Californium is a chemical element with the symbol Cf and atomic number 98. It is a silvery white actinide metal element that was first synthesized by bombardment of curium with alpha particles by a team at the University of California, Berkeley in 1950 and named for the state of California.
Californium is melting point of 900° C and a boiling point of 1745° C. It is a soft malleable metal that is easily cut with a knife. It can form alloys with lanthanide metals. When heated, it reacts with hydrogen, nitrogen and oxygen. It forms salts with nitrogen, and sulfur as wells as the halogen family of elements which include fluorine, chlorine, bromine, iodine, and astatine.
Californium has no stable isotopes. All of its 20 isotopes are radioactive. They vary in atomic weight from 237 to 256 with half-lives ranging from 45 millionths of a second to Cf-251with a half-life of 900 years. Cf-251 and Cf-252 emit gamma radiation. Most isotopes of californium decay by emission of alpha particles to curium or by emission of beta particles to berkelium. A few isotopes can decay to fermium and einsteinium.
Californium is the heaviest element that exists in nature. It is generated by neutron capture and beta decay in rich deposits of uranium ore. It is not very soluble in water and will be present in much larger quantities in soil than in water. There is a small amount of californium created by nuclear explosion and present in nuclear fallout.
Californium-250 is produced by bombarding berkelium-249 with neutrons. Cf-251 and Cf-252 are generated by bombarding Cf-250 with neutrons. Cf-252 has many applications because it is a strong neutron emitter. One fresh microgram of californium will generate 139 million neutrons per minute. Cf-252 used to be mainly used for reactor startup but that use has declined in recent years. It is used to treat some forms of cervical and brain cancer. It is used by universities for educational purposes. It is used inline to analyze bulk materials such as coal. Neutron penetrate into various materials and can be used to image such things as thickness, integrity and other useful physical properties of nuclear fuel rods, airplane parts, and corrosion, bad welds, cracks and trapped moisture in pipelines. Neutrons moisture gauges are used in the oil industry, in gold and sliver prospecting, and to detect groundwater movement. Californium-249 has been used to create a few atoms of ununoctium, element 118, the heaviest element ever synthesized. Bombardment of californium has also been used to synthesized other transuranic elements such as lawrencium, element 103.
Californium has no natural biological function due to its scarcity and high radioactivity. If it enters the body through consuming food, drinking fluids or breathing air contaminated by particles of californium, about two third will be deposited in the skeleton and a quarter in the liver. Californium in the skeletal tissue can interfere with the body’s ability to produce red blood cells. Gamma radiation from Cf-251 and Cf-251can cause bone and/or liver cancer when present in the body.
Toy train with californium-252 used for calibration at Princeton Plasma Physics Laboratory:
