Asymmetric and symmetric fission of excited nuclei of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mi>Hg</mml:mi><mml:mprescripts/><mml:none/><mml:mrow><mml:mn>180</mml:mn><mml:mo>,</mml:mo><mml:mn>190</mml:mn></mml:mrow></mml:mmultiscripts></mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mi>Pb</mml:mi><mml:mprescripts/><mml:none/><mml:mrow><mml:mn>184</mml:mn><mml:mo>,</mml:mo><mml:mn>192</mml:mn><mml:mo>,</mml:mo><mml:mn>202</mml:mn></mml:mrow></mml:mmultiscripts></mml:math> formed in the reactions with <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mi>Ar</mml:mi><mml:mprescripts/><mml:none/><mml:mn>36</mml:mn></mml:mmultiscripts></mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mi>Ca</mml:mi><mml:mprescripts/><mml:none/><mml:mrow><mml:mn>40</mml:mn><mml:mo>,</mml:mo><mml:mn>48</mml:mn></mml:mrow></mml:mmultiscripts></mml:math> ions
A. A. Bogachev, Э. М. Козулин, G. N. Knyazheva, I. M. Itkis, М. Г. Иткис, K. V. Novikov, Deepak Kumar, Tathagata Banerjee, I. N. Diatlov, M. Cheralu, V. V. Kirakosyan, Yerzhan Mukhamejanov, А. Н. Пан, I. V. Pchelintsev, R. S. Tikhomirov, I. V. Vorobiev, Moumita Maiti, Rinku Prajapat, Rishabh Kumar, Gayatri Sarkar, W. H. Trzaska, A. N. Andreyev, I. M. Harca, E. Vardaci
Abstract
Background: Observation of asymmetric fission of $^{180}\mathrm{Hg}$ has led to intensive theoretical and experimental studies of fission of neutron-deficient nuclei in the lead region.Purpose: The study of asymmetric and symmetric fission modes of $^{180,190}\mathrm{Hg}$ and $^{184,192,202}\mathrm{Pb}$ nuclei.Methods: Mass-energy distributions of fission fragments of $^{180,190}\mathrm{Hg}$ and $^{184}\mathrm{Pb}$ formed in the $^{36}\mathrm{Ar}+^{144,154}\mathrm{Sm}$ and $^{40}\mathrm{Ca}+^{144}\mathrm{Sm}$ reactions, respectively, at energies near the Coulomb barrier have been measured using the double-arm time-of-flight spectrometer CORSET and compared with previously measured $^{192,202}\mathrm{Pb}$ isotopes produced in the $^{48}\mathrm{Ca}+^{144,154}\mathrm{Sm}$ reactions. The mass distributions for $^{180,190}\mathrm{Hg}$ and $^{184,192,202}\mathrm{Pb}$ together with old data for $^{187}\mathrm{Ir}, ^{195}\mathrm{Au}, ^{198}\mathrm{Hg}, ^{201}\mathrm{Tl}, ^{205,207}\mathrm{Bi}, ^{210}\mathrm{Po}$, and $^{213}\mathrm{At}$ [J. Nucl. Phys. 53, 1225 (1991)] have been decomposed into symmetric and asymmetric fission modes. The total kinetic-energy distributions for different fission fragment mass regions have been analyzed for $^{180,190}\mathrm{Hg}$ and $^{184}\mathrm{Pb}$.Results: The stabilization role of proton numbers at $Z\ensuremath{\approx}36$, 38, $Z\ensuremath{\approx}45$, 46, and $Z=28/50$ in asymmetric fission of excited preactinide nuclei has been observed. The high ($\ensuremath{\approx}145\text{\ensuremath{-}}\mathrm{MeV}$) and the low ($\ensuremath{\approx}128\text{\ensuremath{-}}\mathrm{MeV}$) energy components have been found in the total kinetic-energy distributions of $^{180,190}\mathrm{Hg}$ fission fragments corresponding to the fragments with proton numbers near $Z\ensuremath{\approx}46$ and $Z\ensuremath{\approx}36$, respectively. In the case of fission of $^{184}\mathrm{Pb}$ only the low-energy component ($\ensuremath{\approx}135\phantom{\rule{0.16em}{0ex}}\mathrm{MeV}$) for the fragments with masses corresponding to the proton numbers $Z\ensuremath{\approx}36$ and 46 has been found.Conclusions: The studied properties of asymmetric fission of $^{180,190}\mathrm{Hg}$ and $^{184,192,202}\mathrm{Pb}$ nuclei point out the existence of well deformed proton shell at $Z\ensuremath{\approx}36$ and less deformed proton shell at $Z\ensuremath{\approx}46$.