Particle beams

Ultra-low energy muon source, μSOL (muon separator online)

Band-Gap Moderated Slow Positive Muon Beams – While positive muons (μ+) typically behave as light protons, they can also act like heavy positrons (e+). Bearing this in mind, Dr. Harshman and coworkers, considering results detailing e+ moderation in large band-gap solids, proposed an analogous mechanism for a moderated μ+ beam. The essential concept is that energy loss per unit length (dE/dx) decreases below the band-gap, resulting in a moderated e+ beam of a few eV; such a mechanism was deemed also applicable for producing a moderated μ+ beam. This research resulted in the discovery of the first practical technique for producing a low-energy (<10 eV) positive muon beam. It was christened with the acronym μSOL, which stands for “muon separator online” [Physical Review Letters 56, 2850 (1986)].

The same 1986 paper reported the first observation of (< 10 eV) Mu (i.e., μ+ee) ions in vacuum.

In 1987, Harshman and co-workers increased the slow muon production rate by a factor of 100 using solid rare-gas moderators, producing a usable flux of slow muons [Physical Review B 36, 8850 (1987)]. The slow muon production technique developed by Harshman and coworkers was adopted by the Paul Sherrer Institut (PSI) for their slow positive muon beam facility (the μSR Yamazaki Prize for this work was awarded to PSI personnel for placing this technology at the end of a PSI surface muon channel).

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