[en] Isomer excitation by gamma-gamma' reactions and aluminium oxide thermoluminescence dosemeters (TLDs) have been used to monitor bremsstrahlung from the 4 MeV electron beam of a linear accelerator type LPR4 produced on a 0.9 mm Pt converter foil. Natural indium and osmium as well as TLDs have been irradiated at different distances (2-11 cm) and angles (0 deg.-90 deg.). Dose rates measured by TLDs were 5-110 kGy.h^-1. Isomer excitation of ¹¹⁵In (half-life 4.5 h) was used for monitoring bremsstrahlung of energies above 1 MeV, while that of ¹⁸⁹Os (half-life 5.8 h) extended the available range down to 200 keV. Isomer production yields measured by gamma spectrometry and found to be about 10^-19-10-18 Bq per nucleus were calibrated against dose rate. A graphical method based on a semiempirical formula was used to evaluate the bremsstrahlung flux as well as the dose rate from the activity of isomeric monitors with uncertainties below 20%. The method is simple, of linear response in a large scale, independent of temperature, and able to monitor extremely high gamma intensities. (author)

[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)