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The energy and time distributions of the decay X-rays of excited, metastable, molecular (dµHe)*-resonances were measured. The comparison of the observed energy spectra with calculated ones suggests that decay from the rotational state J = 1 dominates at the investigated conditions. The muon transfer rates from ground state deuterium to the helium isotopes 3He and 4He at low temperatures were determined from the time distributions of these spectra. Additionally, the temperature dependence of the muon transfer rate was clearly established in deuterium / 4He mixtures.

The present status of research of muon transfer from the ground state of muonic protium to 4He is reviewed. The analysis of a recent measurement in a triple gas mixture of H2+4He+Ne at 15 bar and room temperature is presented and the result is compared to the existing experimental and theoretical rates. The average muon transfer rate from protium to 4He determined from all lifetime measurements is .

A method is proposed for investigating muon transfer from excited muonic hydrogen atoms to an element Z{gt}2, and is applied to argon measurements. It makes use of a comparison between the muonic x-ray intensity patterns of the Lyman series of this element measured in mixtures with and without hydrogen. The analysis of the data taken in two gas mixtures H{sub 2} + Ar at 15 bar with argon concentrations of 2{percent} (0.3{percent}), yields consistent results. In both mixtures, two thirds of the prompt argon x rays proceed from transfer from excited {mu}p{sup {asterisk}} states. The Coulomb capture ratio determined in both mixtures yields a mean value of A(H{sub 2},Ar) = 0.21(2), and agrees with the corresponding pionic ratio. {copyright} {ital 1997} {ital The American Physical Society}

The yields of muonic x rays of the Lyman series of nitrogen, neon and argon have been analysed to determine capture ratios A(Z1,Z2) in about thirty gaseous mixtures under different experimental conditions. In addition, capture ratios A(Z,H) have been determined in hydrogen mixtures by taking into account transfer processes from muonic hydrogen to elements Z. The influence of the spectral flux density of the muons on capture ratios has been analysed. Our per-atom ratios form a coherent set and confirm the value A(Ar,Ne) = 1. 262(10).

Muon transfer from hydrogen isotopes to helium is of importance in muon-catalyzed fusion and serves as a unique tool for the direct observation of the mesomolecular ion (pµHe)*. During two data-taking runs in 1994 and 1995 at PSI, measurements of the transfer from protium to helium were carried out using CCD's and Ge-diodes as independent X-ray detectors to obtain information on the time distribution and intensity of the 7 keV decay X-ray of the mesomolecular ion. Dual1H2 +4 He and triple1H2 + Ne +3,4He gas mixtures at low temperatures were investigated to extract transfer rates. Protium of high purity was available. For the first time a transfer rate from muonic protium to3He was measured. A general survey of our measurements and preliminary analysis is presented.

To investigate the energy dependence of muon transfer to oxygen, we performed measurements in gaseous mixtures of hydrogen and oxygen. The time distributions of the muonic oxygen X-rays showed the same structure as the one observed earlier in H2+SO2 mixtures. In the delayed part of these distributions, one can distinguish a short-time and a long-time component. From the latter, we deduced the transfer rates from thermalized muonic protium, respectively deuterium, to oxygen. The short-time component can be interpreted as being due to muon transfer from epithermal muonic hydrogen atoms. The time parameters are characteristic for the deceleration process as well as for energy-dependent transfer rates. With results of recent research on the formation and the thermalization of muonic hydrogen, we performed Monte Carlo simulations in order to test the hypothesis of an energy-dependent transfer rate.

The experimental muon transfer rates from muonic protium and deuterium to heavier elements show a complexZ dependence. Instead of the expected monotonicZ dependence considerable variations between neighboring elements are observed. Transfer to neon has a specially small rate. Furthermore, the time distribution of the muonic X-rays shows in a number of molecules a complex structure, and depends in the case of a H2 + CH4 gas mixture also on the total pressure.

After the feasibility of vacuum isolated μ−d production was demonstrated at TRIUMF in 1989, development was begun on a target system that would take advantage of the process to aid in the understanding of the muon catalyzed fusion cycle. Minimal neutron backgrounds, the ability to use silicon detectors, and compatibility with tritium were considered important for a very versatile target system. The advantages which the target gives in isolating μCF process will be outlined.

The present situation of muon transfer to helium is summarized. A new gas target for a maximal pressure of 40 b with four thin beryllium windows for the detection of low energy photons is described. First results of an analysis of the time spectra of muonic carbon X-rays in a H2+CH4 gas mixture taken with the new target show a pressure dependent structure.

By analysing the time spectra of the muonic sulphur X-rays in seven different H2+SO2 gas mixtures, the muon transfer rates to the SO2 molecule, deduced from the lifetimes of the µp atoms, agree all well with each other. The muonic oxygen time spectra show an additional structure as if µp atoms of another kind were present. Reduced transfer rates Λ o ′ are reproducible if one uses the model of “ephemeral” µp atoms[1].

Experiments are described which use a solid hydrogen layer to form muonic hydrogen isotopes in vacuum. The method relies on transfer of the muon from protium to either a deuteron or a triton. The resulting muonic deuterium or muonic tritium will not immediately thermalize because of the very low elastic cross sections, and may be emitted from the surface of the layer. Measurements which detect decay electrons, muonic x-rays, and fusion products have been used to study the processes. A target has been constructed which exploits muonic atom emission in order to study the energy dependence of transfer and muon molecular formation.

The muon transfer process in binary and ternary gas mixtures with hydrogen looks like a well known process. 1 From the ground state of the up atom, where the muon has a binding energy of about 2.6 keV, the muon is transferred to higher Z elements onto atomic orbits with much smaller radii than the outer electron shells of the atom Z, and where the muon has a comparable binding energy. The transfer process does therefore not depend on chemical structures and bonds in which the element, to which the muon is transferred, is involved.

The muonic Coulomb capture ratio A(${\mathrm{H}}_{2}$,Ar) has been measured in two different ${\mathrm{H}}_{2}$-Ar gas mixtures using two different methods of evaluation based on the muon transfer from hydrogen. The measured ratios agree with each other, but disagree with the corresponding pionic capture ratio and also with the ratios calculated from muonic and pionic A(He,Ar) and A(He,${\mathrm{H}}_{2}$) capture ratios. The large discrepancies might be related to unsolved problems in muon transfer.

By analysing measured time distributions of the muonic oxygen and sulphur X-rays in a H2+SO2 gas mixture, one finds two different time constants. If these correspond to two lifetimes for the bound μp atom, two kinds of μp atoms exist: one kind transfers its muon only to oxygen, the other to both oxygen and sulphur. The difference in the two μp systems is presently unexplained.

The transfer of negative muons from the ground state of muonic hydrogen to argon and helium has been measured in gaseous mixtures at pressures between 10 and 15 bars and at different relative concentrations. The transfer rate to argon, reduced to liquid-hydrogen density [${\ensuremath{\Lambda}}_{p\mathrm{Ar}}$ =1.42(4)\ifmmode\times\else\texttimes\fi{}${10}^{11}$ ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$], agrees well with those obtained at ten times higher pressures. The transfer rate to helium [${\ensuremath{\Lambda}}_{p\mathrm{He}=0.88(9)\ifmmode\times\else\texttimes\fi{}{10}^{8}}$ ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$], measured in a triple gas mixture, disagrees with the only other experimental value and is about two times higher than recent theoretical predictions. In addition, the muonic x-ray intensities of the Lyman series of argon resulting from muon transfer have been determined. They are well reproduced by a cascade calculation assuming a theoretical initial distribution over n and l states.

Muonic X-ray energies of the K-series of the light natural elements Be, B, C and N have been determined with a precision of 5 to 10 eV. Equivalent nuclear charge radii have been deduced. The results, expressed in terms of rms radii, are of similar or better accuracy than recent electron scattering data. Of particular interest is the rms radius of carbon as a reference value for elastic electron scattering cross sections. A model-independent evaluation yields 〈r 2 〉 1 2 = 2.467 (17) fm .

Single-crystal X-ray data (Mo Kα radiation) are reported for the following: 1. (i) Y3Os4Si12 (orthorhombic, Er3Ru4Si12 structure type, oS76, Cmca, a = 18.495(2) A , b = 8.125(1) A , c = 8.130(1) A , V = 1221.7 A 3 , Z = 4, Dx = 7.417 g cm−3, R = 0.096 for 927 contributing independent reflections); 2. (ii) Y5Os4Si14 (monoclinic, Lu5Co4Si14 structure type, mP46, P21/c, a = 12.779(5) A , b = 8.019(3) A , c = 7.926(3) A , β = 98.69(3)°, V = 802.9 A 3 , Z = 2, Dx = 6.611 g cm−3, R = 0.076 for 2336 reflections); 3. (iii) Y9Os4Si20 (monoclinic, new structure type. mP66, P21/c, a = 19.417(1) A , b = 7.949(3) A , c = 8.005(3) A , β = 95.92(1)°, V = 1229.0 A 3 , Z = 2, Dx = 5.735 g cm−3, R = 0.069 for 1840 reflections). The structures are members of a structure series which is obtained by one-dimensional stacking of two types of two-dimensional structural segments. The principal segment has the composition [Y3Os4Si12] (i) or [Y3Os4Si10] ((ii) and (iii)) and is intergrown either with itself (i), or with segments of silicon-centred yttrium prisms having the AIB2-type structure (ii), or the silicon-deficient α-ThSi2-type structure (iii).

The transfer rate of negative muons from the 1s state of hydrogen to argon has been measured in H2+Ar gas mixtures at total pressures of 100 and 140 bar and argon concentrations C (Ar/H2) of 6*10-4 and 20*10-4. The reduced transfer rates have been found to be independent of the total pressure and of the argon concentration. The mean reduced transfer rate obtained, Lambda pAr=(1.46+or-0.05)*1011 s-1, is compared with the rates measured by other authors.

The osmium-silicon phase diagram was investigated by means of X-ray powder diffraction, differential thermal analysis, metallography, microprobe analysis and electrical resistivity measurements. The existence and type of formation of the following intermetallic compounds was established: OsSi, Os 2 Si 3 and OsSi 2 . These three compounds are semiconducting. A metastable phase was found at 67 at.% silicon.

Muonic x-ray intensities of the Lyman series have been measured in carbon (diamond, graphite, and soot) and in boron and nitrogen in the cubic (diamond) and hexagonal (graphite) structures of boron nitride. By means of muon cascade calculations which reproduce the measured intensities, angular momentum distributions of the captured muons have been determined for carbon and nitrogen in the $\ensuremath{\mu}$-atomic level $n=13$. The boron-to-nitrogen capture ratios have been found to be 0.233\ifmmode\pm\else\textpm\fi{}0.011 in the cubic structure and 0.275\ifmmode\pm\else\textpm\fi{}0.012 in the hexagonal structure. The difference of 18\ifmmode\pm\else\textpm\fi{}3% has to be attributed to the difference in the solid-state structures.

The results of precise measurements of the energies of the 2p32−1s12and 2p12−1s12 muonic X-ray transitions of 92Mo, 94Mo, 95Mo, 96Mo, 97Mo, 98Mo and 100Mo are reported. The data were analyzed in terms of the Barrett moments 〈rke−αr〉 of the nuclear charge distributions from which the equivalent nuclear radii Rk and the differences ΔRk between neighboring isotopes were computed. Systematic shell effects have been observed at the neutron numbers N = 50 and N = 56.

Energies and intensities of muonic X-rays, nuclear γ-rays and μ-capture γ-rays were measured in natural muonic thallium with Ge(Li) detectors. The absolute intensities of higher μ X-rays were reproduced by a cascade calculation starting with a statistical population at n = 20 including K-, L- and M- conversion. The electron screening effect was deduced from energies of higher μ X-rays. Eight prompt nuclear μ-rays were found, due to an excitation of (4.1 ±1.0) % and (14.6 ± 3.0) % of the first 3 2 + level in μ 203 T1 and μ, 205 T1, respectively, and of (8.8 ± 0.9) % of the 5 2 − level at 2.63 MeV in 205 T1. This excitation explains the anomalous intensity ratios of the 2p-ls and 3d-2p fine structure components. From the nuclear y-rays of the first excited states were deduced: the magnetic h.f. splittings e 203 ( 1 2 ) = 2.57 ± 0.15 keV , e 205 ( 1 2 ) = 2.30 ± 0.02 keV, muonic isomer shifts ΔE is (203) = 0.26 ± 0.15 keV, ΔE is (205) = −(0.31 ± 0.11) keV; E2/M1 mixing ratios δ μ 2 (203) = 0.89 ± 0.27, δ μ 2 (205) = 1.00 ± 0.05, and the half-life in the presence of the muon T μ ( 3 2 ) = 1.4 ± 0.1 nsec in 205 T1. The values of e( 1 2 ) and ΔE ls were compared with shell-model calculations. From δ μ 2 and T gm ( 3 2 ) evidence for a magnetic nuclear polarization was found. From the 2p-ls, 3d-2p, 3p-2s and 2s-2p transitions the size and shape of the nuclear charge distribution and a nuclear polarization due to the 1s 1 2 muon of ΔE np = 8.3 ± 1.2 keV and 9.5 ± 1.2 keV for 203 Tl and 205 T1 respectively were determined in agreement with theoretical estimates. An isotope shift of ΔE = 10.35 ± 0.25 keV was measured for the 1s 1 2 state which is compared with data from optical spectroscopy. From an analysis of the time distribution of delayed γ-rays from μ-capture, an isotopic effect of (5.4 ± 2.5) % was found for the capture rates, in fair agreement with predictions from Primakoff's μ-capture formula.

Electric quadrupole X-ray transitions (5g → 3d, 4f → 2p, and 3d → 1s) have been observed in muonic Tl, Pb and Bi. From the 3 → 1 transitions, energy splittings of the n = 3 levels were deduced. From a comparison of the relative intensities of E1 and E2 transitions, the population ratios 5g 5f , 4f 4d , and 3d 3p were deduced. These ratios are well reproduced by a cascade calculation assuming a statistical initial population at n = 20, including K, L and M shell conversion. In the case of 205 T1 discrepancies between the experimental and the calculated 3d-1s/3p-1s intensity ratio can be explained by nuclear excitation. From the 3 p 3 2 → 1 s 1 2 intensity in 209 Bi we can deduce the ratio of the radiationless to the X-ray transition width and give limits for prompt neutron emission from the 3d level.

The muonic x-ray intensities of the Lyman series in pure silicon are investigated. The fitted data are compatible with a statistical initial angular momentum distribution of the captured muons. From a comparison with data measured in diamond, cubic boron nitride and in the two isoelectronic series F/sup -/,Ne,Na/sup +/ and Cl/sup -/,Ar,K/sup +/, we conclude that the calculated muon distribution reflects the symmetry of the electrons through which muon capture proceeds.

Measurements of relative Coulomb capture rates of muons in compounds of nitrogen, sulphur and selenium have been performed. The obtained results may be interpreted as showing a valence state dependence

Lyman series of muonic nitrogen have been measured in BN, NaNO 2 and NaNO 3 . Changes seen in the muonic X-ray intensity structures and the capture ratios may be attributed to the variation of the electron density in the valence shells.

In muonic 190,192Os the magnetic hf-spliting of the 2+ → 0+ nuclear transition was measured. The hf-splittings ΔE( 190 Os ) = 665 ± 80 eV and ΔE( 192 Os ) = 800 ± 80 eV of the 2+ state are reduced at 59% compared to a point-like magnetic moment in agreement with the assumption of a magnetization density of a magnetization density distribution proportional to R2 ϱcharge(R) as calculated from a rigid rotator. The influence of these results on the analysis of muonic isomer shifts is pointed out.

Energies of the 5g-4f muonic X-rays have been measured in nat Hg and 203 Tl with an accuracy of about 25 eV. They are found to be smaller than theoretical energies including recently revised calculations of higher-order vacuum polarization, by about two standard deviations.

The osmium-silicon phase diagram was investigated by means of X-ray powder diffraction, differential thermal analysis, metallography, microprobe analysis and electrical resistivity measurements. The existence and type of formation of the following intermetallic compounds was established: OsSi, Os 2 Si 3 and OsSi 2 . These three compounds are semiconducting. A metastable phase was found at 67 at.% silicon.

We report on muonic Lyman-series x-ray intensities measured in gaseous argon and in K/sup +/, Cl/sup -/, Na/sup +/, and F/sup -/ in the compounds KF and NaCl. The analysis of their structures, including neon, shows that both the spatial symmetry and the binding energy of the electrons of outer shells determine the angular momentum distribution of captured muons. The conclusions are in agreement with the modified model of ''large mesic molecules.''

Negative muons were trapped in gaseous mixtures of hydrogen and oxygen. The time distributions of the muonic oxygen X-rays showed a clear deviation from a single exponential structure. From these time distributions we evaluated the transfer rate from thermalized muonic hydrogen atoms to oxygen. In order to test the hypothesis of an energy-dependent transfer rate to oxygen we performed Monte Carlo simulations of the thermalization and the transfer process. We report on the present status of our investigations.