Isomer Spectroscopy of the Heaviest Elements

Rod Clark(Lawrence Berkeley National Laboratory)

Outline

• Motivation for studying structure of heaviest nuclei

• K-isomers in Z≥100 region

• The Berkeley Gas-Filled Separator (BGS)

• Recent results:• 50Ti+208Pb→256Rf+2n (σ≈20nb)• 48Ca+209Bi→255Lr+2n (σ≈300nb)

• Heavy element spectroscopy with GRETINA+BGS

• Summary

Motivation

• Single-particle levels → shell structure• Next major spherical gaps• Deformed gaps

• Deformation and collectivity• K-isomerism• Rotational structures• Low-lying vibrations

• Pairing properties• Multi-quasiparticle states• Effects on rotation• Effects on alpha decay• Effects fission decay

K-Isomers in Z≥100 Nuclei

Nature 422 896 (2006)

FMA at ANL

RITU at JYFL

S.K.Tandel et al., PRL 97 082502 (2006)

Conversion Electron and Gamma Spectroscopy

M W AC

F ocal P lan eD etector

P u n ch th rou ghD etector

R u th er fordD etectors

Q u adru poleM agn et

G radien t-F ield

M agn et

F lat-F ieldD ipoleM agn et

T arget

E V RT rajectory

B eamT rajectoryB eam G as-F il led

C h am ber

Large acceptance: 45 msr (± 9° vertical, ±4.5° horizontal) Highest transmission ( Ni+Pb: 70% Ca+Pb: 60% Mg+U:

18% ) Large bend angle: 70°

Lowest background rates ( 40Hz/pA 20Hz/pA100Hz/pA )

Berkeley Gas-filled Separator

Focal Plane Detectors

16×16 strip DSSD1mm thick, 5cm by 5cm

1) Recoil implanted in pixel of DSSD2) Burst of conversion electrons in same pixel from isomer decay3) Gamma-rays in coincidence with electron burst4) Recoil decays in same pixel by alpha/fission

Key idea was to tag on isomer by searching for burst of conversionelectrons and using a single pixel as a calorimeter.

G.D. Jones (Liverpool), NIM A 488 471 (2002).

256Rf: Z=104, N=15250Ti+208Pb→256Rf+2n at 243 MeV (σ≈20nb), 200pnA, 6 days

Electrons Gamma Rays

r-e-e-f

r-e-e-f

0+2+4+

K=(2-)3-4-5-6-

≈946

≈46

256Rf104 152

K=(5-) ≈112025(2)s

≈140017(2)s

K=(7-,8-)

t1/2=27(6)s>2200

900

H. B. Jeppesen et al.,Submitted to PRL

255Lr: Z=103, N=15248Ca+209Bi→255Lr+2n at 222 MeV (σ≈300nb), 300pnA, 4 days

7/2

19/2

~x+800

~x+1400

x

247Es: Z=99, N=148-spectroscopy following -decay of 255Lr→251Md→247Es

243 =294

251Md

247Es

243 =294

251Md

247Es

F.P.Hessberger et al., EPJ A 26 233 (2005)A. Chatillon et al., EPJ A 30 397 (2006)

Eisteinium (Z=99) Systematics Re-examined

0+x

243 =294

251Md

247Es

243 =294

251Md

247Es

F.P.Hessberger et al., EPJ A 26 233 (2005)A. Chatillon et al., EPJ A 30 397 (2006)

Eisteinium (Z=99) Systematics Re-examined

0+x

?

Transfermium Spectroscopy with GRETINA+BGS The best heavy element separatorwith the best -ray detector system

Assumptions for simulation:TOT = 1 barnTarget = 0.5 mg/cm2

Beam Current = 50 pnA/ crystal = 0.0067M = 10→ 30.3 kHz/crystal

48Ca+208Pb→254No+2nσ~2 μb

2000

Cou

nts

Energy (keV)

50Ti+208Pb→256Rf+2nσ~20 nb25

Cou

nts 6+→4+

Energy (keV)

Summary• New generation of spectroscopy experiments on heaviest elements

RITU at JYFL, FMA at ANL, BGS at LBNL,GABRIELLA at Dubna, SHIP at GSI, VAMOS at GANIL+…

• Decay spectroscopy at BGS able to reach Sg (Z=106)- single-particle states- K-isomerism- low-lying rotational and vibrational modes

• Prompt spectroscopy with GRETINA at BGS able to reach Rf (Z=104)- rotation versus fission- moments of inertia, alignments- configuration assignments

• Can modern microscopic theories reproduce experiment?