[en] Photoexcitation of ¹⁸⁹Os to its 5.8 h half-life metastable state may be a practical method for monitoring high dose irradiations. The activity of the nuclear isomer provides a response proportional to the dose rate. A metallic powder natural Os sample of 2 g mass pressed into pellet form of diam. 35 mm was irradiated by a 51 TBq ¹³⁷Cs source. The isomeric activities were measured by a Ge detector. Response function of ¹⁸⁹Os isomer production for 300 kV X rays, ¹³⁷Cs and ⁶⁰Co sources, as well as bremsstrahlung of a 4 MeV electron linear accelerator, were also measured and compared with that of ¹¹⁵In isomer production. Aluminium oxide thermoluminescence dosemeters were used for dose measurements. The method is suitable for monitoring radiation fields of high dose rates, where other methods suffer from difficulties (saturation, supralinearity, etc.). Other advantages are simplicity, large scale linearity, and independence of temperature. (author)