Review of loss-free counting in nuclear spectroscopy

This paper is a review of techniques for real-time correction of counting losses in nuclear pulse spectroscopy which became known under the name of loss-free counting (LFC).     

Validation of a loss-free counting system for neutron activation analysis with short-lived indicators

The use of loss-free counting systems makes possible the exact correction for pile-up and dead-time losses during counting of a mixture of short-lived radionuclides even at very high count rates. However, counting statistics cannot be calculated by taking into account only the Poisson distribution of the incoming -quanta, such as is done in existing computer programs for -spectrometry. At moderate count rates Müller statistic was found to account for the observed variability between duplicate countings; however, at higher count rates the variability of weighing factors was found to be significant in comparison with the Müller statistic. While counting statistics could not be correctly estimated for short-lived species, experiments showed excellent accuracy for initial dead times up to 90%.     

Investigation of ancient pottery from Lefkanti,Greece, by epithermal gamma spectroscopy using loss-free counting technology

For the analysis of pottery fragments from ancient Lefkanti, instrumental neutron activation analysis was used. To have a good throughput of samples, a detectable series of short-lived isotopes was selected for the investigation. The problem of the initial high radioactivity, which normally hinders a fast -spectroscopic analysis, was eluded by using loss-free counting technology. This technology allows the measurement of pottery samples of about 100 mg size 1 day after a 30 min epithermal irradiation. Up to 15 samples could be analyzed in one day under these working conditions, having the possibility to analyze the elements As, Eu, Ga, Gd, La, Mn, Sb, Sm, Th, U, W and Zn, which are enough to perform statistical characterizations of potteries.     

The NIST rapid irradiation and counting system

A radiotracer based method for the determination of the rate of expel of a swelling agent from a swelling agent saturated polymer foil induced by a second organic liquid (i.e., blowing agent for foaming of polymers) has been set up and tested. The method was applied to acetone swollen polyetherimide (PEI) foil and 1,1,1-trichloroethane and ethanol (blowing agents) systems. By combining the results of radiotracer measurements with those obtained by measuring foil weights, the amount of the respective blowing agents that replaced acetone in the PEI foil was determined.     

Measurement of the perfection of nanoscale multilayers

In modern materials science the characterisation of nanostructures is becoming increasingly important. For measurement of the quality of nanoscale multilayer arrangement with high spatial resolution a method is described that is based on the broadening of the spots in the Fourier transformation of transmission electron microscopic images of multilayer cross-sections. Using this method on Si/Ge superlattices with periodic lengths between 4 and 12 nm it could be quantitatively shown that the layer perfection decreases with increasing periodic length. The transition from elastic to plastic deformation between the Si and Ge layers at larger periodic lengths can be the reason for this behaviour.     

The Argonne low level14C counting system

A low level¹⁴CO₂ counting system is described. This system was used to process several thousand CO₂ samples derived from atmospheric collections at various altitudes. Special features include counter construction utilizing electrolytic copper and shielding with neutron moderating and absorbing paraffin containing sodium metaborate. The effect of steel shielding thickness is shown, and the anticoincidence counters are described. Purification of the CO₂ for proportional counting is discussed.Work performed under the auspices of the U.S. Department of Energy, under Contract No. W-31-109-ENG-38.     

The resurgence of Coulter counting for analyzing nanoscale objects

This review discusses recent advances in the science and technology of Coulter counting. The Coulter counting principle has been used to determine the size, concentration, and in favorable cases the surface charge, of nanometer-scale colloidal particles, viruses, DNA and other polymers, and metal ions. A resurgence of interest in the field of COulter counting is occurring because of the advent of new technologies that permit fabrication of membranes containing single, robust, and chemically well-defined channels having smaller and more uniform sizes than could be prepared in the past. These channels are prepared from biological materials, such as self-assembling membrane proteins, and from synthetic materials such as polymers, carbon nanotubes, and silicon-based inorganic materials. In addition to particle characterization, there have been a few recent examples of using Coulter counters to study chemical processes, such as the dehybridization of DNA.     

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.     

The use of delayed nuclear track counting for determining bismuth

The predominant use of the nuclear track technique (NTT) in analytical chemistry has been to measure the prompt charged particle emission from neutron induced reactions with stable or fissile nuclides of selected elements. This work describes the use of the NTT for determining bismuth via delayed alpha particle emission from the decay of²¹⁰P. This technique is sensitive and reliable since alpha track counting is highly efficient and can provide information, on elemental spatial distributions. Bismuth determinations in various materials by this technique appears possible to at least the 1.0 microgram per gram level.     

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.     

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%.     

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.     

The application of cherenkov counting in 14 MeV neutron activation analysis

The conventional method of measurement in 14 MeV activation analysis is to employ gamma-ray spectrometry. The method has the advantage of good selectivity but this is at the expense of sensitivity. In order to improve sensitivity the authors have employed Cerenkov counting techniques and by the careful use of absorbers in a specially designed cell together with double decay procedures have still retained a considerable degree of selectivity. The method has been applied to neutron flux measurement and to the majority of the elements in the periodic table.     

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.     

The optimum irradiation,decay and counting times in activation analysis for single and double counting and for different minimization functions

The optimum irradiation, decay and counting times were calculated for single and double counting in the case of 3 isotopes. Two different minimization functions were considered. The results, presented in graphical form, make possible the estimation of the optimum times for the majority of practical cases. An important gain in sensitivity can be obtained by using a double counting technique.     

Crystal perfection and triplet excitons in 1,4-dibromonaphthalene

The phosphorescent behaviour of 1,4-dibromonaphthalene single crystals at liquid-helium temperatures is strongly influenced by the crystal preparation techniques. Crystal unperfections appear to be essential for observing excitonic emission. A comparison is made between crystals grown from the melt, solution and vapour. Experiments on crystals doped with DBN-d₆ confirm the proposed model.     

Towards a quantitative definition of perfection in chromatographic analyses

The paper published by Ghaoui and Rothman [J. High Resolut. Chromatogr. 15 (1992) 36] and particularly its Fig. 5, is further considered here because it contains the germ of an idea of how to measure improvements to a chromatographic method, and how to define the goal of perfection in terms of "zero defects" as required by quality assurance schemes. From this, a new role emerges for signal averaging in capillary chromatography: a role to quantify and measure method improvements, and one which can be generally applied to measure improvements in instrument design too.