Superheavy elements and r-process
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EMENTARY PARTICLES AND FIELDS Theory
Superheavy Elements and r-Process I. V. Panov1)* , I. Yu. Korneev1) , and F.-K. Thielemann2) Received August 14, 2008
Abstract—The probability for the production of superheavy elements in the astrophysical r-process is discussed. The dependence of the estimated superheavy-element yields on input data is estimated. Preliminary calculations revealed that the superheavy-element yields at the instant of completion of the r-process may be commensurate with the uranium yield, but the former depend strongly on the models used to forecast the properties of beta-delayed, neutron-induced, and spontaneous fission. This study is dedicated to the 80th anniversary of V.S. Imshennik’s birth. PACS numbers: 26.30.-k, 25.85.-w, 25.85.Ec DOI: 10.1134/S1063778809060155
1. INTRODUCTION At the present time, about 300 nuclei are known in nature. These are nuclei of various isotopes; they contain one to ninety-four protons. All stable and long-lived nuclei, together with nuclei obtained artificially over the past 50 years (there are about 2000 of them) constitute less than one-fourth of nuclei that exist and which originate from nuclear reactions. All nuclei whose production is not forbidden by conservation laws participate in nucleosythesis processes, up to 70% of them (about 4000) taking part in fast nucleosynthesis. The heaviest artificial nucleus produced so far in accelerator experiments [1] contains 118 protons and has a mass number of 294. Searches for nuclei markedly heavier than those that are known at the present time were initiated by G.N. Flerov and have been performed for many years. Attempts have been made both to find such “superheavy” nuclei in nature and to produce them artificially in heavy-ion experiments performed at accelerators. Their lifetimes must be rather long for their fraction to survive and manifest itself in cosmic rays, ancient rock, or uranium ores. In nature, superheavy elements may be produced, for example, in the astrophysical r-process [2], whose path goes nearly along the neutron drip line [3] and, under certain conditions, may reach the “stability island.” The relative yield of superheavy elements depends strongly both on the astrophysical scenario and on the nuclear data used. Therefore, searches for superheavy elements 1)
Institute of Theoretical and Experimental Physics, Bol’shaya Cheremushkinskaya ul. 25, Moscow, 117259 Russia. 2) ¨ Physik der Universitat ¨ Basel, Klingelbergstraße Institut fur 82, CH-4056 Basel, Switzerland. * E-mail: [email protected]
may prove to be indicative of the scenarios of their formation in nature, on one hand, and may facilitate the choice of theoretical models, whose predictions for mass barriers and lifetimes of exotic nuclei differ strongly, on the other hand. There arises the question of why superheavy nuclei may form a stability island, which is the region of relatively long-lived nuclei having mass numbers in excess of 100. Upon going over to the region of heavy nuclei, Coulomb forces become stronger than nuclear-interaction for
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