Absolute liquid scintillation counting of35S and45Ca using a modified integral counting method

The disintegration rates of³⁵S and⁴⁵Ca samples were determined by the modified integral counting method, which extrapolates the integral count rate to the zero detection threshold of a liquid scintillation spectrometer. The agreement between the extrapolated value and the standardized disintegration rate of the sample is very satisfactory.     

Dioctyl sulfoxide as a stabilizer for scintillation counting

The use of dioctyl sulfoxide (DOSO) as a stabilizer for scintillation counting of uranium(VI), plutonium(IV) and americium(III) has been investigated. It has been observed that the addition of 2% DOSO to the scintillator solution results in a decrease in count rate of Am(III), which is about one third of that obtained with 2% TOPO. Uranium(VI) could be counted with almost the same efficiency with DOSO, TOPO, or as such without any stabilizer. The counting efficiency of plutonium(IV), however, is inferior for DOSO as compared to TOPO.     

Simultaneous particle counting and detecting on a chip

This paper reports a lab-on-a-chip device that performs particle detection and number counting by coupling the fluorescent detection and particle counting simultaneously. The particle number counting is realized by a resistive pulse sensor (RPS) and fluorescent particle detection is achieved by a miniaturized laser-fiber optic detection system. By using a single microfluidic channel with two detecting arm channels placed at the two ends of the sensing section, the RPS signal-to-noise ratio is improved significantly. Two-stage differential amplification is used to further increase the signal-to-noise ratio for both the RPS and fluorescent signals. This method is also highly sensitive, so that we were able to realize the RPS and fluorescent detection of 0.9 microm (mean diameter) fluorescent particles. Excellent agreement was achieved by comparing the results obtained by our system with the results from a commercial flow cytometer for a variety of samples of mixed fluorescent and non-fluorescent particles. The method described in this paper is simple and can be applied to develop a compact device without the need of lock-in amplifier or similar bulky supplemental equipment.     

Design and performance of a miniature TDCR counting system

A portable liquid scintillation counting system based on the triple-to-double coincidence ratio (TDCR) method was developed at Sofia University “St. Kliment Ohridski”. The system consists of a miniature TDCR counter with cylindrical optical chamber and a specialized TDCR counting module named nanoTDCR. The nanoTDCR module is produced by the labZY company and provides several important new TDCR counting functionalities like: individual extending-type dead-time in each channel; simultaneous counting with two different extendable dead-times and two different coincidence windows and simultaneous TDCR counting and spectrum acquisition. The performance of the new system was tested in benchmark comparisons with the LNHB’s primary TDCR counting system of activity measurements of ²⁴¹Am, ³H, ¹⁴C and ⁶³Ni. Good agreement between the two systems was observed.     

Loss-free counting with a digital spectrometer and a software program

The computer program LFREE was written to do loss-free counting with a digital spectrometer. It runs in parallel with the normal data acquisition software and corrects the counting losses once per second without interrupting data acquisition. The spectrometer's live time clock is used to measure the live time fraction. Tests showed that losses are accurately corrected at variable count rates which cause dead times as high as 80%. For half-lives of the order of 10 seconds, the accuracy is limited by the response of the live time clock to very rapidly changing count rates.     

Cerenkov counting technique

A review is presented on the progress made in the Cerenkov counting technique. History, theory, and applications have shown that this technique is simple, easy, and can be used for the determination of low levels of radionuclides with a low background liquid scintilation counter. It has been applied to the measurement of radioactive biological tracers, fission products (⁹⁰sr,⁸⁹Sr) and natural radionuclides (²²²Rn,²²⁶Ra,²²⁴Ra,²¹⁰Pb,²²⁴Th,²²⁸Th,²³⁸U) in various types of samples. Advantages and disadvantages of this technique are summarized.     

Empirical method of counting losses correction in gamma-ray spectrometry at elevated counting rate

Empirical method of counting losses correction in -ray spectrometry at elevated /up to 1000 cps/ counting rate is suggested. Using experimental data it was found that a counting losses correction coefficient was a lineare function of true fractional deadtime of spectrometer. It was shown that counting losses in peak area of⁶⁰Co /1332 keV/ corrected by the empirical method did not exceed 1.2% with fractional dead-time up to 35%.     

The perfection of loss-free counting

Pileup losses in nuclear pulse spectrometry also depend on energy as lower energies produce narrower pulses which in turn have better chances to avoid pulse pileup. Consequently, in our present system individual energy-dependent pileup correction factors are calculated for all events, making it what very probably may be called the first perfect implementation of Loss-Free Counting. Temporal response and quantitative performance of the new system are tested over the whole range of counting rates (up to 10⁶ c/s) and counting losses (up to 99%) by means of short-lived isomeric transitions and a fast rabbit system.     

Bayesian interpretation of counting data

The application of Bayesian inferential methodology is applied to the analysis of counting data. A formulation leading to data-specific probability density functions is developed. A tabulation of frequently used confidence levels is given for the most common experimental situation. Approximate methods based upon the normal distribution are discussed.     

Low-background counting systems compared

A comparison of special low-background germanium counting systems used at the Pacific Northwest Laboratory will be presented. These vary from specially modified instruments in the laboratory to low-cosmic-exposure detectors operated deep underground. The underground detectors have copper cryostats completely electroformed from low-background copper. Electroforming is a process analogous to zone refining in its ability to remove chemical impurities. Shielding techniques and their merit are compared as to difficulty and benefit. Active cosmic veto is directly compared to passive overburden shielding. Special attention is paid to cosmic activation of the cryostat and the germanium crystal itself.Operated for the U. S. Department of Energy by Battelle Memorial Institute under Contract DE-AC06-76RL0 1830.     

Bacteria counting with impedance spectroscopy in a micro probe station

A method to quantify the density of viable biological cells in suspensions is presented. The method is implemented by low-frequency impedance spectroscopy and based on the finding that immobilized ions are released to move freely in the surrounding suspension when viable Escherichia coli cells are killed by a heat shock. The presented results show that an amount of ions corresponding to approximately 2 x 10(8) unit charges are released per viable bacterium killed. A micro probe station with coplanar Ti electrodes was electrically characterized and used as a measuring unit for the impedance spectroscopy recordings. This unit is compatible with common microfabrication techniques and should enable the presented method to be employed using a flow-cell device for viable bacteria counting in miniaturized on-line monitoring systems.     

First analytical results using a multi-ion counting system of a spark source mass spectrometer

Isotope dilution measurements of geological reference materials are described using a newly developed multi-ion counting (MIC) system for a spark source mass spectrometer. Compared with the conventional photoplate detection system, there are considerably improved analytical features of the MIC system, especially the high sensitivity which leads to short measuring times of 1 min to 1 h for trace element analysis on the μg/g — ng/g level.     

Development of a new fluorescence decay measurement system using two-dimensional single-photon counting

A new fluorescence decay measurement system has been developed. The system consists of a spectrograph and a new two-dimensional photon counter. The combination enables measurements to be made of the fluorescence decay as a function of time and wavelength simultaneously. The time resolution is better than 5 ps with deconvolution processing, and the wavelength resolution is approximately 0.15 nm with 1200 grooves mm⁻¹ gratings. The dynamic range is 10⁵. The instrument response function (IRF) of the system is nearly gaussian, and has no tail or “after pulses” which are commonly observed using a photomultiplier in a time-correlated photon counting (TCPC) system. Therefore fast fluorescence decay of several tens of picoseconds can be measured accurately. In addition, the two-dimensional single-photon counting can be performed without wavelength scanning, so that the wavelength-dependent fluorescence decay can be easily and direcly observed with a fast throughput and a high signal-to-noise ratio. The principle of two-dimensional photon counting is discussed together with characteristics including linearity and statistical behavior.     

Development of a single photon counting gamma-ray camera for Compton noise elimination

Journal of Radioanalytical and Nuclear Chemistry - In this study, the noise resulting from Compton scattering was quantified when gamma images were acquired with a 50-mm thick scintillator array...     

Automatic registration of fission fragment tracks with a spark gap counting system

The theoretical aspects of fission track production in polycarbonate foils are briefly discussed. An automatic couning system for fissio tracks based on a spark gap chamber is described. A linear response for a low fission track density, typical of environmental and biological samples, was obtained with a²⁵²Cf source using an electrode of 33.2 mm² The system also functions with electrodes of larger and smaller areas without any major changese in the instrument.     

Applications and problems of parametric counting

The large and expanding field of modern high technology based upon silicon and its compounds is ideally suited for INAA using parametric counting, since neither the silicon nor the impurities present in almost infinite dilution give rise to self-shielding effects. Parametric counting, however, requires a fast and convenient method for determining the thermal, resonance, and fast neutron fluxes during irradiation. The resonance flux should be measured close to 5 eV, because most of the analytically important isotopes with large I _p /σ_o values have their resonance energies in the 1–15 eV region, and because the resonance flux in a commercial reactor does not follow the theoretical 1/E distribution in energy. It is shown in this paper that the resonance flux as measured with the “zirconium method” is practically identical to the resonance flux obtained from cadmium ratio measurements on gold. In addition, the zirconium monitor also yields the thermal and fast fluxes, and has several practical advantages, especially for longer irradiations.     

Sediment varve counting with PIXE

The feasibility of the particle induced X-ray emission (PIXE) technique for varve counting of vertically taken marine and lacustrine sediments was studied aiming at its possible use as a dating procedure by observing the yearly variation of the constituent elements. The samples were impregnated with a low viscosity epoxy resin to obtain slabs with preserved layered structure suitable for the PIXE analyses. PIXE-spectra were taken as a function of depth distance and the normalized X-ray peak area variations were determined. Especially, concentration changes of silicon and iron were found to be clear. Due to the employed sample preparation technique the observed chlorine concentration corresponds to the amount of water in the initial sample. Maximum chlorine concentration appeared at positions where the Si and Fe concentrations were near minimum. By plotting the Si/Cl or Fe/Cl peak area ratios, an even more distinct position dependent variation was noted.