The nucleus 180 73Ta is unusual because it has both odd Z and odd N, yet it is barely un...

The nucleus 180 ⁷³Ta is unusual because it has both odd Z and odd N, yet it is barely unstable with a half-life of 8 hours. It has an isomeric state at excitation energy 0.075 MeV that experimental measurements indicate has a half-life greater than 10¹⁵ y. For many years it was believed that this long-lived excited state was the ground state and might be stable. All the stable odd Z and N nuclei are smaller than ¹⁶O. Why are all heavy elements with both odd Z and N unstable? The spins of the ¹⁸⁰Ta ground state and isomeric states are believed to be 1⁺ and 9^-, respectively. Explain why scientists may have believed for so long that 180Ta was stable.