“I couldn’t find a half life on tantalum 181.”
There is no half life for Tantalum 181, it is a stable isotope:
Isotope Half Life
Ta-179 1.8 years
Ta-180 1.2E15 years
Ta-181 Stable
Ta-182 114.43 days
So what do you think they mean they fired tantalum 181?
If you wrapped a nuclear bomb with tantalum 181, the bomb would create a range of tantalum isotopes wouldn’t it?
Neutron flux from the explosion would form radioactive isotopes of tantalum via neutron capture.