In the present work, data of from a Coulomb excitation experiment of 140Sm was analyzed. The experiment was carried out at the ISOLDE facility at CERN in 2017 to investigate the nuclear structure of 140Sm. This isotope is of great importance to explain nuclear shape transitions, as it lies in between a spherical and deformed shape.
In the experiment, a radioactive ion beam of 140Sm was accelerated into a 208Pb target. Silicon detectors were utilized to determine the energies and angles of the scattered particles, and germanium detectors to measure the γ-rays of excited states in 140Sm. MiniballCoulexSort, a code which is under development at ISOLDE, was applied to sort the data. A fully calibrated data set was obtained, in addition to Doppler corrected γ spectra for 140Sm with good resolution.
As expected, a number of previously known γ transitions were observed. Excited states up to and including the 8+ state at 2970 keV were populated in 140Sm. Two peaks in the γ-ray spectrum do not correspond to any of the known transitions in the level scheme. One peak is observed at approximately 844 keV, and the other at approximately 1860 keV. The results suggests that these peaks are previously unknown transitions.
In particular, the peak at 844 keV may be a member of the γ-vibrational band, which is theoretically predicted to to be built on the observed second 2+ state at 990 keV. The intensity of the new 844 keV transition is relatively strong and it is observed to arrive in coincidence with the 990 keV (second 2+) state, making it a good candidate for the theoretically predicted first 3+ state. Further analysis is needed to determine if the 844 keV transition identifies as the first 3+ state. If verified, the new first 3+ state will certainly clarify the role of triaxial deformation of 140Sm.