A: This work describes the advantages of using directional sheath on Geiger-Müller detector. It has been experimentally demonstrated that the response of the detector to gamma radiation in intermediate energy range 100 keV to 1.5 MeV can be significantly (by up 20 % for 137 Cs and up 44 % for 60 Co sources) improved by using lead sheath surrounding the detector and opened in the direction of the incident radiation due to the interaction of the incident radiation in the sheath.

Two fluoropolymers polyvinylidene fluoride (PVDF) and ethylene tetrafluoroethylene (ETFE), which differ only in chemical structure and have the same atomic composition, were evaluated for use in air simulation for phantom measurements in photon beams. Photon interaction was modelled using US-NIST datasets. In order to mimic the radiation properties of air with another material, values of the following quantities were chosen for comparison: total mass attenuation coefficients, mass-energy absorption coefficients, total electron mass stopping powers, mass collision stopping powers, and mass scattering powers. The calculated ratios of the corresponding coefficients or stopping powers between the material and air were the values of interest. The results for fluoropolymers were compared with other polymers commonly used in the manufacture of phantoms. The results show that in the photon energy range from 150 keV to 1 GeV both fluoropolymers exhibit excellent dosimetric properties slightly better than air equivalent plastic C552. The effect of a carbon-based filler added to the fluoropolymer to ensure the electrical conductivity of the resulting composite was also investigated. It has been found that the increased carbon-based filler content (up to 20 wt% of carbon) added to the fluoropolymer has a very small effect on the radiation properties of the composite.

Different inorganic materials were evaluated as substitutes for air, in photon radiation environments. The materials were evaluated based on their: total mass attenuation coefficients, mass-energy absorption coefficients, total electron mass stopping powers. Common inorganic compounds and mixtures not containing carbon were theoretically tested with the aim to find a solid or liquid air substitute material for photon radiation. As presented in this work, the best results of these tests were achieved for liquid nitric acid diluted in water at 81 wt%. This solution exhibits hitherto unknown properties similar to air for photon radiation in the energy region 0.1 to 1000 MeV and can be used for air photoactivation determination as well. The inherent property of this aqueous solution is that it allows simultaneous determination of all photonuclear reaction yields from nitrogen and oxygen in a wide range of photon energies. Additionally, this aqueous solution does not contain any other constituent elements, which could affect the accuracy of this determination.