"Highlights from radioactive beam experiments using MINIBALL and REX-ISOLDE."

Transcription

1 "Highlights from radioactive beam experiments using MINIBALL and REX-ISOLDE." Piet Van Duppen Instituut voor Kern- en Stralingsfysica, K.U.Leuven for the MINIBALL, REX- and HIE-ISOLDE collaboration

2 Outline MINIBALL at REX-ISOLDE, CERN: Radioactive beams at ISOLDE Coulomb excitation and transfer reactions using MINIBALL Physics case and results: General overview of MINIBALL campaigns (two examples: close to 100 Sn and to 132 Sn) Nuclear structure along Z=28 from N=40 towards N=50 (Coulomb excitation: Cu isotopes, β-decay of 67 Fe- 67 Co- 67 Ni) Evidence for intruder states and shape coexistence Conclusion and outlook HIE-ISOLDE see also talks by V. Bildenstein,, N. Bree,, J. Van de Walle,, D. Mücher

3 CERN 1.4 GeV proton + e.g. 238 U (~50 g/cm 2 ) Resonant Laser Ionization Post acceleration (REX-ISOLDE) Gamma and particle detection with the MINIBALL and CD detector arrays Isotope Separation On Line and Post Acceleration Lecture Notes on Physics 700 (2006) 37-77, Springer Verlag Berlin

4 Radioactive Beam Experiments at ISOLDE ISOLDE-CERN: beams of over 700 radioactive isotopes available at 60 kev physical and chemical properties to purify (e.g. laser ion source, molecular beams) Radioactive ion beam EXperiment at ISOLDE (REX ISOLDE): an efficient concept for post-accelerating radioactive isotopes up to 3 MeV/u, essentially all existing ISOLDE beams proposed in 1995, first experiments 2002 production of energetic isomeric beams (laser ionization) The MINIBALL Germanium array: efficient, flexible Ge array for low-multiplicity experiments with weak RIB segmented Ge detectors in combination with segmented Si detector

5 REX ISOLDE performance 20.0 Total REX-efficiency % (%) original goal A

6 MINIBALL detector array Miniball: 8 clusters, 3 X 6 fold segmented ε MB 1 MeV (12 cm from the target) CD detector DSSSD: 4 quadrants 16 annular strips (θ) ϕ 24 sector strips (φ) θ Coulomb excitation set-up DSSD detector (16 o -53 o ) REX- ISOLDE 67,69,71,73 Cu E~3 MeV/u PPAC Beam dump 120 Sn, 104 Pd Beam monitor detector ~2 mg/cm 2

7 Outline MINIBALL at REX-ISOLDE, CERN: Radioactive beams at ISOLDE Coulomb excitation and transfer reactions using MINIBALL Physics case and results : General overview of MINIBALL campaigns (two examples: close to 100 Sn and to 132 Sn) Nuclear structure along Z=28 from N=40 towards N=50 (Coulomb excitation: Cu isotopes, β-decay of 67 Fe- 67 Co- 67 Ni) Evidence for intruder states and shape coexistence Conclusion and outlook HIE-ISOLDE

8 MINIBALL experiments at ISOLDE Coulomb excitation Neutron transfer reactions g-factor measurements Fusion evaporation studies β-decay studies see also talks by V. Bildenstein, N. Bree, J. Van de Walle, D. Mücher ,186,188 Hg 106,108,110 Sn Se 30,31,32 Mg 20 67,69,71,73 Cu, 68 Cu, 70(m) Cu 68 Ni 96 Sr, 88 Kr, 92 Kr 74,76,78,80 Zn 122,124 Cd 138,140 Xe 140,148,150 Ba O. Niedermaier et al., PRL94 (2005) A.M. Hurst et al., PRL98 (2007) I. Stefenescu et al., PRL98 (2007) J. Cederkall et al., PRL98 (2007) J. Van de Walle et al., PRL99 (2007) I. Stefanescu et al., PRL100 (2008)112502

9 B(E2) systematics for Xe isotopes (T.U.München, Th. Kröll) Xe ~ 10 5 part/s T ~ 19 h 96 Mo (target) REX-ISOLDE --- systematics QRPA MCSM A. Lindroth et al., PRL 82, 4783 (1999) Conclusion: B(E2) values of Cd, Xe (and Ba) around N=82 don t show particular anomalies preliminary Systematics: modified Grodzins rule D. Habs, R. Krücken QRPA: J. Terasaki,- PRC 66, (2002) Monte Carlo Shell Model: N. Shimizu,- J. Phys.Conf. Ser. 49, 178 (2006)

10 Sn isotopes (CERN/Lund, J. Cederkäll, A. Ekström) 106 Sn(2.83 MeV/u, 29%) + 58 Ni(2 mg/cm 2 ) Shell-model calculations including proton-neutron excitation across Z=N=50 needed J. Cederkäll et al., PRL98 (2007) A. Ekström et al., to be published

11 Outline MINIBALL at REX-ISOLDE, CERN: Radioactive beams at ISOLDE Coulomb excitation and transfer reactions using MINIBALL Physics case and results: General overview of MINIBALL campaigns (two examples: close to 100 Sn and to 132 Sn) Nuclear structure along Z=28 from N=40 towards N=50 (Coulomb excitation: Cu isotopes, β-decay of 67 Fe- 67 Co- 67 Ni) Evidence for intruder states and shape coexistence Conclusion and outlook HIE-ISOLDE

12 The Z=28 and N=40,50 shell closures g 9/2 2p 1/ Ni f 5/2 2p 3/2 1f 7/2 1d 3/2 2s 1/2 1d 5/ Ni 28 50

13 50 Z= g 9/2 2p 1/2 1f 5/2 2p 3/2 N=40 g 9/2 N= f 7/2 1d 3/2 2s 1/2 1d 5/2 S. Rahaman,- Eur.Phys.J A34 (2007) 5 Recent mass measurements S 2n : weak gap at N=40 S 2p : strong gap at Z=28

14 Energy systematics of the state J. Van de Walle,- Phys. Rev. Lett. 99 (2007) E(2 + 1)[keV] Ni : Z=28 Zn: Z=30 Ge: Z=32 Neutron Number C. Mazzocchi et al, PLB (2005) - NSCL,MSU J. Van Roosbroeck et al, PRC (2005) - ISOLDE

15 B(E2: ) systematics Zn: J. Van de Walle,- Phys. Rev. Lett. 99 (2007) Ni: N. Bree,- submitted to Phys. Rev. C 40 1g 9/2 2p 1/2 B(E2, )[W.u.] Zn: Z=30 Ni: Z=28 GANIL Ge: Z=32 ORNL CERN f 5/2 2p 3/2 1f 7/2 1d 3/2 2s 1/2 1d 5/2 Neutron Number C. Mazzocchi et al, PLB (2005) - NSCL,MSU O. Perru et al, PRL (2006) GANIL E. Padilla-Rodal et al, PRL (2004) - ORNL O. Sorlin K.U. et al, Leuven PRL 88, 2002 K.-H. Langanke et al, PRC 67, 2003

16 Structure of 68 Ni ν +/-1 or π +/-1 kev (5 - ) (4 - ) (3 - ) 6 - (3 + ) (2 + ) Cu T 1/2 =3.7 min T 1/2 =7.84 ns T 1/2 =30 s πp 1/2 πp 3/2 68 Ni (π +1 ) πg 9/2 9/ /2- πf 5/2 5/ / N=40 ν -1 ν +1 0 J.Van Roosbroeck, Phys.Rev.C kev (5 - ) 2 + ( ) T 1/2 =6.6 s (3 - ) T 1/2 =33 s (6 - ) T 1/2 =44.5 s 70 Cu νg 9/2 νf 1 5/2 νp 1 1/2 68 Ni ν 1 9/ ( νp 1/2 ) 2 L. Weissman, Phys.Rev.C Cu 69 Cu 70 Cu 67 Ni 68 Ni 69 Ni 67 Co π +1 Z=28 β decay 66 Co 67 Co 68 Co π Fe νp 1/2 1 νg 9/2 68 Ni ν +1 νp 1 3/2 ( νg 9/2 ) +2 3/ νf 1 5/2 ( νg 9/2 ) +2 5/ / /2-0 ( νg 9/2 ) +2 1/ /2+ 0 W.F. Mueller, Phys.Rev.Lett. 83, 1999

17 Experiment Monopole interaction: Cu (Z=29) N=40 N=40 N=50 Theory 5/2-3/2-3/2-5/2 - p 1/2 40 g 9/2 f 5/2 p 3/2 f 7/2 28 monopole interaction Z=28 protons neutrons S. Franchoo et al., PRL81 (1998) 3100, PRC64 (2001) N. Smirnova et al., PRC69 (2004) A. Lisetskiy et al, PRC (2004) T. Otsuka K.U. et Leuven al., PRL 85 (2005) ν g 9/2

18 67,69,71,73 Cu systematics C 2 S (πf 7/2-7/2 ) /2 - C 2 S 0.45 g 9/2 2 πp 3/2 2 + ( A-1 Ni) πp 1/2 πf 5/2 7/2-1/2-5/ /2-5/2-1/ (7/2 - ) (7/2 - ) (5/2 - ) (7/2 - ) (7/2 - ) (5/2 - ) 1 Eex (MeV) πp 3/2 3/ /2-1.3 (3/2 - ) (3/2 - ) 0 67 Cu Cu Cu Cu 44 67,69 Cu: B. Zeidman et al., PRC 18, 2122(1978): A+1 Zn(d, 3 He) A Cu 71 Cu: R. Grzywacz et al., PRL 81, 766 (1998). 69,71,73 Cu: S. Franchoo et al., PRL 81, 3100(1998).

19 Coulomb excitation of 73 Cu (1/2 - ) 73 Cu pps at 2.99 MeV/u on a 2 mg/cm 2120 Sn target Beam purity: 73 Cu/total = 17 % 5/2-73 Ga Laser ON 120 Sn (7/2 - ) /2 - (7/2 - ) 961 (5/2 - ) 166 Laser OFF (1/2 - ) (3/2 - ) Cu 44 Unknown B(E2) values determined relative to the known B(E2; ) in 120 Sn or 104 Pd.

20 Results: the 7/2 - states A = Ni B(E2; 7/2-3/2 - ) B(E2; )in agreement with the proposed πp 3/2 2 + nature for the 7/2 - states Only one of the two 7/2- states populated in Coulomb excitation (identification of the πf7/2 intruder state in 71,73 Cu) B(E2) values in 63,65 Cu: R.L. Robinson et al., Phys. Rev. 134, B567, 1964.

21 Results: the 5/2 - states A = at N=40 ( 69 Cu), the 5/2-1 states undergo a significant loss in collectivity, are of different character the low B(E2; 5/2-3/2 - ) value from N=40 onwards indicates that the 5/2 - state is essentially of single-particle character

22 Results: the 1/2 - states A = at N=40 ( 69 Cu), 5/2 - states undergoes a significant loss in collectivity, are of different character the low B(E2; 5/2-3/2 - ) value from N=40 onwards indicates that the 5/2 - state is essentially of single-particle character the proposed 1/2 - shows an important increase in collectivity beyond N=40; onset of collectivity related to the filling of the g9/2 neutron state.

23 Energy 9/2 systematics in the odd-mass Cu isotopes / / /2 + ~2500 7/ / / / / / / / / / / / / / / / /2-1116? 1/ / / / / /2-981 πf 7/2 : π(2p-1h) 7/ πp 3/2 2 + ( A-1 Ni) 1/ /2-961 πp 3/2 2 + ( A-1 Ni) 500 N=28 1/ / /2-670 N=40 5/ /2-454 collective 1/2 - state πf 5/2 3/2-0 5/ / /2-0 3/2-0 3/2-0 3/2-0 3/2-0 3/2-0 3/2-0 3/ / Cu Cu Cu Cu Cu Cu Cu Cu Cu Cu46

24 Energy systematics in the odd-mass Cu isotopes EXP. Shell-model N. Smirnova et al., PRC 69(2004) shell-model calculations with a realistic interaction based on G-matrix with the monopole part modified by F. Nowacki. Valence space consisted of pfg orbitals outside the 56 Ni core. e p =1.5e, e n =0.5e.

25 Production of isomeric beams: resonant laser ionization γ-ray intensity (a.u.) b c a Frequency of first transition (cm -1 ) (4) 6.6 s (3 - ) (6 - ) (3) 33 s Cu 44.5 s J. Van Roosbroeck,- Phys. Rev. Lett. 92 (2004) Purified isomeric beams: Determine properties Study decay characteristics Coulomb excitation and transfer reactions (after post-acceleration)

26 68m,g Cu (2.86 MeV/u, pps, 74% 120 Sn (2.3 mg/cm 2 ) Post-accelerated isomeric beams! 68 Cu 6 - (+1 + ) measuring time: 12.3 h Note: detection of low-energy gamma rays 68 Cu Sn measuring time: 4.98 h Energy (kev)

27 B(E2;6-4 - ) values in 68,70 Cu Shell-model calculations with a test residual interaction for the valence space outside the 56 Ni core. *B(E2;6-4 - ) in 72 Cu from T 1/2, exp (6-) R. Grywacz,- PRL81 (1998) 766 the poor agreement between the experiment and theory for 68,72 Cu pointing to the importance of proton excitations across the Z=28 shell gap; I. Stefenescu et al., PRL98 (2007)

28 Decay study of 67 Fe - 67 Co 67 Ni Ni Ni Leuven Isotope Separator-On-Line Mass Separator 30 MeV Proton Beam Buffer Gas T 1/2 = 329ms Co Fe Laser-ionized reaction products Gas Cell 238 U Targets (10 mg/cm 2 ) T 1/2 =416 ms A + + e - β γ Detection Set-up Lasers A * A

29 Lasers on Fe Lasers OFF Decay study of 67 Fe - 67 Co 67 Ni 67 Fe β Co ~ 500 ms isomer β-gated γ-spectra β Ni single γ-spectra

30 β γ γ correlations: single γ s before ( ms) a β-694 kev (in 67 Co) trigger 491 kev 511 kev Correlated events 491 kev 694 kev Random subtracted Correlations Random events

31 Proton intruder state in 67 Co 1p-2h proton intruder states in 67 Co 50 g 9/2 π(1p-2h) 40 p 1/2 f p 5/2 3/ π 7/2[303] π1/2 - [321] f 7/ π Co ( ) E( π:p 1 2h) = ε ε' Δ + V x jπ j' π pairing πν K.Heyde et al., Phys. Rep. (1983) (1/2 - ) ms (7/2 - ) M3 0 <20 % 329 ms ν 67 Co 40

32 2000 Energy systematics of the neutron rich Co isotopes / ; Ni ; Ni 1/ / / / / /2-1325?/ / / ΔE 1480+ΔE Intruder state lowest in energy midshell between N=28 en N=50 Disappearance of N=40 (in contrast to Z=40 from intruder states at N=49) Evolution of the intruder states towards N=50? Swift onset of deformation for Z<28 7/2-0 3/ / /2-0 7/2-0 7/2-0 7/2-0 ΔE 7/ Co Co Co Co Co Co Co40

33 Outline MINIBALL at REX-ISOLDE, CERN: Radioactive beams at ISOLDE Coulomb excitation and transfer reactions using MINIBALL Physics case and results: General overview of MINIBALL campaigns (two examples: close to 100 Sn and to 132 Sn) Nuclear structure along Z=28 from N=40 towards N=50 (Coulomb excitation: Cu isotopes, β-decay of 67 Fe- 67 Co- 67 Ni) Evidence for intruder states and shape coexistence Conclusion and outlook HIE-ISOLDE

34 HIE-ISOLDE: three objectives REX energy upgrade and increase of current capacity Energy upgrade in three stages: 5.5 MeV/u and 10 MeV/u and lower energy capacity REX trap and breeder upgrade ISOLDE proton driver beam intensity upgrade 2 to 6 μa (linac 4) Faster cycling of the booster New target stations for ISOLDE ISOLDE radioactive ion beam quality improvement Smaller longitudinal and transverse emittance Higher charge state for selected users Better mass resolution Target and ion source development e.g. RILIS

35 Already ongoing work RFQ cooler UK, JYFL, Mainz.. (see talk K. Flanagan) RILIS upgrade Sweden (Wallenberg) REX extension Leuven, UK (Cockcroft Institute..),...

36 Expected yields from HIE-ISOLDE (CERN report ) Multi-step Coulex, transfer reactions, deep-inelastic reactions Construction of a dedicated recoil separator at ISOLDE

37 European Roadmap for Radioactive Ion Beam Facilities EU EURISOL Design Study Laser, RFcool,.. SPL (CERN) decision ESFRI list EU FAIR Design Study P. Butler

38 Conclusion and outlook Good quality post accelerated beams from REX-ISOLDE combined with the MINIBALL segmented germanium array form a powerful tool for experiments on far unstable nuclei: Coulomb excitation, transfer reactions, isomeric beams Coulomb excitation on the neutron-rich Cu isotopes: single particle character of the 5/2-1 states onset of collectivity for the 1/2 - states observation of presumably πf 7/2 (2p-1h) intruder states in 71,73 Cu Beta-decay studies of 67 Fe to 67 Co: low-lying (E=492 kev) isomeric 1/2 - proton intruder state (1p-2h) in 67 Co Challenge for theory to reproduce these findings: proton excitation through Z=28 Outlook A wide spectrum of experiments are possible using beams from REX-ISOLDE and MINIBALL (see e.g. ( HIE-ISOLDE: new opportunities higher energy to 5 and 10 MeV/u higher intensity (increase in proton beam intensity) better quality

39 The collaboration J Van de Walle 1, I Stefanescu 1, P Mayet 1, O Ivanov 1, F Aksouh 1, D. Pauwels 1, J. Diriken 1, D Smirnov 1, JC Thomas 1, T. Cocolios 1, R Raabe 1, M Huyse 1,P Van Duppen 1, O Niedermaier 2, M Lauer 2, V Bildstein 2, H Scheit 2, D Schwalm 2, N Warr 3, D Weisshaar 3, J Eberth 3, J. Jolie 3, M Pantea 4, G Schrieder 4, O Kester 5, F Ames 5, T Sieber 5, S Emhofer 5, B Wolf 5, R Lutter 5, D Habs 5, P Butler 6, J Cederkall 6, P Delahaye 6, S Franchoo 6,8, V. Fedoseev 6, G Georgiev 6, Y Kojima 6, U Köster 6, T Nilsson 6, F Wenander 6, B. Marsh, J Iwanicki 7, A Hurst 7, F Azaiez 8, F Ibrahim 8, O Perru 8, M Stanoiu 8, O Sorlin 8, D Verney 9, Th Behrens 10, Th Kröll 10, R Krücken 10, G Sletten 11, D. Balabanski 12, G. Lo Bianco 12, S. Harissopulos 13 the MINIBALL collaboration and the REX-ISOLDE collaboration 1 IKS KULeuven Belgium 2 Max Planck Institut fur Kernphysik Heidelberg Germany 3 Institut fur Kernphysik Universitat Koln Germany 4 TU Darmstadt Germany 5 LMU Munchen Germany 6 CERN Switserland 7 University of Liverpool Great Britain 8 IPN Orsay France 9 GANIL Caen France 10 TU Munchen Germany 11 Neils Bohr Institute Roskilde Denmark 12 University of Camerino, Italy 13 NCSR Athens, Greece

40

41 Experimental method & setup: 2 H( 66 Ni,p) 67 Ni γ-ray detection: 8 MINIBALL triple clusters 24 6-fold segmented germanium crystals (ε ~8 %) Particle detection (Si) forward barrel: ΔE 140 E 1000 μm forward CD: DE 300 E 1500 μm backward barrel: E 500 μm silicon backward CD: E 500 μm Beam composition: Bragg detector, Laser on/off

42 Experiment vs. particle-core core coupling model A. M. Oros-Peusquens and P. Mantica, NPA 669 (2000) 81. Levels in the odd-a Cu nuclei described as single-particle or holes states coupled to the quadrupole or octupole vibrations of the underlying even-even core. Energies of the excited states in the n-rich 69,71,73 Cu very well reproduced by the model. B(E2) values not available.

43 Instantaneous depopulation of a nuclear isomer Coulex (5 - ) 4 - (3 - ) 6 - (3 + ) T 1/2 =3.7 min Energy πp νg 3/ 2 9/ E2 M1/E π ν Coulex (2 + ) Cu 85 0 T 1/2 =30 s I π Population via Coulex (E2) Decay through faster M1 transition Paar parabola: E2 excitation over the parabola s maximum Mechanism present in other odd-odd nuclei (e.g. 108,110 Ag)? Energy is released and half life of the isotope is changed - interest for nucleosynthesis processes?

44 ( ) E( π:p 1 2h) = ε ε' Δ + V x jπ j' π pairing πν

45 Neutron-rich rich even-a A Cu isotopes - 68,70 Cu - Z=28 68 Cu 68 Ni 70 Cu πp 3/2 νp 1/2 (J π =1 +, 2 + ) πp 3/2 νg 9/2 (J π =3 -, 4 -, 5 -, 6 - ) Isomers N=40 68,70 Zn(t, 3 He),70 Cu β-decay studies πp 3/2 νg 9/2 πp 3/2 νp 1/2 (5 - ) (4 - ) (3 - ) 6 - (3 + ) (2 + ) Cu T. E. Ward et al., PR88, 1802(1969) L. Hou et al., PRC68, (2003) 0.7 <T 1/2 < 4 ns T 1/2 =3.7 min T 1/2 =7.84 ns T 1/2 =30 s (5 - ) 2 + ( ) T 1/2 =6.6 s (3 - ) (6 - ) 70 Cu J.D. Sherman et al. PLB67 (77) 257 T. Ishii et al., Jaeri-Review, , 25 J. Van Roosbroeck et al., PRL92(2004) J. Van Roosbroeck et al., PRC69(034313). T 1/2 =33 s T 1/2 =44.5 s