First direct observation of isomeric decay in neutron-rich odd-odd $^{186}$Ta

TL;DR

This paper reports the first direct observation of isomeric decay in neutron-rich odd-odd $^{186}$Ta, identifying new gamma-ray transitions and measuring the isomer's half-life, advancing understanding of nuclear structure in this isotope.

Contribution

It provides the first direct detection of isomeric decay in $^{186}$Ta and proposes a decay scheme based on new gamma-ray data and comparisons with previous measurements.

Findings

First observation of gamma transitions at 161.1 and 186.8 keV in $^{186}$Ta

Half-life of the isomeric state measured as 17(2) seconds

Proposed decay scheme for $^{186}$Ta based on new data

Abstract

De-excitation $\gamma $ rays associated with an isomeric state of $^{186}$Ta were investigated. The isomers were produced in multinucleon transfer reactions between a $^{136}$Xe beam and a natural W target, and were collected and separated by the KEK Isotope Separation System. Two $\gamma $ transitions with energies of 161.1(2) and 186.8(1) keV associated with an isomeric decay were observed for the first time. The half-life of the isomeric state of the neutral atom $^{186 \rm m}$Ta was deduced as 17(2) s. Based on the comparison with the previous measurements of the isomeric state using the ESR storage ring at GSI Darmstadt and the coupling of angular momenta of individual particle orbitals in odd-odd nuclei, a decay scheme of $^{186 \rm m}$Ta was proposed.