Laszlo Grenacs

Hyperfine effect in the MU - mesonic 11B atom and information on 11Be from muon capture measurements

Abstract The partial rates in the capture of muons by 11B were measured for the ground state and first excited level of 11Be. The transition between the hyperfine states of the μ-+11B mesonic atom was observed indirectly. The 320 keV γ-ray in 11Be, which follws the capture of the muon in 11B, was found to be broadened. Nuclear structure informations were obtained on the ground state and first excited state of 11Be.

Measurement of the induced pseudoscalar form factor in the capture of polarized muons by Si nuclei

Abstract The observation with high-resolution Ge detectors of the 1229 and 2171 keV gamma-rays emitted after the 28 Si(μ, ν) 28 Al(1 + , 2202 keV) reaction allowed us to determine the nuclear-amplitude ratio x ≡ M(2) M(−1) characteristic of this muon-capture reaction. Using the nuclear-structure dependent evaluation of various correction terms (model of Ciechanowicz), our result x = +0.254±0.034 provides for the induced pseudoscalar coupling g p the ratio g p g a (0.848m μ 2 ) = 3.4 ± 1.0 , to be compared to the PCAC prediction of g p g a = 7 . The model dependence of this apparent quenching remains to be assessed.

12B nuclear spin lattice relaxation time and electron-electron interaction in noble metals

Abstract We have measured the Korringa contribution T 1e to the nuclear spin lattice relaxation time of the interstitial 12 B in noble metals. The Korringa product of 12 B shows that the conduction-electron spin susceptibility is exchange enhanced similarly to that sensed by the matrix nucleus. The enhancement factors are equal within the experimental errors for both interstitial and matrix positions in Cu and Ag. The small difference of the enhancement factors in Au can be attributed to a probe effect.

Hyperfine Coupling of B-12 in Noble-metals and Al - Enhancement of the Conduction-electron Spin Susceptibility By E-e Exchange

We have remeasured the Korringa contributionT1e to the nuclear spin lattice relaxation time of the interstitial12B in nobel metals and in Al. TheT1eT times the squared Knight shiftK of12B taken from the literature, that is the Korringa product of12B, shows that the conduction-electron spin susceptibility is exchange enhanced similarly to that sensed by the matrix nucleus. The enhancement factors are equal within the experimental errors for both interstitial and matrix positions in Cu and Ag. The enhancement factors at the boron and at the matrix position are different in Au and Al.

Identification of Cross-relaxation Resonances of B-12 Implanted in Sc Aluminum

Polarized12B nuclei were produced andrecoil implanted in single crystals of fcc aluminum. The boron decay asymmetry andrelaxation times were measured as a function of external magnetic field values andat different orientation angles of the crystal. To identify the resonances at certain field values in the12B depolarization in Al, a consistent theory based on the principle of a multi-spin system and Nuclear level-crossing has been developed. A unique identification of the resonances, based on the resonant interaction between boron andparticular pairs of aluminum neighbours, is perfectly possible. The strong dissipative coupling of the Al nuclei with the electron bath of the lattice hinders a straightforward interpretation of the resonance width anddepth.

All-or-nothing Model and the Low Field B-12 Polarization in Rh Metal

A magnetic field dependent version of the all-or-nothing model of Bloembergen and Rowland is proposed as a working hypothesis for the interpretation of the low field “decoupling-curve” in Rh metal. Further experiments are proposed to check up the validity of the hypothesis.

One-photon |Δm| = 2 nuclear magnetic resonance near level crossings

The one-photon | xutri /b m/|=2 nuclear magnetic resonance in /sup 12/B (/b I/=1) was investigated. It is found that this resonance is quasi-allowed near low-field level crossings. Some of its applications are considered.

Macroscopic polarization signals with stopped muons

The authors point out the merits of macroscopic polarization signals known as Hanle signals, generated with stopped polarized muons.

Optimization of the Recoil-direction-sensitive Target for Muon-capture

The optimal thickness of layers composing nucleus-recoil-sensitive target that enables the measurement of a particular orientation parameter of the final nuclei B-12(gs)(I = 1(+)) and N-16(gs)(I = 2(-)) in the reactions mu(-) + C-12(0(+)) --> upsilon(mu) + B-12(gs)(I = 1(+)) and mu(-) + O-16(0(+)) --> upsilon(mu) + N-16(gs)(I = 2(-)) is estimated according to the current status of art of the slowing down of low energy (recoil energy of B-12 is 376 keV and that of N-16 is 300 keV) charged particles in matter. The choice of materials for orientation preserving (Ni, Ag, Rh) and for orientation-destroying (Al) layers which sandwich the production target layer C or BeO is based on the data obtained with polarized B-12 and N-13 radioactive nuclei beams at the Universite Catholique de Louvain.

Polarization Experiments in the Godfrey-Cycle

From the “new” experiments performed in the A = 12 mass multiplet, viz. i) beta-decay asymmetry of aligned 12B/12N mirror nuclei and ii) the average and longitudinal polarizations of 12B (g.s.) produced by μ-capture in 12C, we learned about the nature of weak interactions: there are no second class axial-vector currents, the weak magnetism is now verified in μ-capture, -the helicity of the “muonic” neutrino is measured with good precision (≃ 10%) (the result agrees with the standard V-A scheme).