Computer analysis of weak spectral components in gamma-ray spectra

Optimal accuracy and precision for relatively weak gamma-ray spectral components were the goal of this study. Such components exhibit small photopeaks situated on large Compton continua; an example of this situation often occurs in measurement of low levels of mercury in biological samples. In this study, four calculational methods were tested: peak area, spectrum stripping, least squares, and peak fitting. All the methods were reasonably accurate on the average. Of significance here is the spread of individual results; the least squares results provided the smallest spread in results, but stripping did almost as well. The other two methods displayed poor precision. In conclusion, the least squares technique gave the best results in terms of accuracy, precision, and ease of application. Work performed at National Bureau of Standards, Washington, D. C., USA.     

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.     

Radioactivity measurement of cylindrical sources by gamma-ray spectrometry

Radioaactive samples in cylindrical beakers have been measured using a high purity Ge spectrometer. Self-attenuation effects at various densities of the radioactive samples filled in cylindrical beakers were studied by experimenal and theoretical methods. Coincidence summing effects for specific nuclides were also determined from the measurements of full-energy peak efficiencies in a given source-to-detector geometry.     

Computer-assisted qualitative analysis of gamma-ray spectra

A computer program is described to perform the identification of isotopes in neutron activated samples. The γ-ray energies as obtained from a Ge(Li) γ-ray spectrum are compared with those of a library, containing data for about 250 isotopes. Isotopes whose γ-ray energies match closely with the unknowns are selected as possible constituents. Unlikely attributions are then eliminated by a careful inspection of the γ-rays found. Further exploitation of half-life, the way of production and the sensitivity for the given irradiation and measurement conditions, allow the selection of the most likely constituents in the source. The results of the automated identification agree closely to those obtained by an experienced investigator. The program is written in FORTRAN IV for a PDP-9 computer with a 16 K word memory.     

Automated statistical control of activities measured by gamma-ray spectrometry

Statistical tests were performed for reviewing the results of routinely performed measurements. Within the operating procedure for routine spectral analysis the current results were compared with the average values obtained from measurements of samples of the same type collected at the same location. The agreement of the current result with the population of the results was assessed by the u-statistic, where the expected spread of the population of the results is given by their standard deviation and their uncertainties. After checking for reliability, the current result was used for updating the average and the spread of the population. Some examples are presented to illustrate how the average and the spread follow changes in the population of the measurement results.     

A mathematical model of monoenergetic gamma-ray spectra

A mathematical model is suggested for the approximation of the monoenergetic gamma-ray spectra obtained by a Ge(Li) detector. Some features of the instrumentation monoline spectra in the energy range upto 2 MeV are considered in detail. Computer program “APPROXIMATSIYA” is described. The program allows to determine the parameters of the mathematical model with the purpose to construct a making up standard spectrum library. The results of the monoline spectrum processing are discussed.     

Kris—A computer program for the least-squares resolution of gamma-ray spectra by half-life and gamma-ray energy

KRIS offers the capability of resolving complex γ-spectra, even when spectra of the individual components are quite similar. A scheme is employed which allows for the use of half-lives as well as γ-ray energies in the least-squares resolution of γ-spectra. Options are also supplied for averaging of repetitive counts, least-squares smoothing of the data, iterative improvement of the weighting factors used in the least-squares solution, and use of either live or clock time counts. The number of control cards required for each sample has been minimized to simplify input. KRIS is written in FORTRAN IV and is being run under Fortran G and the Watfor compiler on the IBM 360/65. The name of the program, KRIS, is not an acronym, nor does it have any scientific significance.     

Program DEIMOS32 for gamma-ray spectra evaluation

The main features of a program for gamma-ray spectra analysis in the Windows environment are described. The program allows handling of HPGe multichannel pulse-height spectra produced by many commercial instruments. It performs the analysis using an interactive manual or automatic mode of evaluation. Results are directed to a number of different output files. The performance of the evaluation can be affected by selecting only regions with prescribed type of peaks. The calibration of the detector efficiency is included. Identification of isotopes and the calculation of their absolute activities are possible. Data can be edited in an internal text editor.     

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.     

Analysis of gamma-ray spectra by using fast Fourier transform (author's transl)]

In order to simplify the mass data processing in a response matrix method for gamma-ray spectral analysis, a method using a Fast Fourier Transform devised. The validity of the method was confirmed by a computer simulation for spectra of a NaI detector. The method uses the fact that spectral data can be represented by Fourier series with reduced number of terms. The estimation of intensities of gamma-ray components is performed by a matrix operation using the compressed data of an observation spectrum and standard spectra in Fourier coefficients. The identification of gamma-ray energies is also easy. Several features in the method and a general problem to be solved in a response matrix method are described.     

Computer analysis of complex gamma-ray spectra from semiconductor detectors

The problem of gamma-ray spectrum analysis is treated by combination of peak-searching, choosing the fitting intervals and fitting the line shape by a shape function. The performance of the program is examined by analysis of a test spectrum,^177mLu.     

Introducing HYPERMET-PC for automatic analysis of complex gamma-ray spectra

In short time activation analysis prompt gamma-activation analysis and in high rate -ray spectroscopy in general, the shape parameters for peaks and back ground usually vary, rendering spectrum evaluation codes based on a fixed shape calibration unsuitable. An interactive version of the well-known, fully automatic -ray spectrum analysis code HYPERMET has been developed in C ++ for the IBM-PC. It runs under MS-DOS, in conventional memory, and can handle up to 16k-channel spectra, recorded with CANBERRA's System 100 and AccuSpec and with ORTEC's ACE plug-in MCA cards. A Windows-like graphics environment is provided with mouse controlled pull-down menus, pop-up windows and rubber band expansion. All basic features of HYPERMET such as fully automatic peak search, nonlinear fitting of multiplets with automatically adjusted Gaussian peak widths exponential tails and a complex background function have been retained. All details of the fitting procedure are recorded in a data base, hence any fitted region can be retrieved and modified interactively, even after a fully automatic spectrum evaluation. The program also provides an output peak list in SAMPO90 format for further processing. The latter format is widely used in a number of sample analysis programs such as KAYZERO a software package fork ₀ standardization in neutron activation analysis.     

Calculated vibrational spectra of weak hydrogen bonds

Potential energy and dipole moment surfaces for the H-bond SH... S in the dimeric methanethiol have been calculated by the SCF-MO-LCGO method, and the vibrational spectrum — transition frequencies and IR absorption intensities at 20 °K — computed. This spectrum is compared with that of the monomeric species and with experimental results. The resulting dimerization energy is 1.4 kcal/mole.     

The role of covariance in the analysis of gamma-ray spectra

When a gamma-ray spectrum contains a number of photopeaks originating from the same nuclide, the calculation of nuclide activity depends not only on the values of, and uncertainties in, the photopeak areas, photopeak efficiencies, gamma-ray emission probabilities and peak area correction factors, but also on the correlations that exist between these quantities. When photopeaks corresponding to a group of nuclides overlap or are unresolved, simultaneous estimation of the activities of all the nuclides present in the group is necessary if the information contained in the spectrum is to be used efficiently — a procedure which can prove important when the only prominent photopeak associated with a nuclide of interest overlaps with the photopeak of another nuclide. Two procedures for activity estimation are described: both procedures take correlations into account; one procedure deals with the special case of activity estimation for a single nuclide, where unresolved photopeaks are absent or neglected; the other procedure deals with simultaneous activity estimation using all the photopeaks associated with an interrelated group of nuclides.     

A simple computer program for high resolution gamma-ray spectra

A computer program is presented, which locates peaks in high-resolution γ-ray spectra and determines their content. The program has been written in Basic; ‘translations’ have been made into Fortran and Algol. For detailed information the reader is referred to the original TNO Report CL 69/137.     

Qualitative and quantitative interpretation of gamma-ray spectra in activation analysis

A method is presented for the automatic identification of the elements present in a sample and the calculation of the corresponding concentrations from the energies and peak areas determined by a spectrum analysis computer program. A preliminary interpretation list is produced in which the possible isotopes are given for each peak in the spectrum. This list is based only on the gamma-ray energies and half-lives of the isotopes. A careful analysis of this list yields groups of identified elements at four different significance levels. The determination of the corresponding concentration is based on the single-comparator method. The procedure is included in an automatic activation analysis system but can also be used separately.     

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.     

Precise measurement of gamma-ray energies and gamma-ray emission probabilities in178m2Hf decay

Nowadays large interest is attached to the production of exotic beams and targets for nuclear structure and reaction studies. The nucleus¹⁷⁸Hf, with is long-lived (T _1/2=31 years) high-spin isomeric statel =16⁺ at a relatively low-excitation energy (2.446 MeV), is indeed a unique probe for studying phenomena in a new way. A wide research program has been underway in the framework of the Hafnium Collaboration which now concems around 80 scientists. Various targets have been prepared and adapted to different types of experiments. Irradiation processes with high-intensity beams, high-purity chemistry methods and isotopic separations have been developed. The obtaining of appreciable amounts of very high purity^178m2Hf by isotopic separation, has made it possible for us to carry out -ray measurements with good statistics and high energy resolution with a -spectrometer, in order to use this isomer as a calibration standard in the 200 to 600 ke V energy range. For example, relative to the main -rays, energies have been determined with an absolute uncertainty of about 2 e V and photon emission probabilities with a relative uncertainty better than 1%.