N 28 Shell Closure and Shapes L Gaudefroy CEA DIF

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

-Role of pn interaction on structure F. Nowacki and A. 9, 35 (2000) Ar. Xiv S. Péru et al. EPJA Poves from First evidence for shell erosion : 20 sd Full Ca Ar f 5/2 p 1/2 p 3/2 28 f 7/2 20 S Experimental difficulty -Evolution of SO with isospin fp N=28 p(s 1/2 & d 3/2) magic number originating from SO interaction 40 Proton removal in -1 st Without SO interaction N=28 d 3/2 s 1/2 d 5/2 b-decay studies around 44 S 8 N/Z => Unexpected deformations requiered to reproduced T 1/2 Shell Structure Empty Si O. Sorlin et al. PRC 47, 2941 (1993) f 5/2 p 1/2 p 3/2 28 f 7/2 20 d 3/2 s 1/2 d 5/2 Shell Structure

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

In this talk Full Ar S -Study of the 46 Ar(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 44 Ar(d, p) reaction. Part II : g-factor measurement in Si De he r. Sp Part I : Empty f. Ca p(s 1/2 & d 3/2) 43 S.

44 Ar(d, p)45 Ar : Principle Study of the fp single particle states at N=28 Ep (d, p) transfer reaction d p 28 44 Ar 45 Ar 26 27 qp, Ep f 5/2 p 1/2 p 3/2 f 7/2 MUST 8 modules Si 960 strips X-Y qp q p, E p Exotic beam 44 Ar @ 10 Me. V. A SPIRAL/GANIL CD 2 CATS Beam tracking Sp SPE ec G tro. 44 Ar 45 Ar

44 Ar(d, p)45 Ar 600 400 200 0 5 E (Me. V) l from the shape C 2 S from the relative normalisation : Results

44 Ar(d, p)45 Ar : Exp. vs Theorie Code ANTOINE : E. Caurier & F. Nowacki Interaction sdpf : S. Nummela et al. PRC 63 (2001) 3/2 3. 90 2020 7/2 2. 10 0 2+ x 7/2 - 47 Ca 45 Ar 27 Satisfactory agreement 27

47 Ca 27 & 45 Ar 27 : Shell Model 3/2 3. 90 2020 7/2 2. 10 0 47 Ca 27 3/2 20 d 3/2 s 1/2 d 5/2 1. 08 1420 3/2 7/2 0. 76 550 1. 52 0 np 3/2 2+ x nf 7/2 p Increase of correlations already at Z=18 45 Ar 27

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

g-factor measurement in -Mass measurement at GANIL: 43 S F. Sarazin et al. PRL 84, 5062 (2000) => Low lying isomeric state 320 488 ns 43 S (3/2 -) (7/2 -) 7/23/2 - d 3/2 s 1/2 d 5/2 16 14 p f 5/2 p 1/2 p 3/2 28 n g factor of the isomeric state : -Direct detemination of spin/parity. -Test the WF of the state. m=g. I f 7/2

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

Results g. Schmidt = ± (j=ℓ ± 1/2) gs=-3. 826 gs 2ℓ+1 Schmidt f 7/2 -0. 546 p 3/2 -1. 275 Exp -0. 317

Experiment vs. Theories f 5/2 p -K=1/2 decoupled band. 1/2 p 3/2 f 7/2 20 Part. 20 d 3/2 Rotor s 1/2 d 5/2 Particule. +Rotor Valence space GS deformed band: b=+0. 35 7/2 - (isom. ) not in this band Rather spherical Code ANTOINE : Caurier & Nowacki - Strasbourg

Experiment vs. Theories Mean Field : -HFB – Gogny D 1 S -Blocking -GCM + GOA Ground State: -K=1/2 (from p 3/2) -b=0. 37 -Decoupling parameter & Inertia parameter=> in agreement with PR States from f 7/2 orbit: -Within 400 ke. V L. Gaudefroy et al. To be submitted to Phys. Rev. Lett. -Around b=0

Conclusion Part I : 44 Ar(d, p) -Structure of 45 Ar 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 43 m. S -Direct evidence of config. inversion f 7/2 -p 3/2 -Successfully interpreted with 3 models -Deformed ground state K=1/2 band -Rather spherical isomeric state

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

Conclusions Z=20 Z=18 Z=16 Z=14

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

p 1/2 f 5/2 Fermi p 3/2 28 f 7/2 d 3/2 s 1/2 n 46 Ar 28 18

Without SO interaction Polarisation du coeur 40 f 5/2 p 1/2 p 3/2 fp 28 f 7/2 20 20 sd 8 d 3/2 s 1/2 d 5/2 Shell Structure

43 S vs 44 S 2+ (7/2 -) 7/2 - 43 S 0+ E 0 -1 n 3/2 - 44 S 0+ S. Grévy et al. EPJ A 25 (2005) Si coexistence de forme dans q = ||2 44 S : cf. le tableau q(01+, 3/2) = q(02+, 3/2) = 0. 5 q(01+, 7/2) = 2 q(02+, 7/2) = 0. 4 Recouvrements compatibles avec mixing important entre deux états 0+ (Sphér. Déform. )

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