Severe Inhibition of Fusion by Quasifission in Reactions Forming<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mmultiscripts><mml:mi mathvariant="normal">T</mml:mi><mml:mprescripts/><mml:none/><mml:mn mathvariant="normal">220</mml:mn></mml:mmultiscripts><mml:mi mathvariant="normal">h</mml:mi></mml:math>

Evaporation residue cross sections have been measured following the fusion of $^{\mathrm{16}}\mathrm{O}$ with $^{\mathrm{204}}\mathrm{P}\mathrm{b}$, forming the compound nucleus $^{\mathrm{220}}\mathrm{T}\mathrm{h}$. These are compared with existing data for the same compound nucleus formed following fusion reactions with $^{\mathrm{40}}\mathrm{A}\mathrm{r}$, $^{\mathrm{48}}\mathrm{C}\mathrm{a}$, $^{\mathrm{82}}\mathrm{S}\mathrm{e}$, and $^{\mathrm{124}}\mathrm{S}\mathrm{n}$ projectiles. At energies where the reduced cross sections of $xn$ evaporation residues would be expected to be the same for all reactions, those for the heavier projectiles are typically a factor of 10 smaller than those for $^{\mathrm{16}}\mathrm{O}$. This inhibition is attributed to strong competition of quasifission with fusion at the low angular momenta associated with evaporation residue formation.

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