Nuclide Identification Research Articles

NEW DEVELOPMENT OF HYPERGAM AND ITS TEST OF PERFORMANCE FOR γ-RAY SPECTRUM ANALYSIS

The HyperGam program was developed for the analysis of complex HPGe <TEX>${\gamma}$</TEX>-ray spectra. The previous version of HyperGam was mainly limited to the analysis of <TEX>${\gamma}$</TEX>-ray peaks and the manual logging of the result. In this study, it is specifically developed into a tool for the isotopic analysis of spectra. The newly developed features include nuclide identification and activity determination. An algorithm for nuclide identification was developed to identify the peaks in the spectrum by considering the yield, efficiency, energy and peak area for the <TEX>${\gamma}$</TEX>-ray lines emitted from the radionuclide. The detailed performance of nuclide identification and activity determination was accessed using the IAEA 2002 set of test spectra. By analyzing the test spectra, the numbers of radionuclides identified truly (true hit), falsely (false hit) or missed (misses) were counted and compared with the results from the IAEA 2002 tests. The determined activities of the radionuclides were also compared for four test spectra of several samples. The result of the performance test is promising in comparison with those of the well-known software packages for <TEX>${\gamma}$</TEX>-ray spectrum analysis.

Recent advances in the use of ASEDRA in post processing scintillator spectra for resolution enhancement

The ASEDRA (Advanced Synthetically Enhanced Detector Resolution Algorithm, patent pending) has been successfully applied as a post processing algorithm to both sodium iodide (NaI(Tl)) and cesium iodide (CsI(Na)) scintillator detectors to synthetically enhance their realized spectral data resolution by as much as a factor of three, wherein from these detectors the “raw” unprocessed spectra are traditionally of poor resolution. ASEDRA uses noise reduction and built-in high resolution Monte Carlo radiation transport based detector response functions (DRFs) to rapidly post-process a spectrum in a few seconds on a standard laptop; gamma lines are extracted with an accuracy that makes the scintillator detectors competitive with higher resolution, higher material cost detectors. ASEDRA differs from other tools in the field, such as Sandia’s GADRAS software, in that ASEDRA performs a differential spectrum attribution and cumulative extraction from the sample spectrum, rather than an integral-based approach, as in GADRAS. Previous publications have highlighted the successful application of ASEDRA in samples with plutonium and various isotopes. A new SmartID nuclide identification package to accompany ASEDRA has recently been implemented for test and evaluation purposes for sample attribution; in addition, the application of ASEDRA+SmartID has occurred with success in long dwell cargo monitoring and SNM detection applications, enabling new protocols for HEU detection. Overall, this paper presents recent developments and results along with a discussion of follow-on steps in the development of ASEDRA as an effective field gamma spectrum analysis tool for low cost scintillators.

GammaLab: a suite of programs for k 0 -NAA and gamma-ray spectrum analysis

The GammaLab is a collection of computer codes, written in MATLAB, for performing calculations involved in k 0 neutron activation analysis. The main features of the program include calibrations including energy-channel, energy-FWHM and energy-efficiency for different geometries, background subtraction, nuclide identification, spectral interference correction, elemental concentration and limit of detection determination. The data input is taken from two files one is the spectrum file stored in IAEA ASCII format and other is report file containing peak energy and peak area data. The information about sample, irradiation and counting conditions, background spectra are retrieved from QAQCData database. GammaLab takes nuclear data such as gamma lines, emission probabilities, half-lives, and k 0 factors from NucData database. The sample results which contain elemental concentrations with uncertainties are stored in the QAQCData database. The program has been evaluated by analyzing several hundred spectra and results were found satisfactory.

Early warning against airborne radioactivity in Bavaria: Measuring network for radioactive immissions

AbstractDuring the Chernobyl accident it became evident that there was no up to date information of the radiological situation in Bavaria as a whole. Therefore an online measuring network was implemented, which provides radioactivity data around the clock from all over Bavaria. It comprises measuring devices for gamma-dose rate, airborne aerosol and iodine activity and precipitation. The data are processed in accessory computers and transferred to the main network computers in Augsburg by means of a subcenter computer at the site of the IfR-station. Alarm levels are low in order to have an early warning against airborne radioactivity. New techniques for remote maintenance of the measuring devices and nuclide identification are being planned and tested.

Detector resolution required for accurate identification in common gamma-ray masking situations

Accurate nuclide identification depends on the ability to determine if specific peaks are present in the spectrum. Several current handheld nuclide identifiers and portal monitors use a variant of a peak quality value for this. The peak quality is usually calculated as the peak area divided by the uncertainty of the peak area and when this quotient is above a threshold value, the peak is said to be present. Other works [Terracol et al. In: 2004 IEEE Nuclear Science Symposium Conference Record, Rome, Italy, 2004, Ryder In: Scanning Electron Microscopy/1977 V. 1, Proceedings of the Workshop on Analytical Electron Microscopy, Chicago, 1977] have developed a formalism to calculate the peak uncertainty for interfering peaks based on the detector resolution, background, individual peak areas, and peak separation. The threshold on peak uncertainty determines the minimum activity that will be identified or detected. Care must be used in the selection of the threshold in order to comply with the false positive and false negative requirements of the detection system regime, or “concept of operations”. The performance standards for the handheld identifiers and portal monitors specify the nuclides required to be identified. From this list and other commonly expected nuclides, the energies of the expected gamma rays can be tallied, yielding a table of the separations of adjacent peaks possible in the collected spectrum. Using the formalism, the peak quality value can be determined as a function of the detector resolution, peak area and background for the energy separations in the table determined above. Results are shown for the cases of HEU and plutonium with the masking nuclides of NORM, 133Ba, or 57Co for both germanium and sodium iodide detectors. Typical resolutions, efficiencies and counting times were used.

Characterisation of nasal swab samples by alpha spectrometry

A positive nasal swab taken at a radiation emergency, when properly collected and analysed, is a good indication of a potential inhalation intake. It may be expected to be a useful method for early dose assessment in cases of accidental inhalation of an alpha emitter. To improve the first estimation of intake activity, the quality of a nasal swab measurement was experimentally investigated. Alpha spectrometry was used to examine the experimental nasal swab samples involved with a plutonium solution or particles. Also, a numerical simulation analysis on the alpha spectrum using advanced alpha-spectrometric simulation was made to characterise the experimental results. It was observed that the alpha energy spectrum had a quite different shape among samples, and it was characterised by the type of contaminant. This could be the second advantage of using alpha spectrometry in addition to nuclide identification. The absorption of alpha radiation within the experimental nasal swab sample was different between the types of contaminants. For a quantitative discussion, the absorption for a swab sample must be determined for each type of contaminant. This new finding could be very useful for first responders. A nasal swab sample measured using an alpha spectrometer will give more useful information during the first response of an emergency.

Methods and software for predicting germanium detector absolute full-energy peak efficiencies

High-purity germanium (HPGe) and lithium drifted germanium (Ge(Li)) detectors have been the detector of choice for high resolution gamma-ray spectroscopy for many years. This is primarily due to the superior energy resolution that germanium detectors present over other gamma-ray detectors. In order to perform quantitative analyses with germanium detectors, such as activity determination or nuclide identification, one must know the absolute full-energy peak efficiency at the desired gamma-ray energy. Many different methods and computer codes have been developed throughout history in an effort to predict these efficiencies using minimal or no experimental observations. A review of these methods and the computer codes that utilize them is presented.

Nuclide identification algorithm based on K–L transform and neural networks

Traditional spectrum analysis algorithm based on peak search is hard to deal with complex overlapped peaks, especially in bad resolution and high background conditions. This paper described a new nuclide identification method based on the Karhunen–Loeve transform (K–L transform) and artificial neural networks. By the K–L transform and feature extraction, the nuclide gamma spectrum was compacted. The K–L transform coefficients were used as the neural network's input. The linear associative memory and ADALINE were discussed. Lots of experiments and tests showed that the method was credible and practical, especially suitable for fast nuclide identification.

Comparison of MCNP and experimental measurements for an HPGe-based spectroscopy portal monitor

The necessity to monitor international commercial transportation for illicit nuclear materials resulted in the installation of many nuclear radiation detection systems in Portal Monitors. To overcome the difficulty of innocent alarms due to a large content of natural radioactivity or medical nuclides, Department of Homeland Security (DHS) supported the writing of the ANSI N42.38 standard (Performance Criteria for Spectroscopy-Based Portal Monitors used for Homeland Security) to define the performance of a portal monitor with nuclide identification capabilities, called a Spectroscopy Portal Monitor. To accomplish the necessary performance, several different HPGe detector configurations were modeled using MCNP for the horizontal field of view (FOV) and vertical linearity of response over the detection zone of 5 meters by 4.5 meters for 661 keV as representative of the expected nuclides of interest. The configuration with the best result was built and tested. The results for the FOV as a function of energy and the linearity show good agreement with the model and performance exceeding the requirements of N42.38.

Direct high-resolution alpha spectrometry from nuclear fuel particles in an outdoor air sample

The potential use of direct high-resolution alpha spectrometry to identify the presence of transactinium elements in air samples is illustrated in the case when alpha-particle-emitting radionuclides are incorporated in nuclear fuel particles. Alpha particle energy spectra are generated through Monte Carlo simulations assuming a nuclide composition similar to RBMK (Chernobyl) nuclear fuel. The major alpha-particle-emitting radionuclides, in terms of activity, are 242Cm, 239Pu and 240Pu. The characteristics of the alpha peaks are determined by fuel particle properties as well as the type of the air filter. It is shown that direct alpha spectrometry can be readily applied to membrane filter samples containing nuclear fuel particles when rapid nuclide identification is of relevance. However, the development of a novel spectrum analysis code is a prerequisite for unfolding complex alpha spectra.

Automation of analysis of airborne radionuclides observed in Canadian CTBT radiological monitoring networks using LINSSI

Linux System for Spectral Information (LINSSI1) is a SQL database and established under Linux. Currently it is compatible with HPGe gammaspectra analysis software UniSampo, Shaman and Aatami. Based on this database and software, an automated analysis pipeline has been setup for Canadian CTBT radiological monitoring networks. This paper has investigated the performance of this pipeline in its capabilities and reliabilities of rapid small peak search, nuclide identification, and radionuclide activity concentration evaluation. Up to now, more than 80 thousand daily monitoring gamma-spectra have been automatically received and processed, the results have been stored in database. The pipeline nuclide detection limits is satisfied for environmental radiation monitoring and nuclear emergency preparedness.

A low-cost system for rapid automatic neutron activation analysis at small research reactors

A system for rapid automatic neutron activation analysis is governed by software performing irradiation control, neutron flux monitoring and gamma-spectrometry with real-time correction of counting losses as well as spectra evaluation, nuclide identification and calculation of concentrations in a fully automatic flow of operations.1,2 Elemental concentrations are derived from a list of experimentally determined specific saturation activities. To expand this list, the “k0_IAEA” software3 is presently under evaluation and will be reported on in this paper. At a Triga reactor, reactor pulse activation may enhance the sensitivity for very short half-lives,4 and will be presented in our paper.

A personal digital assistant-based portable radiation spectrometer

A nuclear spectrometer based on a personal digital assistant (PDA) has been designed, built and tested. This portable radiation spectrometer, PDA SPECTROMETER, can be used for data acquisition and spectrum analysis in a field that requiring output of radiation dose rate and count rate as well as nuclide identification. A Complex Programmable Logic Design (CPLD) circuit block is built for data communication with PDA through RS-232 serial interfaces, backed up by a global positioning system (GPS) unit. The architecture and the data acquisition block are optimized to accommodate high data throughput.

Library correlation nuclide identification algorithm

A novel nuclide identification algorithm, Library Correlation Nuclide Identification (LibCorNID), is proposed. In addition to the spectrum, LibCorNID requires the standard energy, peak shape and peak efficiency calibrations. Input parameters include tolerances for some expected variations in the calibrations, a minimum relative nuclide peak area threshold, and a correlation threshold. Initially, the measured peak spectrum is obtained as the residual after baseline estimation via peak erosion, removing the continuum. Library nuclides are filtered by examining the possible nuclide peak areas in terms of the measured peak spectrum and applying the specified relative area threshold. Remaining candidates are used to create a set of theoretical peak spectra based on the calibrations and library entries. These candidate spectra are then simultaneously fit to the measured peak spectrum while also optimizing the calibrations within the bounds of the specified tolerances. Each candidate with optimized area still exceeding the area threshold undergoes a correlation test. The normalized Pearson's correlation value is calculated as a comparison of the optimized nuclide peak spectrum to the measured peak spectrum with the other optimized peak spectra subtracted. Those candidates with correlation values that exceed the specified threshold are identified and their optimized activities are output. An evaluation of LibCorNID was conducted to verify identification performance in terms of detection probability and false alarm rate. LibCorNID has been shown to perform well compared to standard peak-based analyses.

Automatic activation analysis

Automatic activation analysis (AAA) is rendered possible by a unique neutron activation analysis facility for short-lived isomeric transitions based on a fast rabbit system with sample changer and sample separation, and an adaptive digital gamma-spectrometer for very high counting rates of up to 106 cps. The system is controlled by a computer program performing irradiation control, neutron flux monitoring, and gamma-spectrometry with real-time correction of counting losses, spectra evaluation, nuclide identification and calculation of concentrations in a fully automatic procedure. As spectrometry is done by means of hundreds of sequentially measured pairs of concurrently recorded loss-corrected and non-corrected spectra, concentrations are derived from an optimally weighted average of all individual occurrences in this sequence of spectra which also enable the separation of isomeric transitions with coinciding energies but different half-lives such as 116m2In (162.4 keV, T1/2 = 2.2 s) and 77mSe (162.2 keV, T1/2 = 17.4 s). To clear up repeatedly voiced misconceptions concerning the errors of loss-free counting our findings of 1978 and 1981 are reiterated, namely that the counting error of a peak in a corrected spectrum may be derived consistently from the error of the same peak in the respective non-corrected spectrum and from the error of weighting factors in the corresponding region of interest, according to the principle of propagation of errors. Experimental proof is provided for conditions of stationary as well as rapidly varying counting rates and spectral shapes.

High-energy proton irradiation and induced radioactivity analysis for some construction materials for the CERN LHC

The dose rate to personnel due to remnant radioactivity during maintenance periods will be an important issue at the forthcoming Large Hadron Collider (LHC). Among the most abundant construction materials are aluminum, steel, copper and lead. In order to obtain more reliable estimates on the radioisotope production in a high-energy hadron environment, we irradiated small samples of these materials behind the beam-stop of the CERN 24 GeV/c proton synchrotron. This environment is characterized by high spallation neutron flux and a non-negligible contribution of protons and pions up to the total beam momentum. Gamma-ray spectra of the samples were measured and analyzed with the SAMPO program and detailed nuclide identification was carried out with the SHAMAN program. The total energy emission and results of the spectrum analyses were compared to predictions of the FLUKA hadron cascade simulation package.

A neutron activation analyzer

Dubbed “Analyzer” because of its simplicity, a neutron activation analysis facility for short-lived isomeric transitions is based on a low-cost rabbit system and an adaptive digital filter which are controlled by a software performing irradiation control, loss-free gamma-spectrometry, spectra evaluation, nuclide identification and calculation of concentrations in a fully automatic flow of operations. Designed for TRIGA reactors and constructed from inexpensive plastic tubing and an aluminum in-core part, the rabbit system features samples of 5 ml and 10 ml with sample separation at 150 ms and 200 ms transport time or 25 ml samples without separation at a transport time of 300 ms. By automatically adapting shaping times to pulse intervals the preloaded digital filter gives best throughput at best resolution up to input counting rates of 106 cps. Loss-free counting enables quantitative correction of counting losses of up to 99%. As a test of system reproducibility in sample separation geometry, K, Cl, Mn, Mg, Ca, Sc, and V have been determined in various reference materials at excellent agreement with consensus values.

Novel beta-gamma coincidence measurements using phoswich detectors

We have developed an analysis pipeline for air filter gamma-ray spectra, utilizing the software packages UniSampo for peak analysis and Shaman for nuclide identification. In an automated usage mode, spectra that are received via e-mail are processed into a directory tree, analyzed with UniSampo and Shaman, and finally categorized on the basis of the analysis results. Alarms are generated if anything out of the ordinary is observed. Typical applications for an air filter analysis pipeline are national radioactivity surveillance networks and the global radionuclide monitoring network being implemented for verification of the Comprehensive Nuclear-Test-Ban Treaty (CTBT). Our analysis pipeline system has been used by the Finnish national CTBT-authority, the Finnish National Data Center (FiNDC), since July 1999. Evaluation with a randomly selected set of 1518 air filter spectra showed that our pipeline system produces significantly better analysis results than that utilized by the CTBT Organization (CTBTO): our system found 4.2 more peaks per spectrum than the CTBTO system (9 p increase) and identified 5.6 more peaks per spectrum (14 p increase) on the average.

ZAKI: a windows-based k o standardization code for in-core INAA

A new computer code ZAKI, for k o-based INAA standardization, written in Visual Basic for the WINDOWS environment is described. The parameter α measuring the deviation of the epithermal neutron spectrum shape from the ideal 1/ E shape, and the thermal-to-epithermal flux ratio f, are monitored at each irradiation position for each irradiation using the “triple bare monitor with k o” technique. Stability of the irradiation position with respect to α and f is therefore assumed only for the duration of the irradiation. This now makes it possible to use k o standardization even for in-core reactor irradiation channels without an a priori knowledge of α and f values as required by existing commercial software. ZAKI is considerably versatile and contains features which allow for use of several detectors at different counting geometries, direct inputing of peak search output from GeniePc, and automatic nuclide identification of all gamma lines using an in-built library. Sample results for two certified reference materials are presented.

Experiments on Fission Dynamics with Relativistic Heavy-ion Beams

[Abstract] At GSI, Darmstadt, an experimental program on fission with relativistic heavy-ion beams is in progress. A large range of excitation energies, combined with low angular momentum and small shape distortion is accessible. Full nuclide identification of the reaction residues is achieved by applying inverse kinematics. The nuclide production and the kinematics of fission fragments from a variety of primordial and radioactive projectiles reveal new insight into the influence of shell effects and dissipation on the fission process. The present contribution gives an overview on the experimental methods, the experimental results and the prospects for future progress.