Efficiency calibration and summation effects in gamma-ray spectrometry

Precise, absolute -ray efficiences ( ) and total efficiences ( _T), have been measured at various distances from the detector, using a set of standards. The observed linear variation of and _T as well as / _T with E and provides a simple means of interpolation and extrapolation. Experimental coincidence summation effects were determined for various nuclides and compared with calculated values. The results are found to be in good agreement with each other.     

Efficiency calibration curves in gamma-ray spectrometry for samples with different matrices

A new method for determination of efficiency calibration curves in -spectrometry is described. From the calibration curves for a bulky sample and a point source, the curves for sources with the same geometrical parameters as the bulky sample but different attenuation coefficients may be calculated. The method was tested at an energy of 88 keV on a set of samples with attenuation coefficients between 0.2 and 2 cm² g^–1. The conditions where the new method is useful are discussed.     

Radiochemical isolation and radioactivity calibration of radium-228 by liquid-scintillation counting and gamma-ray spectrometry

Radium-228 was separated from aged thorium nitrate by liquid-liquid, two-phase, extraction and extensively purified, principally by ion-exchange chromatography. The radioactivity concentration of the purified radium-228 was measured by means of liquid-scintillation β-particle measurements of the²²⁸Ac daughter (corrected for progeny ingrowth). The results were confirmed by Ge(Li)well-detector intercomparison with radium-228 in equilibrium with its thorium-232 precursor which had been measured gravimetrically. Three hundred ampoules were provided to the U.S. Environmental Protection Agency, Las Vegas, for distribution.     

Low-level gamma-ray spectrometry for environmental samples

Low-level gamma-ray spectrometry with large volume HPGe detectors has been widely used in analysis of environmental radionuclides. The reasons are excellent energy resolution and high efficiency that permits selective and non-destructive analyses of several radionuclides in composite samples. Although the most effective way of increasing the sensitivity of a gamma-ray spectrometer is to increase counting efficiency and the amount of the sample, very often the only possible way is to decrease the detector’s background. The typical background components of a low-level HPGe detector, not situated deep underground, are cosmic radiation (cosmic muons, neutrons and activation products), radioactivity of construction materials, radon and its progenies. A review of Monte Carlo simulations of background components of HPGe detectors, and their characteristics in coincidence and anti-Compton mode of operation are presented and discussed.     

Software for X- and gamma-ray spectrometry

Summary A computational approach to the true-coincidence summing correction factor evaluating was developed on the basis of the extended version of the MCNP - a general Monte Carlo N-particle transport code. A specially developed utility program generates the MCNP input on the basis of a routinely updated Evaluated Nuclear Structure Data File (ENSDF) library. Necessary information is automatically added to allow accurate simulating of the emission of correlated particles accompanying the decay of a particular radionuclide, including emission of annihilation quanta, K- and L- X-rays, β-particles and conversion electrons. Gamma-ray angular correlations as well as lifetimes of the nuclear excited states are also taken into account. The approach is applicable to correction factor evaluation for ordinary single- and multi-detector spectrometers as well as for Compton suppression systems. The paper describes the developed computational scheme as well as presents the results of its preliminary testing for the case of both point and volumetric sources.     

Ge(Li) gamma-ray spectrometry as a pilot for NaI(Tl) gamma-ray spectrometry

Lithium-drifted germanium semiconductor detectors give much better resolution than do thallium-activated sodium iodide detectors, but much lower sensitivity. They can often advantageously be used in conjunction with NaI(Tl) detectors, to show whether corrections must be applied for activities other than the one to be measured and to provide the necessary information for calculation of the corrections.     

Time resolved gamma-ray spectrometry

A new approach is proposed for the measurement of the time-dependent processes in gamma-ray spectrometry. During data acquisition, the energy and the detection time of each event are recorded and the data are later analyzed off-line. This separation of acquisition and data handling extends the possibilities of the analysis. A series of demonstration experiments was performed to show the feasibility of the method, where the half-lives of radioactive isotopes were determined.     

Mathematical efficiency calibration methods for high quality laboratory based gamma spectrometry systems

The efficiency calibration of laboratory based gamma spectrometry systems typically involves the purchase or construction of calibration samples that are supposed to represent the geometries of the unknown samples to be measured. For complete and correct calibrations, these sample containers must span the operational range of the system, which at times can include difficult configurations of size, density, matrix, and source distribution. The efficiency calibration of a system is dependent not only on the detector, but on the radiation attenuation factors in the detector–source configuration, and therefore is invalid unless all parameters of the sample assay condition are identical to the calibration condition. An alternative to source-based calibrations is to mathematically model the efficiency response of a given detector–sample configuration. In this approach, the measurement system is calibrated using physically accurate models whose parameters can generally be easily measured. Using modeled efficiencies, systems can be quickly adapted to changing sample containers and detector configurations. This paper explores the advantages of using mathematically computed efficiencies in place of traditional source-based measured efficiencies for laboratory samples, focusing specifically on the possibility of sample optimization for a given detector, uncertainty estimation, and cascade summing corrections.     

Three-dimensional data processing for time resolved gamma-ray spectrometry

Summary A new acquisition and evaluation procedure has been introduced for the measurement of time-dependent processes in gamma-ray spectrometry, in order to extract more information, including half-lives, from the data recorded during acquisition and to enable a more comprehensive analysis of the results. These advanced, off-line data evaluation techniques improve the selectivity and the background subtraction and make it possible to estimate the important analytical parameters (e.g., half-lives) more accurately than with the usual decay curve fitting method.     

Table for true summation effect in gamma-ray spectrometry

Probabilities of gamma-ray simultaneous emission have been calculated for the determination of correction factors of full-energy peak areas of radionuclides with a complex decay scheme at measurements of gamma-spectra using HPGe detectors. Coincidence probabilities were determined using the Monte Carlo method for the following radionuclides: ²²Na, ²⁴Na, ⁴⁶Sc, ⁵¹Cr, ⁵²Fe, ⁵⁴Mn, ⁵⁶Co, ⁵⁷Co, ⁵⁸Co, ⁵⁹Fe, ⁶⁰Co, ⁶⁴Cu, ⁶⁵Zn, ⁶⁷Cu, ⁶⁸Ge-⁶⁸Ga, ⁷⁵Se, ⁸⁵Sr, ⁸⁸Y, ⁹⁴Nb, ^108mAg, ¹⁰⁹Cd, ¹¹¹In, ¹²⁴Sb, ¹²⁵Sb, ¹²⁵I, ¹³¹I, ¹³²Cs, ¹³³Ba, ¹³⁴Cs, ¹³⁹Ce, ¹⁵²Eu, ¹⁵³Sm, ¹⁵³Gd, ¹⁵⁵Eu, ^166mHo, ¹⁶⁹Yb, ¹⁷⁷Lu, ¹⁸⁶Re, ²⁰⁷Bi, ²⁰⁸Tl, ²¹²Pb, ²¹²Bi, ²⁴¹Am.     

Application of reference materials in the accurate calibration of the detection efficiency of a low-level gamma-ray spectrometry assembly for environmental samples

A new assembly dedicated for the low-level ψ-ray spectrometric measurements of environmental samples have been installed recently at the International Atomic Energy Agency's Laboratories, Seibersdorf. Calibration of the detection efficiency was performed by a set of 14 IAEA Certified Reference Materials, a standardized solution of¹³⁴Cs, solutions of 2 pure potassium salts, and 2 mixed radionuclide gamma reference standard solutions. These materials, in 1.3 liter Marinelli beakers, were measured by a large HPGe detector. The high precision and accuracy of the calibration procedure is shown by the high significance achieved in the linear fits of the efficiency results, which are traceable to certified and standard reference materials. Small biases between some calibrands were detected. A new corrected result is the 1.37±0.05 Bq/kg activity concentration of¹³⁷Cs in IAEA-A-14 Milk Powder.     

A new system of gamma-ray spectrometry for activation analysis

A new system of γ-ray spectrometry has been designed and constructed. This system performs a precise, quick and automatic activation analysis using our nuclear reactor (TRIGA-II Research Reactor) as a neutron source. The main components are detector system consisted of a high resolution Ge(Li) detector settled in a shielding cabinet and a well-type NaI(Tl) scintillation counter for anti-Compton measurement, and data acquisition and spectra analysis system performed independently by two mini computer. The system has operated for atmospheric aerosols as an example of activation analysis.     

Response operator in semiconductor gamma-ray spectrometry

A response operator technique for analysis of semiconductor -ray spectra utilizing vector model of scaling confirmatory factor analysis (SCFA) is presented. It has been pointed out that the new vector SCFA approach yields a noticeable rise of sensitivy of the semiconductor method for a great deal of spectrometric applications. It results to considerable detection limit decreasing (4–10 times for MSA) as compared to the commonly used traditional approach (peak net area calculation of full energy peak).     

Dosimetric calibration of an annular60Co gamma-ray source

Precise dosimetric calibration of the radiation field of the Gammacell irradiator has been carried out. For measuring spatial dose distribution a cavity ionization chamber in conjuction with a Farmer dosimeter and CaF₂ thermoluminescent dosimeters were used. The results make possible the calculation of doses received by samples of different sizes and shapes.     

Correction by self-attenuation in gamma-ray spectrometry for environmental samples

Summary c/Herrera Oria s/n, 39011, Santan     

Radon measurement by coincidence gamma-ray spectrometry

A method of radon measurement by a multidetector -ray spectrometer,based on coincidence counting of 609 keV photons from two-step cascade transitionsthat follow â – decay of 214 Bi, is proposed. Besides a good accuracy,the method has better sensitivity than some standard methods of radon measurementcurrently in use. Applying this method to the PRIPJAT-2M spectrometer with6 NaI(Tl) detectors, and counting a 1 l sample of well water for 30 minutes,a minimum detectable radon activity of 0.25 Bq/l is experimentally determined.     

Low-level single and coincidence gamma-ray spectrometry

Analyses of anthropogenic and natural gamma-ray emitters in the environment require high sensitive detector systems operating in coincidence-anticoincidence modes. Thanks to an excellent energy resolution and a high efficiency, large volume HPGe detectors have been widely used in low-level gamma-ray spectrometry. In the present paper we discuss the characteristics of single and coincidence (HPGe-NaI(Tl)) arrangements suitable for analysis of environmental samples containing cascade gamma-ray emitters (e.g., ⁶⁰Co), positron emitters (e.g., ²²Na) and single gamma-ray emitters (e.g., ¹³⁷Cs). The detectors were placed in a large volume shields consisting of iron, lead and copper layers. The reduction of background for the single gamma-ray spectrometer is between 60 and 250, depending on the gamma-ray energy. As an improvement of the apparatus, low detection limits for analysis of ¹³⁷Cs (0.3 Bq·kg⁻¹) and ⁶⁰Co (0.1 Bq·kg⁻¹) in environmental samples, respectively, have been obtained.     

The method of moments for multiplet deconvolution in gamma-ray spectrometry

The method of moments is described for deconvolution of a mixture of identical distributions; it is not necessary to know the type of the individual peak distribution. The algorithm for computing the positions and contributions of the peaks forming the multiplet is presented. The real shape of the peak is used. The computational stability of the method of moments for the deconvolution of various types of convolved triple peaks is shown to be satisfactory. The algorithm is used for deconvolution of some double peaks obtained in neutron activation analysis of rock standards. The program is fast and suitable for microcomputers.     

In-situ CeBr3 gamma-ray spectrometry for radioactivity analysis of soil

Journal of Radioanalytical and Nuclear Chemistry - A CeBr3 scintillation detector was applied for in situ gamma-ray spectrometry for radioactivity assessment of soil. The full energy peak...     

Introduction of Marinelli effective solid angles for correcting the calibration of NaI(Tl) field gamma-ray spectrometry in TL/OSL dating

A study is made of the corrections that are needed in the evaluation of the annual radiation dose, for use in TL/OSL-dating, via NaI(Tl) field gamma-ray spectrometry (monitoring of K, Th and U), calibrated via voluminous blocks that are simulating the Auger hole measuring conditions. Two cases are considered: the Heidelberg granite calibration block, which was found to be quasi-infinite, and the Oxford concrete calibration blocks, for which effective concentrations of elements are reported so as to account for their non-infiniteness. The calculations, via the software package ANGLE, are based on the concept of effective solid angles for Marinelli geometries.