Viola and the Heavy Elements

W. Loveland

Oregon State University

Vic’s Contributions to the Heavy Element Field

• Vic’s Nucleus

• Systematics of the properties of the heaviest elements

• TKE release in fission

• Linear Momentum Transfer

• Transfer Product Yields

Vic’s Nucleus--The “Union Card”

• Grad student in the Seaborg group

• Numerous important contributions

• 226U

Current data t1/2=0.35 s, E=7.57 MeV

Systematics of the properties of the heaviest elements

• Masses, Q, Q• V.E. Viola, Jr. and G.T. Seaborg, J. Inorg Nucl.Chem. 28, 697 (1966).• V.E. Viola, Jr., J. A. Swant, and J. Graber, At. Data and Nucl Data Tables 13, 35

(1974). (Z=50-118, A=130-311)

• Lifetimes• V.E. Viola, Jr. and G.T. Seaborg, J. Inorg. Nucl Chem. 28, 741 (1966)• V.E. Viola, Jr. and B.D. Wilkins, Nucl. Phys. 82, 65 (1966)

TKE Release in FissionV.E. Viola, Jr. Nucl. Data A1, 391 (1966)V.E. Viola, K. Kwiatkowski, and M. Walker, Phys. Rev. C 31 1550 (1985).

Simple-Minded Approach

TKE Z1Z2e

2

r0(A11/ 3 A2

1/ 3)Z1Z2e

2F(r)

Simple fit to the data

r0 1.8

Pocket formula

TKE Z1Z2e

2

1.8 A11/ 3 A2

1/ 3

Viola Systematics-1966

TKE 0.1071Z 2

A1/ 3 22.2MeV

Viola systematics-1985

TKE 0.1189Z 2

A1/ 3 7.3MeV

Note limits on range of applicability

Physics Issues

r0 ~ 1.8 2R + D

D Initial Kinetic Energy of Fragments

New Developments

Linear Momentum TransferT. Sikkeland, E.L. Haines, and V.E. Viola, Jr., Phys. Rev 125, 1350 (1962)V,E. Viola, et al., Phys, Rev. C 26,178 (1982).

pfrag

pCN/2

•Diagnostic for the occurrence of incomplete fusion•A tool to study the mechanism of intermediate energycolliisions

Transfer Product Yields

Heavy Element Synthesis

Search for Element 112 in the 238U(48Ca,3n) Reaction

• Y.T. Oganessian et al. reported (Eur. J. Phys A5, 63 (1999))

• 231 MeV 48Ca + 238U 286112 283112 SF

• Two events were observed (t½ = 81 (+147, -32) s)

• Dose = 3.5 x 1018, = 5.0 (+6.3, -3.2) pb

• Somewhat unexpected decay mode

What is so special about 283112 and its synthesis?

• 283112 occurs in the decay of 291116 formed in the 245Cm + 48Ca reaction.

• 283112 occurs in the decay of 287114 formed in the 244Pu + 48Ca reaction.

• 283112 should be the most easily reachable hot fusion product.

Chronology of Studies of 238U(48Ca,3n) 283112 Reaction

• 1999--Vassilissa group reports synthesis of 283112 with ~ 5 pb, t1/2 ~ 3 m, decay =SF, Elab=231 MeV

• 2002--BGS group fails to find 283112, upper~ 0.9 pb, 0<t1/2<1000s, decay =,SF, Ebeam =231 MeV

• 2004--Vassilissa group fails to find 283112 at Ebeam ~ 231 MeV, upper ~ 2.2 pb.

• 2004--Vassilissa group finds 283112 at Ebeam ~ 234 MeV, ~ 4 pb, t1/2 ~5.1 m, decay = SF

• 2004--DGFRS group fails to find 5 min SF activity, says 283112 is an -emitter with t1/2 ~ 6 s (produces this nucleus directly and in decay of 291116 and 287114.)

• 2004--BGS group tries again to make 283112 at Ebeam ~ 236 MeV without success.

• 2005--Swiss group fails to confirm DGFRS or Vassilisa results• 2005--GSI group fails to confirm DGFRS or VASSILISSA results but finds

one event (t~7 s, decay =SF, =0.5 pb)--disagrees with everyone.

Summary of BGS Experiments

Energy (MeV) 230.3 235.6

No. of runs 2 1 E*(MeV) 31.9 36.3

Dose 2.3x1018 1.9x1018

1 event upper limit (pb) 0.8 0.96 84% CL Upper Limit (pb) 1.6 2.0

RESULTS

NO SF events in any irradiation

No EVR-- correlations ( T < 20 s) in any irradiation.

Summary of Experiments

• Vassilissa group 283112 is SF nucleus, with t1/2 ~ 5 min, ~ 4 pb

• DGFRS group 283112 is emitter (SF < 10%), t1/2 = 6 s, ~ 2.5 pb

• GSI group 283112 is SF nucleus, t1/2 ~ 5 s, ~ 0.7 pb

• BGS group 283112 not found, upper ~ 0.9 pb

Thanks, Vic