52 research outputs found
A tentative 4- isomeric state in Sr-98
Annual Report 2001, Institut fuer Kernchemie,
Johannes-Gutenberg-Universitaet, Mainz, GermanyComment: 3 pages, 1 figur
Percolative phase transition on ferromagnetic insulator manganites: uncorrelated to correlated polaron clusters
In this work, we report an atomic scale study on the ferromagnetic insulator
manganite LaMnO using PAC spectroscopy. Data analysis
reveals a nanoscopic transition from an undistorted to a Jahn-Teller-distorted
local environment upon cooling. The percolation thresholds of the two local
environments enclose a macroscopic structural transition
(Rhombohedric-Orthorhombic). Two distinct regimes of JT-distortions were found:
a high temperature regime where uncorrelated polaron clusters with severe
distortions of the MnO octahedra survive up to
and a low temperature regime where correlated regions have a weaker
JT-distorted symmetry.Comment: 4 pages, 4 Figures, submitted to PRL, new version with more data,
text reformulate
Positron-neutrino correlations in 32Ar and 33Ar Decays: Probes of Scalar weak currents and nuclear isospin mixing
The positron-neutrino correlation in the 0^+ \to 0^+ \beta decay of ^{32}Ar
was measured at ISOLDE by analyzing the effect of lepton recoil on the shape of
the narrow proton group following the superallowed decay. Our result is
consistent with the Standard Model prediction; for vanishing Fierz interference
we find a=0.9989 \pm 0.0052 \pm 0.0036. Our result leads to improved
constraints on scalar weak interactions. The positron-neutrino correlation in
^{33}Ar decay was measured in the same experiment; for vanishing Fierz
interference we find a=0.944 \pm 0.002 \pm 0.003. The ^{32}Ar and ^{33}Ar
correlations, in combination with precision measurements of the half-lives,
superallowed branching ratios and beta endpoint energies, will determine the
isospin impurities of the superallowed transitions. These will provide useful
tests of isospin-violation corrections used in deducing |V_{\rm ud}| which
currently indicates non-unitarity of the KM matrix.Comment: 15 pages, 6 figure
Low-lying levels in Xe
The decays of Cs and Cs to Xe have been studied on mass separated samples, using and internal conversion electron measurements. Several new low-lying levels have been established in the Xe level scheme. Half-life evaluations for Cs and Cs have been revisited. The results are compared with other experimental data known in light odd-mass xenon isotopes and with calculations performed in the frame of the multi-shell interacting boson-fermion model
Positron-neutrino correlation in the 0^+ \to 0^+ decay of ^{32}Ar
The positron-neutrino correlation in the decay of
Ar was measured at ISOLDE by analyzing the effect of lepton recoil on
the shape of the narrow proton group following the superallowed decay. Our
result is consistent with the Standard Model prediction. For vanishing Fierz
interference we find , which yields improved
constraints on scalar weak interactions
- decay of the M=-1 nucleus Zn studied by selective laser ionization
- decay of Zn has been studied for the first time. A new laser ion-source concept has been used to produce mass-separated sources for and - spectroscopy. The half-life of Zn was determined to be 86(18) ms. Comparisons are made with previous data from charge-exchange reactions. Our Gamow-Teller strength to the 1 state at 1051 keV excitation in Cu agrees well with the value extracted from a recent (He, t) study. Extensive shell-model calculations are presented
First decay study of the very neutron-rich isotope Br-93
The decay of the mass-separated, very neutron-rich isotope Br-93 has been
studied by gamma-spectroscopy. A level scheme of its daughter Kr-93 has been
constructed. Level energies, gamma-ray branching ratios and multipolarities
suggest spins and parities which are in accord with a smooth systematics of the
N=57 isotones for Z less-equal 40, suggesting the N=56 shell closure still to
be effective in Kr isotopes. So far, there is no indication of a progressive
onset of deformation in neutron-rich Kr isotopes.Comment: 17 pages, 3 figures, Phys. Rev. C, in prin
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A chemically selective laser ion source has been used in a -decay study
of heavy Ag isotopes into even-even Cd nuclides. Gamma-spectroscopic
techniques in time-resolving event-by-event and multiscaling modes have
permitted the identification of the first 2 and 4 levels in
Cd, Cd, and tentatively the 2 state in
Cd. From a comparison of these new states in Cd with the
and level systematics of Pd and Te
isotopes and several recent model predictions, possible evidence
for a weakening of the spherical neutron-shell below double-magic
Sn is obtained
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