Delayed emission

Besides the prompt excimer emission, delayed excimer emission has been observed. The mechanism is through triplet-triplet annihilation process (Section 5.9B) ... 

The optical absorption, measurable via the excitation spectra of secondary emissions (delayed fluorescence,143 phosphorescence,142 EPR triplet spectra,166 etc.). The absorption is the response of the crystal to an excitation spatially homogeneous at the microscopic scale ... 

Fig. 8. Time-resolved and time-integrated emission spectra at T=1.3 K of Pd(2-thpy)2 dissolved in an n-octane ShpoTskii matrix. Concentration = 10 mol/1 Agxc = 337.1 nm (pulse width 3 ns), (a) Time integrated emission (b) Time-resolved emission, delay time t = 0 ps,time window (integration time) At = 10 ps (c) Time-resolved emission, delay time t = 1800 ps, time window At = 1800 ps. The energies of the vibrational satellites are specified relative to the electronic origin at 18,418 cm. (Compare Refs. [56,58])...

Among the very neutron rich nuclides, e.g. some fission products, 0 delayed neutron emission is observed. This decay mode is similar in nature to the delayed p emission. Delayed n-emission is inqx>rtant for the safe operation of nuclear reactors, see Ch. 19. 

The fluorescence lifetime r can be determined directly by monitoring the decay curve of fluorescence intensity following a brief excitation pulse [48] or by detecting the emission delay of intensity modulated excitation light [47]. Using a standard steady-state fluorometer the quantum yield cp is determined, usually by comparison with standard compounds of known quantum yield [49]. 

A number of uncommon decay modes exist which are of little direct relevance to gamma spectrometrists and I will content myself with just listing them delayed neutron emission, delayed proton emission, double beta decay (the simultaneous emission of two 3 particles), two proton decay and the emission of heavy ions or clusters , such as and Ne. Some detail can be found in the more recent general texts in the Further Reading section, such as the one by Ehmann and Vance (1991). 

Time-integrated emission Time-integrated emission Time-resolved emission Delayed Time-resolved Assignments [74] emission Fast ... 

Molecular Phosphorescence Instrumentation for molecular phosphorescence must discriminate between phosphorescence and fluorescence. Since the lifetime for fluorescence is much shorter than that for phosphorescence, discrimination is easily achieved by incorporating a delay between exciting and measuring phosphorescent emission. A typical instrumental design is shown in Figure 10.46. As shown... 

Applications. Both industrial emissions reduction and indoor air-poUution abatement uses will grow. For example, the development of adsorbents with higher capacity for removal of radon from humid air could allow the development of a one-bed, delay-for-decay system in which radon adsorbs, decays to lead, and is precipitated onto the adsorbent. 

There are four modes of radioactive decay that are common and that are exhibited by the decay of naturally occurring radionucHdes. These four are a-decay, j3 -decay, electron capture and j3 -decay, and isomeric or y-decay. In the first three of these, the atom is changed from one chemical element to another in the fourth, the atom is unchanged. In addition, there are three modes of decay that occur almost exclusively in synthetic radionucHdes. These are spontaneous fission, delayed-proton emission, and delayed-neutron emission. Lasdy, there are two exotic, and very long-Hved, decay modes. These are cluster emission and double P-decay. In all of these processes, the energy, spin and parity, nucleon number, and lepton number are conserved. Methods of measuring the associated radiations are discussed in Reference 2 specific methods for y-rays are discussed in Reference 1. 

The function of the oxygen sensor and the closed loop fuel metering system is to maintain the air and fuel mixture at the stoichiometric condition as it passes into the engine for combustion ie, there should be no excess air or excess fuel. The main purpose is to permit the TWC catalyst to operate effectively to control HC, CO, and NO emissions. The oxygen sensor is located in the exhaust system ahead of the catalyst so that it is exposed to the exhaust of aU cylinders (see Fig. 4). The sensor analyzes the combustion event after it happens. Therefore, the system is sometimes caUed a closed loop feedback system. There is an inherent time delay in such a system and thus the system is constandy correcting the air/fuel mixture cycles around the stoichiometric control point rather than maintaining a desired air/fuel mixture. 

Snubbers are passive networks that delay the risetime of the voltage waveform. Historieally, snubbers have been used to keep power deviees within their forward- and reverse-biased safe operating areas (FBSOA and RBSOA) or to eontrol RF emissions from the power supply. They are essentially lossy tank eireuits (L-C eireuits with R). Using them offered more of an advantage than the loss ineurred. Semieonduetor eomponents are more rugged today and the traditional need for the RFC snubber for proteetion has lessened, but oeea-sionally a snubber is still needed. 

The reader should note tliat since many risk assessments have been conducted on the basis of fatal effects, there are also uncertainties on precisely what constitutes a fatal dose of thennal radiation, blast effect, or a toxic chemical. Where it is desired to estimate injuries as well as fatalities, tlie consequence calculation can be repeated using lower intensities of exposure leading to injury rather titan dcatli. In addition, if the adverse healtli effect (e.g. associated with a chemical release) is delayed, the cause may not be obvious. Tliis applies to both chronic and acute emissions and exposures. 

A suitable method for a detailed investigation of stimulated emission and competing excited state absorption processes is the technique of transient absorption spectroscopy. Figure 10-2 shows a scheme of this technique. A strong femtosecond laser pulse (pump) is focused onto the sample. A second ultrashort laser pulse (probe) then interrogates the transmission changes due to the photoexcita-lions created by the pump pulse. The signal is recorded as a function of time delay between the two pulses. Therefore the dynamics of excited state absorption as... 

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