Interpolation and extrapolation of NaI detector efficiencies

The concept of representing a cylindrical detector volume as a virtual point detector in order to simplify the evaluation of the detector efficiency was proposed in the past for HPGe detectors in the case of measuring point sources. In the present work, the validity of the point detector model was studied and confirmed for the direct measurement of small volume sources, when using a common 7.5×7.5 cm² NaI(T1) detector.     

The morse curve as a non-bonded potential function

The morse curve has considerable advantages over the exp-6 and 12-6 potentials as a non-bonded potential function. The three potential functions are compared and the equivalent Morse curves of several commonly used steric potentials are given.     

Sample geometry and efficiency determination of bremsstrahlung radiation of 90Sr on gamma detection systems

Summary The bremsstrahlung radiation energy spectra were produced by hard beta-emitters the ⁹⁰Sr-⁹⁰Y contaminated tea sample sources placed in a copper cylinder (cylinder counting geometry) and encapsulated in two Cu discs (sandwich counting geometry). These energy spectra were directly measured by using two separate gamma-ray spectrometers with a coaxial 110% efficient HpGe detector and a 110 cm³ HpGe well-type detector. The minimum detectable activity and the absolute efficiency of beta-activity for the sandwich and cylinder geometries were found to be 23 Bq ^. kg^-1 and (1.67±0.04)% and 55 Bq ^. kg^-1 and (2.61±0.05)%, respectively. These results indicate that the bremsstrahlung radiation counting method can be applied to some environmental studies when high efficient HpGe detectors, especially well-type HpGe are used.     

CMOS image sensor for detection of interferon gamma protein interaction as a point-of-care approach

Complementary metal oxide semiconductor (CMOS)-based image sensors have received increased attention owing to the possibility of incorporating them into portable diagnostic devices. The present research examined the efficiency and sensitivity of a CMOS image sensor for the detection of antigen–antibody interactions involving interferon gamma protein without the aid of expensive instruments. The highest detection sensitivity of about 1 fg/ml primary antibody was achieved simply by a transmission mechanism. When photons are prevented from hitting the sensor surface, a reduction in digital output occurs in which the number of photons hitting the sensor surface is approximately proportional to the digital number. Nanoscale variation in substrate thickness after protein binding can be detected with high sensitivity by the CMOS image sensor. Therefore, this technique can be easily applied to smartphones or any clinical diagnostic devices for the detection of several biological entities, with high impact on the development of point-of-care applications.     

Experimental determination of the electron tunneling probability as a function of distance for chemical reactions

The kinetics for the tunnelling reaction of trapped electrons with Cu(en)²⁺₃ in a rigid, glassy matrix at 77 K have been measured using pulse radiolysis. The distribution of the Cu(en)³⁺₃ ions was studied in the same system by measurements of ESR line widths, and found to be uniform (random). These measurements help to confirm the measured tunneling distances and the exponential dependence of the rates on the distance between the electron donor and acceptor.     

Neutron conversion efficiency and gamma interference with gadolinium

Gadolinium (Gd) neutron capture plays an important role in both Gd neutron capture therapy and neutron detection. Detailed information about the low-energy electron spectrum emitted after Gd neutron capture is essential for accurately determining the dose delivery to the target and healthy tissues, as well as the effectiveness of Gd against other neutron convertors such as boron (B) and lithium (Li). Owing to issues such as charge extraction associated with the low energy of internal conversion electrons (ICEs) and high gamma interaction of Gd, its competitiveness for certain applications remains debatable. We measured the ICE spectrum of Gd, compared the energy deposition rates of neutron capture products from Gd, B, and Li compounds, and discussed issues associated with gamma sensitivity of Gd.     

Acidity function p(a(H) gamma(Cl)) as a step to pH assessment

The conventional assignment of pH reference buffer standards, pH(S), is achieved by means of a series of procedures that follow from measurement of Harned cell potentials for an electrolyte solution which is the buffer solution of interest. An intermediate step is assessment of the acidity function p( a(H) gamma(Cl))(0), the extrapolated value of a linear representation of the dependence of p( a(H) gamma(Cl)) on m(Cl) for at least three different molalities, m(Cl), of added alkali chloride (0.005; 0.010; 0.015 mol kg(-1) KCl). This experimental value can be compared with a theoretically expected value calculated from the dissociation constants of the buffer species. Whereas these calculations always give negative slopes for diprotic and triprotic acids and zero slope for monoprotic acids, experimental values with negative or positive slopes can be obtained for well fitting straight lines obtained for buffer solutions with ionic strengths from 0.0025 to 0.144 mol kg(-1). Such disagreement between theoretically and experimentally obtained values introduce an extra source of uncertainty in the establishment of pH(S) and on its traceability chain. In this work examples are presented and discussed for which the discrepancy between expected and experimental values leads to different intercept p( a(H) gamma(Cl))(0).     

Retention and column efficiency in reversed phase liquid chromatography as a function of pH for optimization purposes

Summary The effects of pH on both the solute retention and the peak shape of ionogenic compounds are studied in order to propose accurate models for pH optimization purposes. Several mathematical models (theoretical and empirical) for describing the variation of the retention factor versus pH are compared within different pH ranges. Limits of such models used for optimizing the pH by requiring only 3 preliminary experimental runs, are discussed in terms of deviations (≤±5%) of predicted retention times from experimental retention times. An original procedure is developed for selecting the most convenient retention model, from a given set of three retention data. This set is also applied to modeling the variation of both peak width and peak asymmetry with mobile phase pH conditions. Such a procedure is demonstrated as helpful for the separation of ionogenic solutes by considering mobile phase pH as an additional variable that can be useful during optimization procedures.     

Immobilization of fumarase and malate dehydrogenase on agarose efficiency of activity as a function of the enzyme ratio

Two enzymes, L-malate dehydrogenase, L-malate: NAD⁺ oxidoreductase (EC 1.1.1.37) and fumarase, L-malate hydrolyase (EC 4.2.1.2) were immobilized on a (Sepharose 4B) resin by the cyanogen bromide method. Studies showed that the matrix-immobilized fumarase retains the same characteristics as the free enzyme, while the matrix-immobilized malate dehydrogenase has reduced activity. The activity of the coupled enzymes is more enzymeconcentration dependent than the free enzymes, and at a ratio of 0.3 (fumarase: malate dehydrogenase) the simultaneously coupled immobilized enzymes become a better catalytic system. Individually immobilized enzymes, mixed to form a coupled system, yielded the poorest catalytic action.     

Statistical limit of detection of a fluoride-selective electrode as function of different working conditions

Analytical and Bioanalytical Chemistry - This paper deals with the problem of the dependence of the statistical limit of detection of a fluoride ion-selective electrode on different working...     

Detection efficiency calculations using Geant4 for a broad-energy germanium gamma spectrometer

In assistance of radionuclide measurements at Canada’s Comprehensive Nuclear-Test-Ban Treaty (CTBT) laboratory, a Geant4 Monte Carlo application has been developed in simulating a broad-energy germanium detector and calculating detection efficiencies. The detector model was optimized in a reliable and non-biased manner through simultaneous tuning on gap distance and detector dimension, and was validated over various realistic measurement scenarios. All work is based on a series of experiments which covers the typical energy range of gamma radiation in environmental analysis, and considers the variety of the CTBT sample type, dimension and distance-to-detector. In all cases, the predicted efficiencies are consistent with the empirical ones within 5%, with a typical deviation of 3% in majority.     

Improving the efficiency in the detection of gamma activities in environmental soil samples: influence of the granulometry and soil density

Ti(OH)₄ and TiCl₄ modified bentonite (Ti–Na-bent) were applied in the removal of Th(IV) from aqueous solution. Effect of different factors such as pH, contact time, temperature, initial concentration of Th(IV) and efficiency of them for thorium adsorption are investigated. Ti–Na-bent showed high adsorption capacity (q_m?=?231.37 mg/g) and quick adsorption kinetics at lower pH. The adsorption mechanisms involved are: (1) Th⁴⁺, [Th(OH)_4?n]ⁿ⁺ complexed on the outer-sphere of Na-bent and Ti–Na-bent. (2) Ion exchange between Th⁴⁺, [Th(OH)_4?n]ⁿ⁺ and exchangeable cations of Na-bent and the H on the hydroxyl group of Ti(OH)₄. Ti–Na-bent manifested high adsorption capacity for Th(IV), good acid resistance and long-term adsorption stability.

     

Efficient lookup table using a linear function of inverse distance squared

The major bottleneck in molecular dynamics (MD) simulations of biomolecules exist in the calculation of pairwise nonbonded interactions like Lennard‐Jones and long‐range electrostatic interactions. Particle‐mesh Ewald (PME) method is able to evaluate long‐range electrostatic interactions accurately and quickly during MD simulation. However, the evaluation of energy and gradient includes time‐consuming inverse square roots and complementary error functions. To avoid such time‐consuming operations while keeping accuracy, we propose a new lookup table for short‐range interaction in PME by defining energy and gradient as a linear function of inverse distance squared. In our lookup table approach, densities of table points are inversely proportional to squared pair distances, enabling accurate evaluation of energy and gradient at small pair distances. Regardless of the inverse operation here, the new lookup table scheme allows fast pairwise nonbonded calculations owing to efficient usage of cache memory. © 2013 Wiley Periodicals, Inc.     

Gas phase protonation and subsequent dissociations in β-amino alcohols as a function of exoergicity and interfunctional distance

The gas phase protonation of β-amino alcohols and subsequent water loss is investigated in an ion cyclotron resonance spectrometer. It is found that the loss of water is correlated with the formation of oxonium ions (OH protonation). A relationship is found between the extent of internal stabilization at short interfunctional distance in protonated amono alcohols and the exoergicity of protonation required to induce the loss of a water molecule.     

Interpolation of relative retentions as a tool for identification of perhalogenated compounds

Summary Separation of perhalogenated compounds resulting from thermolysis, photolysis or radiolysis of mixtures of halogens in carbon tetrachloride was carried out by programmed temperature gas chromatography. Plots of relative retentions (to CBr₄) vs the number of bromine atoms present for known compounds of the general formula C_xBr_yCl_z (x=1 and 2; y+z=4 or 6) gave three linear correlations (all with r>0.99). These correlations permitted projections of the identities of reaction products for which no standards were available. These projections were later confirmed by CG-MS. *** DIRECT SUPPORT *** A0732166 00010     

Interpolation and extrapolation problems of multivariate regression in analytical chemistry: benchmarking the robustness on near-infrared (NIR) spectroscopy data

Modern analytical chemistry of industrial products is in need of rapid, robust, and cheap analytical methods to continuously monitor product quality parameters. For this reason, spectroscopic methods are often used to control the quality of industrial products in an on-line/in-line regime. Vibrational spectroscopy, including mid-infrared (MIR), Raman, and near-infrared (NIR), is one of the best ways to obtain information about the chemical structures and the quality coefficients of multicomponent mixtures. Together with chemometric algorithms and multivariate data analysis (MDA) methods, which were especially created for the analysis of complicated, noisy, and overlapping signals, NIR spectroscopy shows great results in terms of its accuracy, including classical prediction error, RMSEP. However, it is unclear whether the combined NIR + MDA methods are capable of dealing with much more complex interpolation or extrapolation problems that are inevitably present in real-world applications. In the current study, we try to make a rather general comparison of linear, such as partial least squares or projection to latent structures (PLS); "quasi-nonlinear", such as the polynomial version of PLS (Poly-PLS); and intrinsically non-linear, such as artificial neural networks (ANNs), support vector regression (SVR), and least-squares support vector machines (LS-SVM/LSSVM), regression methods in terms of their robustness. As a measure of robustness, we will try to estimate their accuracy when solving interpolation and extrapolation problems. Petroleum and biofuel (biodiesel) systems were chosen as representative examples of real-world samples. Six very different chemical systems that differed in complexity, composition, structure, and properties were studied; these systems were gasoline, ethanol-gasoline biofuel, diesel fuel, aromatic solutions of petroleum macromolecules, petroleum resins in benzene, and biodiesel. Eighteen different sample sets were used in total. General conclusions are made about the applicability of ANN- and SVM-based regression tools in the modern analytical chemistry. The effectiveness of different multivariate algorithms is different when going from classical accuracy to robustness. Neural networks, which are capable of producing very accurate results with respect to classical RMSEP, are not able to solve interpolation problems or, especially, extrapolation problems. The chemometric methods that are based on the support vector machine (SVM) ideology are capable of solving both classical regression and interpolation/extrapolation tasks.     

Accurate and fast algorithm of the molecular incomplete gamma function with a complex argument

Several efficient algorithms for the accurate and fast calculation of the molecular incomplete gamma function Fm(z) with a complex argument z are developed. The complex incomplete gamma function is arising in molecular integrals over the gauge-including atomic orbitals. Two kinds of algorithms are recommended: (1) a high-precision version and (2) a fast version. The high-precision version is able to guarantee 15 significant figures (10(-15) in the relative error) and the fast version is able to guarantee 12 significant figures (10(-12) in the relative error), at worst, within the double-precision arithmetic. The fast version is about 5-20 times faster than the high-precision version. For most molecular calculations, the fast version will give a satisfied precision.     

Formulation of spectra-based attenuation coefficients in water as a function of depth and off-axis distance for 4, 10 and 15 MV X-ray beams

On the basis of X-ray spectra information for 4, 10 and 15 MV X-rays from a linear accelerator, we propose a method for formulating the attenuation coefficient in water as a function of depth and off-axis distance. It was confirmed by transmission measurement that the formulation provides a good estimation of the attenuation coefficient in water. Using the formulation, we further assessed the effective attenuation coefficient in water as a function of off-axis distance.