Recent developments in HYPERMET PC

HYPERMET PC is a user-friendly -ray spectrum analysis software package developed at Budapest, mainly for the purpose of prompt- neutron activation analysis (PGAA). The peak fitting algorithm is an improved version of the well-known HYPERMET code, and contains a partial peak-parameter calibration to describe peak shapes more accurately in the wide energy range typical for prompt- spectra. A nuclide identification routine has also been developed using a new PGAA library, shown in a parallel paper. The new module for quantitative PGAA includes all the features necessary to obtain concentration values for elements.     

Analysis of gamma-ray continuum spectra to determine the chemical composition

Neutron induced -ray spectra from various geological samples were analyzed to evaluate the usefulness of continuum spectra in deriving the chemical composition information. A fast Fourier transform technique has been used to estimate the signal content of selected energy bands of the continuum spectra. Monte Carlo calculations have been performed using the major -ray energy sources (due to Fe, Ca, Si and Al) to generate the corresponding detected -ray spectra. The experimental spectra are compared to the simulated spectra to check the consistency of the signal distribution between the peak and the continuum. The continuum above and below a chosen -ray line is calculated to find what fraction of the lower energy continuum is due to that line. The accuracy of the relative elemental concentrations determined by this method is confirmed through comparison with laboratory elemental analysis of the samples. It is found that using the continuum could greatly increase the sensitivity and precision of the measurement of elemental concentrations determined from -ray spectra of thick target sources, for spectra having peaks of poor statistical significance. However, for thin target sources or spectra with very good statistics in their peaks, this method may not be very advantageous.     

14 MeV neutron activation analysis of ternary copper ilver selenide by X-ray and gamma-ray spectrometry

14 MeV neutron activation of ternary copper silver selenide gives rise to a predominant activity from the 0.511 MeV annihilation peak from the three elements when -ray spectrometry is used. To overcome the interference problems, X-ray spectrometry was applied to the simultaneous nondestructive determination of silver and selenium, after which copper can be determined by -ray spectrometry. The results of analysis show a relative error not higher than ±5%, when the samples were diluted with H₃BO₃ /90%/ to minimize the interelement effects.     

Nondestructive determination of lead-210 and radium-226 in sediments by direct photon analysis

A method is described for the non-destructive determination of²¹⁰Pb and²²⁶Ra in sediments. The procedure is based on the direct counting of the 46.5-keV -ray of²¹⁰Pb and the 351.9-keV -emission of²¹⁴Pb. The self-absorption of the 46.5-KeV -ray is corrected using a technique involving direct gamma transmission measurements on sample and efficiency calibration standard. Several reference materials when assayed by the described method yielded results in general agreement with the certified values. The application of the method is illustrated through the analysis of the excess²¹⁰Pb profile of a Lake Ontario sediment core.     

Synthesis of organocyclosiloxanes containing cyanoalkyl groups on the silicon atom

The cohydrolysis of-cyanoethyl- and-cyanopropylmethyldichlorosilanes with dimethyldichlorosilane has been studied and the optimum conditions ensuring the maximum yield of rings containing cyanoalhyl groups have been determined.B is(-cyanoethyl)hexamethylcyclotetrasiloxane,-cyanopropylpentamethylcyclotetrasiloxane, and bis(-cyanopropyl)hexamethylcyclotetrasiloxane have been obtained for the first time and characterized.     

Scientists, Spectrometry, and Gamma-Ray Spectrum Catalogues, 1957-2007

The original Gamma-ray Spectrum Catalogue, Ge(Li) and Si(Li) Spectrometry published in 1974 by R. L. Heath has been recreated and enhanced as an electronic file and is available on CD-ROM or over the Internet. This electronic version includes 1998 -ray data from the Evaluated Nuclear Structure Data File database as downloaded in 1998 as well as decay scheme drawings. Future developments of similar catalogues will include -ray spectra from radioactive decay with newer detectors and spectra from neutron interactions with elemental samples and separated isotopes. The electronic form of these catalogues will allow the creation of tutorials on -ray spectrometry and on the data included.     

A New Gamma-Ray Spectrum Catalog for PGAA

A major obstacle to the use of the prompt gamma activation analysis (PGAA) method has so far been the lack of a suitable library. Therefore, new measurements have been performed at the PGAA facility at Budapest Research Reactor (BRR) in order to create a prompt -ray catalog for qualitative and quantitative analysis. Prompt -ray energies and associated k ₀-factors have been determined by internal standardization. The resulting catalog contains prompt -ray data from neutron capture and other reactions such as (n,), and decay -ray data from short-lived reaction products. Data have been measured for nearly all stable elements, from hydrogen to uranium. Generally, data for several isotopes are given, to enable isotopic analysis as well.     

Application of gamma-ray spectrometry for the assay of uranium in crude UF4—An input material used for producing nuclear grade U-metal at the natural uranium conversion plants

A -spectrometric method has been developed for the assay of uranium in crude UF₄, which is used as a secondary source of input material for producing nuclear grade U-metal at natural uranium conversion plants. The method makes use of a NaI (Tl) detector coupled with a multichannel analyzer. The 1 MeV -ray of²³⁸U is used for calibration. A method for the fabrication of uniform -assay calibration standards is also suggested, based on the results of this investigation. The calibration standards were prepared by soaking the matrix in uranium solution and then drying the whole material. The amount of²³⁸U in the crude UF₄ sample was directly estimated by comparing the areas under the 1 MeV -ray peak of known calibration standards with the corresponding areas of the samples to be measured. 100 g each of the standard and the sample were counted. 5 crude UF₄ samples were analyzed by this method. The uranium contents in these samples were found to be in the range of 12.2–28.7 g. To compare the -ray spectrometry results with a completely independent method, chemical analysis by potentiometry of all the samples was also done. The -spectrometric results were found to agree within ±18% with the chemical analysis results.     

A new gamma-ray spectrum catalog and library for PGAA

New measurements have been performed at the PGAA facility at the Budapest Research Reactor (BRR) in order to create a prompt -ray catalog for qualitative and quantitative analysis. The measured spectra were accurately analyzed by HYPERMET-PC. Prompt -ray energies and associated -ray production cross-sections have been determined by internal standardization. The resulting catalog contains prompt -ray data from neutron capture and other reactions such as (n,), and decay -ray data from short-lived reaction products. Data have been measured for nearly all stable elements, from hydrogen to uranium. Generally, data for several isotopes are given, to enable isotopic analysis as well. The whole library, including elemental spectra, will be available as a book.     

Distribution of137Cs,40K,238U and232Th in soils from Northern Venezuela

More than one hundred undisturbed soil samples from Northern Venezuela and the islands of Margarita and Los Roques have been analyzed for¹³⁷Cs,⁴⁰K,²³⁸U and²³²Th by -ray spectroscopy. The specimens were taken from between 5–10 cm below the earth's surface. Thus, they are valid not only for the¹³⁷Cs deposition studies but also for the estimation of the natural -ray dose from primordial radionuclides that form the terrestrial component. The concentration of⁴⁰K was directly determined from its 1461 keV -ray, while those of¹³⁷Cs,²³⁸U and²³²Th were performed using a -ray from one of their daughter radionuclides: the 661 keV -ray of^137mBa for¹³⁷Cs, the 1760 keV -ray of²¹⁴Bi for²³⁸U and the 2620 keV -ray of²⁰⁸Tl for²³²Th. Finally, the concentration values were compared with those of global estimates.     

Some complementary data on response characteristics of high-resolution gamma-ray spectrometers at high count rates as used in activation analysis

It was shown that the peak intensities in a -ray spectrum measured with pile-up rejector are a function of the lower level discriminator settings. There is some systematic shift between the peak areas in spectra taken with pile-up rejector on and off. Explanation of this shift is given by using the 1332 keV⁶⁰Co peak as an example.     

Activation analysis with a 9.1 MeV proton beam

Absolute thick-target -ray yields have been measured for a great variety of elements using an activation method. The data are used to discuss the possibilities of impurity activation analysis by means of 9.1 MeV proton-induced nuclear reactions. The most favourable absolute yields from nuclear reactions and absolute intensity values of main -lines are listed in the table. The tabulated results allow one to associate the impurity content in the irradiated sample with the intensity of the corresponding peaks in the gamma-ray spectrum, to determine the measurement sensitivity and to choose optimum analysis conditions.     

Correction of dynamic error in on-line thickness measurement by gamma-ray transmission

In on—line measurement on sheet thickness by -ray transmission, for the sheet thickness vibrates in counting time, and attenuation of -ray which penetrates matter follows an exponential law, not a linear one. So the measured value of thickness which is taken from mean counting rate deviates from the true value.The paper analyses the causes of this deviation, describes the expression form of the dynamic error which is induced by these deviatons, gives a method to diminish the dynamic error by correcting the deviation.     

A digital photopeak integration in activation analysis

A study of the precision attainable by two methods of -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 -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.     

Modern performance control of gamma-ray spectrometers for INAA

An approach is presented for the performance control of -ray spectrometers allowing for the identification of sources of malfunctioning. The traditional check consists of inspection of the FWHM of the peaks of the control source, their peak positions and areas followed by an energy calibration. The resolution and shape of a peak in the spectrum originating from an applied pulse generator are more responsive to the electronic noise than the -ray peaks. At the laboratory for INAA in Delft, the traditional energy calibration has been replaced by a spectrometer performance control which complements the traditional method by (1) an analysis of the shape of the pulser peak, (2) an inspection of the low energy and high energy tails of the peaks, (3) specification of quantified criteria for approval of the performance, (4) generation of control charts for visual inspection of the parameters determined and (5) extensive documentation of all operational characteristics for eventual correlations. This paper demonstrates how this approach to SPC enables to identify sources which cause malfunctioning of the spectrometer.     

On the importance of line shift and peak broadening corrections in the evaluation of spectra in neutron activation analysis

The evaluation of -ray spectra achieved by Instrumental Neutron Activation Analysis (INAA) is improved if effects of line shift and peak broadening are taken into account, comparing the corresponding -lines in spectra from samples and standards. An algorithm which handles both effects is proposed and its realization in a computer program for routine analysis of archaeological ceramic samples is presented.     

Estimation of the uncertainty components associated with the measurement of radionuclides in air filters using γ-ray spectrometry

This paper discusses and assesses the major sources of uncertainty arising in measurement of radionuclide activity concentrations in air. Besides counting statistics, the main contributors to the overall uncertainty of the activity concentration of long-lived radionuclides are the heterogeneities of the calibration source and the test samples (approximately 4%). In addition, in the case of radionuclides with half-lives of the order of days or shorter, a significant uncertainty results from the variability of the source term because the peak concentration of the radionuclide might occur either at the beginning or at the end of the sampling period. For¹³¹I (T_1/28 days), for instance, the relative standard uncertainty was estimated as 17% owing to this effect. In addition, the uncertainty introduced by the software used for evaluation of the -ray spectra is discussed. Details of the uncertainty components, including their assessed probability distributions and degrees of freedom, and the conversion into standard uncertainties are reported in this paper, following the ISO Guide to the expression of uncertainty in measurement. A standard form for documenting and reporting the uncertainty budged is proposed and illustrated with an example.     

Determination of pre-scission kinetic energy in low energy fission using isotonic charge distribution model

The spectral lines of the 478 keV prompt -ray from^7*Li produced in the¹⁰B(n, )^7*Li reaction were measured for a silicon wafer coated with a thin boron layer using neutron beams. The shapes of the Doppler broadened lines were found to depend greatly on the angle between the measurement axis and the boron layer surface. The angular dependence was interpreted according to whether the energetic^7*Li ions are ejected into air or into the substance in the forward or backward recoil of^7*Li to the -ray detector.     

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.     

Transfer activity coefficient of the proton in water-pyridine mixtures. A comparison of some extrathermodynamic assumptions

Various water-pyridine mixtures have been selected in order to compare several of the most popular extrathermodynamic assumptions involved in the determination of the transfer activity coefficient of the proton, _t(H⁺). Two techniques have been utilized for this purpose: voltammetry [study of the ferrocene, ferricyanide, or thallium(1) systems] and potentiometry at equilibrium (emf measurements of various galvanic cells, including liquid junctions and hydrogen electrode or silver electrode as a test electrode). The assumptions have been classified into various groups [e.g., _t(Z^p+)=_t(Z^q+) or _t(X^–)=_t(Y⁺)], and the values of _t(H⁺) have been experimentally determined in each case. The results vary depending upon the basic assumption (several pH units); less important differences (e.g., 0.5 pH unit) occur within a given group, and this may be assigned to the nature of the reference species chosen. A simple model of solvation has been also examined; the application of the law of mass action to the corresponding equilibrium provides results close to the _t(X^–) =_t(Y⁺)type of assumptions which ultimately leads to most self-consistent results.