Heavy Elements and the Path to FRIB W. Loveland Oregon State - - PowerPoint PPT Presentation

Heavy Elements and the Path to FRIB

• W. Loveland

Oregon State University

The Current Situation

Cold and Hot Fusion

• Cold Fusion
• Pb or Bi Target
• Heavier Projectile

(Ca-Kr)

• E* ~ 13 MeV (1n

reaction, high survival)

• Significant fusion

hindrance

• Hot (Warm) Fusion
• Actinide Target
• Lighter Projectiles

(O-Ca)

• E* ~ 30 – 60 MeV

(low survival)

• Small fusion

hindrance

The neutron-deficient character

• f our efforts

Zagrebaev, Karpov, and Greiner, Acta Physica Polonica B, 45,291 (2014)

Production of Heavy Elements in Complete Fusion Reactions

• We need to know three spin-dependent quantities: (a) the

capture cross section, (b) the fusion probability and (c) the survival probability, and their isospin dependence. Note that J values are determined by the Wsur factor. where

Studies of heavy element formation in RNB reactions

• G.G. Adamian, et al. PRC 69, 044601 (2004)->47K, 50Ca,46Ar
• W. Loveland, PRC 76, 014612 (2007) -> σϕ
• X. J. Bao, et al. PRC 91, 064612 (2015) -> improved σ

Calculational Model For RIB- Induced Reactions

• Fusion Probability
• Survival Probability

RIA/SPIRAL2/FRIB…Beam List

• All “stable” targets

Yield in atoms/day

Cold fusion

You will NOT make new superheavy elements with radioactive beams The intensities are too low

“Window to new n-rich heavy nuclei”

• There is a “window of opportunity” for making new n-

rich heavy nuclei using RIBs. The “window” is defined as a region where the cross sections and beam intensities lead to the production of > 10 atoms/day

Accelerator Window RIA 103-110 SPIRAL2 103-108 FRIB 103-107

What kind of reactions with RNBs are used to form n-rich nuclei?

Reactants Products FRIB Beam Intensity (p/s) Production Rate (atoms/day)

23O + 252Cf 271Sg + 4n

1.6 x 106 1

30Mg + 244Pu 270Sg + 4n

2.1 x 107 3.2

21O + 252Cf 269Sg + 4n

5.0 x 106 7.8

20O + 252Cf 268Sg + 4n

4.3 x 108 1200

25Ne + 246Cm 267Sg + 4n

2.3 x 107 3.2

Atomic Physics and Chemistry of the Transactinides

>10 atom/day list

• 265Rf

252Cf(16C,3n)

• 266Db

252Cf(19N,5n)

• 268Sg

252Cf(20O,4n)

• 268Bh

248Cm(25Na,5n)

• 264Lr

248Cm(19N,3n)

Targeted Radioactive Beams

• Special opportunities may exist if RNB facilities

focus on producing a beam of particular interest.

• Example: 46Ar (from 48Ca fragmentation)

FRIB “fast beam rate” 1.1 x 1010 FRIB “reaccelerated beam rate” 2.3 x 107

Reaction Beam Intensity (p/s) Cross Section (pb) Atoms/day

238U(48Ca,3n)283

Cn 3x1012 0.7 0.5

244Pu(46Ar,4n)28 6Cn

1.1 x 1010 250 0.6

244Pu(46Ar,3n)28 7Cn

1.1 x 1010 140 0.3

What can we do before FRIB?

• Improve our knowledge of capture cross

sections for n-rich projectiles.

• ReA3 (Ta/Pb targets)
• ReA6 (all targets)

Capture Cross Sections

Calculations done using coupled channels code (NRVP website) (Other recommended procedures are PRC 90 064622, PRC 83 054602, etc.) Capture cross sections are generally known within a factor of 2. Is this good?

What about n-rich projectiles?

ReA3 experiments (Oct.2015)

AIRIS projects the availability of 48K at rates similar to 46K from ReA3 TRIUMF says they have 100 x more intense 46K beams

Survival Probabilities (Wsur)

• For the most part, the formalism for

calculating the survival of an excited nucleus is understood.

• There are significant uncertainties in

the input parameters for these calculations and the care needed to treat some situations.

Wsur summary

• Needed items
• Kramers correction
• Damping of shell effects
• Collective enhancement factors
• Pairing corrections
• E* (masses)
• Bf (uncertain to 0.5-1.0 MeV)

Survival Probability (How well do we know the isospin dependence of Bf?)

The situation is more depressing if you go to the heaviest nuclei

Baran et al. (2015)

How can we improve our knowledge of fission barrier heights?

• 49,50Ti + 232Th ->281,282Cn Γn/Γf (ATLAS)
• 49,50Ti + 249Bk ->298,299119 Γn/Γf (ATLAS)
• 32-38S + 232Th-> 264-270Sg Γn/Γf
• 32-38S + 238U-> 264-270Hs Γn/Γf

Intense RNBs can help here (>106/s) (We also need ReA6 energies here)

The Fusion Probability, PCN

• Least well-known factor
• Hardest to measure
• A typical example

PCN(expt.) = 0.05

Excitation Energy Dependence of PCN

          ) ( exp 1 ) *, (

* int *

J E E P J E P

B CN CN

Zagrebaev and Greiner

PCN dependence on fissility

All data E*=50 MeV

Proposed expt. to better define PCN

Multinucleon Transfer Reactions

• The pioneering radiochemical studies of

the 1970s and 80s at LBNL and GSI.

• The basic problem in making heavier nuclei

was that the higher excitation energies that led to broader isotopic distributions caused the highly excited nuclei to fission.

• The contribution of Zagrebaev and Greiner

to to emphasize the role of shell effects in these transfer reactions.

The importance of shell effects

V.I. Zagrebaev and W. Greiner, NPA (in press)

* MNT reactions with RNBs do not look feasible at present (PRC 91 044608)

Conclusions

• We can better define the critical

variables that determine the cross sections for heavy element synthesis using ReA3 and ReA6 (and other RNB facilities).

• We should be able to synthesize new n-

rich nuclei with Z=100-106 with MNT reactions.

Acknowledgements

• This work was supported in part by the

U.S. Dept. of Energy, Office of Science, Office of Nuclear Physics under award number DEFG06-97ER41026 and the National Science Foundation under award number 1505043