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

TL;DR

This study presents high-precision mass measurements of neutron-rich isotopes near $^{132}$Sn, revealing unexpected odd-even staggering behaviors and challenging existing nuclear models, especially around the $N$=82 shell closure.

Contribution

It provides the first measurements of certain r-process nuclei masses and uncovers anomalous odd-even staggering patterns not explained by current theories.

Findings

Strong $N$=82 shell gap at $Z$=50 confirmed

Quenching of neutron pairing gap across $N$=82 in Sn

Unexplained $Z$-dependence in odd-even staggering

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.