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.     

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.     

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.     

Weak nucleon currents in beta decay and muon capture

We made extensive investigations on the weak charged nucleon currents and structure of complex nuclei in weak nuclear processes. Using our new formalism, which has almost no approximation as far as the lepton part is concerned, we have studied the beta-ray spectra and beta-ray angular distributions in the¹²B and¹²N beta decays. The weak magnetism predicted by CVC is in excellent agreement with the experimental data on beta-ray spectra given by the Columbia and Heidelberg groups. It is noticed here that the difference _– – ₊ of the coefficients in the beta-ray angular distributions in aligned¹²B and¹²N is free from ambiguity of the nuclear model. We found practically no second-class induced tensor current with the data given by the Osaka, Louvain and Zürich groups. On the other hand, the sum _– + ₊ of the coefficients represents the time component of the main axial vector current, and it is free from weak form factors. With this sum we studied the exchange-current and core-polarization effects. These two effects are large, and they are almost cancelled out by each other in this case. We also found the strength of the induced pseudoscalar form factor which is generally consistent with PCAC, from nuclear polarizations of¹²B in muon capture of¹²C performed by the Zürich and Tokyo groups. These nuclear polarizations are insensitive to the nuclear model, if the exchange-current and corepolarization effects are properly taken into account.This paper was partially delivered at the Annual Meeting of the Korean Physical Society, Seoul, 1983; the Asia Pacific Physics Conference, Singapore, 1983; and the International Symposium on Nuclear Spectroscopy and Nuclear Interactions, Osaka, 1984.The present paper is based on our recent theoretical investigations, which have been performed by the theory group, Department of Physics, Osaka Unicersity. The author would like to express his sincere thanks to Professors H. Ohtsubo, Y. Yokoo, Drs. T. Sato, K. Koshigiri, M. Nishimura, M. Kobayashi, and Mr. M. Fukui for their collaboration, to Professors C.W. Kim, Y.K. Lee and K. Kubodera for their stimulating discussions during his 1983 summer visit to Johns Hopkins University, to Professors K. Sugimoto, T. Minamisono, V.L. Telegdi, L. Grenacs, T. Yamazaki and K. Nagamine for sending him their experimental results before publication. Numerical calculations were performed with the aid of NEAC ACOS 1000, Computor Center, Osaka University. This work is partly supported by Grant-in-Aid for Scientific Research, The Ministry of Education, Science, and Culture.This paper is dedicated to Professor K. Sugimoto in commemoration of his sixtieth birthday.     

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.     

Ordinary and radiative muon capture in complex nuclei

The total rates of ordinary and radiative muon capture in natural zirconium and molybdenum are calculated within the quasiparticle random phase approximation. The total ordinary-muon-capture rates calculated with the unquenched weak axial-vector coupling are consistent with the experimental data and weakly depend on the weak pseudoscalar coupling. The calculated radiative-muon-capture rates have a clear dependence on the pseudoscalar coupling, but highly overestimate the experimental data. The text was submitted by the authors in English.     

A microscopic theory of muon capture in nuclei

The muon capture rates are calculated for a series of nuclei, using the Hartree-Fock randomphase approximation, and compared with experiment. The recoil term, the binding energy of the muon and finite size effects are calculated in detail. In a schematic model, the validity of the assumption M²_V = M²_A = M²_P is studied, and found to hold reasonably well even for nuclei as heavy as ²⁰⁸Pb.     

Negative muon capture in very light atoms

The transition rates for unbound muons to be captured into atomic bound states are calculated as functions of (1) incident muon center-of-mass energy, (2) muon principal quantum number n, and (3) muon (final) angular momentum l, for the hydrogen, helium, and lithium atoms. These rates reflect differences in electron binding energies. At muon energies of several hundred electron volts, lithium K-shell electrons are more likely to be ejected than the L-shell electron, while this behavior is reversed for energies ? 10 eV. However, in each case when the capture rate is folded with a muon stopping power function, the result is that more than half of the unbound muons are absorbed above 75 eV. Implications for experiments which look at muon transfer processes are noted.     

Search for supersymmetry in light nuclei

The supersymmetry assumption based on a system of valence interacting bosons and odd nucleons has been checked in the second half of the nuclear sd-shell. The dynamical supersymmetric hamiltonian restricted to the linear combination of chosen second-order Casimir invariants has been applied to energy levels of several nuclei organized in supermultiplets. The supersymmetry predictions for nine nuclei are in accord, to a good approximation, with experimental energy levels up to 4–7 MeV.     

Experimental results on radiative muon capture in complex nuclei

Experimental results for the radiative muon capture branching ratio in several nuclei and the photon-muon spin asymmetry in⁴⁰Ca are reported. For the measurements a two arm Nalspectrometer was used. Apart from²⁶O and⁴⁰Ca, where we confirm previous results of our group, new data on¹²C,²⁶Fe,¹⁶⁵Ho and²⁰⁹Bi are presented. No available theoretical models explain all the data consistently. The preliminary results for the asymmetry measurements, obtained using a stroboscopic method are in agreement with previous measurements and with theoretical calculations.Presented at the symposium Mesons and Light Nuclei, Bechyn, Czechoslovakia, May 27–June 1, 1985.     

Inclusive radiative muon capture in nuclei: A status report

The problems connected to the use of the effective Hamiltonian and to the nuclear excitation spectrum for inclusive radiative muon capture in nuclei are reviewed. Results are presented for⁴⁰Ca.Presented at the symposium Mesons and Light Nuclei, Liblice, Czechoslovakia, June 1981.     

Radiative Ml capture in light nuclei

The importance of semi-direct processes in E1 and E2 capture reactions has been well documented. Little is known, however, about M1 capture although a vast body of data indicates a non-statistical nature. We discuss here the importance of the semi-direct M1 process and concentrate in particular on recent experimental results claiming that the M 1 strength in²⁹Si isnearly one order of magnitude smaller than in ²⁸Si, the target nucleus. We use shell model arguments to demonstrate that this reduction is indeed consistent with the semi-direct reaction process and that other mechanisms like2p-2h fragmentation and phonon coupling are not likely to be instrumental in elucidating further the non-statistical nature of the²⁸Si+n reaction.     

Radiative muon capture for N = Z nuclei

The commonly used elementary hamiltonian of radiative muon capture has been confirmed, while the alternative Hwang-Primakoff approach is shown not to be gauge invariant.In the inclusive process on N = Z nuclei, the closure approximation is avoided by using a realistic nuclear excitation spectrum.The study is exemplified by a detailed application to ⁴⁰Ca. Predictions are given for the high-energy photon spectrum, circular polarization and asymmetry with respect to the muon polarization for various values of the pseudoscalar coupling constant g_p. A semi-quantitative agreement is found with the data on the spectrum; more precise experiments are necessary to determine g_p.     

Induced pseudoscalar interaction in weak nucleon current and muon capture in hyperfine states of muonic deuterium

Muon capture rate in muonic deuterium can be calculated with less ambiguities in nuclear wave functions, since we know the bound and scattering states of the two nucleons with higher accuracy theoretically. It is, however, dependent on the pion-nucleon-delta coupling constant through the exchange current effect. This dependence is considerably reduced for the ratio of the capture rates from two hyperfine states of muonic deuterium. This ratio is, therefore, useful to study the strength of the induced pseudoscalar term. Several other physical quantities in light nuclei are also introduced here for the same purpose.     

Neutron emission in muon capture by 40Ca

The neutron spectrum and asymmetry have been calculated for ⁴⁰Ca with different wave functions for the bound proton and the emitted neutron. The asymmetry is shown to be very sensitive to the behaviour of the wave functions near the nuclear surface while the spectrum is mostly sensitive to the strength of the real part of the neutron optical potential.     

Search for the Jacobi shape transition in light nuclei

The -rays following the reaction 105 MeV ¹⁸O + ²⁸Si have been measured using the EUROBALL IV, HECTOR and EUCLIDES arrays in order to investigate the predicted Jacobi shape transition. The high-energy -ray spectrum from the GDR decay indicates the presence of large deformations in the hot ⁴⁶Ti nucleus, in agreement with new theoretical calculations based on the rotating liquid-drop model.Received: 29 November 2002, Published online: 9 March 2004PACS: 24.30.Cz Giant Resonances - 21.60.Ev Collective modelsJ.P. Vivien: Deceased     

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.