PCGAP: Application to analyze gamma-ray pulse-height spectra on a personal computer under Windows NT®

PCGAP is a software code, which was written to provide gamma-ray pulse height spectrum analysis on a personal computer platform. The code was specifically developed for Windows NT for either an Intel^® or DEC Alpha^® based processor. PCGAP includes programs which can be used to control data collection using a Canberra INSPECTOR^® multichannel pulse-height analyzer. With suitable spectrum conversion routines PCGAP can be used to analyze data from almost any multi-channel analyzer. Besides the normal functions associated with a robust spectrum analysis package, PCGAP can be used for radionuclide analysis for actinides via L-X and gamma-ray spectrometry. It can be used to control and analyze data from an INEEL developed pulse injection system for individual spectrum validation. The package includes programs for the manual analysis of spectra using displays which permit the spectroscopist to interactively define the spectral continuum and peak fitting limits, and display the resulting function fitting forms.     

Denoising of gamma-ray spectrum by optimized wavelet thresholding based on modified genetic algorithm in carbon/oxygen logging

In order to reduce noise in gamma-ray spectrum measured by carbon/oxygen logging instrument, an improved wavelet thresholding algorithm was proposed in this paper. This algorithm established a thresholding function with an adjustable parameter, which could obtain various filtering performances by means of different parameters, and then a modified genetic algorithm combined with opposition-based learning theory was put forward to optimize the parameter and wavelet thresholds. By using Monte Carlo simulation, the objective function of the modified genetic algorithm was determined. Finally, the actual measured spectra processing results of the optimized wavelet thresholding algorithm was compared with traditional thresholding algorithms and other filtering algorithms, and the effectiveness of the proposed algorithm was verified based on signal-to-noise ratio index.

     

Loss-free counting in NAA using KAYZERO evaluation software

To account for varying dead time (frequently occurring when the measuring time is comparable with the half lives of the radionuclides in question) the use of Westphal's Loss-Free Counting technique (LFC) is preferable. However, standard gamma-ray spectrum deconvolution programs can not be applied in connection with LFC spectrometers, since this technique strongly influences the counting statistics of measured spectra. As consequence, erroneous results are likely to arise when applying peak search routines or when calculating the standard deviation of fitted peak areas or detection limits. To overcome these shortcomings, an LFC module equipped with Dual LFC Mode option should be used: this accumulates an LFC-corrected spectrum simultaneously with an uncorrected spectrum. The KAYZERO evaluation software has been modified to handle such tandem spectra.     

Study of Doppler broadening of gamma-ray spectra in 14-MeV neutron activation analysis

Neutron reactions producing characteristic photons of isotopes are important for nondestructive analysis of materials. Technique to determine the intensity of neutron induced gamma rays by fitting a spectrum with a Gaussian function using detector resolution curves derived from isotopic sources may fail if the peak is Doppler-broadened. This leads to the miscalculation of the area of the peak and, therefore, to misidentification of the material. This work shows that Doppler broadening occurs in the 14-MeV neutron analysis with photons emitted in inelastic scattering reactions on light nuclei with excited states whose lifetimes are much smaller than the time of flight of a recoiling nucleus in the material. It provides groundwork for analysis of gamma ray spectra utilizing detector response functions measured with a 14-MeV neutron source using actual geometry of an active interrogation system.     

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.     

Performance evaluation of spectral deconvolution analysis tool (SDAT) software used for nuclear explosion radionuclide measurements

The Spectral Deconvolution Analysis Tool (SDAT) software was developed to improve counting statistics and detection limits for nuclear explosion radionuclide measurements. SDAT utilizes spectral deconvolution spectroscopy techniques and can analyze both β-γ coincidence spectra for radioxenon isotopes and high-resolution HPGe spectra from aerosol monitors. Spectral deconvolution spectroscopy is an analysis method that utilizes the entire signal deposited in a gamma-ray detector rather than the small portion of the signal that is present in one gamma-ray peak. This method shows promise to improve detection limits over classical gamma-ray spectroscopy analytical techniques; however, this hypothesis has not been tested. To address this issue, we performed three tests to compare the detection ability and variance of SDAT results to those of commercial-off-the-shelf (COTS) software which utilizes a standard peak search algorithm.     

Determination of boron in marine carbonates by prompt gamma-ray analysis

Boron in carbonate reference samples was measured by neutron-induced prompt gamma-ray analysis (PGA) using cold and thermal neutron guide beams of the JRR-3M reactor. In order to determine B contents in marine carbonates, the Doppler-broadened -ray peak of 478 keV was used together with the correction of interference from Na-peak of 472 keV. We determined B in coral samples within 3% of analytical precision. The data obtained by the present method are mostly consistent with reported values. Here, we report PGA of B in marine carbonates.     

An activation analysis system for short-lived radioisotopes including automatic dead-time corrections with a microcomputer

A system based on an IBM-PC microcomputer coupled to a Canberra Series 80 multichannel analyser has been developed for activation analysis with short-lived radioisotopes. The data transfer program can store up to 77 gamma-ray spectra on a floppy disk. A spectrum analysis program, DVC, has been written to determine peak areas interactively, to correct the counting losses, and to calculate elemental concentrations.     

Computer program for neutron activation analysis with the SLOWPOKE reactor

A FORTRAN computer program for automatic neutron activation analysis is presented. The program locates and identifies peaks in a gamma-ray spectrum, calculates peak areas and the concentrations of the elements of interest in the sample. This program was specifically designed for the SLOWPOKE reactor, it uses a semi-absolute method and does not need standards or flux monitors. The program was written so as to minimize the computation time, and a typical 4096-channel spectrum is processed in five seconds by an IBM 360/75 computer.     

Detection of weak activities by measurement of gamma-ray spectra

The presence of an activity in a measured sample may be verified by observing a relevant full-energy peak in a measured gamma-ray spectrum. Three decision procedures testing the presence of a full-energy peak are compared from the point of view of the test power as well as the sensitivity to background non-linearity. The better performance is achieved with the procedures which take into account an a priori information on the peak shape, rather than with a shape-independent one. The precedure which makes use of a generalized second difference filter is the least sensitive to the background non-linearity and should be preferred in routine use.     

Pattern-based algorithm for peptide sequencing from tandem high energy collision-induced dissociation mass spectra

A new strategy is reported for extracting complete and partial sequence information from collision-induced dissociation (CID) spectra of peptides, CID spectra are obtained from high energy CID of peptide molecular ions on a four-sector tandem mass spectrometer with an electro-optically coupled microchannel array detector, A peak detection routine reduces the spectrum to a list of peak masses and peak heights, which is then used for sequencing, The sequencing algorithm was designed to use spectral data to generate sequence fits directly rather than to use data to test the fit of series of sequence guesses. The peptide sequencing algorithm uses a pattern based on the polymeric nature of peptides to classify spectral peaks into sets that are related in a sequence-independent manner, It then establishes sequence relationships among these sets, Peak detection from raw data takes 10–20 s, with sequence generation requiring an additional 10–60 s on a Sun 3/60 workstation, The program is written in the C language to run on a Unix platform. The principal advantages of our method are in the speed of analysis and the potential for identifying modified or rare amino acids. The algorithm was designed to permit real-time sequencing but awaits hardware modifications to allow real-time access to CID spectra.     

基于无基底扣除的数据趋势累积谱峰检测算法

谱峰的检测分析在色谱技术研究中具有十分重要的作用,但在色谱数据采集、传输的过程中,不同程度的噪声干扰给谱峰检测带来了极大的困难。目前传统的谱峰检测算法普遍通过基底扣除的方式对谱峰的形态进行预定义,将谱峰分为单峰、重叠峰等多个种类。针对不同种类的谱峰采用不同的检测方法,这就导致了传统的谱峰检测算法具有高复杂度、低自动化程度以及容易失真等缺点。因此,该文从另一个角度出发提出了一种新型的谱峰检测算法。该算法取消基底扣除以及谱峰分类这一步骤,直接在源数据曲线的基础上进行谱峰检测,主要分为离散差分、趋势累积以及遍历寻峰3个步骤。首先通过信号量表征数据升降趋势;然后进行数据趋势累积,根据累积总和定位谱峰,采用三点定位的方式,即峰起点、极值点和峰终点描述一个谱峰的位置;最后根据遍历排序的方式进行谱峰的筛选。此外,通过谱峰扣除的方式得到曲线基底部分。采用C语言设计编写了算法程序,并对多个动态比表面积分析仪测定的色谱图进行了检测分析,结果显示使用该算法可以精准区分谱峰部分与基底部分,受数据曲线毛刺、震荡等噪声干扰很小,谱峰的三点定位十分准确,且不受其复杂形态的影响,具有很强的普适性。与其他算法相比,该算法定位准确,结构清晰,具有较好的稳定性以及可靠性。该文报道了无基底扣除以及趋势累积等新型谱峰检测思想在吸脱附色谱曲线中的应用,证明了其在吸脱附色谱峰检测中的有效性和良好的应用前景。     

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.     

Optimisation of irradiation and decay times in nuclear activation analyses

A mathematical model has been developed to describe the behaviour of the statistical error in the determination of gamma-ray peak areas in instrumental activation analysis as a function of the irradiation and decay times. This model has been used to investigate the best values of these parameters for the determination of a particular peak in a complex spectrum. It has also been used to investigate the effect of the maximum count rate on the best precision obtainable.     

Peak shape analysis of core level photoelectron spectra using UNIFIT for WINDOWS

Several approaches used in the peak shape analysis of core level spectra for the purpose of modelling of both peak shapes and background profiles will be discussed. A universal program is presented, which combines options for adequate modelling of the peak shapes and background, implementation of a successful numerical algorithm for an iterative non-linear parameter estimation procedure, and a flexible as well as convenient data handling. The performance of this program code is demonstrated by fitting a synthesized model spectrum. An example for analysis of a complex experimental spectrum is presented, too. An S 2p spectrum recorded from a MBT-treated pyrite surface is successfully analyzed using the presented software and is found to be characterized by five different S 2p contributions.     

Probability for Type I errors in gamma-ray spectrometric measurements of drinking water samples

In gamma-ray spectra, acquired in the absence of the sample, peaks occur which belong to the spectrometer background. When samples are measured, which contain radionuclides that appear in the background also and have activities near the detection level, the background contributes substantially to the peak areas. In the extreme case, when the contribution of the sample is much smaller than the contribution of the background, the peak area attributed to the radionuclide within a sample has the same probability of being positive or negative. Therefore, to interpret the results obtained from measurements of low-activity samples, the performance of the spectrum analysis procedure near the detection level must be known. To test the performance of the spectrum analysis procedure at low activities, the spectrometer background spectra were analyzed as if they had been water samples, prepared as dry residue obtained by evaporation of 50 L of water. The probabilities for false positives together with their decision thresholds are given for radionuclides appearing in the background spectra. For some of the radionuclides that do not appear in the background spectra, probabilities for false detection are given as well.     

Improved radioxenon gamma-spectrometry counting system and its efficiency calibration: Monte Carlo simulation and experimental results at enriched xenon counting environment

To give satisfactory efficiency both for X- and gamma-ray photon, an improved counting system has been developed in CTBT Canadian radioxenon laboratory. The counting system consists of a BEGe detector coupled with a thin carbon fiber window counting cell, that can perform a reliable and efficient radioxenon measurement. A semi-empirical calibration procedure was adopted, which is a combination of experimental measurement and mathematical simulation. Mathematical calibration tool is Monte Carlo simulation software named VGSL. Advanced gamma-spectrum analysis software, named Aatami, was used for gamma-ray peak shape fitting and X-ray multiplets deconvolution. The calculated full energy peak efficiency curve covers from 30 to 700 keV and agrees well with experimental data points within 2%. The efficiency curve can provide radioxenon analysis both for X-rays and gamma-rays with high quality. The efficiency distortion near xenon k-absorption edge of 35 keV, which is caused by high concentrated xenon in the counting cell, is also discussed.     

基于稀疏模型的气相色谱-质谱数据解析及其在严重重叠峰解析中的应用

提出一种气相色谱-质谱（GC-MS）数据解析算法。以色谱峰顶点处的质谱作为待测谱,在谱库中检索一定量相关参考谱,求解关于各纯组分色谱响应值的方程。质谱检索采取分步策略,先利用质谱碎片规律建立高速索引进行粗选,然后使用强峰高概率出峰准则和耐挤压性准则排除无关质谱。为求解色谱响应值方程,提出基于稀疏模型的回归算法,相比传统算法,稀疏算法利于提取待测谱的主要结构,避免"过拟合"。实验结果表明,该质谱检索算法具有较高的精度和规模较小的剩余参考谱集,而所提稀疏模型算法可有效解析严重重叠峰。该算法可作为GC-MS重叠峰解析,特别是严重重叠峰解析的一种有效解决方案。     

Application of a simple peak shape function for the evaluation of gamma and X-ray spectra

The computational method for the rapid evaluation of gamma and X-ray spectra observed by semiconductor detectors in radiometric analysis in presented using a simple peak shape function. The computer programme includes a minimizing routine based on the modified Newton-Raphson method giving a minimized vector of the parameters more rapidly than the conventional approach. The spectra of some gamma-ray emitting fission products and X-ray spectra excited by radioisotopes of materials from copper ore processing were studied. It was found that the simple Gaussian peak function gives the results equivalent to the total peak area method.     

Multi‐scale Gaussian/Haar wavelet strategies coupled with sub‐window factor analysis for an accurate alignment in nontargeted metabolic profiling to enhance herbal origin discrimination capability

Metabolic dataset can provide an overview of different herbal origin, which is conducted by some statistical procedures. Such results often deviate to a certain degree, due to peaks shifts in chromatographic signals. In order to solve this problem, an improved algorithm of combining sub‐window factor analysis with the mass spectrum information is proposed. The algorithm uses a peak detection approach derived either from multi‐scale Gaussian function or Haar wavelet to locate the peaks with different application scope; the candidate drift points at each peak are estimated by Fast Fourier transform cross correlation; Specifically, the best drift points at each candidate peaks are confirmed by sub‐window factor analysis and mass spectrum information in nontargeted metabolic profiling. Finally, the peak regions were aligned against a reference chromatogram, and the non‐peak regions were used linear interpolation. The chromatographic signals of 30 Bupleurum samples were aligned as an illustration of this algorithm, and they could be well distinguished using some statistical procedures. The result demonstrates that the presented method is stronger than other mass‐spectra based algorithms, when facing the alignment of some co‐eluted peaks.