Natalis Severijns

Shape transition in light Pt isotopes: Magnetic moments and electric quadrupole moment ratios for185,187,189Pt

Nuclear orientation and nuclear magnetic resonance experiments were performed on185, 187, 189Pt isotopes oriented in Fe and single crystal Zn at temperatures down to about 6 mK. The hyperfine splitting frequencies of185Pt and187Pt in iron were determined to be 164.9(2) and 261.1(2) MHz, respectively. With the hyperfine field of −126.1(2.5) T, the g-factors are deduced to be |g(185Pt)|=0.172(3) and |g(187Pt)|=0.272(5).The spectroscopic quadrupole moment of187Pt was found to be negative with magnitude similar to that of189Pt, indicating a predominantly oblate ground state deformation for both isotopes. The spectroscopic quadrupole moment of185Pt was found to be positive, with the ratio Q(185Pt)/Q(189Pt)=−3.6(9), clearly indicating a change to prolate ground state deformation.

In-beam Nuclear-polarization By Ion-beam Surface Interaction

Recently, a set-up to polarize nuclei in flight has been developed at the LISOL isotope separator in Louvain-laNeuve. It is constructed in such a way that two complementary methods can be used: Tilted Foil (TF) and Ion Beam Surface Interaction at Grazing Incidence (IBSIGI). Both methods rely on an atomic polarization transfer to the nucleus, via hyperfine interaction. The atomic polarization is obstained by an anisotropic ion beam-surface interaction. This development completes the already existing Low Temperature Nuclear Orientation set-up and expands considerably the possibilities to polarize short lived nuclei. In a first run atomic polarizations of 50 keV N-14-beams were observed. Values up to 10% were obtained.

Search for Radiative β-Decay of the Free Neutron

Results of the first experiment to search for the radiative decay mode of the free neutron are reported. The γ-spectrum was studied in the energy region from 35 keV to 100 keV in six Cs(Tl) scintillators, each set at an angle of 35° to, and shielded from, a central plastic scintillator electron detector. Triple coincidences were recorded with recoil protons detected in a micro-channel plate. A limit for the branching ratio BR < 6.9 × 10−3 (90 % confidence level) was obtained, which is greater that the theoretical prediction by not more than a few tenths of a percent.