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Chapters:
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MuSR /
LevelCrossingDetection< ALC simulation | Index | A special case: a muon with few nuclei > Detection is in principle quite straightforward in the conventional µSR setup. Suppose we have a liquid that forms a muonic radical with just one proton. At the crossing field in longitudinal geometry we would expect to see a precession signal at a small frequency, corresponding to the actual level separation. The frequency must rapidly increase departing from the resonant crossing conditions, both increasing and decreasing the field, while its amplitude also rapidly vanishes. And this is the problem, when the radical couplings are not already precisely known. To find the resonant conditions might be terribly time-consuming at the maximum rates imposed, e.g, by continuous muon beams ({$<50$} kev/s), whereas an efficient search strategy requires a quick measure while scanning the magnetic field. The trick is to sweep a superconducting solenoid while recording integral muon counts at a very high intensity beam. Outside the crossing region the integral polarization {$P_i$} may be obtained, as a normalized difference, in analogy to its time differential (Eq. 4) measurement. Apart from instrumental effects, {$P_i$} will change slowly, or remain constant (at high fields) until the crossing region is entered. Here, since a) for large enough muon rates a sufficient statistics is collected while the field is nearly fixed, and b) the precessing component will be averaged by the integral counting, a dip will appear in the {$P_i(B)$} curve, equivalent to those of the numerically simulated plots. Unfortunately a large magnetic field affects also quite strongly the efficiency of the counters, since it curves the positron trajectories from the sample to the detectors. This produces a field dependent variation of the normalized count difference of instrumental origin, which is not so simple to calibrate. As a consequence the large-scale field dependence of the muon polarization cannot be faithfully reproduced this way. However, for narrow crossing resonances the change in efficiency is negligible and the dips can be easily detected. < ALC simulation | Index | A special case: a muon with few nuclei > |