H.P. Povel

Nuclear γ-rays following muon capture

Abstract The identification of the nuclear γ-rays that occur when muon capture leads to excited nuclei made it possible to evaluate the distribution of excited nuclei formed after the capture process. Mono-isotopic elements were used as targets, and γ-ray spectra were recorded using Ge(Li) detectors. In most cases the observed γ-rays accounted for a high fraction of the capture process. It could be concluded that the probability of zero neutron emission after muon capture was less than 5 % contrary to the findings of Kaplan and the predictions of Singer. The chance of single neutron emission was highest, about 50 %, and it dropped with increasing neutron multiplicity. The probability of forming a particular excited state in an isotope was in general about proportional to the spin, and about inversely proportional to the energy of the state.

Pionic and muonic X-ray transitions in liquid helium

Abstract Energies and intensities of pionic and muonic X-rays in liquid 4 He have been measured with a Si (Li) detector. The energy shift due to strong interaction effects of the pionic 1s level in 4 He was determined to be −75.7±2.0 eV. The natural line width of this level is 45±3 eV. These values are compared with different theoretical predictions. Cascade calculations, including external Auger effect and sliding transitions, have been performed to reproduce the yields of the muonic and pionic transitions. The pionic 2p level width is deduced: Γ 2 p = (1.1 ± 0.5) × 10 12 sec −1 = (7.2±3.3) × 10 −4 eV .

Muonic X-ray measurements with a high-pressure gas target

Abstract Muonic X-rays from a high-pressure gas target were measured. Within a resolving time 0.03 μsec a transfer yield from hydrogen to argon of 0.36 ± 0.05 was obtained at an argon admixture of 1 × 10 −5 and 980 atmospheres. The r.m.s. radii of neon and argon were determined and found to be 3.07 ± 0.08 fm and 3.415 ± 0.005 fm respectively.

Intensities and strong interaction attenuation of kaonic x-rays

Abstract Relative intensities of numerous kaonic X-ray transitions have been measured for the elements C,P,S, and C1, from which level widths due to the strong K-nucleus absorption have been determined. From these and earlier published data, optical potential parameters have been derived and possible consequences on the nuclear matter distribution are discussed.

Precision determination of the strong interaction shifts and widths of the 1s level in pionic 6Li, 7Li, and 9Be

The strong-interaction shifts of the 1s level in pionic 6Li, 7/Li, and 9Be were determined with an accuracy of better than 1%. The corresponding widths were determined with an accuracy of better than 6%. Significant deviations from the theory are observed as far as the absolute values as well as the systematics of the isospin dependence are concerned.

Measurement of the vacuum polarization in muonic atoms

The energy levels in atoms are shifted by radiative correc-tions. While in electron atoms the self-energy is dominating com-pared with the vacuum polarization, the opposite holds for muonic atoms. Muonic transitions, where other corrections caused by the finite size and nuclear polarization are small compared to the vacuum polarization, provide an excellent tool for the measurement of the vacuum polarization.

New determination of the π− and νμ masses

Abstract The rest mass of the π− meson has been determined by measurements of the energies of π-mesonic X-rays with Ge(Li) detectors to be (139.549 ± 0.008) MeV (standard deviation). An upper limit of 0.6 MeV was deduced for the rest mass of the μ-neutrino (90% confidence).

π−-mass and vacuum polarization. A re-evaluation ☆

Abstract The π − -mass and vacuum polarization measurements of the CERN-Karlsruhe-Heidelberg group were re-evaluated. The π − -mass is found to be 139.569±0.008 MeV. A new value of the muonic neutrino rest mass is deduced to be m 2 v = −0.29±0.90 MeV 2 .

MUON CAPTURE PROBABILITY IN ISOTOPES OF BROMINE.

Abstract The muon capture probabilities in 79Br and 81Br have been measured by observing the time distribution of ψ-rays with respect to the stopped muons. The ψ-rays predominantly occur following (μ−;n) reactions. A natural bromine target was used and a Ge(Li) detector recorded X-rays and ψ-rays. The capture lifetimes τ( 79 Br ) = 143.9 ± 7.4 nsec and τ( 81 Br ) = 132.8 ± 8.9 nsec were obtained; they indicate that nuclear structure may be influencing the process.

Nuclear γ-Rays Following μ-Capture

After the cascade process in muonic atoms, the muon decays or is captured by the nucleus from the ls level through the weak interaction μ− + (Z,A) → (Z−1,A) + υμ, where a proton is changed into a neutron. The greater part of the liberated energy, of 107 MeV, is carried off by the neutrino, and depends on the momentum of the initial interacting proton; the energy left for the neutron varies from ~6 MeV for the proton at rest to some tens of MeV. This energy is distributed among the other nucleons of the nucleus (Z−1,A) which is de-excited predominantly by emission of one or more neutrons. After neutron emission, the resulting nucleus may be in an excited state and its de-excitation takes place by γ-ray emission. We have measured the nuclear γ-rays present in the μ-mesic spectra and assigned them to excited states of nuclei (Z−1,A−X) where X = 0, 1, 2, ... is the number of emitted neutrons. Here we report on γ-ray intensities per muon capture present in the muonic spectra of Mn and Co.