Probabilities of delayed processes for nuclei involved in the r-process
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EMENTARY PARTICLES AND FIELDS Theory
Probabilities of Delayed Processes for Nuclei Involved in the r-Process I. V. Panov1)* , I. Yu. Korneev2) , Yu. S. Lutostansky2), and F.-K. Thielemann3) Received February 14, 2012
Abstract—Delayed fission, along with induced and spontaneous fission, is responsible for the suppression of the production of superheavy elements both during the r-process and after its completion. Beta-decay strength functions are required for calculating delayed fission. In the present study, respective strength functions are calculated by relying on the theory of finite Fermi systems and by predominantly employing nuclear masses and fission barriers predicted by a generalized Thomas–Fermi model. The probabilities for delayed fission and for the emission of delayed neutrons are calculated for a number of isotopes. On the basis of calculations performed in order to determine the probabilities for delayed processes, it is shown that some of the delayed-fission probabilities calculated thus far were substantially overestimated. The application of these new results to calculating the r-process may change substantially both the r-process path and the yields of superheavy nuclei. DOI: 10.1134/S1063778813010080
1. INTRODUCTION
the formation of cosmochronometers [5–7]. In the basic r-process, which is characterized, in particular, by long exposures to neutrons, all fission processes contribute to the abundances of heavy nuclei, but, at the stage of cooling, the strongest changes in the abundances of cosmochronometers are due to delayed and (or) spontaneous fission [8, 9].
Fission plays a role of paramount importance in the r-process and affects not only the production of transuranium elements and cosmochronometers, as was assumed earlier, but also the production of the majority of heavy nuclei owing to the fact that fission products of mass number in the range of 100 < A < 160 are involved in the r-process as primary nuclei. For a long time, calculations of nucleosynthesis had relied on fission barriers evaluated more than 30 years ago [1] on the basis of the liquid-drop model in the form proposed by Myers and Swiatecki (for the macroscopic part) and on the basis of a modified harmonic-oscillator model (for the microscopic part). According to the currently prevailing concepts, those predictions are systematically underestimated. More recent [2, 3] calculations yield higher fission barriers, substantially higher in the region of longlived superheavy elements (SHEs). Therefore, it is of importance to revisit fission rates, as well as to estimate their sensitivity to nuclear data used (fission barriers, masses, and so on). Investigations of the effect of fission on element production in the r-process, which were initiated by Seeger, Fowler, and Clayton [4], concerned basically
Nuclei of all chemical elements involved in the fast-nucleosynthesis process under the effect of neutrons (r-process) pickup neutrons in the radiativecapture process until the rate of photodissociation becomes equal to the neutron-capture rate. Neutronr
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