Nuclear series decay chains

The last decade was marked with the discovery of five new members of the Periodic Table The heaviest elements of the last transition element series 110 through 112 were identified in the Gesellschaft fiir Schwerionenforschung (GSI), Darmstadt [1-3] and some decay chains and fission products associated with production of even more heavy elements 116 and 114 were recently reported by the Joint Institute for Nuclear Research (JINR), Dubna [4], This period of time was also very fruitful with studying chemical properties of the very heavy elements [5-9],... 

Some nuclei cannot gain stability by a single emission. Consequently, a series of successive emissions occurs as shown for uranium-238 in figure 21.3. Decay continues until a stable nucleus—lead-206 in this case—is formed. A series of nuclear reactions that begins with an unstable nucleus and terminates with a stable one is known as a radioactive decay chain or a nuclear disintegration series. Three such series occur in nature iu-anium-238 to lead-206, uranium-235 to lead-207, and thorium-232 to lead-208. All of the decay processes in these series are either alpha emissions or beta emissions. 

Another major turning point in the history of nuclear science came with the discovery of fission by Otto Hahn and Fritz Strassmann in December 1938 (Hahn and Strassmann 1939a, b). In several laboratories in Rome, Berlin, and Paris, a complex series of P-decay chains resulting from neutron irradiation of uranium had been investigated since 1934, and these chains had been assigned to putative transuranium elements formed by neutron capture in uranium with subsequent P" transitions increasing the atomic numbers (see Sect. 1.2.3). But then evidence appeared that known elements in the vicinity of uranium, such as radium, were produced as well. When Hahn and Strassmaim attempted to prove this by a classical fractional crystallization separation of radium from barium serving as its carrier, the radioactivity turned out to be barium, not radium hence, new and totally unexpected type of nuclear reaction had to be invoked. 

Decay chain A series of nuclides in which each member transforms into the next through nuclear decay until a stable nuclide has been formed. 

The second paper of 1940 [3 ], entitled Kinetics of Uranium Chain Decay, is no less significant than the first. This pioneering work yielded a whole series of brilliant results for the first time, the need to take into account the role of delayed neutrons in the kinetics of chain nuclear reactions was shown (it is precisely the delayed neutrons which ensure easy control of nuclear reactors), the influence of heating on the kinetics of a chain process was considered in detail, and a number of conclusions were reached which are of much importance for the theory of reactor control. This same paper predicted the formation in the process of chain fission of new, previously unknown, nuclei which strongly absorb neutrons, a prediction which was later fully confirmed. 

Fission products are neutron-rich and thus are negatron emitters. At each mass, a decay series may consist of as many as five radionuclides that decay, one into the other, until the chain stops at a stable element. In a decay series, the fission yield may begin at a smaller value for the initial short-lived radionuclides and increase for subsequent radionuclides to the maximum shown in the figure. Among these fission products are ones with half-lives from days to years that are readily measured for monitoring nuclear reactors and nuclear weapon tests. 

Radioactive nuclei emit a particles, 13 particles, positrons, or y rays. The equation for a nuclear reaction includes the particles emitted, and both the mass numbers and the atomic numbers must balance. Uranium-238 is the parent of a natural radioactive decay series. A number of radioactive isotopes, such as and C, can be used to date objects. Artificially radioactive elements are created by the bombardment of other elements by accelerated neutrons, protons, or a particles. Nuclear fission is the splitting of a large nucleus into smaller nuclei plus neutrons. When these neutrons are captured efficiently by other nuclei, an uncontrollable chain reaction can occur. Nuclear reactors use the heat... 

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