Mechanisms Suppressing Superheavy Element Yields in Cold Fusion Reactions.

Area of Science:

• Nuclear Physics
• Heavy Ion Collisions
• Superheavy Element Synthesis

Background:

• Superheavy element (SHE) formation via fusion reactions is often impeded by fast nonequilibrium processes.
• Understanding these processes is crucial for advancing SHE research and nuclear structure theory.

Purpose of the Study:

• To quantify the impact of nonequilibrium processes on SHE formation.
• To investigate the role of projectile mass and beam energy on compound nucleus formation probability (P_CN).

Main Methods:

• Measured mass-angle distributions and cross sections for ^{48}Ca, ^{50}Ti, and ^{54}Cr reactions with ^{208}Pb.
• Analyzed data across a range of beam energies, from below-barrier to 25% above.

Main Results:

• A significant decrease in symmetric fission yield was observed with increasing projectile mass (from ^{48}Ca to ^{54}Cr).
• Nonequilibrium deep inelastic and quasifission processes were identified as competing pathways, reducing P_CN.
• P_CN decreased by a factor of 2.5 for ^{50}Ti and 15 for ^{54}Cr compared to ^{48}Ca.

Conclusions:

• Nonequilibrium processes strongly influence SHE formation, with heavier projectiles leading to reduced compound nucleus probability.
• The energy dependence of P_CN suggests that cold fusion reactions involving ^{208}Pb are not governed by a diffusion mechanism.