Opportunities for Heavy Element Science with ReA Cody Folden - PowerPoint PPT Presentation

Opportunities for Heavy Element Science with ReA Cody Folden Cyclotron Institute, Texas A&M University 2015 Low-Energy Community Meeting August 20, 2015

How does the nuclear reaction work? s cap P CN  Overall, a fusion reaction is described by: s = s cap P CN W sur W sur

How do you make a heavy nucleus?  The production of a heavy nucleus is a competition between neutron emission and fission.  The evaporation residue cross section can be written as: Fission * E s  s 1 S P W ( *, ) E l , 1 n cap CN sur E Fission n , 1 * E x 2  S   , 2 n  s   P / E cap CN n tot i , 2 Fission n * E  3 1 i S , 3 n E x , 3  n    s   S P / , 4 n cap CN n f i E , 4 n  1 i       / exp[ ( S B )/ T ] n f n f

The Challenge of Heavy Element Experiments with RIBs Today  When producing heavy nuclei, the available beam intensities are modest:’  s cap ~ 150 mb, N t = 500 µg/cm 2 248 Cm, I = 7  10 4 s – 1 39 Ar  R = s N t I = . . . = 1.3  10 – 2 s – 1 ~ 1.1  10 3 d – 1  For now, experiments are limited by production rates.  This limits the experiments that can be done and increases their difficulty as well.

Capture/Fusion Cross Sections with Neutron-Rich Beams  There is some evidence that fusion is more likely with neutron-rich beams. J. F. Liang et al ., PRL 96 , 029903 (2006). W. Loveland et al ., PRC 74 , 044607 (2006).

Coincident Fission Fragment Detector CFFD • Four Parallel Plate Avalanche Counters (30cm x 40cm) • MCP for ns scale start signal. • Portable  measurements at other facilities. • Digital Data Acquisition • Fusion measurements to investigate P CN and σ capture with n-rich and p-rich RIBs at ReA3. • Flexibility of CFFD allows several different detector configurations. • Future: FRIB will provide intensities to continue heavy-ion fusion studies but open opportunities to look at ER cross sections. A. Wakhle, 8/24/2015, Slide 9

The Problem with P CN  Difficult to measure.  Data have large uncertainty.  Theory has large uncertainty. R. Yanez et al ., PRC 88 , 014606 (2013). K. Siwek- Wilczyńska et al. , IJMPE 17 , 12 (2008).

Projectiles with Z  20 Reacting with Lanthanide Targets MOTIVATION: Prospects of SHE Synthesis with Z p > 20 Rxns. Studied: 44 Ca CN 50 Ti CN 48 Ca CN 54 Cr CN 45 Sc CN

Dependence of B f – S n on Model  The model used has a dramatic impact on B f – S n .  This likely has a dramatic impact on the cross section. K. Siwek- Wilczyńska et al. , Int. J. Mod. Phys. E 18 , 1079 (2009).

The Situation with Fission Barriers  Calculations are available, but experimental data are hard to come by. X. J. Bao et al . PRC 92 , 014601 (2015). G. N. Smirenkin, IAEA-Report INDC(CCP)-359 (1993).

Influence of Angular Momentum  The question of angular momentum and its influence on compound nuclei is complex.  Several groups have suggested that angular momentum needs to be reduced to realistically represent what actually contributes to the cross section. G. Henning et al ., Phys. Rev. Lett. 113 , 262505 (2014). See also A. N. Andreyev et al ., Phys. Rev. C 72 , 014612 (2005).

Measurement of  n /  tot  26 Mg + 248 Cm:  25 Mg + 248 Cm:  Some clever math shows that  Neutron-deficient radioactive beams could expand these  The first-chance survival studies. probability was (89 ± 13)%.  Surprisingly high! R. Yanez et al. , Phys. Rev. Lett. 112 , 152702 (2014).

Takeaway Messages  Reaccelerated radioactive beams near he Coulomb barrier can contribute to understanding all three phases of heavy element formation:  Measurements of s cap to understand whether neutron- rich nuclei have increased fusion probabilities.  Measurements of P CN to help reduce experimental and theoretical uncertainties.  Measurements of fission barriers and survival probabilities, which affect the most important component of the cross section.  All of this should go hand-in-hand with a vigorous theory program.

Acknowledgements: Coworkers  Folden Group Members:  M. C. Alfonso  E. R. Bertelsen  T. K. Bhardwaj  M. E. Bennett  M. J. DeVanzo  L. D. Fields  M. M. Frey  D. A. Mayorov  J. A. Sefcik  M. F. Volia  T. A. Werke

Acknowledgements  DOE  K. Siwek- Wilczyńska and A. V. Karpov for  DE-FG02-93ER40773 informative discussions.  DE-FG07-05ID14692/MUSC09-100  Cyclotron Institute staff.  DE-FG02-12ER41869/DE-SC0008126  Welch Foundation: A-1710  NSF: PHY-1004780