Continuing from our 1988 report that ¹⁸⁰Ta gained energy by absorbing x-rays to reach a K-mixing level from the isomer and from the 1990 report of Walker et al. that ¹⁷⁴Hf spontaneously radiated away energy to reach a K-mixing level...In 1995 we studied the systematics for the decay of the 4-QP and 5-QP isomers of the different Hf isotopes.

There were K-mixing levels throughout the Hf's that tended to settle to lower energy with increasing mass.

Systematics predicted a K-mixing level could be reached from the ¹⁷⁸Hf isomer by absorbing less than 250keV from a photon.

C.B. Collins, ...et al., Hyperfine Interactions, 107, 141 (1997).