studies of n≈z nuclei above mass 80
DESCRIPTION
Collaboration NIPNE Bucharest -- LSF LN Legnaro. Studies of N≈Z nuclei above mass 80. - PowerPoint PPT PresentationTRANSCRIPT
EWON – Prague May 10, 2007
Collaboration NIPNE Bucharest -- LSF LN Legnaro
Studies of N≈Z nuclei above mass 80
EWON – Prague May 10, 2007
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
EWON – Prague May 10, 2007
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
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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
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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
EWON – Prague May 10, 2007
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.
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N. Mărginean et al. Phys. Rev. C 63 (2001) 032303(R)
N. Mărginean et al. Phys. Rev. C 65 (2002) 051303(R)
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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
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Projected Shell Model Calculations
N. Mărginean et al. Phys. Rev. C 65 (2002) 051303(R)
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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
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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
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EWON – Prague May 10, 2007
Projected Shell Model Calculations
(empty symbols)
N. Mărginean et al. Phys. Rev. C 69 (2004) 054301
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E3 isomeric
decay
95Ag
τisomer > ≈ 1 μs
[predicted by Ogawa, Phys.Rev. C28,958(1983)]
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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)
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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)
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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
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(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
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Prediction of X(5) nuclei
4.5 < NpNn/(Np+Nn) < 5.5
N=Z = 38,40
(N.V. Zamfir, private comm.)
EWON – Prague May 10, 2007
EWON – Prague May 10, 2007
Quasi- bands identified or extended in
78Sr, 80Sr, 82Zr, 84Zr, 86Zr, 86Mo, 88Mo
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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
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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).
EWON – Prague May 10, 2007
• 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.
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END
EWON – Prague May 10, 2007
EWON – Prague May 10, 2007
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
EWON – Prague May 10, 2007
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)
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~ Grodzins estimate β2 ~ A-7/6E(2+)-1/2
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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
EWON – Prague May 10, 2007
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
N. Mărginean et al. Phys. Rev. C 63 (2001) 031303(R)
Matrix projection
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τisomer > ≈ 1 μs
N=Z+1, 9547Ag48 approaching N,Z=50 : spin gap isomer
N. Mărginean et al. Phys. Rev. C 67 (2003) 061301(R)
1p2n channel predicted Ogawa PR C28,958(1983)
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EWON – Prague May 10, 2007
Estimate for the alignment frequency of 80Zr
Missing alignment
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EWON – Prague May 10, 2007
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
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91Rh
Johnstone-Skouras (2001) – F-FIT eff. inter.
πυ(2p1/21g9/2)
N. Mărginean et al. Phys. Rev. C 72 (2005) 014302
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(preliminary)
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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
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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:
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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?)
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23/2+
N=Z+1; odd-Z
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N=Z+1; even-Z