Emission peak position on the apparent energy scale is a function of the number of photons created in the radioactive decay process. The sample, which is the detector in liquid scintillation (LS) spectroscopy, may contain quenching substances. These inhibit creation of photons and, consequently, radionuclide emission peak shifts towards lower channels. Identification of the radionuclide by its peak position is therefore not straightforward under variable quench in LS spectroscopy. The end point of the Compton spectrum (or external standard quench parameter SQP(E)) gives a direct measure of the sample quench. It is normally used in LS spectroscopy for the measurement of counting efficiency. Because SQP(E) does not depend on the sample emission energy, it can be used in verification of the peak energy together with the peak position. Two known energy calibration lines are required as a function of quench to verify the peak energy.
Authors:R. S. Addleman, M. J. O’Hara, J. W. Grate, and O. B. Egorov
Direct alpha-energy spectroscopy in liquids is possible by placing a chemically selective polymer thin film upon the surface of passivated silicon diodes. By utilizing polymer thin films with high affinity for actinides, we have been able to selectively concentrate actinides of interest upon the diode surface, resulting in a substantial increase in sensitivity relative to a direct measurement. With this film coated diodes, we were able to obtain in-situ alpha spectra with energy resolution comparable to that of conventional alpha-spectroscopy. The response of the thin film coated diode was found to be linear over 104. The sensitivity and reversibility is a function of the membrane complexation chemistry.
Based on a functional description of the standard Ge(Li) spectrometer some of its shortcomings at high counting rates are
discussed and, as a possible solution to the problem, an outline is given of an experimental high rate gamma spectroscopy
with real time compensation of counting losses.
Authors:György Kátay, Maricella Adrian-Romero, Zsolt Németh, Gerald Blunden, Ernő Tyihák, and Levente Albert
Optimum-performance laminar chromatography (previously known as overpressured-layer chromatography; OPLC) exploits the advantages of the optimum laminar flow of mobile phase obtained by use of pump to introduce the mobile phase to the adsorbent layer in an automated, microprocessor-controlled separation system. The optimized flow profile in OPLC is the basis of the efficiency of this new technique. The attractiveness of OPLC is particularly apparent from the width of the separation surface (large number of samples). OPLC has enabled improvement of the velocity profile with a decrease in eddy diffusion.OPLC can be used for efficient separation of formaldehyde (HCHO) and some betaines, potential HCHO generators, in macroscopic fungi. Endogenous HCHO is determined, after conversion to formaldemethone, and characterized from proton magnetic resonance spectroscopic (
H NMR) and electron-impact mass spectrometric (EIMS) data. The results show that macroscopic fungi contain moderate levels of HCHO compared with, for example, the leaves of certain higher plant species. Among the betaines, l-carnitine and glycinebetaine were identified by matrix-assisted laser-desorption ionization mass spectrometry (MALDI MS),
H NMR spectroscopy, and OPLC. Data prove that automated OPLC, a new separation technique, is suitable for efficient separation of natural substances from a large number of samples in one separation; it is, therefore, a prospective complementary methodological direction among separation techniques.
The review discusses various analytical chemical applications of the Mössbauer effect. The labelled atoms used are Mössbauer
isotopes and the measured parameters for analysis are those of the Mössbauer spectra. High efficiency of the technique is
demonstrated by examples in studies of the structure of compounds, polyfunctional with respect to the Mössbauer element, and
of the mecahnism of chemical reactions, first of all, low-temperature solid phase reactions. The application of the emission
Mössbauer spectroscopy is also discussed for analytical purposes.
Authors:E. Evans, D. Warrell, J. Elvidge, and J. Jones
The development of tritium nuclear magnetic resonance spectroscopy now makes it possible to determine the tritium distribution
in virtually any organic compound at the millicurie level of radioactivity. Results of catalytic experiments show that in
some cases a remarkable degree of specificity can be achieved when using procedures that are expected to produce generally
labelled compounds. Conversely there are instances where specific labelling procedures are less than 100% successful.
Fe/OOCH/2.2HCOOH obtained by solvolytic reaction of FeCl2.4H2O in formic acid was studied by Mössbauer spectroscopy. It displays two quadrupole doublets. Upon air contact it easily transforms to a high-spin octahedral iron/III/ complex, whereas Fe/OOCH/2.2H2O undergoes a very slow oxidation. The formate complex coordinated with pyridine could not be prepared, instead we obtained the anhydrous phase Fe/OOCH/2.