A. Chatillon

Heavy Element Spectroscopy At JYFL

A series of experiments to study the properties of transfermium nuclei have been performed at the Department of Physics of the University of Jyvaskyla. The experiments are carried out by a large group of collaborating institutes. These studies have been rendered possible by the coupling of various state‐of‐the‐art detector systems to the RITU gas‐filled recoil separator. In‐beam conversion‐electron and gamma‐ray measurements have been made using the SACRED silicon and JuroGam germanium‐detector arrays, respectively. The introduction of the GREAT spectrometer and TDR data acquisition system have greatly improved the quality of the data obtained at RITU. A brief overview of the instrumentation used and highlights from recent experiments are presented.

EXPERIMENTAL MEASUREMENT OF THE DEFORMATION THROUGH THE ELECTROMAGNETIC PROBE: SHAPE COEXISTENCE IN EXOTIC KR AND SR ISOTOPES

The light krypton isotopes were studied in a series of Coulomb excitation experiments using radioactive beams at GANIL. The static quadrupole moments found in these experiments give firm experimental evidence for the shape coexistence scenario that is based on theoretical calculations and on the systematics of low-lying excited 0+ states. The experimental results are interpreted within a phenomenological two-band mixing model. Configuration mixing calculations based on triaxial Hartree-Fock-Bogolyubov calculations with the Gogny D1S effective interaction have been performed and compared to experimental data.

Shape Coexistence In Light Krypton Isotopes

Coexisting states of prolate and oblate shapes were studied via Coulomb excitation of radioactive 74Kr and 76Kr beams at safe energies at GANIL. The results for the transitional E2 matrix elements for several yrast transitions in both isotopes are in contradiction with the B(E2) values extracted from the lifetimes that are found in the literature. This motivated a new lifetime measurement which showed strong deviations from the previously published values, but is consistent with the results from Coulomb excitation. Having resolved these discrepancies and knowing the B(E2) values with high precision allows to extract the diagonal matrix elements from the Coulomb excitation data. The results confirm the proposed shape coexistence scenario.

Spectroscopy of odd‐proton nuclei in the region of 254No

Two rotational bands have been found in the transfermium nuclei 251Md and 255Lr, the latter being the heaviest nucleus so far studied in‐beam. Both are assigned to a [521]1/2− Nilsson state by comparison to theory. The experiments have been carried out in the Accelerator Laboratory of the University of Jyvaskyla (JYFL), where the array of germanium detectors JUROGAM was used in conjunction with the recoil‐seperator RITU and the focal‐plane setup GREAT for gamma‐spectroscopic studies.

Observation of a Rotational Band in the Odd-Z Transfermium Nucleus {sub 101}{sup 251}Md

A rotational band has been unambiguously observed in an odd-proton transfermium nucleus for the first time. An in-beam {gamma}-ray spectroscopic study of {sub 101}{sup 251}Md has been performed using the {gamma}-ray array JUROGAM combined with the gas-filled separator RITU and the focal plane device GREAT. The experimental results, compared to Hartree-Fock-Bogolyubov calculations, lead to the interpretation that the rotational band is built on the [521]1/2{sup -} Nilsson state.

In‐beam spectroscopy of 254No

Evidence for the presence of non‐yrast states in 254No has been observed in two different in‐beam experiments carried out at the University of Jyvaskyla. Firstly an in‐beam conversion electron spectroscopic study was performed with the SACRED spectrometer, revealing a distribution consisting of high‐multiplicity electron cascades. This provides an indirect proof of the presence of high K‐bands in 254No. In a more recent in‐beam γ‐ray spectroscopic measurement, evidence for the decay of non‐yrast states in 254No has been observed for the first time. It is speculated that the observation of high‐energy γ rays is due to the decay of a K = 3 band‐head state.