Limits on nuclear excitation and deexcitation of 178Hfm2 by electron-nucleus coupling

Nuclear excitation in transitions that are resonant with electronic deexcitations are discussed in the context of recent claims of the triggering of the decay of 178 Hf m2 by irradiation with low-energy photons (C. Collins et al., Laser Phys. 14, 154 (2004)). The upper limits for the NEET cross sections are σ < 10 -31 cm 2 for transitions filling L-shell holes. These results are significantly below the values of 10 -22 cm 2 reported by Collins et al. and confirm the recent results by Tkalya (E. Tkalya, Phys. Rev. C. 68,064611 (2003)). These calculations suggest that NEET is unlikely to be the mechanism responsible for the reported apparent enhancements of 178 Hf nuclear line intensities by X-ray irradiation.