Fission of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:msup><mml:mrow><mml:mi>Hg</mml:mi></mml:mrow><mml:mo>*</mml:mo></mml:msup><mml:mprescripts /><mml:none /><mml:mrow><mml:mn>180</mml:mn><mml:mo>,</mml:mo><mml:mn>182</mml:mn><mml:mo>,</mml:mo><mml:mn>183</mml:mn></mml:mrow></mml:mmultiscripts></mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:msup><mml:mrow><mml:mi>Pt</mml:mi></mml:mrow><mml:mo>*</mml:mo></mml…

Background: The nature of asymmetric fission preactinides is not yet understood in detail, despite intense experimental and theoretical studies carried out at present.Purpose: study symmetric $^{180,182,183}\mathrm{Hg}$ $^{178}\mathrm{Pt}$ nuclei as a function their excitation energy isospin.Methods: Mass-energy distributions fragments $^{180}\mathrm{Hg}, ^{178}\mathrm{Pt}$ (two protons less than $^{180}\mathrm{Hg}$), $^{182}\mathrm{Hg}$ neutrons more $^{180}\mathrm{Hg}$) formed the $^{36}\mathrm{Ar}+^{144}\mathrm{Sm}, ^{142}\mathrm{Nd}$, $^{40}\mathrm{Ca}+^{142}\mathrm{Nd}$ reactions were measured energies near above Coulomb barrier. Fission $^{183}\mathrm{Hg}$ obtained reaction $^{40}\mathrm{Ca}$ with $^{143}\mathrm{Nd}$ was also investigated to see if one extra neutron could lead dramatic changes process due shape-staggering effect radii, known $^{183}\mathrm{Hg}$.The measurements performed double-arm time-of-flight spectrometer CORSET.Results: observed peculiarities fragment mass-energy for all studied may be explained by presence mode three modes, manifested different total kinetic mass splits. yield grows increasing compound nucleus.Conclusions: properties point existence well-deformed proton shell $Z\ensuremath{\approx}36$ deformed $Z$ \ensuremath{\approx} 46.