ray fluorescence (EDXRF) method using 109Cd as the source of excitation was presented. Characteristic Lα X-ray lines of the lanthanides were used for calculations of the net peak area and mass concentrations. The influence of pH value of the solution and addition of organic matter on the complexation was investigated. Percentage of recovery of each lanthanide after separation on DOWEX 50W-X8 resin was also determined. Accuracy of the method was tested on standard reference materials and real environmental samples (red mud material). For that purpose samples of standard reference materials and red mud were prepared as thick targets and directly analyzed (without the separation step) by EDXRF method using 241Am as the excitation source. In that case lanthanides concentrations were determined over their characteristic Kα X-ray lines and results were compared with those obtained after separation/preconcentration step described above. Results showed that selected lanthanides made stable complexes with APDC in the alkaline medium with the maximum recovery at pH = 8. The presence of organic matter slightly modified the complexation by means of somewhat higher recovery percentage at pH lower than 7 and approx. 20% lower recovery at pH higher than 7. Recovery of the elements after separation on DOWEX 50W-X8 resin and preconcentration with APDC at pH = 8 varied from 91.4% (Pr) to only 24.9% in the case of Dy. Concentrations of lanthanides measured in standard reference material and environmental samples of red mud after microwave digestion, separation on DOWEX 50W-X8 resin, preconcentration with APDC at pH = 8 and recalculation on the percentage of recovery were in good agreement with certified values in the case of SRM as well as with the concentrations obtained by direct determination over Kα lines using 241Am excitation source in the case of red mud leading to the conclusion that presented method was applicable for the determination of lanthanides in real environmental samples.

Attenuation of a non-parallel beam of gamma radiation by thick shielding—application to the determination of the 235U enrichment with NaI detectors

The traditional method used to determine the Uranium enrichment by nondestructive analysis is based on the “enrichment meter principle” [1]. It involves measuring the intensity of the 186 keV net peak area of 235U in “quasi-infinite” samples. A prominent factor, which affects the peak intensity, is the presence of gamma absorbing material (e.g., container wall, detector cover) between the sample and the detector. Its effect is taken into consideration in a commonly called “wall thickness” correction factor. Often calculated on the basis of approximations, its performance is adequate for small attenuation factors applicable to the case of narrow beams. However these approximations do not lead to precise results when wide non-parallel beams are attenuated through thick container walls. This paper is dedicated to the calculation by numerical integration of the geometrical correction factor ( K wtc) which describes the effective mean path length of the radiation through the absorbing layer. This factor was calculated as a function of various measurement parameters (types and dimensions of the detector, of the collimator and of the shielding) for the most commonly used collimator shapes and detectors. Both coherent scattering (Rayleigh) and incoherent scattering (Compton) are taken into account for the calculation of the radiation interaction within the detector.

Uncertainty in rate loss corrections based on counting a periodic pulser

Tomographic gamma scanning of waste produces three-dimensional transmission and emission images. These are used to derive item-specific attenuation correction factors that improve the accuracy of non-destructive waste assay. For each vertical layer, data grabs of short duration are acquired as the waste item is rotated and translated. The image reconstruction demands accurate rate loss corrections to minimize assay bias. For this application a pulser was used to perform the necessary rate loss corrections. In this work, we summarize the benefits of the pulser approach and review the basic principles on which the method is based. We extend the treatment to include a derivation of the expression for the uncertainty in the net pulser peak area in the presence of an underlying continuum. We report experimental results, taken using a Canberra model WM2900 Tomographic Gamma Scanner, over a broad range of count-rates and peak-to-continuum ratios. Repeat counts under controlled conditions allowed the correction factor and its variance to be determined and compared against expectations. These results confirm the validity of the correction factor formula and the corresponding expression for its uncertainty. The rate loss analysis has been built into a Monte Carlo Replicate engine to allow the uncertainty to be propagated into the total measurement uncertainty of the final assay.

Measurement of K X-ray fluorescence cross-sections and yields for 5.96 keV photons

The K α , K β , and total K X-rays fluorescence cross-sections, as well as the average fluorescence yields for six elements with 16 ⩽ Z ⩽ 23 have been measured at 5.96 keV. The areas of the K α and K β spectral peaks, as well as the net peak areas, have been determined by a fitting process. Furthermore, the I K β / I K α intensity ratios for these elements have been investigated. The K X-rays emitted by samples have been counted by a Si(Li) detector. Experimental values of the K X-ray fluorescence cross-sections, fluorescence yields, and the I K β / I K α intensity ratios have been compared with theoretical values. In most cases, there is an agreement between the experimental and theoretical values within the standard uncertainties.

Application of micro-PIXE to quantitative analysis of heavy elements sorbed on minerals

Heavy element-sorbing montmorillonite and apatite were analyzed by micro-PIXE to examine its applicability to quantitative analysis of the heavy elements sorbed on these minerals. It was found that the sorbed heavy elements can be evaluated quantitatively using the linear correlation between the following two factors: (a) the concentration of the sorbed element in the mineral and (b) the ratio of the net peak area of characteristic X-ray from the sorbed element and to that from the matrix cation of the mineral. Mineralogical features of the tested minerals including heterogeneity of elemental distribution in the depth direction of the mineral hardly affected the results.

Determination of zinc in clay and pottery materials by instrumental neutron activation analysis

The problems of determination of zinc in clay, ceramics and soils via 65Zn using INAA are discussed. The applicability of different approaches for solving the influence of 46Sc and 152Eu by gamma-spectrometry on the line of 65Zn at 1115.5 keV are experimentally evaluated. The application of the correction program ANGES for the calculation of the net peak area is demonstrated. All discussed approaches are checked by analyses of 10 SRM"s: Ohio Red Clay, Lefkandi brick, IAEA-SRM-Soil-1, IAEA-SRM-Soil-5, IAEA-SRM-Soil-7, IAEA-SRM-SL-3, GBW-08303, GBW-07406, NIST-SRM-2709 and BCR-SRM-520.

Quantitative Compton suppression spectrometry at elevated counting rates

For quantitative Compton suppression spectrometry the decrease of coincidence efficiency with counting rate should be made negligible to avoid a virtual increase of relative peak areas of coincident isomeric transitions with counting rate. To that aim, a separate amplifier and discriminator has been used for each of the eight segments of the active shield of a new well-type Compton suppression spectrometer, together with an optimized, minimum dead-time design of the anticoincidence logic circuitry. Chance coincidence losses in the Compton suppression spectrometer are corrected instrumentally by comparing the chance coincidence rate to the counting rate of the germanium detector in a pulse-counting Busy circuit (G.P. Westphal, J. Rad. Chem. 179 (1994) 55) which is combined with the spectrometer’s LFC counting loss correction system. The normally not observable chance coincidence rate is reconstructed from the rates of germanium detector and scintillation detector in an auxiliary coincidence unit, after the destruction of true coincidence by delaying one of the coincidence partners. Quantitative system response has been tested in two-source measurements with a fixed reference source of 60Co of 14 kc/s, and various samples of 137Cs, up to aggregate counting rates of 180 kc/s for the well-type detector, and more than 1400 kc/s for the BGO shield. In these measurements, the net peak areas of the 1173.3 keV line of 60Co remained constant at typical values of 37 000 with and 95 000 without Compton suppression, with maximum deviations from the average of less than 1.5%.

An innovative method for extracting isotopic information from low-resolution gamma spectra

A method is described for the extraction of isotopic information from attenuated gamma-ray spectra using the gross-count material basis set (GC-MBS) model. This method solves for the isotopic composition of an unknown mixture of isotopes attenuated through an absorber of unknown material. For binary isotopic combinations the problem is nonlinear in only one variable and is easily solved using standard line optimization techniques. Results are presented for NaI spectrum analyses of various binary combinations of enriched uranium, depleted uranium, low burnup Pu, 137Cs, and 133Ba attenuated through a suite of absorbers ranging in Z from polyethylene through lead. The GC-MBS method results are compared to those computed using ordinary response function fitting and with a simple net peak area method. The GC-MBS method was found to be significantly more accurate than the other methods over the range of absorbers and isotopic blends studied.

Accuracy, precision and sensitivity in cyclic INAA with short-lived radionuclides

Repeated irradiation enhances the precision and sensitivity of INAA based on short-live radionuclides, but entail systematic losses due to dead time. The relative standard deviation in the net peak area decreases with the square root of the number of cycles while the systematic bias increases with it. The limits of decision, detection and determination decrease in a somewhat more complicated way with the number of cycles. The derived formulation is applied to the determination of selenium in hair by the 161.9 keV photopeak of77mSe,T1/2=17.8 s.

Application of factor analysis in EDXRF

The application of factor analysis in EDXRF as a method for evaluation of elemental concentrations and calculation of net peak areas is demonstrated in two examples. A quantitative PCR-analysis of sulphur interfered with by molybdenum could be performed by using the XRF-spectra as input with a standard error of analysis (SEA) below 0.2 mg/g for aqueous and 3.6 mg/g for solid samples. By using PCR-predicted net peak areas as input for the empirical evaluation method developed by Lucas-Tooth and Price, the SEA for solid samples could be decreased to 2.3 mg/g. The comparison of PCR to PLS showed no significant difference.

Calculation of Scatter Peak Ratios in XRF Spectra and Application

The backscatter region of an energy-dispersive X-ray fluorescence(EDXRF) spectra obtained by a typical by radioisotope system was examined in detail. Coherent and incoherent scattering peak ratios have been calculated by considering photon energy, self-absorption effect in sample, sample thickness, detector efficiency and counting geometry in region of 5\leq Z\leq 40. The proposed model has been applied to evaluate the net backscatter peak areas for soil (Z\approx 12) and coal (Z\approx 8) samples.

Analytical procedures for measuring the amount and distribution of radioactive constituents in soils

For a research project on the evaluation and distribution of radioactive pollutants in Biscay's plants and soils, it was necessary to establish an analytical procedure to detect and measure extremely low amounts of radioactive elements. For the project 15 cm cores of fourteen soils were taken and divided into three depth levels. Some of these soil samples (<2 mm) were i) air‐dried before radioactive measurements. Additionally, a few samples were measured again after being ii) selectively extracted with ammonium acetate at pH 7 (exchangeable), acetic acid (carbonate), hydroxylamine (associated to Fe‐Mn oxides) and hydrogen peroxide (related to sulphide and organic matter fraction) to estimate the distribution of constituents according to mineral soil species or iii) classified as clay+silt, fine and coarse sand, to study size partition. Radioactive measurements were made with a low‐level gamma spectrometer (Ge‐HP detector + analyser with 8000 channels) whose resolution was 1.64 keV with a relative efficiency of 24.8 per cent for the 1330 keV Co‐60 line. Calibration was made against a standard solution containing nine radio‐nuclides with gamma‐ray energies in the range from 88.03 to 1836 keV. The shielding was 15 cm thick of pre‐war iron. Original or derived soil samples were put into 0.25 liter Marinelli flasks and measured during 24 hours periods. Double distilled water background was discounted. Net peak areas were then analysed at 95% confidence by the Mariscotti method. K‐40 and several radionuclides from U‐Th series were identified as presumably natural constituents, but significant amounts of Cs‐137, a fission product, were also found in most of depth levels of the studied soils. The distribution of these radioactive constituents in some treated samples, according to soil species or fraction size is shown.

Infrared spectrophotometric determination of citral corrected for limonene interference in lemon and orange essential oils

An infrared spectrophotometric method is described to correct for interference by limonene in the determination of citral in orange and lemon essential oils by subtracting the limonene spectrum from the essential oil spectrum. The first derivative trough-to-peak distance between 1684 cm −1 and 1677 cm −1 was most reliable in determining citral, parameters of the zero order absorption spectrum (net absorbance and peak area) performed poorly in comparison.

A digital photopeak integration in activation analysis

A study of the precision attainable by two methods of γ-ray photopeak computation has been carried out. The “total peak area” method (TPA) and the proposed new method have been compared. The method offered is digital and simulates repeatedly accumulations of γ-ray spectra. The method described here computes the apparent net peak area without a clear distinction between peak and non-peak related channels. The proposed method is considered to be the most advantageous because of its relatively high precision.

Revision of the ANSI N42.14 performance standard for Ge gamma-ray spectrometry

A major revision of the American National Standards Institute (ANSI) Standard N42.14, “Calibration and Use of Germanium Detectors for the Measurement of Gamma-Ray Emission Rates of Radionuclides”, is in process. The revised standard is more detailed and addresses aspects of Ge gamma-ray spectrometry not covered in the previous standard. Instructions are provided for initial setup, energy calibration, efficiency measurement, and measurement or calculation of corrections for pulse pileup, radioactive decay and absorption. Performance tests are provided (1) to evaluate the peak-finding algorithm, (2) to verify the independence of the net-peak area with respect to the base-line height, (3) to evaluate the doublet-fitting algorithm, and (4) to verify the accuracy of pulse pileup corrections. A simple procedure to assess the magnitude of cascade-coincidence summing is presented. The assignment of uncertainties, averaging of multiple measurements and propagation of uncertainties are discussed. Appendices to the standard contain procedures for optional use in the (1) setup and characterization of a Ge gamma-ray spectrometer, (2) preparation of working standards or QC samples, (3) measurement of the peak position and area, (4) correction for cascade gamma-ray summing, and (5) construction of a detector shield.

Digital method of net peak area determination in activation analysis

A study of the precision by three methods of gamma-ray photopeak integration has been carried out. COVELL's, “total peak area” method and the proposed method have been considered. The latter was considered to be the most advantageous because of its relatively high precision and simplicity.

Quality assurance in inaa via short-lived isomeric transitions

As a basic step to quality assurance of INAA via shortlived isomeric transitions replicate analyses of NaCl are performed on an INAA facility specifically designed for this purpose and from the series of net peak areas of Na-24m (20 ms) and Cl-38m (715 ms) it can be shown that the system is quantitative and that its precision is determined by counting statistics. Future improvements of the method may be expected from gamma spectrometry systems with higher throughput and better resolution than that of the now used gated integrator. A resolution comparison between a gated integrator and the recently developed Preloaded Filter is given on the basis of the detector applied in this investigation and substantial improvements are examplified.

Optimization of neutron activation analysis by interactive computer graphics

A technique has been developed for obtaining optimum operating conditions in instrumental neutron activation analysis. Computer models of neutron activation and gamma-ray spectrometry are used to generate video displays that show the variation of responses such as the number of elements determinable or average net peak area precision as functions of up to three of sample size and irradiation, decay and counting time. Optimum values of these parameters are found by interactively inspecting these displays. Counting time can be adjusted independently. Displays of the number of elements determinable are particularly useful.

Measurement techniques for characterizing and using low background germanium detectors

An investigation has been undertaken to determine whether an order of magnitude background reduction from present typical cryostat-detector systems can be obtained through the use of low background components. In order to measure progress in this task, a standard, ten-centimeter lead shield was fitted with a five-centimeter, oxygen-free high-conductivity copper liner and a borated polyethylene neutron absorber. This reduced the contribution of uranium-238, thorium daughters, and radium daughters from the shield as seen by the detector by 1.3, 0.02, and 0.1 Bq respectively. The methodology of determining very low net photon peak areas in the presence of high continuum levels to assure maximum accuracy was verified and is presented. By these means the background activities of detectors are being measured at the −10 2 Bq per nuclide and detector component materials at the Bq per gram level, both with total uncertainties of less than 50% 1σ. The hardware and software developed is being used to measure the background activity of the detectors and for the analysis of low activity samples.

The method of net peak area computation for gamma-ray spectra

A study of the precision and accuracy attainable by several methods of gamma-ray peak integration has been carried out. Covell's “total peak area” (TPA) methods and a method using interpolated Lagrange polynomials have been considered. The last method described here uses a higher order polynomial for the nonlinear base line construction. The proposed method was considered to be the most advantageous because of the relatively high accuracy and precision obtained.