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 • Hot (Warm) Fusion • Pb or Bi Target • Actinide Target • Heavier Projectile • Lighter Projectiles (Ca-Kr) (O-Ca) • E* ~ 13 MeV (1n • E* ~ 30 – 60 MeV reaction, high (low survival) survival) • Small fusion • Significant fusion hindrance hindrance

The neutron-deficient character of our efforts Zagrebaev, Karpov, and Greiner, Acta Physica Polonica B, 45,291 (2014)

Production of Heavy Elements in Complete Fusion Reactions where 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 W sur factor.

Studies of heavy element formation in RNB reactions G.G. Adamian, et al. PRC 69, 044601 (2004)-> 47 K, 50 Ca, 46 Ar • W. Loveland, PRC 76, 014612 (2007) -> σ ϕ • X. J. Bao, et al. PRC 91, 064612 (2015) -> improved σ •

Calculational Model For RIB- Induced Reactions RIA/SPIRAL2/FRIB…Beam List •All “stable” targets • Fusion Probability • Survival Probability 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 Production Intensity (p/s) Rate (atoms/day) 23 O + 252 Cf 271 Sg + 4n 1.6 x 10 6 1 30 Mg + 244 Pu 270 Sg + 4n 2.1 x 10 7 3.2 21 O + 252 Cf 269 Sg + 4n 5.0 x 10 6 7.8 20 O + 252 Cf 268 Sg + 4n 4.3 x 10 8 1200 25 Ne + 246 Cm 267 Sg + 4n 2.3 x 10 7 3.2

Atomic Physics and Chemistry of the Transactinides >10 atom/day list  265 Rf 252 Cf( 16 C,3n)  266 Db 252 Cf( 19 N,5n)  268 Sg 252 Cf( 20 O,4n)  268 Bh 248 Cm( 25 Na,5n)  264 Lr 248 Cm( 19 N,3n)

Targeted Radioactive Beams • Special opportunities may exist if RNB facilities focus on producing a beam of particular interest. • Example: 46 Ar (from 48 Ca fragmentation) FRIB “fast beam rate” 1.1 x 10 10 FRIB “reaccelerated beam rate” 2.3 x 10 7 Reaction Beam Cross Atoms/day Intensity Section (p/s) (pb) 238 U( 48 Ca,3n) 283 3x10 12 0.7 0.5 Cn 244 Pu( 46 Ar,4n) 28 1.1 x 10 10 250 0.6 6 Cn 244 Pu( 46 Ar,3n) 28 1.1 x 10 10 140 0.3 7 Cn

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 48 K at rates similar to 46 K from ReA3 TRIUMF says they have 100 x more intense 46 K beams

Survival Probabilities (W sur ) • 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.

W sur summary • Needed items • Kramers correction • Damping of shell effects • Collective enhancement factors • Pairing corrections • E* (masses) • B f (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? • 49,50 Ti + 232 Th -> 281,282 Cn Γ n /Γ f (ATLAS) • 49,50 Ti + 249 Bk -> 298,299 119 Γ n /Γ f (ATLAS) Intense RNBs can help here (>10 6 /s) (We also need ReA6 energies here) • 32-38 S + 232 Th-> 264-270 Sg Γ n / Γ f • 32-38 S + 238 U-> 264-270 Hs Γ n / Γ f

The Fusion Probability, P CN • Least well-known factor • Hardest to measure • A typical example P CN (expt.) = 0.05

Excitation Energy Dependence of P CN Zagrebaev and Greiner 0 P  CN P ( E *, J ) CN    * * E E ( J )  B int   1 exp   

P CN dependence on fissility All data E*=50 MeV

Proposed expt. to better define P CN

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