Experimental studies around N=28… What’s next?

Experimental studies around N=28… What’s next? L. Gaudefroy – CEA/DAM/DPTA/SPN • Various experimental approaches for one physics case • 2) From data to theoretical understanding • 3) What about tomorrow? ESNT – 4-6/02/2008 Saclay

Physics Case : N=28 20 20 8 40 28 From 70’s : Evidences for erosion of N=20 shell closure in neutron rich nuclei. f5/2 N=28 : 1st magic number originating from SO interaction - Evolution of SO with isospin. - Probing pn-interaction responsible Structure evolution fp p1/2 p3/2 f7/2 Without SO interaction d3/2 sd s1/2 d5/2 Shell Structure N/Z Experimental difficulty Ar Ca N=28 => Si S Empty Full Proton removal in p(s1/2 & d3/2)

Z=18 : One neutron transfer 44,46Ar(d,p) ∂s/∂W [mb/str] Orbital p3/2 1420 keV 10 550 1880keV Orbital f7/2 2510 1 0 10 20 30 • Results : • Reduction of the N=28 Gap by ~300keV • between 48Ca28 and 46Ar28 • -Reduction of np3/2-np1/2 SOsplitting • => Central density dependence of SO interaction • -Indication for reduction of nf7/2-nf5/2SO splitting • => Could be due to pd3/2-nfj tensor interaction qp C.M. E* 45Ar [MeV] DWBA 2-body reaction => (E,p) 4-vector of the proton properties of 45,47Ar MUST charged particle array Y. Blumenfeld et al. NIM A 421 (1999) Experimental info : - Excitation energies (E*), - Angular momentum (ℓ) and - Spectroscopic factor (C2S) C2S = |<45Ar(n, ℓ, J) | a+(n , ℓ, J) |44ArG.S>|2 Purity of the final state WF L. G. et al. PRL 97 (2006) A. Signoracci et al. PRL 99 (2007) L. G. et al. PRL 99 (2007)

Z=16 : b-decay and electron spectroscopy of 44S 1365 - 1022  343 keV 1365 keV Results : -b-decay half life of 44S reproduced only for deformed shape (QRPA) O. Sorlin et al. PRC 47 (2003) - Low lying 0+2 => Shape coexistence S. Grévy et al. EPJ A 25 (2005) – Conf. C. Force – PhD Thesis @ganil Experimental info : -b-decay half life / Pn -Excitation energy (via g/e--decay) -Half-life of isomeric state

Z=14 : In-beam g-spectroscopy of 42Si Results : « Collapse of the N=28 shell closure in 42Si » B. Bastin et al. PRL 99 (2007) « 42Si is (…) a well deformed oblate rotor » 2+ 0+ : 770 ± 20 keV NEW Experimental info : -g tansitions from populated states

Cross-fertilization Experiment-Theory Z=20 S. Péru et al EPJA 25 (2000) Constrained HFB Calc. with Gogny Force Z=18 Z=16 Z=14 Empty Full p(s1/2 & d3/2) Ar Ca Si S Spherical N=28 Reduc. Shape Coex Deformation Exp. Data on : - Transfer (49Ca, 45,47Ar) - b-decay (35Si) - 2+1 in 42Si used to constrain sdfp SM interaction F. Nowacki et A. Poves Submitted to PRC PERFECT AGREEMENT L. G. et al. To be Submitted to PRC

Density dependance of SO interaction np1/2 0.5MeV 1.7MeV 2.0MeV np3/2 O. Sorlin et al. : Accepted experiment @ GANIL : 36S(d,p) O. Sorlin et al. : Proposed experiment @ GANIL :34Si(d,p) S : Z=16ps1/2 full Si : Z=14ps1/2 empty (d,p) gives positions of np3/2 and np1/2 orbits Proton removal in s1/2 orbital r (fm-3) ?Case Si ? Case Ar Proton density r (fm) Occupation ps1/2 0% Exp. 100% Theoretical support : -Any model able to provide occupations number of ps1/2 orbit and SPE of np3/2 and np1/2 orbits -Any model able to provide E*, ℓ and C2S (what we’ll measure), and Jp

Indirect evidence of tensor interaction With tensor Z=14 p3/2 Without tensor 14 B(E2) (a.u.) d5/2 f7/2 p n Tensor : - Z=14 and N=28 reduced - proton core poralized by neutrons Expected increase of B(E2) 26 28 22 24 N S. Grévy et al. : Accepted experiment @ GANIL : B(E2) measurement in 36,38,40Si 28 Z=14, N>20 s1/2 Theoretical support : -Any model including tensor interaction (that can be switched ON/OFF) able to provide B(E2) values.

Probing Nuclear Structure Towards the doubly magic 78Ni g9/2 f5/2 p1/2 p3/2 f7/2 28 40 50 Very few exp. info on the evolution of structure while ng9/2 is being filled Z=28, N=40 : 68Ni(d,p) => test of N=50 G. Duchesne, D. Beaumel et al. Accepted @GANIL Proposed to performed also (d,t) & (d,3He) : test of N=40, test of proton occupation numbers First step towards a shell model description of fpg nuclei… but

Probing Nuclear Structure Towards the doubly magic 78Ni M O D E L S H E L L N. A. Smirnova et al., PRC69, 044306 (2004) A.F. Lisetskiy et al., PRC70, 044314 (2004) EPJA25, s01,95 (2005) T. Nikšić et al., PRC71 (2005) 014308 F I E L D M E A N Structure of Cu isotopes : Recent theoretical interest : Shell Model and Mean Field L.G. et al. Accepted experiment @ GANIL b-decay around 75,77Cu From b and g selection rules should be able to constrain spins and models… Depending on the model/approach crossing 3/2-1 – 5/2-1 in 73Cu to 79Cu… Need of experimental evidences on the crossing of pf5/2 – pp3/2 orbits

Collaboration : CEA-Bruyères-le-châtel, DAM/DIF/DPTA/SPN, France IPN, IN2P3-CNRS,F- 91406 Orsay Cedex, France GANIL, BP 55027, F-14076 Caen Cedex 5, France CEA-Saclay, DAPNIA-SPhN, F-91191 Gif sur Yvette Cedex, France IReS, Univ. Louis Pasteur, BP 28, F-67037 Strasbourg Cedex, France Institute of Nuclear Research, H-4001 Debrecen, Pf. 51, Hungary Department of Physics, Florida State University, Tallahassee,Florida 32306, USA Institut für Kernchemie, Universität Mainz, D-55128Mainz, Germany FLNR/JINR, 141980 Dubna, Moscow region, Russia

From SPIRAL 1 to SPIRAL2 Z __50 Sn Full Cd __48 n Pd p f5/2 occupation pg9/2 Ru h9/2 g9/2 p3/2 p1/2 f7/2 Mo __42 h11/2 Zr Empty __40 N=82 • N=82 : important region of accumulation in r-process scenari (peak in solar abondances) • Depends on (n,g) rates With (d,p) reaction : Energy of states, ℓ, C2S, resonances Probe pn tensor interaction : pg9/2 – nh11/2,9/2 pg9/2 – nf5/2,7/2 Determine position of orbitals for direct neutron capture Exemple : 130Cd(d,p) 130Cd ~ 103pps MUST2 + CATS2 + VAMOS  Energy resolution ~ 100keV Low intensity & charge states makes it difficult but not undoable!

Experimental studies around N=28… What’s next?