Precision Mass Measurements beyond ${}^{132}$Sn: Anomalous behaviour of odd-even staggering of binding energies

Abstract

Atomic masses of the neutron-rich isotopes ${}^{121-128}$Cd, ${}^{129,131}$In, ${}^{130-135}$Sn, ${}^{131-136}$Sb, and ${}^{132-140}$Te have been measured with high precision (10 ppb) using the Penning trap mass spectrometer JYFLTRAP. Among these, the masses of four r-process nuclei ${}^{135}$Sn, ${}^{136}$Sb, and ${}^{139,140}$Te were measured for the first time. The data reveals a strong $N$=82 shell gap at $Z$=50 but indicates the importance of correlations for $Z>50$. An empirical neutron pairing gap expressed as the odd-even staggering of isotopic masses shows a strong quenching across $N$=82 for Sn, with the $Z$-dependence that is unexplainable by the current theoretical models.

4 Pages, 5 figures. Revised version which focuses on odd-even staggering