Identification of the slow E3 transition 136mCs -> 136Cs with conversion electrons

TL;DR

This study used conversion-electron spectroscopy at ISOLDE to measure the excitation energy, decay multipolarity, and half-life of the 8- isomer in 136Cs, revealing a new intermediate level and decay pathways.

Contribution

It provides the first measurement of the excitation energy and decay multipolarity of the 136Cs isomer, and identifies a new 105 keV level with spin 4+.

Findings

Half-life of the isomer is 17.5 seconds.

Decay occurs via a slow 518 keV E3 transition.

A new 105 keV level with spin 4+ was discovered.

Abstract

We performed at ISOLDE the spectroscopy of the decay of the 8- isomer in 136Cs by and conversion-electron detection. For the first time the excitation energy of the isomer and the multipolarity of its decay have been measured. The half-life of the isomeric state was remeasured to T1/2 = 17.5(2) s. This isomer decays via a very slow 518 keV E3 transition to the ground state. In addition to this, a much weaker decay branch via a 413 keV M4 and a subsequent 105 keV E2 transition has been found. Thus we have found a new level at 105 keV with spin 4+ between the isomeric and the ground state. The results are discussed in comparison to shell model calculations.