Radioactive decay spontaneous fission: half-lives

The most stable isotope of plutonium is Pu-244, with a half-life of S.OOxlO+ years (about 82,000,000 years). Being radioactive, Pu-244 can decay in two different ways. One way involves alpha decay, resulting in the formation of the isotope uranium-240, and the other is through spontaneous fission. 

Californium is a synthetic radioactive transuranic element of the actinide series. The pure metal form is not found in nature and has not been artificially produced in particle accelerators. However, a few compounds consisting of cahfornium and nonmetals have been formed by nuclear reactions. The most important isotope of cahfornium is Cf-252, which fissions spontaneously while emitting free neutrons. This makes it of some use as a portable neutron source since there are few elements that produce neutrons all by themselves. Most transuranic elements must be placed in a nuclear reactor, must go through a series of decay processes, or must be mixed with other elements in order to give off neutrons. Cf-252 has a half-life of 2.65 years, and just one microgram (0.000001 grams) of the element produces over 170 mhhon neutrons per minute. 

Detection of these elements relies on studying their radioactive decay, which is usually either a-emission or spontaneous fission. A time-correlation process is used in this, a solid-state detector monitors both the time and position of arrival of fusion products. Subsequent decay events at this position give not just the decay information of the atom (half-life, O -particle energy) but also the corresponding information for its decay products, which are recognizable and thus known nuclei. This therefore gives a history of stepwise decay of the initial product. 

Many of the nuclides in the actinide family—U, Np, Pu, etc.—fission spontaneously as one of the modes of radioactive decay. Usually, for a nuclide with multiple modes of radioactive decay, the half-life of the nuclide is determined from the total decay rate, representing all the decay processes for that nuclide. However, in the case of spontaneous fission, a separate half-life for that process alone is used. Examples of nuclides that undergo spontaneous fission are given in Table 2.5. 

Mendelevium was discovered in 1955 by Albert Ghiorso, Bernard G. Harvey, Gregory R. Choppin, Stanley G. Thompson, and Glenn T. Seaborg via the bombardments of a minute quantity of a rare, radioactive isotope of einsteinium ( Es) with a-particles in the 60-inch cyclotron of the University of California, Berkeley, which produced Md. Only 17 atoms were detected. Md is the first element to be produced and chemically identified on a one-atom-at-a-time basis. Mendelevium-256 decayed by electron capture (with a 1.3-hour half-life) to the known daughter nuclide fermium-256 ( Tm), which decayed primarily by spontaneous fission (with a half-life of... 

U. Production of Xe has occurred over geological time by the spontaneous fission of and extinct (half-life tm = 82 Ma), while Xe production occurred by radioactive decay of extinct (ti/2 =17 Ma). 

Any single radionuclide not listed above with decay mode other than alpha emission or spontaneous fission and with radioactive half-life less than 2 hours Submersion[1].. 

---