unsur 138Name of the isotope: Cesium-138; Cs-138 Symbol: 138 Cs or 138 55 Cs Mass number A: 138 (= number of nucleons) Atomic number Z: 55 (= number of protons) Neutrons N: 83 IsotopicAs of now, Unsur 138 may be a placeholder name for a element that would join the extended periodic table. The atomic number 138 suggests that could possibly are part of the list of