Introduction

Emanating from radioactive isotopes in the ground and from space, radiation has been a constant presence on the earth's surface ever since the planet came into existence approximately 4.5 billion years ago. This was the environment in which life on Earth began 3.5 billion years ago. The long, gradual period of evolution that followed eventually resulted in the emergence of the ancestors of humankind approximately 2 million years ago. Organisms have thus come into being, evolved, and lived in the presence of radiation for an extraordinary long time, and it is therefore unsurprising that organisms accustomed to such an environment utilize small amount of radiation as stimulation. That such organisms have also evolved with mechanisms to protect them against the harmful effects of radiation can be regarded as only natural. Since 1988, Central Research Institute of Electric Power Industry has, with the cooperation of both Japanese and international research institutions, focused its investigations on the effects of low radiation doses on organisms. In the 21st century, radiation is expected to become an increasingly important resource for humans in areas such as the use of radiation in medicine and industry and the peaceful use of atomic energy. With this firmly in mind, CRIEPI established Low Dose Radiation Research Center on October 2000 with the express aims of further promoting research as widely as possible. In addition to performing in-house research, Low Dose Radiation Research Center is dedicated to strengthening ties with outside research institutions and serving as a research network base, gathering and disseminating information that promotes an accurate understanding and application of the effects of low radiation doses on organisms.