The Negative Parity Bands in $^{156}$Gd

Abstract

The high flux reactor of the Institut Laue-Langevin is the world most intense neutron source for research. Using the ultra high-resolution crystal spectrometers GAMS installed at the in-pile target position H6/H7 it is possible to measure nuclear state lifetimes using the Gamma Ray Induced Recoil (GRID) technique. In bent crystal mode, the spectrometers allow to perform spectroscopy with a dynamic range of up to six orders magnitude. At a very well collimated external neutron beam it is possible to install a highly efficient germanium detector array to obtain coincidences and angular correlations. The mentioned techniques were used to study the first two negative parity bands in $^{156}$Gd. These bands have been in the focus of interest since they seem to show signatures of a tetrahedral symmetry. A surprisingly high B(E2) value of about 1000 W.u. for the $4^- \rightarrow 2^-$ transition was discovered. It indicates that the two first negative parity bands cannot be considered to be signature partners.