Cascade decay

Table 8. Spontaneous radiative lifetimes (s) of the A FT and bands. Cascade decay...

CHj radicals from a surface site and that surface diffusion is fast resulting in a low stationary concentration of mobile radicals. High surface coverage of CHjI would thus slow down the migration of the radical to the surface. The cascade decay observed was attributed to a continuum of trapping potentials on the surface. 

The cascade decay of CH on silica gel has also been reported by Joppien and Willard (19) over the temperature range of 77 K to room temperature. The decay rate was resolved into multiple first and second order processes. The activation energies for the 3 first order decay processes were 3, 5 and 6 kcal/mol respectively. 

The decay of H-atoms on PVG (51) also showed a similar cascade decay but followed second order kinetics. Similar cascade decay of radicals have been reported to occur in polymers which have been Y-irradlated (54) and is attributed to the trapping of radicals in preferential sites within the solid. 

A cascade decay of CH radicals on basic AI2O2 was followed over the temperature range of 298 K to 474 K (57). The radicals were stable at room temperature for months and did not decay in the presence of 0. A study of the decay kinetics of such stable CH radicals would be most interesting. 

These limits include the effects of cascade decays, evaluated assuming a fixed value of the parameters /x and tan/Z. The limits are weakly sensitive to these parameters over much of parameter space. Limits assume GUT relations between gaugino masses and the gauge coupling. Mass m > 250 GeV, CL = 95% [tanjS = 2, /x < 0, A = 0]... 

Another subject which will be of interest for those who wish to apply nuclear chemistry for analytical purposes, is the sum peak method . The prindple of this method is based on a perturbed angular correlation (PAC) for two y-emissions in cascade decay from a radioactive nucleus. The emission angle betweoi the two y s has a distribution pattern which reflects the mode of radiative decay, as well as depetuling on the environmental conditions. The sum peak which is seen in a y-ray spectrum as a result of simultaneous detection of the twoy-rays as one event, is therefore influenced by the environments in which the source is placed. In the sum peak method, intendty ratios of the stun peak to the single peak can be used and chan in the ratios due to the environments can be observed. 

There are several cascade codes developed for reproducing the cascade decays of exotic atoms (see, e.g., Borie and Leon 1980 Markushin 1999 Jensen and Markushin 2002). The cascade process is studied by detecting X-rays and Auger electrons from transitions in all exotic atoms and via laser spectroscopy in metastable antiprotonic helium (see O Sect. 28.6.3.2). It was experimentally observed that medium-heavy muonic atoms such as p Ar lose all atomic electrons via Auger effect by the time the muon reaches the ground state (Bacher et al. 1988). 

Hie pf distribution for b-, c- and udsg-svtnts is shown in Fig. 4.13. The b-spectrum contains a contribution from cascade decays b-r-c + X p, + X in addition to the direct semileptonic decays b ii+X. The p p spectrum of -events is significantly harder than the p f spectrum of c- and M /sg-events, while the c- and a<7ig-spectrum turn out to be rather similar. 

Similar assignments = 0 have been made for (3685) on the basis of its cascade decay... 

In the cascade decay of a laser-excited state, lower-lying states are populated as illustrated in the figure for the case of alkali atoms. This provides further possibilities for laser spectroscopy investigations. 

In Fig.9.16 a fluorescence light spectrum for Cs is given as recorded with the apparatus shown in Fig.9.I5. The 12 Dg/2 state is populated by step-wise excitation. In cascade decays, as illustrated in Fig.9.1, lower-lying P and F levels are populated and fluorescence lines are obtained in the blue and UV, and in the red spectral regions, respectively. 

As can be seen from the inserted experimental curve, such a linewidth can be approached. In Fig. 9.38 a further example of this type of spectroscopy is given. Here a broadband cw laser has been used to populate the rather long-lived 5d (r-l zs) state in in the cascade decay of the... 

Beam-Foil Techniques. The beam-foil method has been discussed in Sect. 6.1. It is a very general method for measuring lifetimes of atoms and ions. However, the non-selective excitation, leading to cascading decays, places heavy demands on the data analysis and sometimes a detailed study of the different cascade channels is necessary for reliable lifetime evaluations. While the nonselective excitation frequently constitutes a problem, it is also an advantage of the method since a multitude of excited states are populated. For measurements of multiply charged ions in particular, the technique provides unique measurement possibilities where other techniques are not applicable. 

The spectrum below is recorded in fluorescence from a collimated cesium atomic beam, excited on the D F transition by a single mode tunable dye laser. The D level is populated in cascade decay from the P state, which is excited with a broadband CW dye laser. The Fabry-Perot fringes at the bottom correspond to a free spectral range of 50 MHz. 

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