Another method of dead time correction

A new method of the correction of counting losses caused by a non-extended dead time of pulse detection systems is presented. The approach is based on the distribution of time intervals between pulses at the output of the system.     

The correction for the counting yield in nuclear spectroscopy

Pulser and live timer are alternate tools. Dead time effects can be expressed in terms of a pulse rate dependent factor of the counting yield. The task of their correction should be shifted from the live timer of the ADC to a central timing unit. A new method is proposed, combining the advantages of the pulser and the live timer, where by each selected and accepted event is adjoined to a clock time interval and each selected but not accepted event to a dead time interval. The length of each interval is determined by the arrival of the next selected event.     

The use of the modified simplex method for automatic phase correction in fourier-transform nuclear magnetic resonance spectroscopy

FT-n.m.r. spectra were automatically phase-corrected using the modified simplex method. Three optimization criteria for phase correction were investigated. Best results were obtained by maximization of the intensity minimum and maximization of the summed intensities below the baseline. The maximization of spectral area consistently failed to correct the spectral data satisfactorily.     

Real-time correction of counting losses in nuclear pulse spectroscopy

Reviewing the current status of real-time correction of counting losses in nuclear pulse spectroscopy, the pileup problem is identified as the last question not resolved satisfactorily up to now. Correction of pileup losses in provided, at least in principle, by the classical pulse generator method, however, severe limitations in test frequency prohibit its application to real-time correction of counting losses. A solution is offered by the novel principle of the virtual pulse generator which obviates the shortcomings of the classical method simply by not introducing pulses into the spectroscopy system. Instead, the probability for pileup-free pulse processing is determined by suitable tests of the system status at arbitrarily high test frequencies. After a discussion of the principles of the new method and its application to a real-time correction system experimental evidence is provided for the complete correction of counting losses of more than 98% under conditions of stationary as well as variable counting rates up to the limit of stable operation of the underlying spectroscopy system which is 800 000 c/s for an experimental high-rate gamma spectrometer.     

A rapid spreadsheet method for the estimation of dead time

Summary A method has been developed for the rapid estimation of chromatographic column dead time. This utilises a commercial spreadsheet running on a Personal Computer, allowing automated dead time calculation in less than 30 seconds. Retention data from the literature have been used to illustrate the accuracy of this carbon number method. The method was also validated by using GC retention data experimentally recorded during this work.     

A convenient method for routine estimation of dead time in gas chromatography

A set of retention times (tR) of n-alkanes at different temperatures and the primary dead times (tM) are used to determine the 4 numerical constants (a, b, c, and d) of an equation. This equation is rearranged into a second equation, used in turn for routine calculation of the secondary dead time (tMS) of each chromatogram from any member of the n-alkane series. Equation 2 can be used to calculate the tMS of both packed and capillary columns. The calculated tMS values are in good agreement with those of the tM values. The greatest difference is 3.38%, but it is speculated that the percent difference would be lower when more tR data are collected for the determination of the 4 numerical constants of Equation 1. Error in measurement of retention time undoubtedly would affect the accuracy of the estimated dead time, but it is attenuated by a factor of 1 + e(a + bN + c/T + dN/T).     

Alternating iterative regression method for dead time estimation from experimental designs

An indirect method for dead time (t ₀) estimation in reversed-phase liquid chromatography, based on a relationship between retention time and organic solvent content, is proposed. The method processes the retention data obtained in experimental designs. In order to get more general validity and enhance the accuracy, the information from several compounds is used altogether in an alternating regression fashion. The method was applied to nitrosamines, alkylbenzenes, phenols, benzene derivatives, polycyclic aromatic hydrocarbons and β-blockers, among other compounds, chromatographed in a cyano and several C18 columns. A comprehensive validation was carried out by comparing the results with those provided by the injection of markers, the observation of the solvent front and the homologous series method. It was also found that different groups of compounds yielded the same t ₀ value with the same column, which was verified in different solvent composition windows. The method allows improved models useful for optimisation or for other purposes, since t ₀ can be estimated with the retention data of the target solutes.       

A numerical interpolation of Kováts indices without dead time correction

Summary Comparison with normal procedures shows that numerical interpolation of the logarithms of gross retention times generates quite useful Kováts indices for gas chromatographic analysis. The dead time concept is not used in the interpolation.     

A simple method for correcting baseline artifacts in nuclear magnetic resonance spectroscopy

A simple baseline correction program is described. It depends on an adjustable threshold for initiation of a data-sorting process between the signals and baseline of a computer-stored n.m.r. spectrum. An application is discussed.     

A transmission dielectric time domain spectroscopy method for aqueous systems

A transmission method in dielectric time domain spectroscopy, suitable for aqueous systems, is described. It is demonstrated that the method can be applied to aqueous electrolytes. The dielectric spectra of solutions of the non-electrolyte glucose and the electrolytes CuSO₄ and sodium carboxymethyl cellulose are given as illustrative applications.     

On the thin cell method in time domain spectroscopy

A simple physical picture is given of Fellner-Feldegg's thin cell method in time domain spectroscopy. From this picture an accurate analytical relation is derived for the total reflection coefficient.     

A new transmission method in dielectric time domain spectroscopy

A new transmission TDS method for permittivity measurements using the linear dependence of the attenuation coefficient and the phase coefficient with sample length is described. Experimental results for methanol in carbontetrachloride at room temperature are reported.     

Comparisons of several dead time correction methods in the case of a mixture of short- and long-lived nuclides

Several dead time correction methods were compared experimentally with the exact correction method and their limits were discussed. These correction methods were applied to neutron activation analysis of a biological sample. A special electronic circuit and an additional counting equipment were used to obtain the fractional dead time with a suficiently high frequency.     

A probe method for studying dibromocarbene by time resolved infrared spectroscopy

Dibromocarbene reacts with tertiary-butylisocyanide to form a ketenimine. The absolute rate constant of the reaction (k_TBI = 2.3 × 10⁹ M⁻¹ s⁻¹) was determined by laser flash photolysis techniques with UV-vis detection of the dibromocarbene-pyridine ylide. The ketenimine was detected by TRIR spectroscopy at 2040 cm⁻¹. Isocyanide trapping of carbenes to form ketenimines is proposed as a general method of studying IR silent carbenes by TRIR spectroscopy.     

Extending the dynamic range of proton transfer reaction time-of-flight mass spectrometers by a novel dead time correction

Proton transfer reaction time-of-flight mass spectrometry (PTR-TOF-MS) allows for very fast simultaneous monitoring of volatile organic compounds (VOCs) in complex environments. In several applications, food science and food technology in particular, peaks with very different intensities are present in a single spectrum. For VOCs, the concentrations range from the sub-ppt all the way up to the ppm level. Thus, a large dynamic range is necessary. In particular, high intensity peaks are a problem because for them the linear dependency of the detector signal on VOC concentration is distorted. In this paper we present, test with real data, and discuss a novel method which extends the linearity of PTR-TOF-MS for high intensity peaks far beyond the limit allowed by the usual analytical correction methods such as the so-called Poisson correction. Usually, raw data can be used directly without corrections with an intensity of up to about 0.1 ions/pulse, and the Poisson correction allows the use of peaks with intensities of a few ions/pulse. Our method further extends the linear range by at least one order of magnitude. Although this work originated from the necessity to extend the dynamic range of PTR-TOF-MS instruments in agro-industrial applications, it is by no means limited to this area, and can be implemented wherever dead time corrections are an issue.     

A thin sample transmission method in dielectric time domain spectroscopy

A simple relation, which gives the permittivity analytically, is derived to approxiate the transcendental equation in the total transmission method in dielectric time domain spectroscopy. The limits for the applicability of the method are discussed. Results given for 1-butanol and 2-propanol.     

High-temperature spectroscopy for nuclear waste applications

Instrumentation has been developed to perform uv-vis-nir absorbance measurements remotely and at elevated temperatures and pressures. Fiber-optic spectroscopy permits the interrogation of radioactive species within a glovebox enclosure at temperatures ranging from ambient to >100 °C. Spectral shifts as a function of metal-ligand coordination are used to compute thermodynamic free energies of reaction by matrix regression analysis. Pr³⁺ serves as a convenient analog for trivalent actinides without attendant radioactivity hazards, and recent results obtained from 20–95 °C with the Pr-acetate complexation system are presented. Preliminary experimentation on Am(III) hydrolysis is also described.