Study of 254Es by Coulomb Excitation Gamma-Ray Spectroscopy

The 254Es gamma-ray spectrum was investigated by making coincidence between the gamma rays and scattered 58Ni nuclei. The gamma spectrum is made from coincidence data after gain matching and Doppler shift correction. From the gamma spectrum, energy and relative intensity of transitions of 254Es are deduced. The extracted data could help to extend the 254Es level scheme and in the future may permit to determine its quadrupole deformation.日本物理学会2021年次大

Nuclear structure study of 254Es via Coulomb Excitation Gamma-ray Spectroscopy

Exploring the new elements toward the high end of the nuclear chart is one of the most interesting topics in nuclear physics. A region of long-lived superheavy elements with proton and neutron numbers near Z=114, Z=120, N=184 – the so-called “Island of Stability” (IoS) is predicted to be the next “promised land”. Currently, access to the IoS is limited by the very low cross sections that affect present experimental techniques. Single-particle orbitals neighboring the deformed shell gaps in the region near Z=100 and N=152 are predicted to be linked to the spherical shells in the IoS. This link provides indirect information on the shell structure of nuclei in the IoS. 254Es (Einsteinium-254, Z=99, N=155) is an isotope in the region of deformed shell gaps and currently the heaviest target available for Coulomb excitation experiments.A 254Es Coulomb excitation experiment was performed at the JAEA-Tokai Tandem accelerator using 58Ni beam with an energy of 250 MeV. The very rare 254Es was produced at the High-Flux Isotope Reactor at ORNL, USA, and the target was produced using less than a microgram of material. The scattered beam particles were detected by two segmented CD-silicon detectors placed backward and forward from the target in coincidence with γ rays detected by 4 LaBr3(Ce) scintillators, 4 single-crystal Ge detectors and 4 Clover-type Ge detectors. Safe Coulomb excitation of 254Es was achieved for the first time to study its excited states. The particle-gamma coincidence spectrum created after Doppler-shift correction was analyzed. From the gamma spectrum, several new transitions of 254Es were observed indicating a rotational band structure. The extracted data will permit extending the 254Es level scheme and to determine its quadrupole deformation.日本物理学会第77回年次大