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?

 Overall, a

fusion reaction is described by: s = scapPCNWsur

PCN Wsur scap

How do you make a heavy nucleus?

 The evaporation residue

cross section can be written as:

* 1

E

* 2

E

* 3

E

1 , n

S

2 , n

S

3 , n

S

1 , n

E

2 , n

E

3 , n

E

4 , n

S

4 , n

E



Fission Fission Fission

   

s s s s

 

      

 

cap CN sur cap CN n tot cap CN n f

( *, ) / /

x i i x i i

P W E l P P

1 1

 The production of a heavy nucleus is a competition

between neutron emission and fission.

    

n f n f

/ exp[ ( )/ ] S B T

The Challenge of Heavy Element Experiments with RIBs Today

 When producing heavy nuclei, the available beam

intensities are modest:’

 scap ~ 150 mb, Nt = 500 µg/cm2 248Cm, I = 7  104 s–1 39Ar  R = sNtI = . . . = 1.3  10–2 s–1 ~ 1.1  103 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.

• W. Loveland et al., PRC 74, 044607 (2006).
• J. F. Liang et al., PRL 96, 029903 (2006).

• A. Wakhle, 8/24/2015, Slide 9

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 PCN

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

• pportunities to look at ER cross sections.

The Problem with PCN

 Difficult to measure.  Data have large uncertainty.  Theory has large uncertainty.

• K. Siwek-Wilczyńska et al., IJMPE 17, 12 (2008).
• R. Yanez et al., PRC 88, 014606 (2013).

Projectiles with Z  20 Reacting with Lanthanide Targets

MOTIVATION: Prospects of SHE Synthesis with Zp > 20

• Rxns. Studied:

44Ca CN 48Ca CN 45Sc CN 50Ti CN 54Cr CN

Dependence of Bf – Sn on Model

 The model

used has a dramatic impact on Bf – Sn.

 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.

• G. N. Smirenkin, IAEA-Report INDC(CCP)-359 (1993).
• X. J. Bao et al. PRC 92, 014601 (2015).

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

 26Mg + 248Cm:  25Mg + 248Cm:  Some clever math shows

that

 The first-chance survival

probability was (89 ± 13)%.

 Surprisingly high!

• R. Yanez et al., Phys. Rev. Lett. 112, 152702 (2014).

 Neutron-deficient

radioactive beams could expand these studies.

Takeaway Messages

 Reaccelerated radioactive beams near he Coulomb

barrier can contribute to understanding all three phases of heavy element formation:

 Measurements of scap to understand whether neutron-

rich nuclei have increased fusion probabilities.

 Measurements of PCN 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

 DE-FG02-93ER40773  DE-FG07-05ID14692/MUSC09-100  DE-FG02-12ER41869/DE-SC0008126

 Welch Foundation: A-1710  NSF: PHY-1004780

 K. Siwek-Wilczyńska

and A. V. Karpov for informative discussions.

 Cyclotron Institute staff.