IS451-Looking at the shape transition at N=60 by safe Coulex of Sr isotopes

E.Clément Novembre 2011

IS451-Looking at the shape transition at N=60 by safe Coulex of Sr isotopes

E.Clément-GANILISOLDE Workshop 2012


The n-rich nuclei between Z=37 and Z=40 present at N=60 one of the most impressive deformation change in the nuclear chart

Systematic of the 2+ energy (Raman’s formula : b2~0.17 0.4)

+ 2n

( )

S. Naimi et al., Phys. Rev. Lett. 105, 032502 (2010).

M. Albers et al., Phys. Rev. Lett. 108, 062701 (2012)


E(0+ )

[keV

]

+ 2n

0+2

Low lying 0+ states were observed in Sr and Zr isotopes

Shape isomer in the odd-mass Sr, Zr

Shape coexistence scenario


402p1/2

1g9/2

ll1g7/2

50

282p3/2

ll llll1f5/2 ll ll

2d5/2

3s1/2

ll ll

llll

40

1g7/2

50

K. Sieja et al PRC 79, 064310 (2009)

0+2 state created by 2p-2h excitation across Z=40

2d5/2

Beyond N=60, the p-n interaction participates to the lowering 0+

2 state and to the high collectivity of 2+

1 state.

1h11/2


0+2 state created by 2p-2h excitation across Z=40

Beyond N=60, the p-n interaction participates to the lowering 0+

2 state and to the high collectivity of 2+

1 state. In the current valence space, need higher effective charge to reproduce collective propertiesp and n orbital from the core or higher shells.

Mean-field calculations reproduce the near spherical and highly deformed configuration away from N=60

The nuclei here are one of the best examples of the interplay between single-particle and collective modes of excitation in the nuclear matter

T. Rzaca-Urban Phys. RevC 79, 024319 (2009) – SM calculations

H. Goutte et al, CEA-Bruyère-Le-Chatel Private communication

…

²


N=58

N=60

IS451 objectives: electromagnetic properties of the excited states in the Sr isotopes with re-accelerated beam

2011- Coulomb excitation of 98Sr

Q0s = -6 (9) efm²

B(E2↓) = 462 (11) e²fm4

2007- Coulomb excitation of 96Sr

The Electric spectroscopic Q0 is null as its B(E2) is rather large

Quasi vibrator character No quadrupole deformation

The GSB seems to be more connected to the 0+

2 than 0+3


98Sr (T1/2 = 653 ms) has a relatively weak extraction/production rate

We choose the atomic extraction as 98A+ and relied on the in-trap b-decay of the short –lived 98Rb (T1/2 = 96 ms ) for the purification

PSB

UCx Target

Atomic extraction

HRS A= 98

98Rb (>95 % ) + 98Sr (< 5%)

Trap

EBIS

Proton beam98Rb (~2 % ) + 98Sr (~80%) +98Y (~ 9 %) 98Zr (~ 6%)

Isr ~ 6.104 pps

After several 98Rb periods : 161 + 158 ms

MINIBALL


Trapping time: 100 ms/300ms/500ms

Several ways of sharpening the time-of-flight distribution for mass 98 were tested, without success

Preliminary conclusions

It is difficult to clearly state where the in-trap decay is the most efficient (either in the trap or in the EBIS).

The daughter nuclides delivered from the trap are not efficiently cooled.

This possibly explains why the in EBIS decay was found more efficient during the experiment of J. Van de Walle 61-62Fe from the decay of 61-62Mn (IS468).

P. Delahaye et al.

Non-decayed 98Rb b-decay product

The peak disappear after a sufficiently long trapping time


37 Cl10+ 6

1 X (short-

lived)

98Rb :102 ms98 Sr : 6

53 ms

98Y98Zr : 30 sec.

98mRb : 96 ms

0+ (4,5) :2 se

c.

(0- ) :

548 ms

98Rb

98Sr

98Y

98Zr

98Nb

Beam composition after post-acceleration

DE measurement at MINIBALL

Energy loss (MeV)

15N

60Ni

64Zn

83Kr

38Ar

p off Beam Gate close EBIS-contamination

p off Beam Gate open Long lived from target

p on Beam Gate open Short lived from target

? ?


We used 2 Target : 208Pb & 60Ni Clean kinematic matrix Doppler corrected, particle-g prompt gated

98Sr : Coulomb excitation results

208Pb target

60Ni target

Target excitation


115 keV

4+

6+

Gated on the 2+ decay

g-g matrix Many transitions are in coincidence


(115)

(319)

Other unknown transitions might belong to 98Rb

Gate on 115 keV

Gate on 319 keV


Conclusion

oWe successfully performed the Coulomb excitation of 96-98Sr beams and many transitions have been observed in 98Sr

oWe used the in-trap and in-ebis b-decay

oThe effect of different configurations of the trapping and breeding time are not understood

oWe observed new transitions in 98Sr analyzed using g-g coincidences after coulomb excitation of a RIB.

oWe might have identified excited states in 98Rb

o E2-M1 electromagnetic matrix elements analysis on-going

o Next step : Zr beams and transfer reaction on Sr


AGATA@GANIL

The GANIL facility will host the European AGATA germanium array during 2014 and 2015

Gamma-ray spectroscopy of very neutron-rich nuclei populated in Deep Inelastic collisions or induced fission

Spectroscopy of heavy elements towards SHE and N=Z nuclei

Spectroscopy using existing and new SPIRAL1 beams

Submission of the LoI by February 8th, 2013

AGATA@GANIL Workshop GANIL, 18-20 February, 2013

http://pro.ganil-spiral2.eu/events/cw/agataws.

http://pro.ganil-spiral2.eu/events/cw/agataws


96Rb (N=59)

165

999451 259

380

98Rb ?? (N=61)

No excited states are known in 98Rb Level scheme very similar to 96Rb

No coincidence with known transition in 98Sr

98Sr : Coulomb excitation results g-g analysis


Pb

t = 4 ns ~ t.o.f

After DC

t.o.f is longer and longer

98Sr : Coulomb excitation resultsPlunger type analysis


Path = t.o.f

t = 2.9 (3) ns (4.0(1) ns)

Not yet fully understood the difference

Geometrical effect ( cluster) ?

Influence of higher lying states ?


Decay curve


115

319(0+,3-)m

(2+,5-)

144


Cos y Cos y

EDc

Isomeric state ! t = 1.2 (3) ns


First Sr beam at REX-ISOLDE

We choose the molecular extraction as 96Sr19F+ to not suffer from the Rb contamination

PSB

UCx Target

7 to 1.3 105

96Sr19F+/C

Molecular extraction

HRS A= 115

96Rb

( Trap HS ) …. off

EBIS

Separator

115In

Proton beam

A/Q = 4.17

Pure 96Sr23+ REX-beam2.87 MeV/u 1 to 0.5 ~104 pps

2007 – Coulomb excitation of 96Sr

IS451-Looking at the shape transition at N=60 by safe Coulex of Sr isotopes

Documents

Transcript of IS451-Looking at the shape transition at N=60 by safe Coulex of Sr isotopes