First observation of the low-lying isomer state of ¹⁰¹In

Isochronous mass spectrometry has been applied to ¹¹²Sn projectile fragments at the HIRFL-CSR facility in Lanzhou. To produce short-lived nuclei of interest, we used projectile fragmentation of ¹¹²Sn³⁵⁺ primary beams in a ∼ 10 mm thick ⁹Be production target. The fragments were selected and analyzed by RIBLL2 and injected into the experimental storage ring (CSRe) every 25 s. To measure revolution times of stored ions, we used a Time-Of-Flight detector installed in CSRe. A new particle identification method was developed to distinguish ions on the measured revolution time spectrum for each injection. Based on this method, the shifts of the revolution time due to instable dipole magnet fields can be corrected and the ground and isomeric states of ¹⁰¹In have been well-resolved. The measured excitation energy is consistent with the theoretical value in the error range of 112 keV. The lifetime of the isomeric states of ¹⁰¹In is more than 200 μs. (authors)