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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: 50 Ti+ 208 Pb→ 256 Rf+2n ( σ≈ 20nb)
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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
Nature 422 896 (2006) K-Isomers in Z≥100 Nuclei RITU at JYFL FMA at ANL
Conversion Electron and Gamma Spectroscopy S.K.Tandel et al., PRL 97 082502 (2006)
Berkeley Gas-filled Separator 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/pmA20Hz/pmA100Hz/pmA )
Focal Plane Detectors 16×16 strip DSSD 1mm thick, 5cm by 5cm 1) Recoil implanted in pixel of DSSD 2) Burst of conversion electrons in same pixel from isomer decay 3) Gamma-rays in coincidence with electron burst 4) Recoil decays in same pixel by alpha/fission Key idea was to tag on isomer by searching for burst of conversion electrons and using a single pixel as a calorimeter. G.D. Jones (Liverpool), NIM A 488 471 (2002).
256Rf: Z=104, N=152 50Ti+208Pb→256Rf+2n at 243 MeV (σ≈20nb), 200pnA, 6 days Electrons Gamma Rays r-e-e-f r-e-e-f
>2200 t1/2=27(6)ms Kp=(7-,8-) ≈1400 17(2)ms 6- Kp=(5-) 5- ≈1120 4- 25(2)ms 3- ≈946 256 Kp=(2-) Rf 152 104 900 4+ 2+ ≈46 0+ H. B. Jeppesen et al., Submitted to PRL
~x+1400 ~x+800 19/2 x 7/2 255Lr: Z=103, N=152 48Ca+209Bi→255Lr+2n at 222 MeV (σ≈300nb), 300pnA, 4 days
247Es: Z=99, N=148 g-spectroscopy following a-decay of 255Lr→251Md→247Es
Eisteinium (Z=99) Systematics Re-examined 251Md 251Md a1 a2 a g=294 g=243 g=243 g=294 0+x 247Es 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 251Md 251Md ? a1 a2 a g=294 g=243 g=243 g=294 0+x 247Es 247Es F.P.Hessberger et al., EPJ A 26 233 (2005) A. Chatillon et al., EPJ A 30 397 (2006)
Transfermium Spectroscopy with GRETINA+BGS 50Ti+208Pb→256Rf+2n σ~20 nb 25 6+→4+ Counts 2000 48Ca+208Pb→254No+2n σ~2 μb Counts Energy (keV) The best heavy element separator with the best g-ray detector system Assumptions for simulation: sTOT = 1 barn Target = 0.5 mg/cm2 Beam Current = 50 pnA eg / crystal = 0.0067 Mg = 10 → 30.3 kHz/crystal 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?
