Measurements of cross sections for the fusion-evaporation reactions<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow/><mml:mrow><mml:mn>2</mml:mn><mml:mn>0</mml:mn><mml:mn>4</mml:mn><mml:mo>,</mml:mo><mml:mn>2</mml:mn><mml:mn>0</mml:mn><mml:mn>6</mml:mn><mml:mo>,</mml:mo><mml:mn>2</mml:mn><mml:mn>0</mml:mn><mml:mn>7</mml:mn><mml:mo>,</mml:mo><mml:mn>2</mml:mn><mml:mn>0</mml:mn><mml:mn>8</mml:mn></mml:mrow></mml:msup></mml:mrow><mml:mi mathvariant="normal">Pb</mml:mi><mml:mrow><mml:msup><mml:mrow><mml:mo>+</mml:mo></mml:mrow><mml:mrow><mml:mn>48</mml:mn></mml:mrow></mml:msup></mml:mrow><mml:mi mathvariant="normal">Ca</mml:mi></mml:math>and<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow/><mml:mrow><mml:mn>207</mml:mn></mml:mrow></mml:msup></mml:mrow><mml:mi mathvariant="normal">Pb</mml:mi><mml:mrow><mml:msup><mml:mrow><mml:mo>+</mml:mo></mml:mrow><mml:mrow><mml:mn>34</mml:mn></mml:mrow></mml:msup></mml:mrow><mml:mi mathvariant="normal">S</mml:mi><mml:mo>:</mml:mo></mml:math>Decay properties of the even-even nuclides<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow/><mml:mrow><mml:mn>238</mml:mn></mml:mrow></mml:msup></mml:mrow><mml:mi mathvariant="normal">Cf</mml:mi></mml:math>and<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow/><mml:mrow><mml:mn>250</mml:mn></mml:mrow></mml:msup></mml:mrow><mml:mi mathvariant="normal">No</mml:mi></mml:math>

In preparation for recent experiments on the synthesis of superheavy nuclei with $Z=114$ in the reaction ${}^{244}\mathrm{Pu}{+}^{48}\mathrm{Ca},$ we modified the Dubna gas-filled recoil separator and its detection system and carried out bombardments of lead targets with ${}^{48}\mathrm{Ca}$ projectiles. We studied excitation functions of the reactions ${}^{206}\mathrm{Pb}{(}^{48}\mathrm{Ca},1\ensuremath{-}4n)$ and ${}^{204,207,208}\mathrm{Pb}{(}^{48}\mathrm{Ca},2n).$ Maximum cross sections for the evaporation of 1--4 neutrons in the complete fusion reaction ${}^{206}\mathrm{Pb}{+}^{48}\mathrm{Ca}$ were measured to be ${\ensuremath{\sigma}}_{1n}=60 \mathrm{nb},$ ${\ensuremath{\sigma}}_{2n}=500 \mathrm{nb},$ ${\ensuremath{\sigma}}_{3n}=30 \mathrm{nb},$ and ${\ensuremath{\sigma}}_{4n}=0.3 \mathrm{nb}.$ In the bombardment of an enriched ${}^{204}\mathrm{Pb}$ target, we simultaneously obtained excitation functions of the ${}^{204,206,207,208}\mathrm{Pb}{(}^{48}\mathrm{Ca},2n)$ reactions induced on the isotopic admixtures present in the target material. The maximum cross sections for the evaporation of two neutrons from the compound nuclei ${}^{256}\mathrm{No},$ ${}^{255}\mathrm{No},$ and ${}^{252}\mathrm{No}$ were measured to be 2.1 $\ensuremath{\mu}\mathrm{b},$ 1.3 $\ensuremath{\mu}\mathrm{b},$ and 10 nb, respectively. The spontaneously fissioning even-even isotope ${}^{250}\mathrm{No},$ with a half-life ${T}_{1/2}=36 \ensuremath{\mu}\mathrm{s},$ was identified for the first time in this experiment. In the reaction ${}^{207}\mathrm{Pb}{+}^{34}\mathrm{S},$ we measured the excitation function for the production of the 21-ms spontaneously fissioning isotope ${}^{238}\mathrm{Cf},$ confirming our preliminary identification of this nuclide based on the results of cross bombardments.

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