Beta spectrum determination

The activities of some isotopes, in particular °Sr- °Y, can also be detected by liquid-crystal spectrometry with the use of the Cherenkov phenomenon [10, 11]. The Cherenkov effect is used to determine beta isotopes emitting particles whose iiniax IS above 500 keV [12]. The main advantage of beta activity determination by the Cherenkov effect is the use of analytical preparation used for another chemical analysis (e.g. calculation of recovery). Moreover, the addition of low energy beta or alpha radiation does not disturb the measurement, thereby lowering the cost of analysis. The weakness of this method is the decreased recovery registration and the decline in information about the realistic appearance of the beta spectrum [13]. The determination of beta isotopes in environmental samples is very difficult and requires their chemical isolation. The type of sample and the time of chemical analysis determine the choice of analytical method. Also, the time between contamination and sample collection is important procedures used for samples recently contaminated are different to those used for old samples in which the decay of short-lived radionuclides has aheady taken place [1, 5]. 

Pure beta-emitting isotopes exist and may be used for calibration, but only after the energy spectrum is cast into a form called the Kurie plot. The beta spectrum is continuous and extends from zero energy up to a maximum end point kinetic energy (see Fig. 13.12). Because of the shape of the spectrum, it is impossible to accurately determine the end point energy. However, from the... 

Phosphorous. The presence of trace amounts of phosphorus in metals and semiconductors is known to affect material properties. The produced in the (n,y) reaction is a pure emitter and has to be separated and rigorously purified. Paul (1998,2000) developed a method for P determination in steels and other high-temperature refractory alloys of interest to the aircraft industry. Irradiated samples were dissolved passed through cation-exchange columns to remove Co, Ni, and Cr followed by repeated precipitations of magnesium ammonium phosphate and ammonium phosphomolybdate. One of the major advantages of this technique is the determination of the chemical yield by gravimetry. Phosphorus was determined by INAA in matrices other than metals, e.g., polymers. In this case, the beta spectrum was corrected for interferences and self-absorption (St-Pierre and Kennedy 1998). A modified version of this procedure has been used to certify implanted phosphorus in silicon (Paul et al. 2003). 

In the last decade, neutrino experiments have demonstrated that neutrinos are massive particles which may oscillate among three autostates. Such experiments [77-82] have evidenced the mass difference between the autostates, but not the neutrino mass scale value. The only way to determine the neutrino mass is the knowledge of the shape of the end point of energy spectrum in beta decays. In the hypothesis of the Majorana neutrino (neutrino coincides with antineutrino and its rest mass is different from zero), the measure of the decay half-life in the neutrinoless double-beta decay (DBD) would be necessary. A number of recent theoretical interpretations of neutrino oscillation experiments data imply that the effective Majorana mass of the electron neutrino (as measured in neutrinoless DBD) could be in the range 0.01 eV to the present bounds. 

Applications. The —y coincidence method can be used to determine trace amounts of a -emitting isotope in the presence of large quantities of a y emitter with no coincident beta. The application of this technique is illustrated by the spectrum of a separated cesium sample... 

Combined SAXS/Circular dichroism beamline. Biological macromolecules, such as proteins, carbohydrates and nucleic acids, are composed of many optically active or chiral units that exhibit large Circular Dichroism (CD) signals. CD spectroscopy has therefore been used extensively in the study of proteins, where asymmetric carbon atoms in their amino acid backbone give rise to a CD spectrum. The shape of the spectrum depends on the protein s secondary structure content and allows the proportions of helix, beta structure, turns and random to be determined. 

It has been assumed that the chemical procedure used to isolate the element after the addition of carrier has been successful, and the final product is free from all extraneous activity. Frequently the reliability of this assumption can be verified without a great deal of difficulty, by the application of some or all of the following checks (1) determination of the half-life (2) determination of the maximum beta energy (3) examination of the gamma spectrum. 

Poly(ethylene 2,6-naphthalate) (PEN) film containing alpha, beta and amorphous phases were prepared, and the amorphous contribution digitally subtracted to yield the characteristic spectra of the amorphous, alpha, and beta phases. In other words, the amorphous spectrum is determined by melting the polymer, so after subtraction, one knows the spectrum of all of them. The alpha crystal form adopts an all-rran conformation, while the beta crystal form adopts a conformation with appreciable gauche character. Conformational changes in PEN occur due to the rotation of the naphthalene ring as well as rotation of the ethylene glycol units. The normalised absorbances of the bands at 824 and 814 cm were correlated to polymer density, and can be used to represent the amorphous and alpha crystalline phases, respectively (56). 

The nature of the oxidized side chain can be determined from the NMR spectrum, which displays an ABX-spin system and two singlets for geminal methyl groups next to a carbon-oxygen bond (45). All signals for the 3-methylbutanoyl side chain are present, but no absorptions for a 3-methyl-2-butenyl side chain are found. It follows that this chain has been cleaved oxidatively. A similar mechanism is operative in the formation of the most important oxidation product of the hop beta acids, hulupone (56, Fig. 28) (see 13.1.1.1.2.). The reaction proceeds with ring contraction... 

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