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DNA-complexed heterodimers of the aryl hydrocarbon receptor (AhR) with the Ah receptor nuclear translocator (Arnt) are the molecular switches for nuclear signaling of 2,3,7, 8-tetrachlorodibenzo-p-dioxin (TCDD). AhR-Arnt heterodimers regulate genes involved in the metabolism of xenobiotics or fatty acids and various genes important for growth and differentiation. In this report several potent methods, such as the limited protease digestion, gel shift and gel shift clipping assays, allowed the investigation of ligand-stabilized conformations of AhR monomers in comparison to that of AhR-Arnt heterodimers. Interestingly, the ligand sensitivity of monomeric AhR was found to be very low at 25 nM, whereas DNA-dependent methods consistently provided EC(50) values between 0.12 and 0.6 nM for AhR in a heterodimeric complex, i. e. an approximate 100-fold higher ligand sensitivity. This indicates that complex formation of AhR with Arnt on DNA is an important and critical step in transforming AhR into a high affinity receptor for TCDD. A comparison of wild-type AhR with different C-terminal receptor truncations suggests that the PAS-B subregion of its PAS domain is of central importance for stabilization of a functional, i. e. ligand-sensitive, AhR-Arnt conformation, whereas the PAS-A subregion appears to be critical for dimerization of AhR and Arnt. In conclusion, the results of this study provide important information on the ligand sensitivity of AhR and AhR-Arnt heterodimer conformations.

This study is concerned with a device that is capable of detecting and locating gamma ray sources with high angular resolution and a 4π solid angle of acceptance. Three types of sensors were developed. The simplest detector is based on an ionization chamber (IC) configured with electrodes of high and low Z (atomic number) materials. Two other types of sensors developed in this study were a Geiger-Mueller (GM) and a Scintillation Counter (SC) with similar materials. The experimental results that were obtained with the IC imager demonstrate that sensors can be built to locate a gamma ray source with a resolution of 1.25″ and a 4π solid angle of acceptance. The three device types can function at high and low dose rates as low as background (i.e. depending on type) and energies from 14 keV to 20 MeV. Results obtained with the SC detector for directional measurements of four sources, three 137Cs and one 60Co source, and in another experiment of two sources, 137Cs and X-rays of 174 keV, are presented.

Irradiation of an insulator by gamma rays can produce voltage and charge buildups near thin layers of foreign material within the insulator. Measurements have been made of the current produced as a function of atomic number and thickness of the perturbing layer. Current was also measured as a function of separation from the perturbation, as was voltage buildup within the insulator close to the perturbation.