Decay level crossing

Fig. 1. Schematic for /zSR and fiLCR experiments. For pSR the muon spin polarization vector starts off in the x direction (open arrow). It then precesses about an effective field (the vector sum of the external field and the internal hyperfine field), which is normally approximately the z direction. The muons are detected in the M counter, and positrons from muon decay are detected in the L or R counters. For pLCR, the muon spin polarization is initially along the external field or t axis (solid arrow). The positron rates in the F and B counters are measured as a function of external field. A sharp decrease in the asymmetry of the F and B counting rates signifies a level crossing.

Level crossing spectroscopy has been used by Fredriksson and Svanberg44 to measure the fine structure intervals of several alkali atoms. Level crossing spectroscopy, the Hanle effect, and quantum beat spectroscopy are intimately related. In the above description of quantum beat spectroscopy we implicitly assumed the beat frequency to be high compared to the radiative decay rate T. We show schematically in Fig. 16.11(a) the fluorescent beat signals obtained by... 

Figure 15 also shows a case of level crossing involving the weaker Auger process, namely 4d- 5s5pml Auger fluctuation and the decay of a 4d-core hole in 49In. 

It is important to note, that this line narrowing effects only occur if the phase of the decaying signal is preserved. This is always the case when the detection is based on interference effects, such as level crossing, quantum beats or interferometric detection, if the shutter is placed behind the interference device. For these examples the cosine Fourier transform can be measured separately. If, however, the detection only measures the power spectrum of the fluorescence, without phase information, the signal is represented by... 

Determination of gold concentrations to ca 1 ppm in solution via atomic absorption spectrophotometry (62) has become an increasingly popular technique because it is available in most modem analytical laboratories and because it obviates extensive sample preparation. A more sensitive method for gold analysis is neutron activation, which permits accurate determination to levels < 1 ppb (63). The sensitivity arises from the high neutron-capture cross section (9.9 x 10 = 99 barns) of the only natural isotope, Au. The resulting isotope, Au, decays by P and y emission with a half-life of 2.7 d. 

Two open reservoirs with cross-sectional areas Ai, A2 and liquid depths hi and h2 respectively are connected by a pipeline of length L and diameter D. The resulting liquid levels form a decaying oscillatory response to final steady state. Ramirez (1976) provides a detailed model derivation for this problem and shows how the problem is solved by analogue computation. The parameters are the same as those used by Ramirez. 

Since (/iv//av)/(/i//2) can be measured and kx and k2 are just the observed reciprocal decay constants of levels tx and r2, it is possible to determine the ratio of the intersystem crossing rate constants K KX. This information is difficult if not impossible to obtain in other ways. The results for several molecules are shown in Figure 6.3. 

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