Search for tetrahedral states and X(5) Search for tetrahedral states - PowerPoint PPT Presentation

Search for tetrahedral states and X(5) Search for tetrahedral states and X(5) symmetry in Yb nuclei with N~90 symmetry in Yb nuclei with N~90 through Coulomb excitation using HIE- through Coulomb excitation using HIE- ISOLDE and Miniball ISOLDE and Miniball C.M. Petrache – University Paris-Sud & CSNSM Orsay - ISOLDE, CERN - Strasbourg, France - Darmstadt, Germany - Köln, Germany - Athens, Greece - Kolkata, India

ISOLDE RILIS Yields of Yb nuclei ISOLDE RILIS Yields of Yb nuclei

Coulex of stable 168 168 Yb - Yb - 176 176 Yb Yb Coulex of stable

Octahedral and thetrahedral shapes Octahedral and thetrahedral shapes

Tetrahedral symmetric surfaces at Tetrahedral symmetric surfaces at increasing values of rank λ λ deformations deformations increasing values of rank α 32 = 0.1, 0.2, 0.3 α 32 = 0.1, 0.2, 0.3

Octahedral and thetrahedral spectra Octahedral and thetrahedral spectra Octahedral Tetrahedral Octahedral Tetrahedral 4-fold degeneracies => new large (magic) gaps 4-fold degeneracies => new large (magic) gaps

Disapperarance of the α α 30 pear-shape Disapperarance of the 30 pear-shape octupole effects in the Yb isotopes octupole effects in the Yb isotopes J. Dudek J. Dudek

Tetrahedral symmetry competition (the effect of (the effect of α α 32 ) Tetrahedral symmetry competition 32 ) and octupole effects in the Yb isotopes octupole effects in the Yb isotopes and J. Dudek J. Dudek

Desexcitation patterns Desexcitation patterns E3 E3 E3 E3 E3 E3 E3 E3

Desexcitation patterns Desexcitation patterns

Fusion Fusion Coulex Coulex

160 Yb case The 160 Yb case The ➢ The 160 160 Yb The Yb nucleus (Z=70 and N=90) is double-magic nucleus (Z=70 and N=90) is double-magic with respect to the predicted tetrahedral symmetry. with respect to the predicted tetrahedral symmetry. ➢ The properties of the low-spin states, crucial to The properties of the low-spin states, crucial to establish the symmetry, are not yet well known. establish the symmetry, are not yet well known. ➢ The spin and parity assignments to a low-lying 1255 The spin and parity assignments to a low-lying 1255 - or 4 + ? keV state are contradicting: 3 - or 4 + ? keV state are contradicting: 3 ➢ -, 5 -, 6 , 7 - states and The identification of the first 3-, 5-, + , 7- 6 + The identification of the first 3 states and their decay in-band and towards the ground-state their decay in-band and towards the ground-state band or other unobserved bands is crucial for the band or other unobserved bands is crucial for the discovery of the tetrahedral bands. discovery of the tetrahedral bands.

160 Yb case The 160 Yb case The ➢ To check if the populated negative-parity states are To check if the populated negative-parity states are members of the tetrahedral band, one should measure members of the tetrahedral band, one should measure the de-excitation transition the de-excitation transition with good accuracy with good accuracy probabilities B(E3)↓, ↓, B(E2) B(E2)↓ ↓ and B(E1) and B(E1)↓ ↓ knowing that knowing that probabilities B(E3) the B(E2)/B(E1) branching ratios corresponding to the in- the B(E2)/B(E1) branching ratios corresponding to the in- band to out-of-band are predicted 1÷ ÷2 2 orders of magnitude orders of magnitude band to out-of-band are predicted 1 smaller than in the standard octupole states. smaller than in the standard octupole states.

Critical point X(5) symmetry in Critical point X(5) symmetry in N~90 nuclei N~90 nuclei ➢ 160 Yb, 162 Yb, 164 Yb) are the The The nuclei with N~90 ( nuclei with N~90 ( 160 Yb, 162 Yb, 164 Yb) are the candidates in which the critical point symmetry X(5) candidates in which the critical point symmetry X(5) is expected to be best realized. is expected to be best realized. ➢ The branching ratios of transitions from non-yrast The branching ratios of transitions from non-yrast states will constitute a more stringent test of the states will constitute a more stringent test of the model predictions. model predictions.

Shape phase diagram Shape phase diagram Level scheme in X(5) Level scheme in X(5) in IBM in IBM Iachello, PRL 94 (2004) Iachello, PRL 87 (2001) Iachello, PRL 94 (2004) Iachello, PRL 87 (2001)

160 Yb, 162 Yb, 164 Yb nuclei 160 Yb, 162 Yb, 164 Yb nuclei

Transition between X(5) and rigid rotor Transition between X(5) and rigid rotor Deformation dependent models with different potentials: Deformation dependent models with different potentials: confined β β-soft (CBS) -soft (CBS) confined Pietralla, PRC 70 (2004); K. Dusling, PRC 73 (2006) Pietralla, PRC 70 (2004); K. Dusling, PRC 73 (2006)

Contaminants Contaminants 156 Yb (1x10 4 , 26 s) : Dy - 4x10 9 (stable), Er - 6x10 8 (19 min), Eu - 1.3x10 6 (15 d) 158 Yb (1x10 6 ,1.5 min) : Dy - 2x10 9 (stable), Ho - 1x10 10 (10 min), Er - 6x10 8 (2 h), Tm - 1x10 9 (4 m) 160 Yb (1x10 7 , 4.8 min) : Lu - 5x10 6 (36 s), Tm - 1x10 8 (9 min), Er - 4 x10 8 (28 h), Ho - 3x10 10 (25 m) 162 Yb (1x10 8 , 19 min) : Lu - 2x10 7 (1.4 min), Tm - 3x10 8 (24 s) 164 Yb (1x10 10 , 76 min) : Lu - 3x10 7 (3 min), Tm - 4x10 7 (5 min) 166 Yb (3x10 8 , 57 h) : Hf - 6x10 5 (7 min), Lu - 3x10 7 (2 min) 168 Yb (1x10 9 , stable) : Hf - 6x10 5 (26 min), Lu - 3x10 7 (1.4 min)

Radiation Radiation β - - β - - α (90%) α (90%) β β 152 Er 152 Er 148 Dy 148 Tb 148 Gd (75 y) 148 Dy 148 Tb 148 Gd (75 y) α (10%) α (10%) α (12%) α (0.1%) α (12%) α (0.1%) β - - β - - β β α (0.06%) α (0.06%) 156 Yb 156 Tm 152 Ho 152 Dy 156 Yb 156 Tm 152 Ho 152 Dy -4 ) Long livetime → negligible (~3x10 -4 ) Long livetime → negligible (~3x10 α (0.002%) α (0.5%) α (35%) α (0.002%) α (0.5%) α (35%) 158 Yb 158 Yb 154 154 Er Er 150 150 Dy Dy 146 Gd (48 d) 146 Gd (48 d) Weak branch → negligible (~10 -5 -5 ) ) Weak branch → negligible (~10

160 Yb on 106 Pd GOSIA calculations for 160 Yb on 106 Pd GOSIA calculations for T. Konstantinopoulos T. Konstantinopoulos

28 shifts beam on target 28 shifts beam on target 3 shifts beam preparation 3 shifts beam preparation 4 shifts beam change 4 shifts beam change Thank you for your attention ! Thank you for your attention !