N=28, Shell Closure and Shapes

LEA - COLLIGA – Catania : 13-16 October 2008

L. Gaudefroy CEA/DIF – Bruyères-le-Châtel

Courtesy of M. Rejmund

N=28

-1st magic number originating from SO interaction

-Evolution of SO with isospin

-Role of interaction on structure

28f7/2

p3/2

f5/2p1/2

20

d5/2

d3/2s1/2

Shell Structure

Wit

hout

SO

inte

ract

ion

20

8

sd

fp

40Ca

Ar

S

Si

(s 1

/2 &

d3/

2)

Full

Empty

Pro

ton r

em

oval in

N/Z Experi

men

tal diffi

cult

y

N=28

S. Péru et al. EPJA 9, 35 (2000)F. Nowacki and A. Poves from ArXivFirst evidence for shell erosion :

-decay studies around 44S=> Unexpected deformations requiered to reproduced T1/2

O. Sorlin et al. PRC 47, 2941 (1993)

28f7/2

p3/2

f5/2p1/2

20

d5/2

d3/2s1/2

Shell Structure

N=28

Progressive erosion of the gap predicted in both MF and SM frameworks

-E(2+) = 1577 keVH. Scheit et al. PRL 77, 3967 (1996)

-E(2+) = 1297 keVT. Glasmacher et al. PLB 395, 163 (1997)

-E(2+) = 1330 keVS. Grévy et al. EPJ A 25 (2005)

2+ 0+ : 770 ± 20 keV NEW

-E(2+) = keVB. Bastin, S. Grévy et al. PRL 99 (2007)

In this talk

Ca Ar S Si

(s1/2 & d3/2)Full Empty

Sphe

r.

Def

.

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.

44Ar(d,p)45Ar : Principle

p,Epdd

28f7/2

p3/2

p1/2

44Ar26

f5/2

(d,p) transfer reaction

45Ar27

p

Study of the fp single particle states at N=28

MUST8 modules Si 960 strips X-Y

Exotic beam44Ar @ 10 MeV.A

SPIRAL/GANIL CD2

CATSBeam

tracking

p, Ep SPEGSpectro.

45Ar44Ar

p

Ep

0 5 E (MeV)

200

600

400

l from the shape

C2S from the relative normalisation

44Ar(d,p)45Ar : Results

44Ar(d,p)45Ar : Exp. vs Theorie

Interaction sdpf : S. Nummela et al. PRC63 (2001)

Code ANTOINE : E. Caurier & F. Nowacki

Satisfactory agreement

45Ar27

47Ca27

0

2020

7/2

3/2

2.10

3.90

2+ x 7/2-

47Ca27 & 45Ar27 : Shell Model

47Ca27

0

2020

7/2

3/2

2.10

3.90

45Ar27

0

1420

7/2

3/2

1.52

1.08

5503/2 0.76

d3/2

20

s1/2

d5/2

2+ x f7/2

p3/2

Increase of correlations already at Z=18

More exotic N=27 isotones

E = ESPE + EMono + EMulti

Orbits HF-MF Correl

2

9

12

15

Z EMulti (MeV)

Ca

Ar

S

Si

S. Péru et al. EPJA 9, 35 (2000)

L. Gaudefroy et al. PRC 78, 034307 (2007)

g-factor measurement in 43S

-Mass measurement at GANIL: F. Sarazin et al. PRL 84, 5062 (2000)

=> Low lying isomeric state

(7/2-)

(3/2-)

43S

320

488ns

p3/2

p1/2

s1/2 28f7/2

f5/2

d5/2

d3/2

14

16

3/2-

7/2-

g factor of the isomeric state :

-Direct detemination of spin/parity.

-Test the WF of the state.

= g I

Principle

Fragmentation :~300 43S/sec

B

t

I(t)

H = - µ BH = g.I B

t

R(t)

G - BG + B

R(t) = A cos(t+) = -gB

LISE@GANIL

Results

gSchmidt = ±gs

2ℓ+1(j=ℓ ±1/2)

Schmidt Exp

f7/2

p3/2gs=-3.826

-0.546

-1.275-0.317

Experiment vs. Theories

-K=1/2 decoupled band.

Rotor

Part.

Particule.+Rotor

GS deformed band: =+0.35

7/2- (isom.) not in this bandRather spherical

f7/2

p3/2

f5/2p1/2

d5/2

d3/2s1/2

20 20

Valence space Code ANTOINE : Caurier & Nowacki - Strasbourg

Mean Field :

-HFB – Gogny D1S-Blocking-GCM + GOA

Ground State:

-K=1/2 (from p3/2)

-=0.37

-Decoupling parameter &Inertia parameter=>in agreement with PR

States from f7/2 orbit:

-Within 400keV

-Around =0

Experiment vs. Theories

L. Gaudefroy et al. To be submitted to Phys. Rev. Lett.

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

Collaboration

France :CEA-Bruyères-le-châtel, IPNO, GANIL, CEA-Saclay, CSNSM, CENBG, IReS, LPSCBulgaria :Faculty of PhysicsGermany :Universität MainzHungary :INRIsrael :Weizmann InstituteJapan :RikenUSA :FSURussia :FLNR/JINR

Conclusions

Z=20

Z=18

Z=16

Z=14

Perspectives

Z=20

Z=18

Z=16

Z=14

Même phénomène dans 41Si => 42Si déformé

44S

42Si

N=28

43S 45S

43Si41Si

43P

Hypothèse:Bandes de rotation partout!

Décrire la structure de cesnoyaux dans un cadre SM

Travail en cours avec T. FaulL. Gaudefroy et al. soumis à PRC

p3/2

p1/2

f5/2

f7/2

d3/2

28

46Ar2818

s1/2

Fermi

Polarisation du coeur

28f7/2

p3/2

f5/2p1/2

20

d5/2

d3/2s1/2

Shell Structure

Wit

hout

SO

inte

ract

ion

20

8

sd

fp

40

3/2-

7/2-

(7/2-)

43S

43S vs 44S

0+

44S

0+

2+

E0

S. Grévy et al. EPJ A 25 (2005)

-1n

Si coexistence de forme dans 44S : cf. le tableau

|<f| a(nlj) | |2(01

+,3/2) = (02+,3/2) = 0.5

(01+,7/2) = 2(02

+,7/2) = 0.4

Recouvrements compatibles avec mixingimportant entre deux états 0+ (Sphér. Déform.)

Principe de l’expérience

Faisceau primaire :48Ca @ 60 A.MeV

Cible : Be

Système de détection