Energy spectra and asymmetries of neutrons emitted after muon capture

Inclusive energy spectra and the energy dependence of the asymmetry parameter have been measured for neutrons emitted after muon capture in O, Si, Ca and Pb. In addition a neutron-neutron coincidence measurement has been performed for Ca. The results of these measurements confirm the exponential shape of the energy spectra and the positive asymmetry observed by Sundelin and Edelstein. The observation of neutrons with energies above 50 MeV and the observation of simultaneous emission of two high-energy neutrons suggest the importance of short-range nucleonnucleon correlations in this process.     

High-energy neutrons emitted after muon capture in 40Ca

The energy spectrum of neutrons emitted after ω-capture in ⁴⁰Ca has been measured up to the kinematical endpoint of 92 MeV using two recoil telescopes. The neutron energy was deduced from the energy and angle of recoiling protons which originate from interactions of neutrons in a liquid scintillator. The neutron spectrum above 30 MeV is reproduced fairly well by a simple calculation based upon a reaction mechanism in which the muon is adsorbed, like in pion capture, by a pair of nucleons.     

Emission of neutrons following muon capture in heavy nuclei

The energy and multiplicity distribution of neutrons following muon capture in heavy nuclei is investigated. High energy neutrons (E > 10 MeV) are shown to be emitted directly by the fundamental capture process.     

Asymmetry of the most energetic neutrons emitted after muon capture by nuclei

The asymmetry of the most energetic neutrons emitted after μ capture by nuclei is calculated in a pure shell model to second-order nonrelativistic approximation. For closed-shell nuclei this limiting value is independent of the model used and of the nucleus considered except for a small kinematical dependence.     

Energy spectra of neutrons emitted following the absorption of stopped negative pions in light nuclei

Energy spectra of neutrons emitted following the absorption of stopped negative pions in carbon, nitrogen and oxygen were measured from about 2.5 MeV up to the kinematical limit. The experiments were carried out at the biomedical pion channel πE3 of the Swiss Institute for Nuclear Research (SIN). The evaporation part of the spectra was extrapolated to zero energy using the formula of Le Couteur. Various parameters like mean neutron energies and neutron multiplicities are given. The data are compared with experimental data obtained by other authors and with results of intranuclear cascade calculations.     

Gamma-rays following muon capture

The energy and intensity of γ-rays following capture of muons by Si, Ti, Mn, Fe, Co, Ni, Y, Ag and Au were measured with a Ge(Li) detector. In most cases it was possible to identify the final nucleus from the energy of the γ-ray observed. In general, this showed that one or more neutrons were emitted in the initial stages of de-excitation. In the case of capture by Fe and Ni the evidence pointed to a mode of de-excitation by the emission of a proton and a neutron and in Ti by γ-rays alone. In these measurements it was possible to account for as much as 60% of the muons captured in Co, less in the other elements, and only 15 % in Si.     

Longitudinal polarization of the emitted neutron in direct muon capture

The neutron longitudinal polarization has been calculated for ⁴⁰Ca using different wave functions for the bound proton and the emitted neutron. It is shown to be more sensitive to the final state interaction than to the details of the nuclear density.     

Energetic neutrons from muon capture by a heavy nucleus

The spectrum of energetic neutrons observed in a recent experiment on $\text{μ}{}^{\mathrm{?}}\text{+}{}^{165}\text{H}{}_0\text{→ n + X + ν}{}_{\mathrm{\mu }}$ is discussed using a simple model. It is found that the neutron spectrum can be reproduced reasonably well in terms of the nuclear Fermi motion deduced from other sources of information such as high-energy heavy-ion collisions.     

Energy spectra of single neutrons and charged particles emitted following the absorption of stopped negative pions in 4He

Energy spectra have been measured of single neutrons, protons and deuterons emitted following the capture at rest of negative pions in ⁴He. The neutron energy spectrum has been measured with an energy resolution of 4% at 90 MeV. The absolute number of stopped pions has been measured.     

Neutron emission following muon capture in heavy nuclei

The energy distribution of neutrons following muon capture in heavy nuclei is investigated. It is shown that the experimental high energy tail (E > 10 MeV) of the neutron distribution can be explained by a direct emission process.     

The nuclear excitations and particle emission following muon capture

The nuclear muon capture process is studied as an excitation of the analogues of various harmonics of the multipole giant resonance. The excitation energy distribution is calculated with the use of the hydrodynamical model of the nucleus. The following particle emission cascade (including precompound states) is considered and the obtained particle spectra as well as yields of various residual nuclei are in a fair agreement with the existing experimental data.     

Nuclear orientation following muon capture by spin zero nuclei

It is shown that in the proposed experimental set-up of the Louvain-Saclay collaboration, the nuclei recoiling into the forward (or backward) hemisphere in the reaction $\text{μ}{}^{\mathrm{?}}\text{+ A(J}{}_{\mathrm{<mtext>i</mtext>}}\text{= 0) → B(J}{}_{\mathrm{<mtext>f</mtext>}}\text{≧ 1) + ν}{}_{\mathrm{\mu }}$ will not only be polarized but also aligned. A general expression for the alignment of the recoiling nucleus is derived in terms of the other observables and it is shown to be independent of nuclear structure and the dynamics of the muon capture interaction. Numerical results are presented for muon capture by ¹²C and ¹⁶O.     

Negative muon capture in3He

We compute the partial capture rate of negative muons in³He by following the analysis of Peterson to include the relativistic corrections and the exchange effects, for various values of theg _p /g _A ratio. We also calculate the total capture rate. The ground state of³He is assumed to be spherical. The radial dependence of the ground state wave function is taken to be (a) one parameter Irving function, (b) a modified three-parameter Irving function and (c) a function having ‘soft-core’, whose parameters have been fixed in a variational calculation of the binding energy of the triton using a non-local momentum-dependent potential involvingp ² terms. The calculated values of the capture rates are compared with the experimental data to find a value for theg _p /g _A ratio.     

Spin-isospin excitations and nuclear muon capture

Muon capture rates in complex nuclei are calculated on basis microscopic models of nuclear structure. The calculation results are consistent with experimental values, unsuppressed spin-isospin transitions, and in contrast to the data obtained from the cross sections for nuclear charge-exchange (p, n) and (n, p) reactions.     

Radiative muon capture in medium-heavy nuclei

Radiative muon capture in nuclei is thoroughly investigated in view of its sensitivity to the pseudoscalar coupling constant g_P. In the photon energy domain of interest (k ? 60 MeV) the effective one-body hamiltonian in use is shown essentially to hold true, with minor corrections due to the muon propagator in the nuclear field and to the two-step process. The closure approximation is avoided by appropriately integrating the response function calculated in the Fermi gas model, in the energy-momentum transfer plane.Theoretical predictions in medium-heavy nuclei of the high-energy photon spectrum, of photon polarization, and of muon-spin photon angular correlation are given for various values of the pseudoscalar coupling constant.     

Search for emission of nucleons and nucleon pairs following muon capture in selected light nuclei

Preliminary results of measurements of proton energy spectra and search for coincidentp, n pair emission following negative muon capture in¹²C,¹⁶O,²⁷Al are given. A very clear signal for proton emission is found, which can be exploited in future detailed studies.Presented at the symposium Mesons and Light Nuclei, Bechyn, Czechoslovakia, May 27–June 1, 1985.This work was supported in part by the U.S. National Science Foundation, grant 83-10044-A 2, the German Bundesministerium für Forschung und Technologie, the International Buero Julich, and the Swiss National Science Foundation.     

Angular-distribution neutron-emission spectra of niobium following bombardment by fast neutrons

Neutron-emission spectra at ten angles between 20 and 160 degrees and incident neutron energies of 5.9, 7.1 and 8.4 MeV were measured relative to the neutron field emitted after spontaneous fission of ²⁵²Cf. The angular distribution of inelastically scattered neutrons appears to be essentially isotropic where it can be separated from the dominant elastic scattering peak. Above an excitation energy of 4 MeV the spectra are well described by a Maxwellian temperature distribution.     

Neutrino disintegration and muon capture in the deuteron

Neutrino and antineutrino disintegration of the deuteron and muon capture in the deuteron are studied. The final-state interaction between the nucleons is considered. The two-nucleon final state is found for the realistic potentials suggested by Reid and Ulehla et al.     

Neutron-neutron interaction and muon capture by deutron

The reaction μ⁻ + d → 2n + v_μ is studied in the non-relativistic approximation using the Primakoff weak interaction Hamiltonian including relativistic corrections. The neutron-neutron interaction is treated (a) by the Om?es-Muskhelishvili equation, (b) in a potential model, (c) using the Bethe-Longmire procedure. Influence of D-state admixture in deutron upon the transition rates and neutron spectrum is investigated.