Conversion electron sources

Conversion electron sources In increasing order of electron energy. 

Resonant y-ray absorption is directly connected with nuclear resonance fluorescence. This is the re-emission of a (second) y-ray from the excited state of the absorber nucleus after resonance absorption. The transition back to the ground state occurs with the same mean lifetime t by the emission of a y-ray in an arbitrary direction, or by energy transfer from the nucleus to the K-shell via internal conversion and the ejection of conversion electrons (see footnote 1). Nuclear resonance fluorescence was the basis for the experiments that finally led to R. L. Mossbauer s discovery of nuclear y-resonance in ir ([1-3] in Chap. 1) and is the basis of Mossbauer experiments with synchrotron radiation which can be used instead of y-radiation from classical sources (see Chap. 9). 

Fig. 7.67 Conversion electron Mossbauer spectra of the 73 keV y-rays in Ir recored at 4.2 K using a metal source, (a, b) metallic iridium, 5 mg cm, (c, d) iridium dioxide, 5 and 1 mg cm , respectively. Measuring time about 10 h for spectra a-c and 20 h for spectrum d (from [308])...

A pen register is a mechanical device that records the numbers dialed on a telephone by monitoring the electrical impulses caused when the dial on the telephone is released. It does not overhear oral communications and does not indicate whether calls are actually completed. They can be used to record the telephone number dialed by the subject of the surveillance. Trap and trace devices, are used to record the telephone numbers of incoming calls received by the subject [114]. They are also used to capture source and address information for computer conversations (electronic mail) [115]. 

For a fuel, an electron source is needed. Water is the ultimate electron source from an economical point of view. Water photolysis is the simplest among the chemical conversion systems of solar energy. Photochemical reduction of nitrogen or carbon dioxide to produce ammonia or hydrocarbons with the electrons from water is also an attractive system of conversion. 

Polymers are attracting much attention as functional materials to construct photochemical solar energy conversion systems. Polymers and molecular assemblies are of great value for a conversion system to realize the necessary one-directional electron flow. Colloids of polymer supported metal and polynuclear metal complex are especially effective as catalysts for water photolysis. Fixation and reduction of N2 or C02 are also attractive in solar energy utilization, although they were not described in this article. If the reduction products such as alcohols, hydrocarbons, and ammonia are to be used as fuels, water should be the electron source for the economical reduction. This is why water photolysis has to be studied first. 

Most often the transmission mode is found to be the most convenient in Mossbauer spectroscopy, i.e., the y radiation passes from the source through the absorber, and the attenuation of the primary beam is measured at the various Doppler velocities. However, there are a number of cases where a "scattering geometry may be advantageous (SO). The basis for this geometry lies in those processes that take place after resonant absorption of y radiation by the Mossbauer isotope. Specifically, after excitation the Mossbauer isotope may reemit the y ray, or it may decay by emission of internal conversion electrons and X rays [with the probability of internal conversion equal to a/(l + a)]. 

Indirect activation of the C-0 bond of the aryl alcohol is further developed by conversion to corresponding triflate. The C-0 bond in the aryl triflate has been achieved in the homocoupling reaction catalyzed by a palladium(O) or nickel(O) complex in the presence of an electron source (either a cathode or zinc power) (Eq.47) [110]. 

Figure 3.19 Configurations for QD solar cells, (a) A QD array used as the i region of a p-i-n junetion cell configuration (b) QDs used to sensitise a nanoerystalline film of TiOa to visible light. This configuration is analogous to the dye-sensitised solar eell with the dye replaced by QDs (e) QDs dispersed in a blend of electron- and hole-conducting polymers. In these configurations the oceurrenee of MEG could produce higher photocurrents and higher conversion effieieney. Source Nozik (2002).

Reduced ferredoxin reacts with proteins that participate in the dissimilatory reduction of sulfate to sulfide oxidized ferredoxin reacts with pyruvate dehydrogenase that catalyzes the conversion of pyruvate to acetyl CoA (phosphoroclastic reaction). In sulfate reduction, molecular hydrogen is the electron source, and in the phosphoroclastic reaction, protons are the terminal electron acceptor and hydrogenase mediates electron transfer between cytochrome c3 and protons or molecular hydrogen. 

Although the conventional experimental technique uses a transmission g ibmetry and a scintillation or proportional counter, spectra have also been recorded using counting of the internal conversion electrons in a doublelens /S-spectrometer [21] the source and absorber matrices were j8-tin. 

Therefore, a nucleus that undergoes internal conversion is a source of groups of monoenergetic electrons with energies given by Eqs. 3.37. A typical internal conversion electron spectrum is shown in Fig. 3.6. The two peaks correspond to K and L electrons. The diagram on the right (Fig. 3.6) shows the transition... 

The energy calibration of any spectrometer requires the use of sources of known energy and preferably of monoenergetic sources. Monoenergetic electron sources are provided by accelerators and by radioisotopes emitting internal-conversion (IC) electrons (see Chap. 3). 

A thin solid-state detector with spectrometer is also useful for identifying and quantifying conversion electrons. Figure 9.2 shows the spectrum of conversion electrons from a thin source of For radionuclides that also emit beta par-... 

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