108Sn studied with intermediate-energy Coulomb excitation Dissertation zur Erlangung des Grades “Doktor der Naturwissenschaften” am Fachbereich Physik der Johannes Gutenberg-Universität in Mainz Leontina Adriana Banu

Outline Motivation Why to study 108Sn ? Why to study it with Coulomb excitation ? Experimental method description Most significant features of intermediate-energy Coulomb excitation Experimental set-up Data analysis Experimental results Theoretical interpretation

Average energy of the first excited states Why to study 108Sn ? Average energy of the first excited states in even- even nuclei N=Z Number of neutrons (N) Number of protons (Z) Sn(N,Z) = B(N,Z) – B(N-1,Z) N odd Z even 2 8 20 28 50 82 126 Neutron separation energy [MeV] insight into the structure of 100Sn by studying the nuclei in its vicinity how rigid is the the doubly-magic core when valence neutrons are being added ? (studying A=102-130 Sn isotopes) investigation on quadrupole polarization of the doubly-magic core (E2 core polarization effect) B(E2;0+->2+)=|<f||OE2||i>|2 is the most sensitive to E2 collective effects 100Sn Z = 2,8,20,28,50,82 N = 2,8,20,28,50,82,126 magic numbers shell closures Nuclear shell model 112Sn 62 108Sn 58 100Sn (N=Z=50) principle test ground

Why Coulomb excitation to study 108Sn ? Electromagnetic decay of lowest excited 2+state: transition probability lifetime 2+ 0+ E () 1207 keV 0 keV Lifetime measurement B(E2) value B(E2) determination: Coulomb excitation B(E2) value cross section ((E2) ~ B(E2)) 0+ 2+ 4+ 6+ 108Sn 905 253 1206 6+ ( ~ 7 ns) isomeric state E2 2+ (< 0.5 ps) B(E2;6+->4+) = 3 W.u. E2 Z. Phys. A352 (1995) 373 (HI,xn) reaction

Intermediate-energy Coulomb excitation Nuclear excitation ~ 3% E=1.3 MeV D = 70 cm n Nuclear excitation (±) Lorentz boost (+) Doppler broadening (-) Atomic background radiation (-)  Coulomb excitation target ( in our case )  = 0.43 Detector opening angle Dq=3° Composite detector  = 0.57 DEg0/Eg0 [%]  = 0.43  = 0.11 1 Ge-Cluster detector qlab [deg]

GSI accelerator facility UNILAC SIS ESR FRS

Experimental set-up Beam direction 108Sn/112Sn Primary beam Secondary beam @ reaction target: 124Xe @ 700 A•MeV 108Sn/112Sn Primary beam CATE (Si) CATE (CsI) (~ 150 A•MeV) 9Be, 4 g/cm2 projectile fragmentation (production method) in-flight fragment separation 197Au, 0.4 g/cm2 (Bρ-E-Bρ method)

Fragment identification before/after target Selection with FRS Selection with CATE 108Sn

Scattering angle measurement Beam tracking g CATE MW MW Target 511 keV Si CsI Qg  ~ 50% Qp rest 40K Event–by–event Doppler shift correction: in-flight γ 2 βcosΘ 1 β E - = Impact parameter determination:

Analysis of intermediate-energy Coulomb excitation Elastic scattering dominates Nuclear excitation contribution grazzing = 1.5° ± 0.5° Analysis of intermediate-energy Coulomb excitation Fragment selection before secondary target Fragment selection after secondary target Scattering angle selection (1°- 2°) Prompt  time ‘window’ Ge-Cluster multiplicity: M(E > 500 keV) = 1

Experimental results B(E2; 0+ -> 2+) = 0.230 (57) e2b2 Measure: -particle coinc. particle singles I Np exp. theory Deduce B(E2) for 108Sn as follows: 0.240 (14) e2b2 --- previous work B(E2; 0+ -> 2+) = 0.230 (57) e2b2 A. Banu et al., submitted to Phys. Rev. C (2005)

Theoretical interpretation theory (neutron valence + proton core excitations and 90Zr as closed-shell core) theory (neutron valence and 100Sn as closed-shell core) Neutron/proton single-particle states in a nuclear shell-model potential: t=0 t=2 t=4 Neutron number B(E2 ) e2 b2 This work •••••••• Proton np-nh core excitations (t=n) & 100Sn core is open

Conclusion and Outlook 108Sn the heaviest Z-nucleus studied with intermediate-energy Coulomb excitation B(E2;0+->2+) measured for the first time The experimental result is in agreement with latest large scale shell model calculations This work brings more insight into the investigation of E2 correlations related to 100Sn core polarization 108Sn further step towards 100Sn

“Art is I, Science is We.” - Claude Bernard Thanks to… J. Gerl (GSI), J. Pochodzalla (Uni. Mainz) - thesis advisors C. Fahlander (Lund), M. Górska (GSI) - spokespersons H. Grawe, T.R. Saito, H.-J. Wollersheim (GSI) M. Horth-Jensen et al. (Oslo Uni.), F.Nowacki et.al (IRES) and last but not least…

The local RISING team Thank you...

-residual interaction in a jn configuration Seniority scheme in Sn isotopes: 2 6+  = 0 2 4+  = 0 2 2+  = 2 0+ energy axis  jn J 6+ min   4+ j j j 2+ J j j j j J j J 0+ E(j2J) ~ V0tan(/2) for T=1, J even -residual interaction in a jn configuration (V12() = -V0(r1-r2))

Data Summary Primary beam SIS energy (MeV/nucleon) Primary beam intensity (s-1) 124Xe 700  6 × 107 Secondary beam Sec. beam abundance (%) Sec. beam rate (s-1) Sec. beam energy @ target (MeV/nucleon) 112Sn  60 2400 147 108Sn  62 2480 142 E(21+->0+) (keV) Data collection time (h) 1257  33 1206  58

Single-particle states in shell-model potential l -> orbital angular momentum Spectrsoscopic notation: l= 0, 1, 2, 3, 4, 5, 6 s, p, d, f, g, h, i •••••••• 2j+1 njl j -> total angular momentum j = l + s j = l ± ½ s = 1/2 2j+1 nucleons /orbital inert core + active valence nucleons

Single-particle states in shell-model potential l -> orbital angular momentum Spectrsoscopic notation: l= 0, 1, 2, 3, 4, 5, 6 s, p, d, f, g, h, i 2j+1 njl j -> total angular momentum j = l + s s = 1/2 j = l ± ½ 2j+1 nucleons /orbital

Generalized seniority scheme: B(E2;0+ -> 2+) ~ f(1-f) where Generalized seniority scheme: f = (N – 50)/ 32