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

ESNT – 4-6/02/2008 Saclay

1) Various experimental approaches for one physics case

2) From data to theoretical understanding

3) What about tomorrow?

L. Gaudefroy – CEA/DAM/DPTA/SPN

Physics Case : N=28

From 70’s : Evidences for erosion of N=20 shell closure in neutron rich nuclei.

28f7/2

p3/2

f5/2p1/2

20

d5/2

d3/2s1/2

Shell Structure

Wit

hout

SO

inte

ract

ion

20

8

N=28 :

1st magic number originating fromSO interaction

- Evolution of SO with isospin.

- Probing -interaction responsibleStructure evolution

sd

fp

Ca Ar S Si

(s1/2 & d3/2)

Full EmptyProton removal in

N/Z

Experimental difficulty

N=28 =>

40

Results :

-Reduction of the N=28 Gap by ~300keV between 48Ca28 and 46Ar28

-Reduction of p3/2-p1/2 SO splitting => Central density dependence of SO interaction

-Indication for reduction of f7/2-f5/2 SO splitting=> Could be due to d3/2-fj tensor interaction

E* 45Ar [MeV]

550

1420 keV

1880keV

2510

Z=18 : One neutron transfer 44,46Ar(d,p)

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

p C.M.0 10 20 30

∂/∂

[

mb

/str

]

1

10

Orbital p3/2

Orbital f7/2

DWBA

L. G. et al. PRL 97 (2006)A. Signoracci et al. PRL 99 (2007)L. G. et al. PRL 99 (2007)

Results :

--decay half life of 44S reproduced onlyfor 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

Z=16 : -decay and electron spectroscopy of 44S

Experimental info :

--decay half life / Pn

-Excitation energy (via /e--decay)-Half-life of isomeric state

1365 keV

1365 - 1022 343 keV

Results :

« Collapse of the N=28 shell closure in 42Si »B. Bastin et al. PRL 99 (2007)

« 42Si is (…) a well deformed oblate rotor »

Z=14 : In-beam -spectroscopy of 42Si

Experimental info :

- tansitions from populated states

0

1

2

3

4

17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

neutron number N

2+ e

ner

gy

(MeV

)

CaS

Si

2+ 0+ : 770 ± 20 keV NEW

Cross-fertilization Experiment-Theory

Ca Ar S Si

(s1/2 & d3/2)Full Empty

Sphe

rica

lN=28

Red

uc.

Shap

e Coex

Def

orm

atio

n

S. Péru et al EPJA 25 (2000)Constrained HFB Calc. with Gogny Force

PERFECT AGREEMENT

Exp. Data on :- Transfer (49Ca, 45,47Ar)- -decay (35Si)- 2+

1 in 42Siused to constrain sdfp SM interactionF. Nowacki et A. Poves Submitted to PRC

L. G. et al. To be Submitted to PRC

Z=20

Z=18

Z=16

Z=14

Density dependance of SO interaction

(f

m-3)

Proton density

Occupation s1/2

0% 100%Exp.

r (fm)

p1/2

1.7MeV

p3/2

2.0MeV0.5MeV

Proton removal in s1/2 orbital

Case Ar?Case Si ?

O. Sorlin et al. : Accepted experiment @ GANIL : 36S(d,p)O. Sorlin et al. : Proposed experiment @ GANIL : 34Si(d,p)

S : Z=16s1/2 full Si : Z=14s1/2 empty

(d,p) gives positions of p3/2 and p1/2 orbits

Theoretical support :

-Any model able to provide occupations number of s1/2 orbitand SPE of p3/2 and p1/2 orbits

-Any model able to provide E*, ℓ and C2S (what we’ll measure), and J

Indirect evidence of tensor interaction

S. Grévy et al. : Accepted experiment @ GANIL :

B(E2) measurement in 36,38,40Si

Theoretical support :

-Any model including tensor interaction (that can be switched ON/OFF)able to provide B(E2) values.

Z=14, N>20s1/2

2814

p3/2

d5/2

f7/2Tensor :

- Z=14 and N=28 reduced - proton core poralized by neutrons

Expected increase of B(E2)

B(E

2)

(a.u

.)

N

With tensor

Without tensor

22 24 26 28

Z=14

Probing Nuclear Structure Towards the doubly magic 78Ni

28f7/2

p3/2

f5/2p1/2

40g9/2

50

Very few exp. info on the evolution of structure while g9/2 is being filled

Z=28, N=40 :

68Ni(d,p) => test of N=50G. 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

Need of experimental evidences on the crossing of f/2 – p3/2 orbits

Structure of Cu isotopes :Recent theoretical interest : Shell Model and Mean Field

N. A. Smirnova et al., PRC69, 044306 (2004) A.F. Lisetskiy et al., PRC70, 044314 (2004)EPJA25, s01,95 (2005)

SHELL

MODEL

MEAN

FIELD

T. Nikšić et al., PRC71 (2005) 014308

Depending on the model/approachcrossing 3/2-

1 – 5/2-1 in 73Cu to 79Cu…

Probing Nuclear Structure Towards the doubly magic 78Ni

L.G. et al. Accepted experiment @ GANIL

-decay around 75,77Cu

From and selection rules should be able to constrain spins and models…

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

N=82

Zr

Mo

Ru

Pd

Cd

Sn

__40

__50

__48

__42

Z

occ

upati

on

g9

/2

Empty

Full

f7/2

f5/2

g9/2

h11/2

h9/2

With (d,p) reaction :

Energy of states, ℓ, C2S, resonances

Probe tensor interaction : g9/2 – h11/2,9/2

g9/2 – f5/2,7/2

Determine position of orbitals fordirect neutron capture

p3/2

p1/2

N=82 : important region of accumulation in r-process scenari (peak in solar abondances)Depends on (n,) rates

Exemple : 130Cd(d,p) 130Cd ~ 103pps

MUST2 + CATS2 + VAMOS Energy resolution ~ 100keV

Low intensity & charge states makes it difficult but not undoable!