Parent isotope

The electrospray ionisation mass spectrometric analyses were performed using a Finnigan LCQ ion trap mass spectrometer. The samples were dissolved in methanol or chloroform methanol system (10 1 v/v) and such solutions were introduced to the ESI source by continuous infosion by means of the instrument syringe pmnp with the rate of 3 iL/min. The ESI source was operated at 4.25 kV and the capillary heater was set to 200°C. For ESI-MS" experiments mass selected mono-isotopic parent ions were isolated in the trap and collisionally activated with 33% ejection RF-amplitude at standard He pressure. The experiments were performed in the positive and negative-ion mode. 

Element Isotopes (isotopic Parent radionuclide (T1/2) Radioactive decay... 

Alloys with other useful properties can be obtained by using yttrium as an additive. The metal can be used as a deoxidizer for vanadium and other nonferrous metals. The metal has a low cross section for nuclear capture. 90Y, one of the isotopes of yttrium, exists in equilibrium with its parent 90Sr, a product of nuclear explosions. Yttrium has been considered for use as a nodulizer for producing nodular cast iron, in which the graphite forms compact nodules instead of the usual flakes. Such iron has increased ductility. 

Natural Isotopic Abundances. The relative abundances of natural isotopes produce peaks one or more mass units larger than the parent ion (Table 7.75a). For a compound C H O N, a formula allows one to calculate the percent of the heavy isotope contributions from a monoisotopic peak, Pto the Pm + 1 peak ... 

Compounds that contain chlorine, bromine, sulfur, or silicon are usually apparent from prominent peaks at masses 2, 4, 6, and so on, units larger than the nominal mass of the parent or fragment ion. Eor example, when one chlorine atom is present, the P + 2 mass peak will be about one-third the intensity of the parent peak. When one bromine atom is present, the P + 2 mass peak will be about the same intensity as the parent peak. The abundance of heavy isotopes is treated in terms of the binomial expansion (a -I- h) , where a is the relative abundance of the light isotope, b is the relative abundance of the heavy isotope, and m is the number of atoms of the particular element present in the molecule. If two bromine atoms are present, the binomial expansion is... 

The most important types of radioactive particles are alpha particles, beta particles, gamma rays, and X-rays. An alpha particle, which is symbolized as a, is equivalent to a helium nucleus, fHe. Thus, emission of an alpha particle results in a new isotope whose atomic number and atomic mass number are, respectively, 2 and 4 less than that for the unstable parent isotope. 

Most areas of research and appHcations involving the use of radioisotopes require a knowledge of what radiations come from each isotope. The particular apphcation determines what type of information is needed. If the quantity of a radionuchde in a particular sample or at a particular location is to be deterrnined and this value is to be deterrnined from the y-ray spectmm, the half-life of the nucHde and the energies and intensities or emission probabiUties of the y-rays of interest must be known. Usually it is preferable to use the y-rays for an assay measurement because the d- and P-rays ate much more readily absorbed by the source material, and may not reach the sample surface having their original energies. Once these energies are altered they caimot be used to identify the parent radionuchde. 

All of these daughter isotopes occur naturally thus it is always necessary to show that in the rocks of interest the daughter element present originated only from the decay of the parent, or the fraction of the daughter isotope that is from the decay of the parent must be separately determined. 

For example, the presence of Sr in the absence of the more abundant Sr (82.7%) would clearly indicate that its origin is from the decay of Rb. For the Pb isotopes, a more detailed set of measurements might be needed. In this case the normal Pb abundances can be altered by the presence of any or all of the indicated Th and U isotopes, so not only the abundances of the Pb isotopes, but also those of the potential parent isotopes must be determined. 

Thorium isotope concentrations and ratios, as well as parent and daughter isotope concentrations, are used to date and study the formation and metamorphosis of rocks and sediments. For example, has been used to date coral reef terraces (4). / Th disequiUbria and Th/ Th... 

Joly observed elevated "Ra activities in deep-sea sediments that he attributed to water column scavenging and removal processes. This hypothesis was later challenged with the hrst seawater °Th measurements (parent of "Ra), and these new results conhrmed that radium was instead actively migrating across the marine sediment-water interface. This seabed source stimulated much activity to use radium as a tracer for ocean circulation. Unfortunately, the utility of Ra as a deep ocean circulation tracer never came to full fruition as biological cycling has been repeatedly shown to have a strong and unpredictable effect on the vertical distribution of this isotope. 

The equation for the decay of a nucleus (parent nucleus - daughter nucleus + radiation) has exactly the same form as a unimolecular elementary reaction (Section 13.7), with an unstable nucleus taking the place of a reactant molecule. This type of decay is expected for a process that does not depend on any external factors but only on the instability of the nucleus. The rate of nuclear decay depends only on the identity of the isotope, not on its chemical form or temperature. 

Fischer projection of acyclic form, 56-57 glycosides, 132-135 C-glycosyl compounds, 139-140 N-glycosyl derivatives, 137-139 glycosyl halides, 136-137 glycosyl residues, 125 isotopic substitution and isotopic labelling, 91 me so forms, 59 optical rotation, 59 parent structure choice, 53... 

H H non-bonded interactions are of great importance in organic compoimds, and thus it was of interest to attempt to investigate H H non-bonded potential functions via the determination of a steric isotope effect in the configurational inversion of an unsubstituted biaryl. In view of the extensive work of Harris and her co-workers in the 1,1 -binaphthyl series (see, for example, Badar et al., 1965 Cooke and Harris, 1963), and since the parent compound is one of the simplest hydrocarbons that may be obtained in enantiomeric forms, the determination of the isotope effect in the inversion of l,l -binaphthyl-2,2 -d2 (9) was... 

Work on mercury alkyls has been done by Heitz and Adloff (31-33), who studied Hg(CH3)2, Hg(C2Hj)2 and HgPh2. They found no isotope effect between " Hg, Hg, and ° Hg, and no correlation with the respective conversion coefficients. They also noted that the retentions could not be satisfactorily explained by exchange of the respective ligands, and thus concluded that the molecules are reformed by an epithermal not by a thermal process. Parent yields were typically 74, 15, and 8% for the diphenyl-, dimethyl- and diethylmercury, respectively. 

By applying an extension of the clearance concept 30, 31), in vitro metabolism was used to predict in vivo toxin elimination. Hepatocytes were incubated with 0.5 to 10 pg unlabeled PbTx-3 containing 0.1 pg radiolabeled toxin as tracer. Disappearance of parent compound and the appearance of metabolites were measured by HPLC equipped with a Radiomatic isotope detector. (1.6 nmol/min/g liver)... 

The main difficulty in obtaining the vinyl radical is that the species easily loses the hydrogen atom and is converted into acetylene. Nevertheless, a very low concentration of the radical H2C=CH has been achieved (Shepherd et al., 1988) by vacuum UV photolysis of ethylene frozen in an argon matrix, and a Fourier transform IR study of this intermediate has been carried out. A variety of and deuterium-substituted ethylene parent molecules were used to form various isotopomers of vinyl radical. On the basis of its isotopic behaviour and by comparison with ab initio... 

For nuclear y-resonance absorption to occur, the y-radiation must be emitted by source nuclei of the same isotope as those to be explored in the absorber. This is usually a stable isotope. To obtain such nuclei in the desired excited meta-stable state for y-emission in the source, a long-living radioactive parent isotope is used, the decay of which passes through the Mossbauer level. Figure 3.6a shows such a transition cascade for Co, the y-source for Fe spectroscopy. The isotope has a half-life time //2 of 270 days and decays by K-capmre, yielding Fe in the 136 keV excited state ( Co nuclei capmre an electron from the K-shell which reduces the... 

Most Mossbauer experiments are currently performed with commercially available radioactive sources. For some applications, however, a so-called source experiment may be useful, in which the sample is labeled with the radioactive parent-isotope of the Mossbauer nucleus such as Co. The y-radiation of the radioactive sample is then analyzed by moving a single-line absorber for Doppler modulation in front of the detector. 

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