1 / 28

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 .

makara
Download Presentation

Prospects for the Discovery of the Next New Element

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  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

More Related