Direct Energy Conversion from Gamma Ray to Electricity Using Silicon Semiconductor Cells
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1264-BB05-01
Direct Energy Conversion from Gamma Ray to Electricity Using Silicon Semiconductor Cells K. Hashizume1, H. Kimura1, T. Otsuka1, T. Tanabe1 and T. Okai2 1
Interdisciplinary Graduate School of Engineering Sciences, Kyushu Univ., Fukuoka 812-8581, Japan 2 Applied Quantum Physics and Nuclear Engineering, Kyushu Univ., Fukuoka 812-8581, Japan
ABSTRACT Gamma cells using p-type Si substrates with various resistivities were fabricated with a vacuum evaporation method. The energy conversion efficiency from gamma ray to electric power successfully reached about 2% for the gamma cell with a resistivity of 50~100 Ω·cm. INTRODUCTION Large amounts of nuclear spent fuel and high level radioactive waste are generated in nuclear power stations and reprocessing plants every year and stored in storage facilities for 2030 years. The spent fuel and radioactive waste still have residual energies, such as high-intensity gamma rays. Currently, these energies are wasted but if the gamma ray energy was effectively converted other forms of energy, they could be a promising and long-lasting power source. Therefore, there are some proposals to use the gamma ray energy effectively. Horiuchi et al. [1, 2] tried to convert the gamma ray to electricity energy using several types of Si solar cells and scintillation materials. In this application, gamma ray energy is converted to visible light with the scintillation materials and then the light converted to electricity energy. The drawback of this method might be low energy conversion ratio because the conversion ratio is a product of two conversion processes. It is known that the semiconductor radiation detectors can generate a electric current in gamma-ray irradiation even without applying a reverse bias [3,4]. Hence we have tried to convert the gamma ray to electric power directly and with a high efficiency using semiconductor materials, structures of which resemble solar cells and the semiconductor detectors (we call it a gamma cell hereafter). In the cells, mechanism of the electric power generation is similar to the solar cells and semiconductor detectors, i.e. the intense gamma ray is converted to low energy electrons and low energy X rays by interaction between gamma rays and cell materials, and then electron-hole pairs are generated in the cells by the low energy electrons and low energy X rays. The electron-hole pairs are separated to each electrode like solar cell due to p-n or Schottky junction forming in the cells. Si solar cell itself can convert gamma ray to electricity, but the conversion efficiency is very low because the cell structure is optimized for solar light, not for gamma ray. For the gamma cell, it is important that the recombination of the electron-hole pairs generated in the cell should be suppressed. Since the recombination should be related to the specific resistivity of the semiconductor cell, we examined the influences of the resistivity on the electric power generation by using the gamma cells made of Si single crystal with various specific resistiviti
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