μ+charge exchange and muonium formation in low-pressure gases

Abstract

Using the basic muon-spin-rotation technique, the fractions of energetic positive muons thermalizing in diamagnetic environments (f") or as the paramagnetic muonium atom M& ---, M&.Muons are produced with kinetic energies of 4.1 MeV or greater, far larger than the energy regime of atomic interest. During its slowing down process in matter, the p+ undergoes charge exchange with molecules X of the medium, @++X~(p+e ) +X+, in complete analogy with proton charge exchange. The neutral muonium atom (Mu) formed with cross section o. io has as its nucleus a positive muon but otherwise can be regarded simply as a light isotope of the hydrogen atom. ' ' The fraction of muons that thermalize in matter as either "free" p+ or as Mu atoms can easily be measured and interpreted in terms of well-established concepts in proton charge exchange.There are three basic things to be learned from 26 2527 1982 The American Physical Society FLEMING, MIKULA, AND) GARNER the present study.(1) Unlike the proton experiments, the p+ beam stops in the gas so that, in principle, one is able to probe the regime of charge exchange on the approach to thermal energies. In this regard, the information content is similar to that available from protons as thick target yields.

The hot atom chemistry of muonium in alkane vapors

“…In general these differences are small, manifest in the fraction of muons appearing in diamagnetic environments ( fD). In contrast to the present study of alkane vapors, it is noted that, in other gases, only in Kr and Xe is fMu = 1.0 observed (28), cases in which hot atom chemical reactions are not possible. The concept that muonium is formed as a result of cyclic charge exchange is also believed to be the case in recoil tritium atom chemistry (3,4,6,32).…”

“…The source of this "wall effect" is the initial defining counter (318-mm thickness) and thin (118-mm) entrance window, which scatter some fractions of the more energetic muons into the A1 walls, where they precess as diamagnetic muons (with amplitude Aw) and hence contribute to fD. This can be corrected for experimentally, as discussed elsewhere (28)(29)(30) and can also be modeled from a Monte Carlo calculation of the muon stopping distribution. In the tables below (and in eqs.…”

“…The energy loss processes that the muon then undergoes can be divided into three stages (28)(29)(30), in analogy with related studies of proton charge exchange (31). Most of the incident energy is lost in the first stage, where Bethe-Bloch ionization dominates until a kinetic energy of -30keV is reached.…”

“…where A, , is the maximum possible amplitude for the experimental conditions (typically -0.3); the factor of two accounts for the loss of observable Mu due to the p+-e-hyperfine interaction (28)(29)(30)42).…”

“…From such a study one can hope to learn about the sensitivity of hot atom reaction dynamics to changes in isotopic mass, as in previous work on thermal reactions (11)(12)(13)(14); indeed, a factor of 27 between the masses of Mu and T is the widest possible isotopic variation at the most sensitive end of the mass scale. The Dresent paper is the first time that the subject of hot Mu reacti;ity has been addressed directly, although it has often been referred to (15,(28)(29)(30). It is hoped that comparison with the analogous hot tritium studies will help to sharpen the criteria for different theoretical models of hot atom reaction dynamics.…”