Lifetime experiments

Lifetime measurements have elements in eommon with both eounting and time-of-flight experiments [4, 5]. In a lifetime experiment there is an initiating event that produees the system tliat subsequently deeays witli the emission of radiation, partieles or both. Deeay is statistieal in eharaeter taking as an example luielear deeay. 

Four parameters often used to determine a fireball s thermal-radiation hazard are the mass of fuel involved and the fireball s diameter, duration, and thermal-emissive power. Radiation hazards can then be calculated from empirical relations. For detailed calculations, additional information is required, including a knowledge of the change in the fireball s diameter with time, its vertical rise, and variations in the fireball s emissive power over its lifetime. Experiments have been performed, mostly on a small scale, to investigate these parameters. The relationships obtained for each of these parameters through experimental investigation are presented in later sections of this chapter. 

The investigation of the stability of P -alumina in ZEBRA cells, which always contain some iron, showed an increase of resistance under certain extreme conditions of temperature (370 °C) and of voltage. This is related to the interaction of the P alumina with iron and it was shown that iron enters / -alumina in the presence of an electric field when current is passing, if the cell is deliberately overheated. However, it was found that only the P -phase but not the P"-phase was modified by the incursion of iron. The resistance of the iron-doped regions was high. It was shown that the addition of NaF inhibits access of the iron to the / " -alumina ceramic. By doping practical cells these difficulties have now been overcome and lifetime experiments show that the stability of / "-alumina electrolytes are excellent in ZEBRA cells. 

Solid-surface fluorescence and phosphorescence quantum yield values were obtained from +23° to -180°C for the anion of p-aminobenzoic acid adsorbed on sodium acetate (11). Fhosphorescence lifetime values were also obtained for the adsorbed anion from +23° to -196°C. Table 1 gives the fluorescence and phosphorescence quantum yield values acquired. The fluorescence quantum yield values remained practically constant as a function of temperature. However, the phosphorescence quantum yield values changed substantially with temperature. The phosphorescence lifetime experiments indicated two decaying components. Each component showed a gradual increase in phosphorescence lifetime with cooler temperatures, but then the increase appeared to level off at the coldest temperatures. 

When o-, m- and p-nitroanisole with 14C-labelled at the methoxy group were irradiated under identical conditions in methanol in the presence of sodium methoxide, only m-nitroanisole underwent methoxy exchange, with the limiting quantum yield (

labelled isotope experiments support a a complex intermediate and indicate an Sjv23Ar mechanism (direct substitution in the triplet state) for this reaction (equation 12) and for 4-nitroveratroles (equation 13). Further evidence from quenching and lifetime experiments also support a direct displacement SAr2Ar mechanism for the photosubstitution reaction of nitroaryl ethers with hydroxide ions13. 

Simmonds PG, Alyea FN, Cardelino CA, et al. 1983. The atmospheric lifetime experiment. 6. Results for carbon tetrachloride based on 3 years data. J Geophys Res 88 8427-8441. 

A Room-Temperature Emission Lifetime Experiment for the Physical Chemistry Laboratory 186... 

We now briefly review experimental evidence for the existence of some simple positronium compounds more detailed accounts have been given for early lifetime experiments by Goldanskii (1968) and for the liquid phase by Mogensen (1995). In the case of PsCl we shall see how traditional positron experiments using lifetime and ACAR techniques have provided strong evidence for the stability of this compound, in accord with theory. The first direct experimental evidence of the existence of PsH came from a positron-beam experiment (Schrader et al, 1992). 

One of the first studies of PsCl was that of Tao (1965), who used a lifetime experiment (subsection 1.3.1) in this experiment positronium was formed in argon or N2 gases to which small quantities of CI2 vapour had been added. The intensity of the long-lived ortho-positronium component was found to decrease as the CI2 concentration was increased,... 

Luminescence is more sensitive than LRS and can detect the presence of V205 in V-loaded LaY crystals even at low ( 1% V) levels. Luminescence lifetime experiments at 610 nm will need to be performed with a more powerful light source and with a monochromator placed between the sample and the detector in order to observe LaV04 formation at low V concentrations. Such experiments are now in progress in our laboratory. 

FIGURE 11.17 BCAP0350 lifetime experiment. The capacitance and series resistance are recorded as a function of the duration of a constant voltage polarization of 2.5 VDC and a constant temperature of 50°C. 

The simulation of hydrogen by muons has proved to be extremely valuable in the identification of potential sites for hydrogen in semiconductors and insulators. Although the muon has a mass one-ninth that of the proton, its interaction with the host lattice, both electronically and chemically, is virtually identical to that of a proton. During its 2.2 microsecond lifetime (experiments are frequently undertaken over a timescale of up to ten lifetimes), the muon can diffuse, interact with, and adopt positions in the lattice that protons themselves would occupy. If the temperature is sufficiently low, muons can capture electrons to form muonium atoms. The reduced mass of muonium is within 0.5% of that of... 

The other possibility for the discovery of such tropospheric sinks, either singly or in combination, lies through comparisons of the total amounts of CChF and CChF2 found in the atmosphere with the amounts expected still to be there if stratospheric photodecomposition is the only important removal process [Rowland and Molina, 1976]. An alternative to this integral approach is the differential, trend analysis method in which incremental changes in atmospheric burden are compared with incremental emissions to the atmosphere over a particular period of time. The most complete application of the trend analysis procedure has been carried out through the Atmospheric Lifetime Experiment (ALE) sponsored for its first several years by C.M.A. and now by N.A.S.A. [Cunnold et al., 1978, 1983a,b Prinn et al., 1983 Simmonds et al., 1983]. 

CuNNOLD D.M., Prinn R.G., Rasmussen RA., Simmonds P.G., Alyea FJ4., Cardelino CA., Crawford A.J., Fraser P.J. and Rosen R.D., The atmospheric lifetime experiment, 3. Lifetime methodology and application to three years of CPClj data. J. Geophys. Res., 88, 8379-8400 (1983a). 

Prinn R., Rasmussen R., Simmonds P., Alyea F., Cunnold D., Fane B., Cardelino C., and Crawford A. (1983) The atmospheric lifetime experiment 5. Results for CH3CCI3 based on three years of data. J. Geophys.Res. 88,8415-8426. 

Cannabis is the most frequently used substance in the EU. Lifetime experience (any use during a person s lifetime) in the adult population ranges from 10 % in Finland to 20 or 30 % in Denmark, Spain and the UK (Figure 1). Amphetamines are generally used by 1 to 4 % of adults, but by up to 1 0 % in the UK. Ecstasy has been tried by 0.5 to 4 % of European adults and cocaine by 0.5 to 3 %. Experience of heroin is harder to estimate because of its low prevalence and more hidden nature, but is generally reported by under 1 % of adults. 

Lifetime experience of cannabis, amphetamines and cocaine among adults in some EU countries, measured by national population surveys, 1994-98... 

Lifetime experience of cannabis among adults in Finland by level of urbanisation, 1998... 

Lifetime experience is a poor indicator of recent drug use since it includes all those who have ever tried drugs, whether only once or some time ago. Use during the previous year (last-1 2-months prevalence) is a more accurate measure of recent use (Figure 4). 

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