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Prospects for the Discovery of the Next New Element

Prospects for the Discovery of the Next New Element. C. M. Folden III Cyclotron Institute, Texas A&M University NN2012, San Antonio, Texas May 31, 2012. Periodic Table 2012. The heaviest elements are all produced artificially !. The Fission Barrier. B f is the fission barrier .

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Prospects for the Discovery of the Next New Element

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  1. Prospects for the Discovery of the Next New Element C. M. Folden III Cyclotron Institute, Texas A&M University NN2012, San Antonio, Texas May 31, 2012

  2. Periodic Table 2012 The heaviest elements are all produced artificially!

  3. The Fission Barrier • Bf is the fission barrier. • It is caused by a change in the surface and Coulomb energies at constant volume and density.  4pe0

  4. The Future of Heavy Elements in 1976 • It was believed that nuclides with Z > 104 would have no macroscopic fission barrier. • See J. Randrup et al., Phys. Rev. C 13(1), 229 (1976).

  5. Shell Correction Energies Near Z = 108, N = 162 • The reason we have so many transactinide elements is (partially) due to shell effects. • Evidence: • t½(257Rf) = 4.7 s • t½(270Hs) = 3.6 s • Cross sections • etc. A. Sobiczewski and K. Pomorski, Prog. Part. Nucl. Phys. 58, 292 (2007).

  6. Silver Bullets • We have used a number of “silver bullets” that have allowed us to create ever heavier elements: • Z = 107-112 (Cold Fusion Reactions): • Shell Stabilization Near Z = 108, N = 162. • Shell-Stabilized Targets (minor effect). • Deformed Products (more on this later).

  7. Shell Effects in SHE Production • The shell effects for Z = 113-118 (warm fusion reactions) are not as pronounced as for Z = 107-112 (cold fusion reactions).

  8. Fission Fission Fission How do you make a heavy nucleus? • The evaporation residue cross section can be written as:

  9. Detailed Balance and Level Density • Any change is the same as the opposite change in reverse: • Estimate Gn/Gf by integrating over the level densities for neutron emission and fission: W. J. Świątecki, K. Siwek-Wilczyłńska, and J. Wilczyłński, Phys. Rev. C 71, 014602 (2005). R. Vandenbosch and J. R. Huizenga, Nuclear Fission (Academic Press, New York, 1973), pp. 227-33.

  10. The Canonical Expansion • The level density is a function of energy: r(E) • Expand around E = E* – Bn and use d(ln r)/dE 1/T:

  11. Bf – Bn as a Function of Projectile • The projectile has a major influence on Gn/Gf. Better Worse Figure courtesy of D. A. Mayorov.

  12. Silver Bullets • We have used a number of “silver bullets” that have allowed us to create ever heavier elements: • Z = 107-112 (Cold Fusion Reactions): • Shell Stabilization Near Z = 108, N = 162. • Deformed Products (more on this later). • Shell-Stabilized Targets (minor effect). • Z = 113-118 (Warm Fusion Reactions): • The neutron-richness of 48Ca is exceptional among available projectiles. It increases Bf and decreases Bn.

  13. Current and Future History of Elements Above 118 • JINR studied the 244Pu(58Fe, 4n)298120 reaction and reported an upper limit cross section of 0.4 pb (0.74 pb at 84% confidence). • GSI Experiments: • 248Cm(54Cr, 4n)298120 • Compare with 248Cm(48Ca, 4n)292Lv: sEVR 3.3 pb • 249Cf(50Ti, 4n)295120 • Compare with 249Cf(48Ca, 3n)294118: sEVR 0.5 pb • 249Bk(50Ti, 4n)295119 (in progess) • Other reactions have been proposed: • 252Cf(50Ti, 4n)298120 • 238U(64Ni, 4n)298120

  14. 48Ca and 54Cr Induced Reactions 162Dy(48Ca, xn)210-xRn 248Cm(48Ca, xn)296-xLv 162Dy(54Cr, xn)216-xTh 248Cm(54Cr, xn)302-x120 Column 4 shows the difference Ecm – B, where Ecm is the center of mass projectile energy and B is the average interaction (representing sum of Coulomb, centripetal, nuclear potentials) barrier height. E*CN is the excitation energy of the CN system. Column 6 gives the remaining excitation energy of a nucleus following emission of 4 neutrons each with binding energy Sn. Values were calculated based on estimated projectile energy needed to remove 4 neutrons, leaving the residual nucleus with excitation energy below either the Sn or Bf, whichever is lower in energy.

  15. Upgraded Capabilities at Texas A&M • As part of an upgrade sponsored principally by DOE, the K150 88” cyclotron is being recommissioned. Supplied by 6.4-GHz ECR Supplied by 14.5-GHz ECR http://cyclotron.tamu.edu/facility_upgrade.pdf

  16. MARS Device Acceptance Dp/pBrmax MARS 9 msr ±4% 1.8 T m SHIP ~4 msr ±10% 1.2 T m BGS 45 msr ±9% 2.5 T m R.E. Tribble, R.H. Burch, and C.A. Gagliardi, NIMA 285, 441 (1989). R.E. Tribble, C.A. Gagliardi, and W. Liu, NIMB 56/57, 956 (1991).

  17. 162Dy(48Ca, xn)210-xRn and 162Dy(54Cr, xn)216-xTh Excitation Functions • Difference in dotted lines is mostly due to changes in Bn – Bf. • Difference between dotted and solid lines is due to collective effects. ≈7100 Preliminary Figure courtesy of D. A. Mayorov.

  18. Collective Effects • Consider a deformed nucleus. It will have some number of states above the fission saddle point.

  19. Collective Effects • Consider a spherical nucleus. It will have many more (rotational) states at the fission saddle point.

  20. Experimental PCN Values • PCN decreases substantially with increasing Aproj. PCN ≈ 0.5 Preliminary PCN ≈ 0.25 PCN < 0.1 Figure courtesy of D. A. Mayorov.

  21. Summary: 48Ca versus 54Cr • Changing from 48Ca to 54Cr changed the cross section by >7.1  103. • The change in PCN was >5, in line with calculations. • A lower cross section would cause this limit to increase. • The difference in survivability is 7.8  103. • Of this, only 2 orders of magnitude is due to the change in Bn – Bf. • D(Bn – Bf)  6 MeV • The remaindermay be due to collective effects.

  22. Effects of Bn – Bf and z on Reactions with Odd-Z Targets • The energetics of 54Cr are much less favorable than 48Ca. • Not surprisingly, there is a strong dependence on the Coulomb parameter z. V.I. Zagrebaev et al., http://nrv.jinr.ru/nrv/

  23. Effects of Bn – Bf and z on Reactions with Odd-Z Targets z • The same data as the previous plots. Cross Sections: V.I. Zagrebaev et al., http://nrv.jinr.ru/nrv/

  24. Implications for Reactions with Projectiles Heavier Than 48Ca • The change from 48Ca to 50Ti or 54Cr affects the cross section: • Good Things: • scap is flat at best. • Slight increase in separator efficiency. • Bad Things: • Substantial decrease in PCN. • Substantial decrease in Wsur. • (Possibly) slight decrease in beam intensity.

  25. Implications for the Production of Element 120 • The 248Cm(54Cr, 4n)298120 reaction has three serious problems: • A reduction in PCN relative to 248Cm(48Ca, 4n)292Lv. (Beam changed from 48Ca to 54Cr). • The high fissility of the compound nucleus. • (Possibly) No increase in survivability due to the predicted closed shell at N = 184. • Our data suggests that predictions of sEVR on the order of tens of femtobarns are reasonable. • 249Cf(50Ti, 4n)295120 may be more feasible due to a more favorable PCN.

  26. Silver Bullets • We have used a number of “silver bullets” that have allowed us to create ever heavier elements: • Z = 107-112 (Cold Fusion Reactions): • Shell Stabilization Near Z = 108, N = 162. • Deformed Products (more on this later). • Shell-Stabilized Targets (minor effect). • Z = 113-118 (Warm Fusion Reactions): • The neutron-richness of 48Ca is exceptional among available projectiles. It increases Bf and decreases Bn. • Z > 118 (Warm Fusion Reactions): • It is not clear if there is another silver bullet. • We may need more beam or another type of reaction.

  27. Future Work • We will move to odd-Z projectiles in late 2012. • We will investigate 50Ti + 162Dy in late 2012. • We want to move down the periodic table toward transactinides. • The K150 is being developed to provide increased intensity for medium-mass beams.

  28. Acknowledgements • M. C. Alfonso • M. E. Bennett • D. A. Mayorov • T. A. Werke • K. Siwek-Wilczyńska and A. V. Karpov for many informative discussions. • U.S. DOE • Welch Foundation (grant A-1710) • Texas A&M University College of Science

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