Thermally Stimulated Current Radiation Dosimeter

Thermally stimulated current (TSC) radiation dosimeters were made from the borosilicate sealing glass used to make transistor headers. These dosimeters, consisting of a metal-glass-metal sandwich structure with electrodes (Kovar or Nicoseal) bonded to the glass with glass-to-metal seals, were experimentally studied to determine how they operate, and how they can be used in the design of a practical dosimetry system. Exposure to ionizing radiation (Co60-gamma or 175 kV X-rays) created trapped charge in the glass. Heating the dosimeter from one side, so as to produce a temperature gradient across the glass, released the trapped charge and produced a TSC which was observed as a TSC vs. temperature glow curve. The integrated charge output from a dosimeter was proportional to the radiation dose. This output for a given dose increased with increasing temperature gradient but was relatively independent of the heating rate. Eiectrodes that were pressed against the glass rather than bonded with a glass-to-metal seal were found to yield large current reversals and thus are unsuitable for dosimetry applications. A simple model is proposed to explain the origin of the TSC and the qualitative behavior of this current. The TSC dosimeter is small, rugged, and inexpensive. Because it produces an electrical output, it requires simpler readout equipment than other dosimetry systems currently available, such as the LiF, TLD system. Its main disadvantage is the rapid fading of the stored charge in the glass at room temperature (~50 percent five hours after irradiation).