Spectral line shape fitting in instrumental neutron activation analysis of pottery

The γ-ray spectrum of a neutron-activated clay standard is analyzed by spectral line shape fitting and the results are compared with an empirical analysis of the spectrum based on detector calibrations. It is concluded that trace element analysis of pottery may be simplified and enhanced by a combination of spectral line shape fitting and detector calibrations.     

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.     

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.     

High‐resolution peak analysis in TOF SIMS data

High mass resolution time‐of‐flight secondary ion mass spectrometry (TOF SIMS) can provide a wealth of chemical information about a sample, but the analysis of such data is complicated by detector dead‐time effects that lead to systematic shifts in peak shapes, positions, and intensities. We introduce a new maximum‐likelihood analysis that incorporates the detector behavior in the likelihood function, such that a parametric spectrum model can be fit directly to as‐measured data. In numerical testing, this approach is shown to be the most precise and lowest‐bias option when compared with both weighted and unweighted least‐squares fitting of data corrected for dead‐time effects. Unweighted least‐squares analysis is the next best, while weighted least‐squares suffers from significant bias when the number of pulses used is small. We also provide best‐case estimates of the achievable precision in fitting TOF SIMS peak positions and intensities and investigate the biases introduced by ignoring background intensity and by fitting to just the intense part of a peak. We apply the maximum‐likelihood method to fit two experimental data sets: a positive‐ion spectrum from a multilayer MoS₂ sample and a positive‐ion spectrum from a TiZrNi bulk metallic glass sample. The precision of extracted isotope masses and relative abundances obtained is close to the best‐case predictions from the numerical simulations despite the use of inexact peak shape functions and other approximations. Implications for instrument calibration, incorporation of prior information about the sample, and extension of this approach to the analysis of imaging data are also discussed.     

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.     

XPS and XAES of polyethylenes aided by line shape analysis: The effect of electron irradiation

X-ray photoelectron spectroscopy (XPS) and X-ray induced Auger electron spectroscopy (XAES) have been used to investigate different polyethylene surfaces, i.e. low density polyethylene (PELD), high density polyethylene (PEHD) and polyethylene of ultra high molecular weight (PEUHMW). The ratio of Csp²/sp³ was evaluated from (i) fitting of XPS C 1s spectra, (ii) the width of XAES C KLL spectra (parameter D) and (iii) line shape analysis by the pattern recognition (PR) method using the fuzzy k-nearest neighbors (fkNN) rule. The proposed approaches investigate: (i) the differences between various polyethylene surfaces, (ii) their surface changes and degradation due to electron irradiation under various doses and (iii) their stability under electron beam irradiation.The results of proposed approaches, i.e. C 1s fitting, C KLL width evaluation and PR line shape analysis applied to C 1s and C KLL transitions, are qualitatively consistent. The unirradiated polyethylenes indicate nearly Csp³ hybridizations. Under an electron dose a rapid decrease of Csp³ is observed, starting at a dose of 100 Cm⁻². The quantitative differences observed between results obtained from analyses using the C KLL and C 1s spectra, can be explained with a smaller average information depth of C KLL transition. However, quantitative discrepancies between results of various approaches using the same electron transition, i.e. C KLL or C 1s, are smaller. The surface degradation due to X-ray irradiation was negligible in comparison to electron beam irradiation. The PR method was efficient in identifying the polyethylene surfaces under various electron doses. The largest stability under an electron beam is exhibited by the PEUHMW.     

Isotopically resolved {ie30-01} electronic spectrum of Ag3 and calculation of its Jahn-Teller effects

Ag₃ was produced by pulsed-nozzle laser vaporisation and jet-cooled in a Ne supersonic expansion. Onecolor resonant two-photon ionisation (R2PI) spectra of the {ie30-02} transition of Ag₃ were separately measured for all four isotopic combinations. Long vibrational progressions are observed, involving clearly resolved bands at low energy, merging into a dense but resolvable spectrum up to 1000 cm¹ above the origin. Both the ground {ie30-03} and excited {ie30-04} states of Ag3 are susceptible to Jahn-Teller distortion along the degenerate e′ bending coordinate. The Jahn-Teller analysis includes both linear and quadratic terms, simultaneously with the spin-orbit coupling. Following extensive parameter fitting, the absorption spectrum is calculated, and bands assigned. The spin-orbit splitting is quenched below the localization energy, but becomes observable ≈ 300 cm^-1 above the origin.     

Nuclear magnetic resonance study of exchanging systems—IV : Complete line shape analysis of nitrogen inversion of ethylenimine by the density matrix method

An NMR spectrum of completely dehydrated ethylenimine 1 in liquid phase was found to show well resolved multiplets for the aziridine ring protons at room temperature. The computer analysis was made to determine the NMR parameters. Temperature dependent NMR spectra show that the nitrogen inversion of 1 is slow enough in the NMR time scale at room temperature. In order to obtain the kinetic parameters of this inversion, the complete line shape analysis for the NMR spectra of 1 as an AA′BB′C spin system was performed using the density matrix method, and fitting the calculated spectra with the observed at various temperatures. The activation parameters are obtained as follows: Ea = 15·9±0·4 Kcal/mole Δ^≠ = 17·1±0·8 Kcal/mole ΔH^≠ = 15·3±0·4 Kcal/mole at 25·° ΔS^≠ = ?6·2+-1·2 e.u. Some discussion is made about the activation parameters of the nitrogen inversion of various aziridines.     

Application of Lie algebraic method to the calculation of rotational spectra for linear triatomic molecules

The Hamiltonian describing rotational spectra of linear triatomic molecules has been derived by using the dynamical Lie algebra of symmetry group U1(4) U2(4). After rovibrational interactions being considered, the eigenvalue expression of the Hamiltonian has the form of term value equation commonly used in spectrum analysis. The molecular rotational constants can be obtained by using the expression and fitting it to the observed lines. As an example, the rotational levels of v2 band for transition (02°0-0110) of molecules N2O and HCN have been fitted and the fitting root-mean-square errors (RMS) are 0.00001 and 0.0014 cm-1, respectively.     

Subtraction of atmospheric water contribution in Fourier transform infrared spectroscopy of biological membranes and proteins

The contribution of the absorption of H₂O vapor in the IR spectrum of proteins Interferes with the analysis of the shape of amide I and II bands and prevents correct assignments to be performed, in particular after Fourier self-deconvolution of the spectra Mathematical treatments of the spectra have previously been proposed to subtract the water vapor contribution from the sample spectrum. Here we propose to take advantage of the intrinsic bandwidth difference existing between the absorption bands of the water vapor and these of the liquid or solid sample. When a nominal resolution of 8 or 4 cm⁻¹ is chosen, atmospheric water bands are broad and rather featureless. The subtraction coefficient applied may vary by about 50% according to the operator. Conversely, when the spectrum of the same sample in the same conditions is recorded with a nominal resolution of 0.5 cm⁻¹, subtraction coefficients are exactly evaluated by integration and the visual evaluation can not be mistaken by more than 5%. The very sharp features arising from imperfect matching between the atmospheric water band shapes in the reference and in the sample spectrum completely disappear if the difference spectrum is now convoluted to a final resolution of 4 cm⁻¹. Incidence of the subtractions obtained at different resolutions on the evaluation of protein secondary structure is evaluated.     

Description of the shape of thermoanalytical curves : Part 3. A Method for estimating kinetic constants from parameters characterizing peak shape

The relationships between empirical parameters characterizing the shape of thermo-analytical curves and the constants of the kinetic equation, dα/dt = A exp (?E/RT)(1 ? α)ⁿ, are studied. A procedure is developed for the estimation of the three constants of this equation from the empirical parameters. The efficiency of this method is compared to that of model fitting. In evaluation of the confidence intervals of estimated constants and in the case of identification, least-squares (or similar) fitting is shown to be inferior because of its low sensitivity to properties other than the position of the peak along the temperature axis. This lack of sensitivity may be a major cause of the apparent kinetic compensation effect often encountered in the field of thermal analysis.     

Solubility of monazite chemical components in humic acid solutions

The α-factor is a measure of the epithermal neutron flux deviation from the ideal distribution 1/E, where E is neutron energy. It defends on the position of the irradiation channel in reactor. A determination method of the α-factors in irradiation channels of Dalat reactor is presented by fitting the epithermal neutron spectrum obtained from the calculation using MCNP code. The fitting α-values were compared to those by experiment used the “Cd-ratio” method with monitors ¹⁹⁷Au–⁹⁴Zr and ¹⁹⁷Au–⁶⁴Zn. It shows that the α-values calculated from neutron spectra agree well with experimental ones. The difference between both data is about 6%.     

Multi-component analysis of low-density polyethylene oxidative degradation

The oxidative degradation of polyethylene in various conditions has been studied. In order to gain insight into the oxidation process, a method for the curve-fitting analysis of the IR carbonyl band between 1800 cm⁻¹ and 1600 cm⁻¹ in oxidized low-density polyethylene (LDPE) has been developed. Up to 10 components were needed to fit the band envelope, whose assignments and peak positions were based on the literature and on the synthesis of an appropriate model compound. The determination of the other band parameters, such as peak width and peak shape, necessary for reliable best fitting of the absorbance envelopes, was obtained by overall fitting optimization process. By using the available extinction coefficients, the quantitative determinations of the main oxidized species, i.e. ketones, carboxylic acids, esters, γ-lactones and ketoacids, were obtained with a reasonable confidence by rigorous parameter setting. The method was applied to the IR analysis of LDPE samples oxidized in different conditions (under thermal and irradiation stimulation), either as beads or films, as a function of time. Total hydroperoxide concentrations were also quantitatively estimated by a modified iodometric titration procedure. A good linear correlation between concentrations estimated by chemical titration and by intensity analysis of the free hydroperoxide IR band was observed.     

MicroSAMPO — Personal computer based advanced gamma spectrum analysis system

The widely used SAMPO Ge(Li) and HPGe gamma spectrum analysis program has been adapted to IBM Personal Computers in a thoroughly revised version MicroSAMPO. The program is intended for peak search, peak fitting, nuclide identification and activity calculations. The use of calibrated peak shape functions for peak area determination makes it possible to resolve complex multiplets with strongly overlapping peaks. Menu-driven user interface, colour graphics diplays, semi-automatic calibrations and interactive options have been designed to make the program more user-friendly. It is well suited for both spectroscopic research and routine analysis.     

Peak alignment of NMR signals by means of a genetic algorithm

Nuclear magnetic resonance (NMR) analysis of complex samples, such as biofluid samples is accompanied by variations in peak position and peak shape not directly related to the sample. This is due to variations in the background matrix of the sample and to instrumental instabilities. These variations complicate and limit the interpretation and analysis of NMR data by multivariate methods. Alignment of the NMR signals may circumvent these limitations and is an important preprocessing step prior to multivariate analysis. Previous aligning methods reduce the spectral resolution, are very computer-intensive for this kind of data (65k data points in one spectrum), or rely on peak detection. The method presented in this work requires neither data reduction nor preprocessing, e.g. peak detection. The alignment is achieved by taking each segment of the spectrum individually, shifting it sidewise, and linearly interpolating it to stretch or shrink until the best correlation with a corresponding reference spectrum segment is obtained. The segments are automatically picked out with a routine, which avoids cutting in a peak, and the optimization process is accomplished by means of a genetic algorithm (GA). The peak alignment routine is applied to NMR metabonomic data.¹     

SDAT implementation for the analysis of radioxenon β–γ coincidence spectra

The standard deconvolution analysis tool (SDAT) was developed for analysis of radioxenon β–γ coincidence spectra measured as part of the international monitoring system as defined in the comprehensive nuclear-test-ban treaty. The SDAT software analyzes each β–γ coincidence spectrum by fitting library vectors of each radionuclide of interest: ^131mXe, ^133mXe, ¹³³Xe, and ¹³⁵Xe. Detector background and radon are incorporated as optional components of the sample solution. Results are reported in mBq m^?3. A new graphical user interface has been developed to facilitate ease of use and improve the data visualization. Automated energy versus channel calibration algorithms were developed and implemented based on ¹³⁷Cs β–γ coincidence spectra. Details on the user tool and testing are included.     

Automated quantum mechanical total line shape fitting model for quantitative NMR-based profiling of human serum metabolites

An automated quantum mechanical total line shape (QMTLS) fitting model was implemented for quantitative nuclear magnetic resonance (NMR)-based profiling of 42 metabolites in ultrafiltrated human serum samples. Each metabolite was described by a set of chemical shifts, J-couplings, and line widths. These parameters were optimized for each metabolite in each sample by iteratively minimizing the difference between the calculated and the experimental spectrum. In total, 92.0 to 98.1 % of the signal intensities in the experimental spectrum could be explained by the calculated spectrum. The model was validated by comparison to signal integration of metabolites with isolated signals and by means of standard additions. Metabolites present at average concentration higher than 50 μM were quantified with average absolute relative error less than 10 % when using different initial parameters for the fitting procedure. Furthermore, the biological applicability of the QMTLS model was demonstrated on 287 samples from an intervention study in 37 human volunteers undergoing an exercise challenge. Our automated QMTLS model was able to cope with the large dynamic range of metabolite concentrations in serum and proved to be suitable for high-throughput analysis.

Solid-State NMR Characterization of Biodegradable Shape-Memory Polymer Networks

Copolymer networks synthesized from dilactide and diglycolide were characterized by solid-state ¹³C CPMAS NMR in terms of composition, cross-link density, and rate of cross-linking by UV irradiation. The latter is directly evident by a signal at 44 ppm in the ¹³C NMR spectrum. Comparison of solid-state NMR data with the determination of the gel content revealed that this NMR method is sensitive to the chemical cross-link density whereas the gel content is also influenced by physical constraints such as entanglement. Furthermore, these copolymer networks show a shape-memory effect, i.e. a temporary macroscopic shape can be programmed by heating the network above its glass transition temperature together with fixation during cooling. Reheating without fixation recovers the permanent shape. The recovery of the permanent shape could be followed by ¹H DQ NMR buildup curves for a sample that was stretched by 80%.     

Vibrational analysis of the benzophenone molecule and influence of its conformation on vibrational transitions

IR and Raman spectra of benzophenone and several of its isotopomers (d_5⁻, d_l0⁻, ¹³C- and ¹³Cd₅-benzophenone) are the experimental basis for the normal coordinate analysis. The possibility of determining the conformation of the benzophenone molecule in solution from its vibrational spectrum is considered carefully. The dihedral angle between the central part of the molecule and the phenyl ring has been determined by fitting the calculated to the observed spectra. The final force field for the molecule was obtained for the dihedral angle of 35°.     

Studies on nitramide and its methyl derivatives with ab initio calculations. IV. The harmonic force field and vibrational spectra of dimethylnitramine and its isotopic derivatives

The complete harmonic vibrational force field of dimethylnitramine has been calculated at the Hartree-Fock level using 4–21G basis set. The harmonic force field was then scaled with scale factors previously derived from N-methylnitramine, and the vibrational spectrum of dimethylnitramine was computed. This a priori prediction, made with no reference to observations on dimethylnitramine, agrees with the experimental IR spectrum in gas phase with a mean deviation of 8.4 cm^?1. Some of the scale factors were reoptimized by fitting of the computed force field to experimental data. The new set of scale factors reduced the mean deviation to 4.5 cm^?1, and was used to predict the vibrational spectrum of deuterated form of dimethylnitramine(-6D). Dipole moment derivatives were also calculated and used to predict infrared intensities which are comparable with experimental values.