Photon cross sections for resonant de-excitation of nuclear isomers as a precursor to a gamma-ray laser

Integrated cross sections (ICS) for triggered decay of nuclear isomers have recently become accessible in experimental studies that were motivated bot h by general physical interest and by applications, such as a possible gamm a-ray laser. Theoretical predictions for ICS are reviewed here and an equat ion is derived based on the Blatt-Weisskopf probability for an electromagne tic transition between two nuclear levels. This formula is effectively equi valent to the recognized Breit-Wigner expression despite their development from essentially different approaches. The results of a recent high-sensiti vity experiment on the Ta-180(m) isomer de-excitation induced by bremsstrah lung are analyzed in this context. An important parameter of the de-excitat ion branch probability is determined now over a wide energy range from 1 to 10 MeV, including previously reported results.