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Californium (Cf) is an artificial element, and thus a standard atomic mass cannot be given. Like all artificial elements, it has no stable isotopes. The first isotope to be synthesized was 245Cf in 1950. There are 20 known radioisotopes ranging from 237Cf to 256Cf and one nuclear isomer, 249mCf. The longest-lived isotope is 251Cf with a half-life of 900 years. == Californium-252 == Californium-252 (Cf-252) undergoes spontaneous fission and is used in small sized neutron sources. Fission neutrons have an energy range of 0 to 13 MeV with a mean value of 2.3 MeV and a most probable value of 1 MeV. This isotope produces high neutron emissions and can be used for a number of applications in industries such as nuclear energy, medicine, and petrochemical exploration. The neutron sources produced from Cf-252 are most notably used in the start-up of nuclear reactors. Once a reactor is filled with nuclear fuel, the stable neutron emissions from the source material initiates the chain reaction known as fission. Californium 252 has also been used in the treatment of serious forms of cancer. In patients suffering from certain types of brain and cervical cancer, Cf-252 can be used as a more cost-effective substitute for radium. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Isotopes of californium」の詳細全文を読む スポンサード リンク
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