Nuclear photoactivation cross sections for short-lived isomeric states excited with a 6 MeV linac

Photoactivation cross sections for short-lived (T _{1 2} < 20 s) isomeric states in ¹⁶⁷Er, ⁷⁹Br, ¹⁹¹Ir, ¹⁸³W, ¹⁹⁷Au, ⁷⁷Se, ¹³⁷Ba and ⁸⁹Y were determined using bremsstrahlung from a 6 MeV medical therapy linac. A portable NaI(Tl) spectrometer and pneumatic transfer system was designed to avoid impacting normal use of the linac. Comparison with data obtained at the PITHON flash X-ray source (1.5 MeV endpoint energy) indicates that cross sections for populating these isomers through gateway states in the range 1.5-6 MeV are more than three orders of magnitude greater than corresponding cross sections below 1.5 MeV. The results are significant for the development of photoactivation techniques to measure short (<100 ns), nonreproducible bremsstrahlung pulses.