Patent Number: 039393666
Section: summary

The present invention relates to a method of converting radioactive energy to electric energy and a device for performing the same method. There is known a method of atomic energy power generation in which nuclear fission energy is converted to thermal energy and thermal energy is further converted to electric energy. With the development of such atomic energy power generation, there has been a rapid increase in the amount of radioactive substance; resulting from the reprocessing of used nuclear reactor fuel and in the radioactive fission products of nuclear reactors. Research is being carried out to find uses for these radioactive substances and, in particular, research is actively being carried out toward the development of a device for converting the radioactive energy emitted from such substances to electric energy. That is to say efforts are being put into the development of an atomic energy battery. Heretofore, there have been known a variety of methods for converting the radioactive energy emitted from radioactive substances into electric energy and, in general, these conventional methods can be classified into the following four systems on the basis of the converting mechanism. A. Direct converting system: Radioactive energy emitted from the radiocative substance is directly converted to electric energy. More particularly, in one example of the system conversion is accomplished by either (i) inserting a radioactive substance (.alpha. radiation source) into a vacuum glass container, the inner wall of which is silverplated and is used as the collector electrode or (ii) surrounding a radioactive substance (.beta. radiation source) disposed in a vacuum container with a solid state dielectric which serves as the collector electrode. However, with this system, the conversion efficiency is low, being less than 0.05%, and thus this system has not been put to practical use. B. Two-step type converting system: This system utilizes two steps for the energy conversion, i.e., radioactive energy emitted from the radioactive substance is used first to induce a certain physical phenomenon and then the phenomenon is caused to produce electric energy. Examples of this system which have been known are (i) to produce electron-hole pairs in a semiconductor by irradiating the semiconductor with a radioactive ray from a radioactive substance and then to derive electric current resulting from an electric field generated at the P-N junction of the semiconductor which causes electrons to move toward the N type region thereof and the holes toward the P type region thereof, (ii) to produce recoil electrons due to Compton scattering by surrounding a radioactive substance (.gamma. radiation source) with an insulating material and then to collect the recoil electrons and (iii) to polarize a gas introduced into the space between a pair of electrodes of metals, whose work functions are different from each other, by irradiating the gas with a radioactive ray from a radioactive substance or by introducing a gaseous radioactive substance etc. into the space and inducing a voltage due to the difference in contact potential difference between the polarized gas and the respective metal electrodes. However, the energy conversion efficiency of this system is less than 0.4%. c. Three-step type converting system: In this system, radioactive energy from a radioactive substance is used to change the physical state of certain substances through two sequential steps and then the resulting state produces electric energy. For example, a mixture of a radioactive substance and a fluorescent material is sandwiched by a pair of photo-electric cells and the fluorescent material is illuminated by the radioactive rays from the radioactive substance. The photo-electric cells detect this luminescence and generate an electromotive force. In general, this system requires a very complex structure but nevertheless provides poor conversion efficiency on the order of less than 0.01%. d. Heat-engine type converting system: This system includes the thermoelectric type converting method, the thermionic type converting method and the heat engine type converting method, and, in some of these methods, there is provided a conversion efficiency as high as 5%. However, the devices used in these converting methods require very complex construction and are not economical. As mentioned above, conventional converters of relatively simple construction generally provide relatively low conversion efficiency. On the other hand, conventional converters of more complex construction generally provide higher efficiency but are not economical. The primary object of the present invention is to provide a two-step type converting system for converting radioactive energy to electric energy and a device for performing the same with a simple construction and with high efficiency.