Plutonium-239, neutron capture

Fm and heavier isotopes can be produced by intense neutron irradiation of lower elements, such as plutonium, using a process of successive neutron capture interspersed with beta decays until these mass numbers and atomic numbers are reached. 

In the evaluation of these parameters, the chain of plutonium isotopes produced and consumed must be taken into account. Successive neutron captures create plutonium-239, -240, -241, and -242. Isotopes having odd mass number are fissile, the others are not. 

Americium - the atomic number is 95 and the chemical symbol is Am. The name derives from America where it was first synthesized in a series of successive neutron capture reactions in the element plutonium, Pu, in a nuclear reactor in 1944 by American scientists under Glenn T. Seaborg at the University of California lab in Berkeley, California, using the nuclear reaction Pu ( n, y) Y) P Am. Americium is the sixth element in the Actinide... 

The most common use of uranium is to convert the rare isotope U-235, which is naturally fissionable, into plutonium through neutron capture. Plutonium, through controlled fission, is used in nuclear reactors to produce energy, heat, and electricity. Breeder reactors convert the more abundant, but nonfissionable, uranium-238 into the more useful and fissionable plutonium-239, which can be used for the generation of electricity in nuclear power plants or to make nuclear weapons. 

Am-241 may be prepared in a nuclear reactor as a result of successive neutron capture reactions by plutonium isotopes ... 

Curium-242 isotope may be obtained in the same way from plutonium-239 by successive neutron capture and 3 decay ... 

Heavier isotopes Es-253, Es-254 and Es-255 can be produced in a nuclear reactor by multiple neutron capture reactions that may occur when uranium, neptunium and plutonium isotopes are irradiated under intense neutron flux. These and other isotopes also are produced during thermonuclear explosions. 

Plutonium has a short half-life (24,360 years), so any plutonium initially in Earth s crust has long since decayed. The same is true for any heavier elements with even shorter half-lives from which plutonium might originate. Trace amounts of plutonium can occur naturally in U-238 concentrations, however, as a result of neutron capture, where U-238 becomes U-239 and after beta emission becomes Np-239 and after further beta emission becomes Pu-239. (There are elements in Earth s crust with half-lives even shorter than plutonium s, but these are the products of uranium decay—between uranium and lead in the periodic table of elements.)... 

The identification of an isotope of element 95, by Seaborg, Ghiorso, James, and Leon Morgan in late 1944 and early 1945, followed the identification of this isotope of element 96 (242Cm) as a result of the bombardment of 7j Pu with neutrons in a nuclear reactor. The production reactions, involving multiple neutron capture by plutonium, are... 

The uranium and thorium ore concentrates received by fuel fabrication plants still contain a variety of impurities, some of which may be quite effective neutron absorbers. Such impurities must be almost completely removed if they are not seriously to impair reactor performance. The thermal neutron capture cross sections of the more important contaminants, along with some typical maximum concentrations acceptable for fuel fabrication, are given in Table 9. The removal of these unwanted elements may be effected either by precipitation and fractional crystallization methods, or by solvent extraction. The former methods have been historically important but have now been superseded by solvent extraction with TBP. The thorium or uranium salts so produced are then of sufficient purity to be accepted for fuel preparation or uranium enrichment. Solvent extraction by TBP also forms the basis of the Purex process for separating uranium and plutonium, and the Thorex process for separating uranium and thorium, in irradiated fuels. These processes and the principles of solvent extraction are described in more detail in Section 65.2.4, but the chemistry of U022+ and Th4+ extraction by TBP is considered here. 

Plutonium is a man-made element, and only infinitesimal traces occur naturally. It melts at 641°C and boils at 3330°C. 239Pu is formed in nuclear reactors by neutron capture in 238U, followed by two successive beta decays (Fig. 5.1). Further neutron captures lead to 240Pu and 241 Pu. 238Pu is formed from 239Pu by (n,2n) reactions, or from 235U by three successive neutron captures and two beta decays. Table 5.1 shows the half-lives, alpha and X-ray energies of the principal Pu isotopes. 

For elements beyond plutonium, successive neutron capture is required. This is, obviously. 

Actinides in the environment can be classified into two groups (i) the uranium and thorium series of radionuclides in the natural environment and (ii) neptunium, plutonium, americium and curium which are formed in a nuclear reactor during the neutron bombardment of uranium through a series of neutron capture and radioactive decay reactions. Transuranics thus produced have been spread widely in the atmosphere, geosphere and aquatic environment on the earth, as a result of nuclear bomb tests in the atmosphere, and accidental release from nuclear facilities (Sakanoue, 1987). Most of these radionuclide inventories have deposited in the northern hemisphere following the tests conducted by the United States and the Soviet Union. 

The fissionable isotopes are U-233, U-235, Pu-239, and Pu-241. The fertile isotopes U-238 and Th-232 are converted to fissionable isotopes by neutron absorption (U-238 into plutonium isotopes and Th-232 into U-233). Natural uranium contains 0.71% U-235, 99.28% U-238, and 0.006% U-234. Fuel enriched in U-233 and plutonium must be produced from thorium and U-238, respectively (Fig. 1) by neutron capture the neutrons are provided initially by fission of U-235. 

Derivation Multiple neutron capture in plutonium in nuclear reactors, plutonium isotopes yield241 Am and 243Am on (3 decay. The metal is obtained by reduction of the trifluoride with barium in a vacuum at 1200C. 

Use Source of fissionable isotope uranium-235, source of plutonium by neutron capture, electric power generation. 

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