Plutonium spontaneous fission decay

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. 

Uranium-235 and U-238 behave differently in the presence of a controlled nuclear reaction. Uranium-235 is naturally fissile. A fissile element is one that splits when bombarded by a neutron during a controlled process of nuclear fission (like that which occurs in a nuclear reactor). Uranium-235 is the only naturally fissile isotope of uranium. Uranium-238 is fertile. A fertile element is one that is not itself fissile, but one that can produce a fissile element. When a U-238 atom is struck by a neutron, it likely will absorb the neutron to form U-239. Through spontaneous radioactive decay, the U-239 will turn into plutonium (Pu-239). This new isotope of plutonium is fissile, and if struck by a neutron, will likely split. 

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

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... 

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. 

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. 

Very small amounts of Np, as well as of Pu, have been discovered on earth the half-lives of Pu (in the 4/i -t- 3 series) is 2.411 x 10 y. Both isotopes are too short-lived to have survived the 4 eons since the solar system was formed. However, they are always found in minerals containing uranium and thorium and it is believed that the neutrons produced in these minerals through (o(,n) and (y,n) reactions with U and Th as well as by spontaneous fission of form the neptunium and plutonium through n-capture and 3-decay processes. The n-production rate in the uraniuniJ eisl pitchblende (containing —50% U) is about 50 n/kg s. The typical value for the " Pu/" U ratio in minerals is 3... 

The nuclide gCf emits neutrons through spontaneous fission in 3% of all decays, the rest being a-decays. All the other neutron sources listed involve a radioactive nuclide whose decay causes a nuclear reaction in a secondary substance which produces neutrons. For example, ffSb produces neutrons in beryllium powder or metal as a result of the initial emission of 7-rays, in which case there is no coulomb barrier to penetrate. Radium, polonium, plutonium, and americium produce neutrons by nuclear reactions induced in beryllium by the a-particles from their radioactive decay. For the neutrons produced either by spontaneous fission in californium or by the a-particle reaction with beryllium, the... 

The decay heat power comes mainly from five sources (1) unstable fission products, which decay via a, p-, p+, and y ray emission to stable isotopes (2) unstable actinides that are formed by successive neutron capture reactions in the uranium and plutonium isotopes present in the fuel (3) fissions induced by delayed neutrons (4) reactions induced by spontaneous fission neutrons (5) structural and cladding materials in the reactor that may have become radioactive. Heat production due to delayed neutron-induced fission or spontaneous fission is usually neglected. Activation of light elements in structural materials plays a role only in special cases. 

In these very heavy atoms, spontaneous fission is often the predominant mode of decay, and it is also the process most liable to large errors in half-life prediction. Nix, in a letter of considerable practical interest, computes the total energy release in fission, the average number of neutrons per fission (v), and the neutron energy for a few superheavy nuclides. Some of these results are shown in Table 1 the inclusion of a plutonium isotope provides a comparison with a known actinide. 

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