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Abstract

Masses of ¹¹²Sn projectile fragments were measured employing isochronous mass spectrometry at the Cooler Storage Ring in Lanzhou. Different from the previous data analysis method, relying on the arithmetic mean revolution times of the stored fragments, we introduce an exponentially modified Gaussian function to describe the asymmetric peak shapes. This new approach enables us to properly deconvolute the overlapping peaks of stored ions and to accurately determine their masses. The mass excesses of ¹⁰³Sn and the low-lying 1/2⁻ isomers in ⁸⁷Mo, ⁹¹Ru, and ⁹⁵Pd were directly measured for the first time, and the masses of ⁶⁹As, ⁷³Br, ⁷⁵Kr, ⁷⁹Sr, and ⁸¹Y were redetermined with higher precision comparable to that of Penning-trap mass spectrometry. Based on the new mass value of ¹⁰³Sn, the previously unknown masses of ¹⁰⁴Sb, ¹⁰⁷Te, ¹⁰⁸I, ¹¹¹Xe, and ¹¹²Cs were obtained indirectly by using the literature proton and/or α decay energies. Systematic trends of the excitation energies of the J^π=1/2⁻ isomers in the N=47,49 isotones are well reproduced by the state-of-the-art shell model calculations with the tensor forces included.