The influence of the statistical error in measuring radioactive samples in direct isotope dilution analysis is analytically
studied for several practically important sets of conditions. Formulas are given to calculate the optimum amount of radioactive
substance to be added in order to minimize the error involved. Both cases with negligible background count rates and cases
where the background must be considered are treated. In some cases recommendations are given for the times of measurement
of background, undiluted and diluted sample.
In radiotracer measurements of the flow rate of marine surface sands, the chief difficulty is to determine the average thickness of the radiotracer spot. The simultaneous use of two detectors may appreciably reduce the uncertainty in the final result.
A variant of the instrumental neutron activation analysis, most frequently used for simultaneous measurement of Sc, Co, Rb,
Cs, Ta, La, Eu, Ba, Sr, Hf, Zr, Th and U was investigated from the point of view of the accuracy. The importance of error
introduced at each stage of the analytical procedure was studied.
An automated, highly reproducible fast-transfer system (0.36±0.01 sec) has been developed, an oscillator/multichannel-scaling
system has been developed to follow rapidly-changing spectrometer dead-times, the mathematics has been developed, and the
data processing steps have been computerized. Three induced activities have been studied in some detail:207mPb (0.80 sec),38mCl (0.70 sec) and20F (11.03 sec). Both steady-state and high-intensity pulsed reactor irradiations, with and without a Cd liner, have been used.
The dead-time correction method has been carefully checked, and the overall method has been tested by the analysis of two
NBS Standard Reference Materials: orchard leaves (for Cl and Pb) and bovine liver (for Cl).
The method of multiple γ-ray peak ratio determination has been applied to the nondestructive neutron activation analysis of
uranium in rocks and ores. The photopeaks of239Np gamma-rays produced by the activation of238U and those of the fission products of235U are a measure of the quantity of uranium in the irradiated sample, provided that the uranium is of natural isotopic composition.
The ratios between the integrated areas of the different photopeaks are calculated and compared with those obtained for a
uranium standard. The uranium concentration in the sample is calculated from the photopeaks whose ratios correspond, within
the error limits to those of pure natural uranium. High accuracy better than ±2% has been obtained.
The novel method of thermoluminescence (TL) dating of megalithic (cyclopean) limestone monuments and/or marble statues will be briefly reviewed. The problems and recent examples to be discussed include: (a) the determination of the accumulated archaeological dose, Dar, (b) the sample homogeneity, (c) the scattering in TL measurements, (d) the rate in solar bleaching of TL, and (e) dose-plateau inconsistencies. In retrospect, the solar bleaching of TL in some marbles refers to at least 30 mm depth, the scattering of TL measurements at best varies around ±10%, and the partial bleaching technique should be prudently applied for Dar determination. The extension of this method to date (by TL or OSL) for other rock types is discussed.
Structure sensitive thermal analysis results on linear macromolecules can be obtained when correcting measurements with heat capacity instead of “baseline” data. The ATHAS (Advanced Thermal Analysis) effort in heat capacities of crystals, glasses and liquids is described, and applied to the interpretation of microphase separated samples. Semicrystalline homopolymers, block-copolymers, and blends are to be discussed.
Three types of direct isotope dilution analysis (IDA) are mathematically treated: substoichiometric dilution analysis, the
determination of sorbent capacity, and direct IDA with a constant amount of substance lost in the separation step. Tables
and graphs are given for an easy determination of the amount of radioisotopeW0 to be added and for the estimated error involved.