Determination of oxygen and silicon in rocks by 14-MeV neutron-activation analysis and its precision

Oxygen and silicon have been determined in the six new U.S. Geological Survey standard rocks and two standard refractory materials by 14-MeV neutron-activation analysis, followed by both single and multichannel analyser counting of the induced (16)N (4.5-8 MeV gamma radiation) and (28)Al activities (1.78 MeV photopeak). Owing to the long analysing time per pulse, dead-time corrections are necessary in multichannel analyser counting. Four methods were investigated in this work: counting in the live-time mode without additional correction, short counting corrected by an external live-time scaler, the method of Bartoseck, and the method of Schonfeld. Each measurement was controlled by a simultaneous measurement with a single-channel analyser. Silica ignited at 1000 degrees was used as a reference. Correction was made for the interfering elements, F, P, Al, Fe and Mg, using literature data. Attention was paid to neutron, gamma and beta attenuation. For oxygen the mean coefficient of variation for a single determination with a single-channel analyser was 1.7 % for silicon 1.1 %. The mean results for single-channel counting were compared with literature values.     

Corrections of counting losses in gamma-spectrometry of short-lived radionuclides

A short-lived radionuclide is characterized essentially by the decrease of its activity even while it is counted. The relations used between the number of counts recorded in a given time and the half-life in order to obtain the true counting rate are reviewed. Moreover, in gamma-spectrometry with multichannel analysers having variable dead-time, counting losses are observed. Exact corrections are calculated for pure short-lived radionuclides and for mixtures of one short-lived and one or more long-lived radionuclides. Based on these calculations, the approximations given by the built-in “live-timer” device of the analysers and by a new “actual-time” concept (with external live-time measurement) are evaluated. Curves are drawn as functions of the ratio counting time vs. half-life, to ensure minimal errors of less then 1%.     

Instrumental correction of time dependent counting losses in high rate gamma-ray spectrometry

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.     

Simple methods for dead-time and pile-up corrections in analytical gamma-ray spectrometry

In the paper the mathematical methods for dead-time and pile-up corrections are discussed. The dead-time correction formulae for a system of two short-lived isotopes and constant component (background) are reported which mathematical problem has not been solved so far. The new electronic circuit for simultaneous measurements of clock- and live- (or dead-) times is described. It is shown that using this circuit one can correct the counting loss for both effects simultaneously. Finally, the advantages and disadvantages of mathematical methods for dead-time and pile-up corrections are discussed based on the authors' several-year laboratory practice.     

Coincidence losses in activation analysis

Coincidence losses may introduce a considerable error in γ-ray spectrometry and are thus a serious potential source of inaccurate activation analysis. A simple first order correction for coincidence losses can be applied by measuring the counting interval in both the true-time and in the live-time modes; the proposed equation is shown by two experiments to hold up to an integral count rate of at least 4·10⁴ cps.     

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%.     

A portable, photon analysis spectrometer for the assay of X- and gamma-ray emitting radionuclides

A portable, battery-powered, multichannel analyzer (MCA) for use with Ge spectrometers has been developed for in-field use for the assay of x-and γ-ray emitting radionuclides. The spectrometer is capable of operating to rates greater than 150,000 counts per second. The analyzer is a Canberra InSpector MCA, that is equipped with the INEEL ultra-stable dual-energy pulser, and pulse injection with subsequent removal (PISR) circuitry. PCGAP, a set of MCA control and spectral analysis programs, was developed for use on a PC with a Windows NT Operating System. It includes an interactive peak analysis program as well as automatic spectral analysis programs for the X- and γ-ray regions, and a number of utility programs. The pulser peaks are calibrated with radioactive sources in terms of energy (i.e., their energy equivalents are measured) using the PCGAP spectral analysis package so that energy shifts, including those due to changes in temperature or count rate, do not cause a loss of energy calibration. The number of injected low- and high-energy-equivalent pulses is known so the stored pulser pulses can be used for a dead-time and random summing correction. The pulser peaks are also used to monitor any deterioration in spectral quality caused by noise, ground loops, etc. The results of performance tests to demonstrate the capabilities of this pulser-equipped InSpector are reported.     

Determination of Al,Ca, V and Mn by INAA: Application to the Reference Material IAEA-395 “Urban Dust”

Instrumental NAA based on short-lived radionuclides implies high initial total count rates which change appreciably over the counting period. This in turn necessitates corrections for three negative biases: losses due to differences in counting time between samples and standards; pile-up losses, and (residual) influence of dead-time. The procedure is demonstrated for the determination of Al, Ca, V and Mn in the IAEA Reference Material 395 Urban Dust. The obtained data are in good agreement with the reference values for this material. By limiting the total relative dead-time to 25%, statistical uncertainties are below 5%.     

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%.     

A correction for dead-time losses in γ-ray spectrometry for a mixture of short-lived radionuclides

A simple procedure for the correction of residual dead-time losses in γ-ray spectrometry of mixtures of short-lived radionuclides is given. It is based on the value of the total deadtime at the beginning of the measurement and three constants which are characteristics for a given matrix. The application to the instrumental neutron activation analysis of fluorine and sodium in bone is given as an exaple.     

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.     

Dead-time correction of counting losses in the γ-spectrometry of short-lived nuclides

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.     

Correction of counting losses of the preloaded fil ter pulse processor

By adapting noise filtering to individual pulse intervals, the Preloaded Filter (PLF) pulse processor (1) combines high resolution with optimum throughput efficiency. As a consequence, its output pulse interval distribution contains strong non-random components which render conventional ADC dead-time correction an impossibility. Quantitative correction of dead-time and pileup losses of the PLF processor may be achieved, however, with the Virtual Pulse Generator (2), together with a new, distribution-independent method of measuring ADC losses which is based on a pulse counting technique.     

A new evaporation procedure for monitoring of iodine-125 in liquid waste

A simplified monitoring method of 125I in liquid waste was devised. The waste water of 200 cm3 was taken on a Saran (polyvinylidene chloride) film covering a stainless steel vat. A stable iodine (20 mg) and sodium hydroxide (1 mmol) was added. The water was evaporated using an infra-red lamp. After heating to dryness, the Saran film was folded and transferred into a polyethylene tube. The radioactivity of 125I was counted with a well type NaI(Tl) scintillation counter. When a multi-channel analyzer was available for counting, an absolute decay rate of 125I was calculated with single and sum photo-peak counts. The radioactivity of 125I counted by a single-channel counter must be corrected with the counting efficiency of about 55%, with a special emphasis of a self absorption of photons. The recovery of 125I for concentrations below the permissible level was more than 98%.     

Routine multielement instrumental neutron activation analysis of silicate rocks using short-lived radionuclides

By means of thermal neutron activation and countings on the small planar and large coaxial Ge(Li) detector, 13 elements are determined in various silicate rocks, using short-lived radionuclides with half-lives from 2 min to 15 h. A method of routine analysis with simple dead-time and pile-up correction is described and tested with the standard rocks AGV-1 and G-2.     

An alternative approach to the corrections of deat-time losses

A new approach to the problem of the dead-time of pulse detection systems is proposed. The presented method of the correction for counting losses is based on the evaluation of the shortest time interval between two successive output pulses.     

Preparation of Multitracer Nuclides from 232Th(NO3)4 Irradiated by 40Ar Ion Beam

Nuclear counting statistics at high count rate are assessed on a -ray spectrometer set-up with a Wilkinson analog to digital convertor. The validity of recent theoretical formulas for the standard deviation, before and after pulse-loss compensation, is checked. The experimental counting uncertainty is well reproduced by theory. Without pulse-loss compensation (cf. real-time mode), it is dependent on the size and position of the considered region of interest in the spectrum. With pulse-loss compensation (cf. live-time correction) the relative deviation from Poisson statistics is equal for all regions of interest in the spectrum.     

一种消除在线多通道近红外分析仪各通道光谱差异的方法

针对在线多通道近红外分析仪因光纤耦合器件加工精度和装配过程存在细微差异而引起通道间光谱不一致的问题,在对光谱差异进行解析的基础上,提出了一种运算简捷、且在实际应用中易于实现的平均光谱差值校正(MSSC)方法,并与常用的模型传递算法如斜率／偏差(S／B)算法、分段直接校正(PDS)算法,以及通过偏最小二乘-人工神经网络(PLS-ANN)建立多通道混合校正模型进行了对比。结果表明,该方法可有效消除各通道所测光谱之间存在的差异,实现了多通道分析模型的通用性。     

Comparison of NAA and ICP-MS for the determination of major and trace elements in environmental sample

Summary Major and trace elements in soil and plant samples, including standard reference materials were determined by means of neutron activation analysis (NAA) and inductively coupled plasma-mass spectrometry (ICP-MS). The analytical procedure for NAA utilized dried powder samples. The concentration of iodine in soil samples was determined by radiochemical NAA. The irradiated samples were cooled and then counted with a Ge gamma-ray detector connected to a multi-channel analyzer. For ICP-MS analysis, the samples were decomposed by microwave digestion with an acid mixture. The concentration of I in the soil samples was measured by ICP-MS after separation by ignition. The analytical values for most elements in the environmental samples by both methods were in good agreement, whereas sample treatments were different. Measured value of Zr in the soil samples by ICP-MS was about 50% lower than that by NAA. It should be assumed that some minerals of Zr in soil particles were not entirely dissolved by the acid mixture. Analytical results of Cd for three different Cd levels in unpolished rice flour samples (NIES 10-a, b and c) determined by ICP-MS were in agreement with certified values. The concentration of Cd in the sample with the lowest Cd level, as determined by NAA with 57% counting error, was 3 times higher than the certified value.     

High-precision energy-dispersive x-ray fluorescence analysis of manganese in ferromanganese

A high-precision x-ray fluorescence method for the determination of manganese in ferromanganese is described. The method involves excitation of the sample with a ¹⁰⁹Cd isotopic source and measurement with a high-resolution Si(Li) detector. To preserve the optimal energy resolution even at high count rates, the system incorporates a pulsed optical feedback preamplifier and a pulse pile-up rejector. The rejected pulses are corrected for by means of an adequate live-time correction circuit. Processing of the spectra is accomplished with the aid of a digital computer. The relative precision of the method is approximately 0.2%.