Fritz Peter HeßbergerGSI – Helmholtzzentrum für Schwerionenforschung mbH,

D-64291 Darmstadt, GermanyHelmholtz – Institut Mainz, D-55099 Mainz, Germany

NN2015 12th International Conference on Nucleus – Nucleus Collisions

Catania, Italy21 – 26 June 2015

Version 18. 6. 2015

Exploration of Nuclear Structure and Decayof Heaviest Elements at GSI - SHIP

The Strong Force

Quark – Gluon - Plasma Formation and development of stars Development of the universe Synthesis of the chemical elements Structure of the atomic nuclei

One of the four basic interactions,playing among others an essential role for

The Strong Force

146 148 150 152 154 1560,0

0,5

1,0

1,5

2,0

Neutron shell N = 152

Shell strength parameter 2nof nobelium isotopes ( Z = 102)

SLy4 - prediction

exp. values

2n

/ MeV

Neutron Number

0

200

400

600

0

200

400

600

1/2-[521]

7/2-[514]

experiment

0+x30+x20+x1

294+x3253+x2

210+x1

E* /

keV

E* /

keV

7/2+[633]

3/2-[521]

253Es251Es249Es247Es245Es243Es

1/2-[521]

7/2+[633]

7/2-[514]

3/2-[521]

HFB - SLy4 (Chatillon et al. EPJ A30, 397 (2006))

Physics Motivation for Synthesis and NuclearStructure Investigations of SHE

Why synthesis and nuclear structure investigations ?

Atomic nucleus is quantum mechanical ensemble of nucleons (p, n)

Properties determined by ‚fundamental‘ interactions- nucleon – nucleon interaction- Coulomb interaction- spin – orbit interaction- ….

Understanding decay properties and structure of nuclei is thus essential for understanding ‚fundamental‘ interactions

Superheavy nuclei (SHE) are a specific class of exotic nuclei ensembles of ‚extremely‘ large numbers of protons and neutrons despite of high density of nuclear levels ‚gaps‘ between single particle

states occur at certain numbers of Z and N indicating ‚shell closures‘ no macroscopic (‚collective‘) fission barrier any more, stability against

prompt disruption due to ‚shell effects‘; Bf depends on single particle levels shell structure determines nuclear mass excess determines Q-values forα- and β- decay

Physics Motivation for Synthesis and NuclearStructure Investigations of SHE

Understanding nuclear structure of SHE is

essential for understanding their

properties and stability

i.e. the ´limits of our world´

Topic Questions Are there proton and neutron shells at all ?

How strong are they ?Where are they located ?

140 145 150 155 160 165 170 175 180 185 190

100

105

110

115

120

125

neutron number

prot

on n

umbe

r

<1

<104

<104 <10-4

<1

<1<1

>104

<10-4

<10-8

N=184N=162

Z=114

Z=108

-decay

-decay

SF expected decay modes and halflives

Expected Decay Modes and Halflives of SHE

Nuclear Structure

Synthesis

Velocity separator SHIP

SHIPSeparation time: 1 – 2 μsTransmission: 20 – 50 %Background: 10 – 50 HzDet. E. resolution: 18 – 25 keVDet. Pos. resolution: 150 μm Dead time: 25 μs

Decay Spectroscopy of SHE

Nuclear structure investigations require a large amount of events, but production rates of SHE are low (ca. 240 /d/nb)

Nuclear structure of odd-A even Z nuclei is similar along isotone line

Nuclear structure of odd-A even Z nuclei is similar alongisotope line

Study of systematics of (low lying) Nilsson levels inodd A nuclei

Decay schemes of the N=153 Isotones 255No, 257Rf, 259Sg

199.

9 (M

2+E3

)

163.

3 (M

1)

257Rf255No

251Fm

(35+x) (8255 (3 %)

(8290 (5 %)

(3/2+ ?) 392354

200

353.

8(E1

)19

4.5

(M1)

166.

8 (M

1)

7941 (0.4 %)

7742 (19%)

7903 (11 %)

(7/2+[624])

21 s

(1/2+[620])

(5/2+[622])

(9/2-[734])

(1/2+[631])

192.

1 (E

2)

358.

3 (E

2)

0

394

558

(1/2+[620])

8095 (58 %)

(7893 4 %)

(8962)

9021(8950)

(8680)

8778

(8510)(8450)

24 s

5.7 s4.9 s

510

450

258

16716

7(M

2+E3

)

62

0

91(M

1)28

3 (E

2)

(1/2+[620])?

(3/2+)

(3/2+,5/2+,7/2+)

(11/2-)

(9/2-[734])

(5/2+[622])

(1/2+[620])

(11/2-[725])

(9/2-[734])

(11/2-[725])

40 s

(1/2+[620])?

253No 255Rf

9240

9545

9702

9610

9035

594

(1/2+[620])

(11/2-[725])

259Sg

594

(462)

ca.150

0

411 ms

254 ms

(5/2+[622])

F.P. Heßberger et al. Z.Phys. A 359,415 (1997)B. Streicher et al. EPJ A 45, 275 (2010)

F.P. Heßberger et al. EPJ A29,165 (2006) S. Antalic et al. EPJ A 51:41 (2015)

Decay Study of 257Rf

direct production 208Pb(50Ti,n)257Rf(F.P. Heßberger et al. Z.Phys. 359, 415 (1997))

production by α-decay of 261Sg(B. Streicher et al. EPJA 45,275 (2010))

(data scaled to same intensity in theregion E = 8.7-8.8 MeV)

real effect ??

(T1/2 = 4.9 s) (T1/2 = 5.7 s)

Decay Study of 257Rf

SHIP – Exp. 2014

Decay Study of 257Rf

prand < 10-6

Decay Study of 257Rf

coincidence not observed in production by α-decay of 261Sg

assignment to 257Lr unlikely due to α-α-correlation to 253No

certainly related to decay of 257mRf

Eα+Eγ = 8.86 MeV, but Eα(257mRf) = 9.03 MeV suggests population of a level at E* ≈ 170 keV (5/2+ isomer !!!) cannot be 11/2-(257mRf) 11/2-(253No) transition; prefers M1

transition to 9/2- gs. and not E3 transition to 5/2+ isomer α-transition only slightly hindered (HF ≈5-10); no parity change,

no spin-flip

x

x

x

xxxx

xx

Decay Study of 257Rf – expected levels in 253No

Nilsson-Levels in N=151 Isotonesexperimentt Z.H. Zhang et al. PRC 85, 014423

(2012)M. Bender et al. NPA 723, 356 (2003),and priv. comm. 2015

M. Asai et al. PRC 83, 014315 (2011)A. Parkhomenko, A. Sobiczewski,Acta. Phys. Pol. B36, 3115 (2005)

S. Cwiok et al. NPA 573, 356 (1994)

Ident. 11/2-and confirm 7/2-

in 253No

Nilsson-Levels in N=153 Isotonesexperimentt

Z.H. Zhang et al. PRC 85, 014423(2012)

M. Bender et al. NPA 723, 356 (2003),and priv. comm. 2015

S. Cwiok et al. NPA 573, 356 (1994)A. Parkhomenko, A. Sobiczewski,Acta. Phys. Pol. B36, 3115 (2005)

Ident. 11/2-in 255No

156 158 160 162 164 166 168 170 172 174 176 178 180102

104

106

108

110

112

114

116

118

118-294

117-294117-293

Lv-293Lv-292Lv-291Lv-290

115-290115-289115-288115-287

Fl-289Fl-288Fl-287Fl-286Fl-285

Cn-285Cn-284Cn-283Cn-282Cn-281

113-283113-282 113-284 113-285 113-286

Rg-282Rg-281Rg-280Rg-279Rg-278

Ds-281Ds-279Ds-277

Mt-278Mt-277Mt-276Mt-275Mt-274

Hs-277Hs-275Hs-273

Bh-274Bh-272Bh-271Bh-270

Sg-271Sg-269

Db-270Db-268Db-266Db-267

Rf-267Rf-265

Lr-266

StrukturSWK/Abbildungen/NukaSHE

Neutron Number

Pro

ton

Num

ber

Z – Identification of SHE α-chains terminated by sf sf of o-o – nuclei strongly hindered maybe no sf of o-o nucleus observed;

but sf of e-e daughter af EC EC is a ‚certain‘ source for K-X-rays Z – identification by delayed

coincidences betweenK – X-rays and sf

test-case: 258Db

Predict. SF - halflives266Rf: 23s268Rf: 1.4s270Rf: 20 ms

sf (

EC (

EC (

EC(?) (

254Lr

258Db

254No

258Rf18 s

1.9 s | 4.3 s

15 ms

55 s

_

Direct Prove of EC of 258Db

From delayed coincidencesT1/2(sf) = 14.5 ± 5.2 ms

sf (

EC (

EC (

EC(?) (

254Lr

258Db

254No

258Rf18 s

1.9 s | 4.3 s

15 ms

55 s

_

258Rf:Eα= 9.05±0.03 MeV, bα = 0.31 ± 0.11 (J. Gates et al. PRC 77, 034603 (2008))Eα= 9.07±0.02 MeV, bα = (0.07 +0.08/-0.04, preliminary ) (this work)

Alpha – decay branch 258Rf

Proof of EC Decay of 257Rf

configuration• stop detector: 1 DSSD (6060 strips)• box detectors: 4 SSSD (32 strips)• overall particle - γ-efficiency ≈ 40%

chamber• compact (overall length 35 cm)• Al-cap with thin window (1,5 mm)• compatible due to 150 mm standard flange• electronics partly integrated (vacuum)

DSSD• integrated cooling (Cu-frame) and

connection (flex-PCB)• 6060 strips/mm (pitch 1 mm)• 300 µm

configuration• stop detector: 1 DSSD (6060 strips)• box detectors: 4 SSSD (32 strips)• overall particle - γ-efficiency ≈ 40%

chamber• compact (overall length 35 cm)• Al-cap with thin window (1,5 mm)• compatible due to 150 mm standard flange• electronics partly integrated (vacuum)

DSSD• integrated cooling (Cu-frame) and

connection (flex-PCB)• 6060 strips/mm (pitch 1 mm)• 300 µm

Enhanced Focal Plane Detector Set-up forSHE Spectroscopy

D. Ackermann, J. Maurer, M. Vostinar,J. Piot, N. Kurz,P. Wieczorek,J. HoffmannF.P. Heßberger et al.

Enhanced Focal Plane Detector Set-up forSHE Spectroscopy

First on-line test at LISE – Wienfilter GANIL, november 201440Ar (4.66 AMeV) + 174Yb 209,210Ra

energy resolution≈ 20 keV (FWHM)

DSSD – analog signal processing

209,210RaFWHM = 45 keV

single trace

energy / channels

Enhanced Focal Plane Detector Set-up forSHE Spectroscopy

Digital signal processing FEBEX + conventional PADSSD, Ge-detectors, .....● fast timing ● deadtime free ● pulse shape analysis options

Conclusions

Decay spectroscopy and ground state mass measurement are powerful toolsto investigate nuclear structure of SHE in terms of ordering of nuclear levels energy systematics of Nilsson levels identification of neutron (and proton) shell determination of shell strenghts the stability of (multi) quasi-particle states

Measuring X-rays from EC in delayed coincidence with the decay (α, sf) isprobably an alternative method for Z – identification of SHN.

population of excited levels in daughter nuclei by EC decay is an additionalsource for nuclear structure information

Future Goals: identification of ‚missing‘ levels relevant for strength and location of the

‚SHE – shells‘ at Z ≤ 106 detailed nuclear structure investigations at Z > 106 ‚more‘ detailed study of K – isomers at Z = 100 - 110

SHIP – SHE Nuclear Structure Collaboration (Spokesman: F.P. Heßberger)

GSI, DarmstadtM.Block, S.Heinz, F.P.H., B.Kindler, I.Kojouharov, J.Khuyagbaatar, B.Lommel

Helmholtz Institut MainzA. Mistry, M. Laatiaoui, J. Even (now at TRIUMF, Vancouver)

Comenius University Bratislava, SlovakiaS. Antalic, B. Andel, Z.Kalininova (now at JINR, Dubna), S.Saro (deceased)

GANIL, Caen, FranceD. Ackermann, H. Savajol, J. Piot, M. Vostinar

JAEA Tokai, JapanK. Nishio