Californium-251 is a radioactive isotope of the element californium, which is a synthetic element first discovered in 1950. It has a half-life of about 898 years, making it one of the more stable isotopes of californium. Californium-251 is primarily used in scientific research and has applications in neutron activation analysis and as a neutron source in various industrial processes. Due to its radioactivity, Californium-251 must be handled with care in controlled environments. It emits neutrons, which can be useful in certain types of nuclear reactors and in medical applications, such as cancer treatment. Its unique properties make it valuable in both research and practical applications.