Single-pass transmission

Carburization of rhenium filaments has been used to optimize Th and Pa ionization efficiency for TIMS analysis on single filaments (Esat 1995). ReC has a greater work function than Re metal, and elemental oxidation state is maintained in the reduced or metal state by the presence of carbon in the filament. Using this method and a mass spectrometer with improved ion optics, Esat (1995) was able to improve Th transmission and ionization efficiency by about a factor of 30 over conventional methods. Using more conventional mass spectrometry, Murrell et al. (personal communication) were able to improve ionization efficiency for Pa and Th by a factor of 5-10 over conventional graphite sandwich loads on Re filaments (Goldstein et al. 1989 Pickett et al. 1994). For Pa analysis, one drawback is that Pa and U ionization commonly overlap using this... 

Fig. 2.27. Total collision probability and fractions of single, double, triple and quadruple collisions versus collision gas pressure. The transmission of the main beam /(is given on the right ordinate. Values are for an ion of collision cross section 5 x 10 cm and 1 cm collision path 10 Torr= 1.33 Pa. Reproduced from Ref. [9] with permission. John Wiley Sons, 1985.

Ladas et al. measured the rate of CO oxidation by Oj on a variety of Al203-supporicd Pd catalysts at 445 K. CO pressure equal to 1.2 X 10 " Pa. and PqJPco equal to 1.1 [S. Ladas, H. Poppa, and M. Boudart, Sutf. Sci., 102 (1981) 151]. The alumina was a flat single crystal onto which Pd particles were deposited by a metal evaporation method. The resulting Pd particle si/c was measured directly by transmission electron microscopy. 

Table I. Single crystal PAS, PACD and transmission measurements of NalK COAc). ...

The interaction of MNPs with DNA is a well-known phenomenon [86-89], and single- or double-strand DNA is decorated by MNPs, which can easily be imaged by transmission electron microscopy (TEM) or AFM [90-92]. Various surface-functionalized AuNPs have been prepared to attach AuNPs securely to DNA molecules. In numerous studies, such AuNPs were prepared by surface modifications with cationic thiols [54, 55, 92] or intercalators [93, 94]. The ID chains of AuNPs coated with cationic trimethyl(mercaptoundecyl) ammonium monolayers were electrostatically assembled along DNA molecules in solution by the relative molar quantities of AuNPs and DNA base pairs. Since psoralen acts as a specific intercalator for A-T base pairs, the functionalized AuNPs were assembled onto the pA-pT ds-DNA [93]. Furthermore, UV irradiations induced the reaction between the psoralen units and the thymine of DNA, and then covalently fixed AuNPs to the DNA. 

Here Tyi (ryii) represents the y-decay width in the first (second) minimum. Di describes the level distance between class-I states and p stands for the excitation energy of the P-vibrational state. The widths Ta and Fb caused by the tunneling of a state through the inner and outer fission barrier, respectively, can be determined using the transmission probabilities Pa,b through a single barrier with height a and E, respectively, calculated by Hill and Wheeler (1953) ... 

In the same way that variations in somce intensity, beamsplitter efficiency, and detector response are compensated in transmission spectrometry by ratioing the single-beam spectra measured with and without the sample in the beam, in PA spectrometry the single-beam spectrum of the sample is ratioed against the spectrum of an optically opaque and thermally thick reference. As noted above, carbon black and heavily carbon-filled polymers make excellent reference materials for PA spectrometry. 

McClelland et al. [3] have shown that PA spectra of polymers may be identified by comparing them to library spectra measured by transmission even when a modest amount of saturation has occurred. They recommend that after the ratio of the single-beam PA spectrum of a sample to a carbon-black reference has been calculated, the spectrum should be scaled so that its maximum value corresponds to 90%... 

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