Jess H. Brewer

Canadian Inst. for Advanced Research
and Dept. of Physics & Astronomy,
Univ. of British Columbia, Vancouver, BC, Canada V6T 1Z1

This page is under construction at     /~jess/musr/
It is easy to get the impression that only positive muons are employed in µSR. Although most µSR is µ+SR, it is also possible to use negative muons in much the same way; however, there are good reasons why µ-SR is used only when there is no alternative. I will explain briefly why this is, and then I will list a few cases where there is no alternative and where the results justify the difficulty of the method.

  1.   Drawbacks of µ-SR:
  2. Negative muons do what any good ``heavy electron'' should: they are captured by a nucleus to form a muonic atom in which the muon's orbital is about 200 times smaller in radius than the corresponding electronic orbital. This means that the nucleus of the (electronic) atom is converted to Z-1 (where Z is the atomic number), which is not in itself a bad thing. However, no less than 80% of the muon polarization is lost through spin-changing transitions in the atomic cascade as the muon emits X-rays on its way to the 1s ground state.
    Another problem is that the negative muon undergoes nuclear capture (via µ- p --> n vµ) once it gets to the 1s state of the muonic atom. In heavy elements (like lead) the muon in the 1s orbital actually has a large fraction of its probability density inside the nucleus; this means that only ~4% of the muons have a chance to decay before they are captured by the nucleus.

  3.   µ-SR Examples:
  4. Summary of applications and limitations of µ-SR
    Summary, cont'd
    µ-SR in muonic atoms with nonzero nuclear spin
    Spin precession frequencies of various muonic atom hyperfine states
    µ-SR in muonic 9Be and muonic 27Al
    Residual polarization method for measuring hyperfine state populations, initial polarizations and transition rates in muonic atoms
    Hyperfine structure of selected "bare" muonic atoms

  5. Sorry, this page is still under construction!

Jess H. Brewer
Last modified: Fri Jul 20 20:15:24 PDT 2001