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: *

1E

*

2E

*

3E

1,nS

2,nS

3,nS

1,nE

2,nE

3,nE

4,nS

4,nE

Fission

Fission

Fission

s s

s

s

cap CN sur

cap CN n tot

cap CN n f

( *, )

/

/

x

ii

x

ii

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

opportunities 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 CN48Ca CN45Sc CN

50Ti CN54Cr 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-Wilczyńskaand A. V. Karpov for informative discussions.

Cyclotron Institute staff.