Plutonium spontaneous fission

In 1964, workers at the Joint Nuclear Research Institute at Dubna (U.S.S.R.) bombarded plutonium with accelerated 113 to 115 MeV neon ions. By measuring fission tracks in a special glass with a microscope, they detected an isotope that decays by spontaneous fission. They suggested that this isotope, which had a half-life of 0.3 +/- 0.1 s might be 260-104, produced by the following reaction 242Pu + 22Ne —> 104 +4n. 

Another safety issue to be considered which might be exacerbated in the reprocessing option is that the plutonium generated in power reactors, called reactor-grade plutonium because it is made up of a variety of plutonium isotopes, contains plutonium-241, which is subject to spontaneous fission (8). The mixture of isotopes makes it extremely difficult to build an effective nuclear weapon. However, an explosive device could be built using this mixture if control of detonation is sacrificed (48). 

Neutron radiation is emitted in fission and generally not spontaneously, although a few heavy radionueleides, e.g. plutonium, undergo spontaneous fission. More often it results from bombarding beryllium atoms with an a-emitter. Neutron radiation deeays into protons and eleetrons with a half-life of about 12 min and is extremely penetrating. 

Holden NE (1989) Total and spontaneous fission half-lives for uranium, plutonium, americium and curium nuclides. Pure Appl Chem 61(8) 1483-1504... 

Stevens, R.F. Barnes, D. J. Henderson and R. J. Huizenga Alpha and spontaneous fission half-lives of Plutonium-242. Physic. Rev. 103, 340 (1956). 

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. 

Plutonium-244 decays by -emission and spontaneous fission with a half-life of 82 Ma. The branching ratio, fission/a-emission, is 0.00125. The former existence of 244Pu in the solar system is indicated by the presence of fission tracks in meteorite samples and... 

CAS 53850-36-5). Rulherfordium. Researchers ul Dubna (Russia), in 1964. bombarded plutonium with accelerated 113-115 MeV neon ions. During this process, an isotope that decayed by spontaneous fission was observed. It was reported that Ihe isotope had a half-title of 0.3 0.1 second and it was reasoned that the isotope was 104. resulting from... 

Radioisotopes that decay by spontaneous fission with the direct accompanying release of neutrons are usually associated with the natural elements of uranium and thorium and the manmade element plutonium. However, the rate of decay of these elements by fission is so slow that it is only by incorporating them into large nuclear piles or chain reactors that they can be utilized as intense neutron sources. In the US Dept of Energy National Transplutonium Program, small quantities of elements heavier than plutonium are produced for basic research studies and to discover new elements with useful properties. One of these new elements, californium-252 (2S2Cf), is unique in that it emits neutrons in copious quantities over a period of years by spontaneous fission... 

For use in nuclear weapons, the concentration of °Pu in the plutonium should be low, because the presence of this nuclide leads to the production of appreciable amounts of neutrons by spontaneous fission if the concentration of °Pu is too high the neutron multiplication would start too early with a relatively small multiplication factor, and the energy release would be relatively low. Higher concentrations of " Pu also interfere, because of its transmutation into " Am with a half-life of only 14.35 y. To minimize the formation of " °Pu and " Pu, Pu for use in weapons is, in general, produced in special reactors by low bum-up (<20 000 MWth d per ton). 

A related problem is the conspicuous xenon isotope anomalies in various meteorites. The heavy fraction [79-87] enriched in Xe was originally [79, 80] ascribed to y-ray or neutron-induced fission of Pu (half-life 83 million years, only 0.08 percent probability of spontaneous fission otherwise, He emitter) and a controversy maintained about plutonium(IV) occupying sites in (quite scarce mineral fractions) and forming xenon or the noble gas directly incorporated from the protoplanetary cloud. Some of the most remarkable components of the... 

The major difficulty with synthesizing heavy elements is the number of protons in their nuclei (Z > 92). The large amount of positive charge makes the nuclei unstable so that they tend to disintegrate either by radioactive decay or spontaneous fission. Therefore, with the exception of a few transuranium elements like plutonium (Pu) and americium (Am), most artificial elements are made only a few atoms at a time and so far have no practical or commercial uses. 

Another radiation problem arises from fast neutrons produced in spontaneous fission of the even-mass plutonium isotopes. Half-lives and specific activities for spontaneous fission of the plutonium isotopes are listed in Table 8.17. 

Pu. The isotope Pu is produced by neutron capture in Pu. It is not fissionable by thermal neutrons, but, like all other plutonium isotopes, it fissions with fast neutrons. Pu is converted to a fissionable nuclide by neutron capture. Therefore, like Th and it is a fertile material. It undergoes alpha decay, with a half4ife of 6580 years, to form which then decays to Th, the parent of the 4n decay series discussed in Chaps. 6 and 8. Like the other even-mass plutonium isotopes, Pu produces neutrons by spontaneous fission. It is present in greater concentration in reactor plutonium than any of the other even-mass plutonium isotopes. 

Persotmel working with plutonium must be protected by light shielding. The external radiation to be shielded includes ganunas from alpha and beta decay, internal conversion x-rays, ganunas, and neutrons from spontaneous fission, and neutrons from (a, n) reactions in materials of low atomic number. Neutron yields for various types and forms of plutonium are listed in Table 9.15. 

Cm. The isotope Cm, with a half-life of 350 days, is the highest-mass curium isotope produced in appreciable quantities in the kradiation of Cm. Very pure Cm is now being produced by tiie alpha decay of Cf, which is the principal transcurium isotope produced in the long-term neutron irradiation of plutonium, americium, curium, and berkelium. Cf decays with a half-life of 2.65 years, 3 percent by spontaneous fission and 97 percent by alpha emission. 

After the discovery of uranium radioactivity by Henri Becquerel in 1896, uranium ores were used primarily as a source of radioactive decay products such as Ra. With the discovery of nuclear fission by Otto Hahn and Fritz Strassman in 1938, uranium became extremely important as a source of nuclear energy. Hahn and Strassman made the experimental discovery Lise Meitner and Otto Frisch provided the theoretical explanation. Enrichment of the spontaneous fissioning isotope U in uranium targets led to the development of the atomic bomb, and subsequently to the production of nuclear-generated electrical power. There are considerable amounts of uranium in nuclear waste throughout the world, see also Actinium Berkelium Einsteinium Fermium Lawrencium Mendelevium Neptunium Nobelium Plutonium Protactinium Rutherfordium Thorium. 

All isotopes of technetium are unstable toward ft decay or electron capture and traces exist in Nature only as fragments from the spontaneous fission of uranium. The element was named technetium by the discoverers of the first radioisotope—Perrier and Segre. Three isotopes have half-lives greater than 105 years, but the only one that has been obtained on a macro scale is "Tc (fi, 2.12xl05 years). Technetium is recovered from waste fission-product solutions after removal of plutonium and uranium. It is an interesting irony that the supply of technetium, which does not exist in Nature, might easily be made to exceed that of Re, which does, because of the increasing number of reactors and the very low ( 10-9%) abundance of Re in the earth s crust. 

Monoenergetic heavy ions necessary for energy calibration can be provided only by accelerators. Fission fragments, which are heavy ions, cover a wide spectrum of energies (Fig. 13.19). The isotope Cf is a very convenient source of fission fragments produced by the spontaneous fission of that isotope. Uranium, plutonium, or thorium fission fragments can only be produced after fission is induced by neutrons therefore, a reactor or some other intense neutron source is needed. 

N.E. Holden, Total and Spontaneous Fission Half-lives for Uranium, Plutonium, Americium and Curium Nuclides, Pure Applied Chemistry 61, 1483 (1989). 

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