Radiation dosimetry by measurement of polarization and depolarization

Abstract

This invention provides a method of measuring exposure to radiation, particularly x-rays, gamma rays and other forms of penetrating radiation. A dielectric body is provided and is equipped with a pair of electrodes on opposite sides thereof. In accordance with one procedure which may be called radiation induced thermally activated depolarization (RITAD), an electrostatic bias polarization is produced in the dielectric body, preferably by heating it to an elevated temperature, impressing a voltage between the electrodes to produce internal polarization in the body, and cooling the body while maintaining the voltage, so as to freeze in the bias polarization. The voltage is then removed, and the electrodes may be short circuited. The body is then exposed to the radiation to be measured. After such exposure, a current measuring circuit is established between the electrodes. The electrical currents in such circuit are observed and measured as the energy level of the body is raised, preferably by heating the body. One or more current peaks related to the radiation are observed at temperatures where no current is observed in the absence of the exposure to radiation. The magnitude of such current peaks is a measure of the total radiation dosage. Such observed current peaks are indicative of radiation induced thermally activated depolarization in the dielectric body. Many different dielectric materials may be employed, such as calcium fluoride, strontium fluoride, lithium fluoride and various ceramic materials such as magnesium oxide and beryllium oxide. In a modified procedure, which may be called radiation induced thermally activated polarization (RITAP), the dielectric body is not given an initial bias polarization, but rather is exposed to radiation without any such initial polarization. After such exposure, the electrodes on the dielectric body are connected into a series circuit which includes a current measuring instrument and a battery or some other source of a uni-directional voltage. The electrical current in such circuit is then observed and measured as the energy level of the dielectric body is raised, preferably by heating the body. If the dielectric body has been exposed to radiation, a polarization current peak is observed at a characteristic temperature. The magnitude of the peak is a measure of the total radiation dosage. The voltage source may then be removed from the circuit so that the current measuring instrument is connected directly across the electrodes. The dielectric body is then heated to a higher temperature. At one or more characteristic temperatures, one or more depolarization current peaks are observed. The direction of the depolarization currents is opposite from the direction of the polarization current. The magnitude of the depolarization current peaks is also a measure of the total radiation dosage.