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N=28, Shell Closure and Shapes

N=28, Shell Closure and Shapes. L. Gaudefroy CEA/DIF – Bruyères-le-Châtel. Courtesy of M. Rejmund. LEA - COLLIGA – Catania : 13-16 October 2008. N=28. f 5/2. f 5/2. p 1/2. p 1/2. p 3/2. p 3/2. f 7/2. f 7/2. F. Nowacki and A. Poves from ArXiv. S. Péru et al. EPJA 9, 35 ( 2000 ).

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N=28, Shell Closure and Shapes

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  1. N=28, Shell Closure and Shapes L. Gaudefroy CEA/DIF – Bruyères-le-Châtel Courtesy of M. Rejmund LEA - COLLIGA – Catania : 13-16 October 2008

  2. N=28 f5/2 f5/2 p1/2 p1/2 p3/2 p3/2 f7/2 f7/2 F. Nowacki and A. Poves from ArXiv S. Péru et al. EPJA 9, 35 (2000) d3/2 d3/2 s1/2 s1/2 d5/2 d5/2 Shell Structure Shell Structure N=28 Ca Full Ar Experimental difficulty Proton removal in p(s1/2 & d3/2) S N/Z 28 20 20 20 28 8 40 Si Empty • 1st magic number originating from SO interaction • Evolution of SO with isospin • Role of pn interaction on structure fp Without SO interaction First evidence for shell erosion : b-decay studies around 44S => Unexpected deformations requiered to reproduced T1/2 O. Sorlin et al. PRC 47, 2941 (1993) sd

  3. N=28 -E(2+) = 1577 keV H. Scheit et al. PRL 77, 3967 (1996) -E(2+) = 1297 keV T. Glasmacher et al. PLB 395, 163 (1997) -E(2+) = 1330 keV S. Grévy et al. EPJ A 25 (2005) -E(2+) = keV B. Bastin, S. Grévy et al. PRL 99 (2007) 2+ 0+ : 770 ± 20 keV NEW Progressive erosion of the gap predicted in both MF and SM frameworks

  4. In this talk Empty Full p(s1/2 & d3/2) Ar Ca Si S Def. Spher. Part I : -Study of the 46Ar(d,p) reaction. -Reduction of N=28 Gap -Reduction of SO splittings -Density dependence of SO & tensor L. Gaudefroy et al. – PRL 97, 092501 (2006) A. Signoracci & B.A. Brown – PRL 99, 099201 (2007) L. Gaudefroy et al. – PRL 99, 099202 (2007) -Study of the 44Ar(d,p) reaction. Part II : g-factor measurement in 43S.

  5. 44Ar(d,p)45Ar : Principle p d d MUST 8 modules Si 960 strips X-Y qp,Ep qp, Ep SPEG Spectro. Exotic beam 44Ar @ 10 MeV.A Ep CATS Beam tracking SPIRAL/GANIL CD2 45Ar 44Ar qp Study of the fp single particle states at N=28 (d,p) transfer reaction f5/2 p1/2 p3/2 28 f7/2 44Ar26 45Ar27

  6. 44Ar(d,p)45Ar : Results 600 400 200 0 E (MeV) 5 • lfrom the shape • C2S from the relative normalisation

  7. 44Ar(d,p)45Ar : Exp. vs Theorie 3/2 3.90 2020 2+ x 7/2- 7/2 2.10 0 47Ca27 Code ANTOINE : E. Caurier & F. Nowacki Interaction sdpf: S. Nummela et al. PRC63 (2001) 45Ar27 Satisfactory agreement

  8. 47Ca27 & 45Ar27 : Shell Model 3/2 3.90 2020 7/2 3/2 1.08 2.10 0 1420 47Ca27 np3/2 20 d3/2 2+ x nf7/2 3/2 0.76 s1/2 550 7/2 1.52 0 d5/2 45Ar27 p Increase of correlations already at Z=18

  9. More exotic N=27 isotones E = ESPE + EMono + EMulti Correl HF-MF Orbits S. Péru et al. EPJA 9, 35 (2000) EMulti (MeV) Z Ca 2 Ar 9 S 12 Si 15 L. Gaudefroy et al. PRC 78, 034307 (2007)

  10. g-factor measurement in 43S f5/2 p1/2 d3/2 p3/2 16 s1/2 7/2- 28 14 d5/2 f7/2 n p 488ns (3/2-) 3/2- 320 (7/2-) 43S -Mass measurement at GANIL: F. Sarazin et al. PRL 84, 5062 (2000) => Low lying isomeric state g factor of the isomeric state : -Direct detemination of spin/parity. -Test the WF of the state. m = g I

  11. Principle H = - µ B H = g.I B R(t) = A cos(wt+f) w = -gB B I(t) R(t) G - B G + B t t Fragmentation : ~300 43S/sec LISE@GANIL

  12. Results Exp gs Schmidt gSchmidt = ± 2ℓ+1 f7/2 -0.546 (j=ℓ ±1/2) -0.317 p3/2 -1.275 gs=-3.826

  13. Experiment vs. Theories f5/2 p1/2 p3/2 f7/2 d3/2 s1/2 d5/2 Part. Rotor Particule.+Rotor 20 20 Valence space -K=1/2 decoupled band. GS deformed band: b=+0.35 7/2- (isom.) not in this band Rather spherical Code ANTOINE : Caurier & Nowacki - Strasbourg

  14. Experiment vs. Theories Mean Field : -HFB – Gogny D1S -Blocking -GCM + GOA Ground State: -K=1/2 (from p3/2) -b=0.37 -Decoupling parameter & Inertia parameter=> in agreement with PR States from f7/2 orbit: -Within 400keV -Around b=0 L. Gaudefroy et al. To be submitted to Phys. Rev. Lett.

  15. Conclusion Part I : 44Ar(d,p) -Structure of 45Ar already points toward an increase of correlations. -SM description of N=27 isotones showing the evolution of multipolar energy. -Agreement with mean field description in this mass region. Part II : g-factor of 43mS -Direct evidence of config. inversion f7/2-p3/2 -Successfully interpreted with 3 models -Deformed ground state K=1/2 band -Rather spherical isomeric state

  16. Collaboration France : CEA-Bruyères-le-châtel, IPNO, GANIL, CEA-Saclay, CSNSM, CENBG, IReS, LPSC Bulgaria : Faculty of Physics Germany : Universität Mainz Hungary : INR Israel : Weizmann Institute Japan : Riken USA : FSU Russia : FLNR/JINR

  17. Conclusions Z=20 Z=18 Z=16 Z=14

  18. Perspectives 43S Z=20 Z=18 N=28 Z=16 Z=14 Même phénomène dans 41Si => 42Si déformé 44S 45S 43P 41Si 43Si 42Si • Hypothèse: • Bandes de rotation partout! • Décrire la structure de ces noyaux dans un cadre SM Travail en cours avec T. Faul L. Gaudefroy et al. soumis à PRC

  19. p1/2 f5/2 p3/2 f7/2 46Ar28 18 Fermi 28 d3/2 s1/2 n

  20. Polarisation du coeur f5/2 fp p1/2 p3/2 f7/2 Without SO interaction d3/2 sd s1/2 d5/2 Shell Structure 20 28 20 8 40

  21. 43S vs 44S (7/2-) -1n 7/2- 3/2- 43S q(01+,3/2) = q(02+,3/2) = 0.5 q = |<Yf| a(nlj) | Yi>|2 q(01+,7/2) = 2q(02+,7/2) = 0.4 0+ 2+ E0 0+ 44S S. Grévy et al. EPJ A 25 (2005) Si coexistence de forme dans 44S : cf. le tableau Recouvrements compatibles avec mixing important entre deux états 0+ (Sphér.  Déform.)

  22. Principe de l’expérience Faisceau primaire : 48Ca @ 60 A.MeV Système de détection Cible : Be

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