Californium-252 is a neutron emitter with a high specific activity, making it useful in a variety of applications, the most spectacular of which is in brachytherapy for cancer patients. Radiation oncology has exhausted nearly every option for treating radioresistant tumors by photon brachytherapy, and therefore new types of radiation need to be studied to improve the curability of cancer. Audience: Californium brachytherapy is used in only a few radiation therapy centers in the world, so the book will be highly instructive for radiation oncologists, medical physicists and radiobiologists. The nuclear techniques used in clinical applications may also interest nuclear physicists and engineers.