Electronic Catalogue of Mesoroentgen Spectra
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CLEI Experiment
Electronic Catalogue of Mesoroentgen Spectra D. R. Zinatulina* Joint Institute for Nuclear Research, Dubna, Moscow oblast, 141980 Russia Received December 25, 2018; revised January 11, 2019; accepted January 11, 2019
Abstract—The energy spectra of μX rays for molybdenum and ruthenium targets were measured by means of high-purity germanium (HPGe) detectors in a muon beam at the Research Center for Nuclear Problems (RCNP, Osaka, Japan). The results of these measurements were included in the electronic atlas of mesoroentgen spectra. This information is necessary for identification of gamma lines, calibrating detectors, correctly choosing structural materials, and investigation the composition of matter. DOI: 10.1134/S1063778819030165
1. INTRODUCTION The muon is one of the six known leptons. In its properties [1], it is similar to the electron but differs from it by a higher mass (mμ = 105.67 MeV) and by a finite lifetime: with a lifetime of τμd = (2197.03 ± 0.04) ns, the muon decays to an electron of energy about 50 MeV, a muon neutrino, and an electron antineutrino; that is, μ− → e− + νμ + ν e .
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In just the same way as the electron, the muon has its antiparticle, μ+ , which has the same lifetime. In order to study muon interaction with matter, one needs muon beams that have a rather high intensity and, simultaneously, a low energy. Among the facilities that provide such beams, the meson factory at the Paul Scherrer Institute (PSI, Switzerland) [2] is most widely known. After finding its way to a target, a muon undergoes deceleration in it till full stopping and thereupon decays. In contrast to a positive muon, a negative muon (below, we consider only this muon species) interacts actively with surrounding matter, forming so-called mesoatoms [3, 4]. A muon stopped in the vicinity of any target nucleus descends successively to the 1s-wave state, emitting a cascade of mesoroentgen photons (μX). The Pauli exclusion principle does not forbid this process, since a muon is not an electron, so that all orbits are free for it. Since the muon mass is 200 times as high as the electron mass, the radii of the muon orbits in a mesoatom are smaller than the radii of the electron orbit in the respective atom by a factor of 200; accordingly, the transition energy is 200 times higher. In contrast to ordinary x-ray radiation, the energy of mesoroentgen radiation *
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amount to several MeV units rather than to several tens of keV units. The formation and thermalization of a mesoatom proceed within a time of about 10−13 s, and from the experimental point of view conventionaly it is prompt. It is noteworthy that not all of the mesoatoms are thermalized via μX emission. Some of them emit Auger electrons, but their fraction is less than one percent; only at very large values of the charge number Z does it reach 1% to 2%. The energies of levels of mesoatoms and the energies of transitions between them take individual values for each chemical element. For example, the energy of the 2p−1s transit
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