共查询到20条相似文献,搜索用时 15 毫秒
1.
G. P. Westphal 《Journal of Radioanalytical and Nuclear Chemistry》1982,70(1-2):387-410
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. 相似文献
2.
G. P. Westphal 《Journal of Radioanalytical and Nuclear Chemistry》2008,275(3):677-685
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). 相似文献
3.
D. L. Upp R. M. Keyser D. A. Gedcke T. R. Twomey R. D. Bingham 《Journal of Radioanalytical and Nuclear Chemistry》2001,248(2):377-383
All nuclear spectroscopy systems, whether measuring charged particles, X-rays, or gamma-rays, exhibit dead time losses during the counting process due to pulse processing in the electronics. Several techniques have been employed in an effort to reduce the effects of dead time losses on a spectroscopy system including live time clocks and loss-free counting modules. Live time extension techniques give accurate results when measuring samples in which the activity remains roughly constant during the measuring process (i.e., the dead time does not change significantly during a single measurement period). The loss-free counting method of correcting for dead time losses, as introduced by HARMS and improved by WESTPHAL (US Patent No. 4,476,384) give better results than live time extension techniques when the counting rate changes significantly during the measurement. However, loss-free counting methods are limited by the fact that an estimation of the uncertainty associated with the spectral counts can not be easily determined, because the corrected data no longer obeys Poisson statistics. Therefore, accurate analysis of the spectral data including the uncertainty calculations is difficult to achieve. The Ortec® DSPEC
PLUS
implements an improved zero dead time method that accurately predicts the uncertainty from counting statistics and overcomes the limitations of previous loss-free counting methods. The uncertainty in the dead-time corrected spectrum is calculated and stored with the spectral data (Patent Pending). The GammaVision-32® analysis algorithm has been improved to propagate this uncertainty through the activity calculation. Two experiments are set up to verify these innovations. The experiments show that the new method gives the same reported activity and associated uncertainties as the well-proven Gedcke-Hale live time clock. It is thus shown that over a wide range of dead times the new ZDT method tracks the true counting rate as if it had zero dead time, and yields an accurate estimation of the statistical uncertainty in the reported counts. 相似文献
4.
Marshall M. Siegel 《Analytica chimica acta》1981,133(1):103-108
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. 相似文献
5.
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. 相似文献
6.
It is shown that the so-called refractive index or “n2” correction used when calculating luminescence quantum efficiencies is generally inappropriate. For accurate evaluations no refractive index correction is required provided that a simple modification to luminescence spectrometers is carried out. 相似文献
7.
Zakharov E. Abugassa I. Arbuzov S. A. 《Journal of Radioanalytical and Nuclear Chemistry》1990,146(2):95-102
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%. 相似文献
8.
P. M. Grant P. Robouch R. A. Torres R. J. Silva 《Journal of Radioanalytical and Nuclear Chemistry》1992,161(2):527-532
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. 相似文献
9.
The derivation of the refractive index (n) correction in luminescence spectroscopy is extended to cases with excitation beams. The accepted “l/n2 correction” is found to be valid for a large number of experimental arrangements in contrast to the analysis of a recent paper. 相似文献
10.
A dead-time correction system, based on CAMAC-modules is developed for the -ray spectrometry of short-lived radionuclides. The linearity of the method is realized up to about 104 cps. 相似文献
11.
Xiaolin Hou 《Journal of Radioanalytical and Nuclear Chemistry》2018,318(3):1597-1628
Liquid scintillation counting (LSC) is a major technique not only for measurement of pure beta emitting radionuclides, but also radionuclides decay by electron capture and alpha emission. Although it is a conventional radiometric technique, but still a competitive techniques for the measurement of many radionuclides. This paper summaries the major development of this measurement technique in instrumentation, methodology and applications in the past decades. The progresses in the instrumentation and methodology mainly focus on the commercialization of triple-to-double coincidence ratio based LSC techniques and its application in the determination of different radionuclides. An overall review and discussion on the LSC based analytical methods for the determination of major radionuclides in environmental researches, decommissioning of nuclear faculties and nuclear application are presented, in both measurement techniques and sample preparation using radiochemical separation. Meanwhile the problems and challenges in the development and application of the LSC are also discussed. 相似文献
12.
13.
G. Kennedy 《Journal of Radioanalytical and Nuclear Chemistry》1995,193(2):239-245
A method has been developed for the correction of counting losses in NAA for the case of a mixture of short-lived radionuclides. It is applicable to systems with Ge detectors and Wilkinson or successive approximation ADC's and will correct losses from pulse pileup and ADC dead time up to 90%. The losses are modeled as a constant plus time-dependent terms expressed as a fourth order polynomial function of the count rates of the short-lived radionuclides. The correction factors are calculated iteratively using the peak areas of the short-lived radionuclides in the spectrum and the average losses as given by the difference between the live time and true time clocks of the MCA. To calibrate the system a measurement is performed for each short-lived nuclide. In a test where the dead time varied from 70% at the start of the measurement to 13% at the end, the measured activities were corrected with an accuracy of 1%. 相似文献
14.
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. 相似文献
15.
A method for quench correction of samples with double radioactive labelling is described. Each nuclide makes a contribution to the counting rate of three channels of a liquid scintillation counter. This channel overlap is an essential requirement of the calibration procedure rather than a limitation, and allows more freedom in the choice of counting conditions. After calibration with suitable standards the method will tolerate wide variations in the ratio of one isotope to the other extending to single label samples of either isotope. This is the outstanding advantage over the channel ratio method which requires a statistically significant counting rate for the higher energy isotope. The method takes advantage of the facilities offered by a computer which may be on line or remote.14C and tritium are used to demonstrate the utility of the method. 相似文献
16.
A Colle-Salvetti (CS)-type electron-nucleus correction in the nuclear orbital plus molecular orbital theory is proposed. The CS-type correction is designed to satisfy the cusp condition for the electron-nucleus interaction. Since the CS-type correction is expressed in terms of the electron and nucleus densities, its evaluation is computationally feasible. Numerical assessment confirms that the CS-type correction performs well for the small G2 set. 相似文献
17.
M. F. Barakat 《Journal of Radioanalytical and Nuclear Chemistry》1983,78(1):227-231
Serious errors could be introduced into experimental results due to the observed non-additive nature of the count rate data recorded by gamma scintillation counters, particularly when the samples are subjected to excessive dilution. Simple procedures for correcting the experimental results are suggested. 相似文献
18.
I. Salma L. Almási É. Zemplén-Papp 《Journal of Radioanalytical and Nuclear Chemistry》1990,140(2):263-270
A CAMAC system was installed for pulse height analysis and correction of counting losses due to the dead-time of a multichannel analyzer and the pulse pile-up. A computer program was developed to control the whole system, and to collect and store data in both conventional and cyclic measurement modes. 相似文献
19.
20.
S. Mohammad Modarresi S. Farhadd Masoudi Majid Karimi 《Journal of Radioanalytical and Nuclear Chemistry》2018,316(1):129-137
A procedure for self-attenuation and sample height correction in HPGe gamma spectrometry efficiency has been presented. An MCNP model of an HPGe detector was used to calculate the full energy peak efficiency (FEPE) for a group of different samples with different heights in Marinelli beaker geometry. A proper function has been fitted to the simulation results to obtain the correction function. The function has been used to calculate the FEPE of a spiked soil sample in different sample heights by considering the experimentally known FEPE of another standard solution source. A good agreement between the experiments and calculations have been shown. 相似文献