The assessment of the statistical counting uncertainty is discussed for two pulse loss correction methods in nuclear spectrometry: the 'loss-free counting' technique based on the virtual pulse generator method and the 'zero dead time' technique with 'variance spectrum'.
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.
The boundary conditions in which Poisson statistics can be applied in nuclear spectrometry are investigated. Improved formulas for the uncertainty of nuclear counting with deadtime and pulse pileup are presented. A comparison is made between the expected statistical uncertainty for loss-free counting, fixed live-time and fixed real-time measurements.
A spreadsheet application is developed for the prediction and optimization of the analytical performance of instrumental neutron activation analysis for matrices of more or less known composition. It assists in feasibility testing, sensivitity enhancement and cost reduction.
Some modifications are presented to Sima’s simple analytical model for the calculation of the total detection efficiency of
a well-type γ-ray detector, aiming at improving its accuracy and broadening its applicability. The modifications pertain to
some general improvements in the photon transmission probabilities through absorbing materials and implementation of specific
equations for solid angle and mean path length through materials that describe the case of eccentrically positioned sources
as well as volume sources. In particular, some improvement is achieved by implementing a contribution from elastic scattering
The concepts of the Guide to the expression of Uncertainties in Measurements for chemical measurements (GUM) and the recommendations of the Eurachem document "Quantifying Uncertainty in Analytical Methods" are applied to set up the uncertainty budget for k0-NAA. The "universally applicable spreadsheet technique", described by Kragten, is applied to the k0-NAA basic equations for the computation of uncertainties. The variance components — individual standard uncertainties — highlight the contribution and the importance of the different parameters to be taken into account.
The apparent tendency to underestimate the uncertainty of experimentally determined half-life values of radionuclides is discussed.
It is argued that the uncertainty derived from a least-squares analysis of a decay curve is prone to error. As it is quite
common for a series of activity measurement results to be autocorrelated, the prerequisite of randomness of data for common
statistical tests to apply is not fulfilled. In this work, an alternative data analysis method is applied that leads to a
more realistic uncertainty budget. The uncertainty components are being subdivided in three categories according to the relative
frequency at which they occur, an appropriate uncertainty propagation formula applied and then the total uncertainty obtained
from an independent sum. An attempt is made to apply the protocol to problematic cases in literature, yet it is clear that
the reporting is usually incomplete for a full uncertainty analysis. Suggestions are made for a concise but more complete
reporting style, for the sake of traceability.
High-resolution alpha-particle spectrometry was performed on three uranium materials enriched in 235U. Besides the 235U peaks, separate peaks belonging to impurity traces of 234U could be quantified. Relying on the isotopic composition of the uranium, as determined by mass spectrometry, the ratio of
the half-lives of 238U and 235U was determined via the activity ratio of 234U and 235U in the materials. As an intermediate link, the 234U/238U half-life ratio was taken from published mass spectrometric analyses of ‘secular equilibrium’ uranium material. The resulting
half-life ratio T1/2(238U)/T1/2(235U) = 6.351±0.031 is in agreement with the commonly adopted half-life values determined by Jaffey et al.
The k0 and Q0 values for 94Zr(n,)95Zr(E = 724.2+756.7 keV) and 96Zr(n,)97Zr(
–) 97mNb (E = 743.4 keV) were re-investigated. The aim was to further improve the reliability of the neutron spectrum characterization (f and monitoring) in k0-NAA, based on "bare monitor" methods with the use of these Zr radionuclides. So as to achieve this goal, experimental determinations were performed in three reactor centers: KFKI AEKI, Budapest (WWR-M reactor); INW, Gent (THETIS reactor); SCK·CEN, Mol (BR1 reactor). The results were: Q0(94Zr) = 5.306; Q0(96Zr) = 251.6; k0(95Zr, 724.2+756.7 keV) = 2.000E-4; k0(97Zr/97mNb, 743.4 keV) = 1.237E-5. This means that the newly evaluated k0-values are about 4.7% lower than the formerly reported ones. It is also emphasized that the 97Zr half-life is 16.74 hours, contrary to the 1% higher values usually reported.
A simple and accurate method is presented to evaluate the burnup effects involved in the neutron activation of 197Au prior to any neutron flux characterisation, based on the spectrometry of the 198Au and 199Au decay gammas. The obtained burnup factor can be used as input for reactor neutron field characterisation techniques using 197Au(n,)198Au as a monitor. This way an iterative procedure is avoided.