F.W. Schlepütz

Spectroscopy of single and correlated charged particles emitted following bound pion absorption in 6Li and 7Li

Abstract Inclusive energy spectra of protons, deuterons and tritons as well as spectra and angular distributions of two coincident charged particles emitted following stopped negative pion absorption in 6 Li and 7 Li were measured. Energy and missing mass spectra, angular distributions and yields of two coincident charged particles are presented. Peaks corresponding to quasi-free absorption on different clusters and specific final-state interactions are observed in the coincidence spectra of the Li isotopes. In the dt spectrum of 6 Li as well as in the tt spectrum of 7 li evidence for 4 H formation with a resonance energy of 2.7 MeV and a reduced width of 2.3 MeV is found.

Spectroscopy of two coincident charged particles emitted following bound pion absorption in 12C, 59Co and 197Au

Abstract Energy spectra and angular distributions of two coincident charged particles emitted following stopped negative pion absorption in 12 C, 59 Co and 197 Au were measured. Most of the data can be understood within the framework of a pair absorption model including final-state interactions. Ground-state transitions in the missing mass spectra of 4 H and 4 He deduced from the αα and tα spectra of 12 C, respectively, show that reactions involving a large part of the nucleus also occur.

A new upper limit for the decay μ+ → e+γ☆

Abstract A search for the decay μ+→e+e+e−, in which no candidate was found, yields a new upper limit for the branching ratio Rμ→3e μ + → e + e + e − ν ν decays were observed, in agreement both in number and momentum distribution with V - A theory.

Inclusive neutron and charged particle spectra from the absorption of stopped negative pions in nickel isotopes

Abstract Energy spectra of neutrons and charged particles emitted after the absorption of stopped negative pions in the Ni isotopes 58Ni, 60Ni, 62Ni and 64Ni have been measured. The data are compared with model calculations for pion absorption on a peripheral nucleon pair and subsequent secondary reactions. The sum of the mean number of emitted neutrons and protons 〈n〉 + 〈p〉 is 7.2 ± 1.2, independent of the neutron number N, whereas the difference 〈n〉 — 〈p〉 increases linearly with N from 1.6 ± 0.8 for 58Ni to 5.0 ± 1.1 m for 64 Ni . The experimental results are compared with measurements of residual nuclei from stopped π−- and p-induced reactions in the above-mentioned Ni isotopes.

Measurement of neutron energy spectra and neutron-gamma angular correlations for the muon capture process 16O(μ−, νμxn)14, 15N

Abstract Neutron-gamma coincidence spectra have been measured for muon capture in 16O. The γ-spectrum is dominated by the ground state transitions from the 3 2 − (6.32 MeV ) and 1 2 + + 5 2 + (5.3 MeV ) states of 15N that are populated after the emission of one neutron. The neutron energy spectra and the neutron energy dependence of the ny angular correlation coefficient A2 for these final states are presented. The observed transitions in 14N and the associated neutron spectra give direct evidence for the emission of two correlated neutrons. The data are discussed in terms of direct neutron emission plus emission via giant resonance intermediate states of 16N. The large yield for the emission of one and two fast neutrons is explained by a capture mechanism involving short-range nucleon-nucleon correlations.

Inclusive neutron spectra from the absorption of stopped negative pions in heavy nuclei

Abstract Energy spectra of neutrons emitted after the absorption of stopped negative pions in heavy nuclei from 165Ho to 238U have been measured and interpreted in terms of models for pion absorption on a peripheral nucleon pair and subsequent secondary reactions. The mean number of evaporation, direct and total neutrons, their mean energies and nuclear temperature parameters have been deduced from the inclusive neutron spectra. The extracted nuclear temperatures and level density parameters for heavy nuclei show no shell effects in the energy region excited by the stopped pion reaction. For 238U the ratio of pre- to post-fission neutron yields has been deduced from the experimental data.

True absorption and scattering of pions on 16O and 18O

Abstract The inclusive pion inelastic scattering and true absorption cross sections on 16 O and 18 O were measured at 165 MeV for π ± and at 315 MeV for π + . The results show large effects of the two neutrons in 18 O on the absorption and inelastic scattering cross sections at the resonance energy. In particular, the inelastic scattering of π + from 18 O is considerably smaller than from 16 O and this effect is attributed to the coupling between the reaction channels.

Observation of the (π−, π−n) and (π+, π+p) reactions at 165 MeV

Abstract The (π − , π − n) and the (π + , π + p) reactions were studied on C, Fe, and Bi at 165 MeV by coincidence measurement o outgoing particles. The nucleon-knockout reaction is the dominant inelastic process at backward pion-scattering angles at this energy. The quasifree (π − , π − n) and (π + , π + p) cross sections were determined from the π-N an correlations. Their σ qf ( π − , π − n)/ σ qf ( π + , π + p) ratio is consistent with unity for C and is larger than the N / Z ratio for the heavier nuclei.