EWON – Prague May 10, 2007 Collaboration NIPNE Bucharest -- LSF LN Legnaro Studies of N≈Z nuclei...

EWON – Prague May 10, 2007

Collaboration NIPNE Bucharest -- LSF LN Legnaro

Studies of N≈Z nuclei above mass 80


M.Axiotis1, D.Bazzacco2, D.Bucurescu3, G. de Angelis4, E.Farnea2, A.Gadea4, M.Ionescu-Bujor3, A.Iordǎchescu3, W.Krolas5, Th.Kröll6, S.Lenzi2, S.Lunardi2, N.Mǎrginean3,4, T. Martinez4, R.Menegazzo2, D.R.Napoli4, P.Pavan2, B.Quintana7, C.Rossi Alvarez2, C.Rusu3,4, P.Spolaore4, C.A.Ur2,3,

J. Wrzesinski5

recent youngs: C. Mihai3, G. Suliman3

[1] - N.R.C. Demokritos Athens[2] - Università Padova[3] - H.H.-NIPNE Bucharest[4] - INFN, L.N. Legnaro[5] - H.N. – INP Krakow[6] - T.U. München[7] - Universidad Salamanca

The collaboration


Short history of collaboration: Since 1990, γ-ray spectroscopy with fusion-evaporation reactions, first with GAMIPE, then with

GASP. (NIPNE-INFN collab. agreement; since 2000: LSF-TRM)

• High-spin states in different nuclei• Highly-deformed & SD structures (decay out, lifetimes, A≈130)• Spectroscopic studies of nuclei in the exotic region N≈Z, A=80-90• Static moments of isomeric states in exotic nuclei• Spectroscopy of n-rich nuclei with CLARA- PRISMA


Topics(prompt γ-ray spectroscopy of N≈Z nuclei above mass

80)

• T=0 np pairing• Spin-gap isomers• Shell model description• Evolution of collectivity


Experimental Studies of “heavy” N≈Z Nuclei

Production• Fusion-evaporation• Fragmentation

Identification Coincidence with evaporated

particles Direct A and Z measurement

Low cross sections(with stable beams)

High ‘background’

10-5 10-4 10-3 10-2 10-1 100

88Ru 2n

88Tc pn87Tc p2n

88Mo 2p87Mo 2pn

86Mo 85Mo n

87Nb 3p85Nb p

84Nb pn

84Zr 2p82Zr

Relative Yield

Ancillary detectors

γ-ray SpectroscopyGe arraysBeta-decay studies

32S+58Ni, 105 MeV

Charged particle ballsNeutron arraysMass spectrometers


Experimental Facilities

GASP

GASP (config. 1)abs (40 HPGe) 3%

Peak/Total 60%

abs (80 BGO) 76%

ISIS (40 ΔE-E Silicon

telescopes)

p 56-60%

35-38%

N-Ringn 2-5%

Beam

EWON – Prague May 10, 2007 p-drip line: G.A.Lalazissis et al, Nucl. Phys. A719,209c(2003): Relativistic HB calc.


N. Mărginean et al. Phys. Rev. C 63 (2001) 032303(R)



New data:

72Kr : C.Andreoiu et al., Phys. Rev. C75(2007)041301(R)

76Sr : P.J.Davies et al., Phys. Rev. C75(2007)011302(R)

No evidence for isoscalar (T=0) np pair field

isovector mean-field theory OK (isovector np pairing + isospin symmetry conservation) [ Afanasjev & Frauendorf, PRC71(2005)064318 ] (CRHB calculations)

Signature of T=0 np pairing ?Delayed Alignment in N=Z Nuclei:

J=0 T=1

J=1…2j T=0


Projected Shell Model Calculations



N=Z+1

81Zr

Experiment: 28Si(90 MeV) + 58NiTarget: 2 x 0.5 mg/cm2 58Ni 81Zr - αn channel, intensity 2·10-4

N. Mărginean et al. Phys. Rev. C 69 (2004) 054301


N=40[422]5/2

[301]3/2[431]1/2

1 neutron hole + 82Zr

N=40[422]5/2

[301]3/2[431]1/2

1 neutron particle + 80Zr

Fermi


Projected Shell Model Calculations

(empty symbols)



E3 isomeric

decay

95Ag

τisomer > ≈ 1 μs

[predicted by Ogawa, Phys.Rev. C28,958(1983)]


Shell Model Effective Interactions

SLGT0 - Serduke, Lawson, Gloeckner, NPA256(1976)45;

Herndl, Brown, NPA605(1996)195 A>86, N,Z=[38-50] π,υ(2p1/2,1g9/2)

Gross-Frenkel - Gross, Frenkel, NPA267(1976)85

F-FIT, … - Johnstone, Skouras, EPJA11(2001)125 (fit to increased number of exc. energies in mass 86-100 nuclei)

Other SM calculations: Hasegawa et al., P+QQ Hamilt., (2p1/2,1g9/2,1f5/2,2p3/2 ) (88,89,90Ru)


ν,π(p1/2,g9/2)SLGT0 resid. inter.

C. Rusu et al , Phys. Rev. C 69 (2004) 024307

N.Mǎrginean et al, Phys. Rev. C67(2003)061301(R)


2.86

2.0 2.25

2.75

2.5

2.0

2.25

1.75

1.5

2.30

2.52

2.84

2.5


(F. Iachello

Phys. Rev. Letters 85 (2000) 3580)

134Ba

(F. Iachello

Phys. Rev. Letters 87 (2001) 052502)

152Sm

Unharmonic vibrator

Stable quadrupole deformation

-soft

rotor

Axially symmetric

rotor

Shape phases, phase transitions and critical points

Critical points: parameter-free analytical approximations


Prediction of X(5) nuclei

4.5 < NpNn/(Np+Nn) < 5.5

N=Z = 38,40

(N.V. Zamfir, private comm.)


Quasi- bands identified or extended in

78Sr, 80Sr, 82Zr, 84Zr, 86Zr, 86Mo, 88Mo


Phase Transition in IBA Triangle

2]

~[~~

41

ddsddsQ

LLQQN

naH dIBA

0+

2+

4+ 2+

3+

4+

Fine grid on parameter space

2 merit function including both energy and branching ratios

New parameters:2/7

2/71

1

yx

*

*

82Zr80Sr

78Sr


Conclusions• N≈Z nuclei, mass 80 - 100: theatre of many interesting nuclear structure phenomena

• First spectroscopic measurements of the heaviest known N=Z (88Ru) and N=Z+1 (81Zr, 85Mo, 89Ru, 91Rh, 93Pd,95Ag) nuclei.

• ”Systematic delay” in alignment frequency in N=Z even-even nuclei. Is it “abnormal”? (T=0 neutron-proton pairing?) need for: - measurements at higher spins; - direct determinations of: s.p. energies, deformations.

• Deformed Odd-A (N=Z+1) nuclei: rich information (more bands) - possible delayed alignment observed. Implications for the N=Z core? (polarization of the mean-field; the T=1 pair field induced by additional neutron in 81Zr).


• Evolution of the Collectivity: maximum of collectivity (deformation) around N,Z=38,40 but still far from ideal rotor; X(5) “island”? (new “indicators” needed for 76,78Sr, 80Zr, (78Zr) )

• Extensions of these data are necessary (in spin: e.g.,88Ru to higher states; in mass: 92Pd; N=Z+1 nuclei).

• Shell model (Z≥44; N≥45): old residual interactions (SLGT0, GF, JS) in (p1/2,g9/2) space perform reasonably well. Isomers explained. But: yrast π = + (g9/2) states are not so sensitive – not critical tests!

• Exceptional support within LSF LN-Legnaro; full use of the capabilities of GASP and its ancillaries: ISIS and N-wall.


END


Reaction Target Beam intens.

(8+), [pnA]

Trigger

condition

28Si (90 MeV) +

58Ni

2 x 0.5 mg/cm2

142Ge,2BGO

32S (105 MeV) +58Ni

1.1 mg/cm2

62Ge,3BGO

40Ca(130MeV)+ 54Fe

6.5 mg/cm2

4 - 62Ge,1BGO

40Ca(135MeV)+ 58Ni

6.0 mg/cm2

82Ge,1BGO

GASP experiments


Reaction Channel Studied

Nucleus σ σ (% σF) Status

28Si+58Ni90 MeV

2n 84Mo ~ 7 μb ~ 4 10-5 1 γ known

before

αn 81Zr ~ 0.3 mb ~ 2 10-4 unknown

32S+58Ni105 MeV

2n 88Ru 5-10 μb ~ 4 10-5 unknown

αn 85Mo 0.13 mb 7 10-4 unknown

40Ca+54Fe130 MeV

αn 89Ru ~ 40 μb ~ 1-2 10-4 unknown

p2n 91Rh ~ 65 μb ~ 2-3 10-4 unknown

40Ca+58Ni135 MeV

αn 93Pd unknown

p2n 95Ag unknown

PR C56,2497(1997)PR C65,051303R(2002)

PR C61,024310(2000)PR C69,054301(2004)

PR C63,031303(2001)

PR C65,0334315(2002)

PR C70,044302(2004)

PR C72,014302(2005)

PR C69,024307(2004)

PR C67,061301R(2003)

Simultaneous publications: 93Pd: D.Sohler et al., EPJ A19,169(2004) 95Ag: J.Döring et al., PR C68,034306(2003)


~ Grodzins estimate β2 ~ A-7/6E(2+)-1/2


M.Hasegawa et al., Phys. Rev. C69,034324(2004)

Shell model, P+QQ Hamiltonian, (1g9/2,2p1/2,1f5/2,2p3/2)-N

max. dimens. for 88Ru (N=12): 165 x 106

Strengthened isoscalar QQpn interaction


Identification of

N=Z: 88Ru

Experiment: 32S(105 MeV) + 58Ni– Target: 1.1 mg/cm2 58Ni on 10 mg/cm2 Au– 88Ru populated as 2n channel, intensity 4·10-5

– Four gamma-ray cascade identified by coincidence with neutrons and anticoincidence with charged particles

Sum of gates 616 + 800 +964 keV:

GASP + ISIS + 6 n-detectors


Matrix projection


τisomer > ≈ 1 μs

N=Z+1, 9547Ag48 approaching N,Z=50 : spin gap isomer


1p2n channel predicted Ogawa PR C28,958(1983)


Estimate for the alignment frequency of 80Zr

Missing alignment


JΠ Ex (keV) SLGT0 GF F-FIT

(9/2+) 0 0 0 0

(13/2+) 840 112 22 56

(17/2+) 1787 48 -116 -42

(21/2+) 2655 -81 -308 -226

(25/2+) 3103 -75 -316 -241

(29/2+) 4136 -1 -365 -245

(1/2-) 173 112 186

(5/2-) 792 195 330 187

(9/2-) 1292 258 368 208

(13/2-) 1905 82 168 2

(17/2-) 2278 97 190 46

EXP. Ecalc. - Eexp. (keV)

91Rh – comparison with 3 Shell Model calculations


91Rh

Johnstone-Skouras (2001) – F-FIT eff. inter.

πυ(2p1/21g9/2)



(preliminary)


General structure of a collective nucleus:Basic information on:

g.s.b. 02

+ - band (quasi-beta band)

2γ+ - band (quasi-gamma band)

Energy ratios: E(41+)/ E(21

+); E(02+)/E(21

+); E(2γ+)/E(21

+); etc.

Elmag. trans. Probab.: B(E2; 2γ --> 01)/ B(E2; 21 --> 01);

B(E2; 2γ --> 01)/ B(E2; 21 --> 21); etc.

Ex.: U(5) R(4/2) = 2.0 R(02+/21

+) = a (~2) R(22+/21

+) = a (~2)

O(6) 2.5 a (>~2.0) a (>~2.0)

SU(3) 3.33 a (>~12) a (>~12)

X(5) 2.91 5.67 4.23

E(5) 2.19 3.03 2.20

a = depends on additional Hamiltonian parameters


56Ni + 40Ca ---> 88Ru + 2α

88Ru cross-sections : with 56Ni beam : ~ 30 mb with 32S beam: 5-10 μb --------------------------------------- R ~ 3 x 103 (56Ni/32S)

Beam 56Ni : [~ 3 x 107 ions/sec (2003, ANL)] ------→ ~ 1011 (FAIR)

Beam 32S (GASP): ~ 6 pnA ≈ 4 x 1010 ions/sec ----------------------------------------

R ~ 1 (56Ni/32S)

Overall gain with 56Ni : ~3000 (assuming GASP (3%) γ-efficiency and same target !) with Ge-array of increased efficiency :

gain >> ~ 3000 !

N=Z 88Ru with RIB:


S.Takami et al., Phys. Lett. B431,242(1998)M.Yamagami et al., Nucl Phys. A693,579(2001)J.Dudek et al., Phys. Rev. Lett. 88,252502(2002)

Exotic deformation: ~ 80Zr : tetrahedral deformation (spin-gap isomers?)


23/2+

N=Z+1; odd-Z


N=Z+1; even-Z

EWON – Prague May 10, 2007 Collaboration NIPNE Bucharest -- LSF LN Legnaro Studies of N≈Z nuclei...

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Transcript of EWON – Prague May 10, 2007 Collaboration NIPNE Bucharest -- LSF LN Legnaro Studies of N≈Z nuclei...