Feeding of low-energy structures with different deformations by the GDR decay: the nuBall array coupled to PARIS M. Kmiecik, A. Maj, B. Fornal, P. Bednarczyk et al. IFJ PAN Kraków for the PARIS collaboration ALTO nu-ball hybrid spectrometer workshop 2016 Orsay, May 19-20, 2016

Plan Motivation Studying nuclear shapes by GDR measurements – examples of the method Jacobi shape transitions GDR feeding of superdeformed states Nuclear deformation at highest spin studied using isomer gated GDR Idea to apply described methods in experiments using nuBall + PARIS in regions of shape coexistence and shape isomer link between deformation of hot compound nucleus and evaporation residues population of states of different deformation by high-energy γ–rays from GDR decay Outlook

Motivation link between deformation of hot compound nucleus and deformation of cold evaporation residue n a GDR g GDR GDR high energy gamma rays - hot nucleus shape low energy transitions - deformation of excited residue Excitation energy [MeV] Angular momentum [h]

GDR good probe for shape information oblate G prolate G triaxial

GDR strengths for hot, rotating nuclei is more complicated thermal shape fluctuations Coriolis splitting K. Mazurek – LSD calculations potential energy calculated with LSD (Lublin-Strasbourg Drop) model: Dudek & Pomorski Phys. Rev. C67 (2003) 044316 oblate oblate triaxial triaxial prolate Jacobi shapes Low energy component in GDR strength function

Examples of using the GDR to study nuclear shapes

a) Search for Jacobi shape transition in light nuclei: 46Ti a) Search for Jacobi shape transition in light nuclei: 46Ti* decay to 42Ca Experiment @ IRES: 105 MeV 18O + 28Si  46Ti* Lmax  35 , E* = 88 MeV, v/c  4.3% Setup: Euroball IV (26 clovers + 15 clusters) HECTOR (8 big BaF2) EUCLIDES (40 Si telscopes)

GDR gated on discrete transitions in 42Ca MC Cascade fit – 5-L M. Lach et al., Eur Phys J. A12, 381 (2001) A. Maj et al., Nucl. Phys. A731, 319c (2004) Jacobi shape transition and seen for the first time Coriolis effect

b) GDR feeding of SD states M. Kmiecik et al., Acta Phys. Pol. B36 (2005) 1169 sd / spher nd / spher sd / nd feeding of the highly deformed states by the low energy GDR component spher nd sd M. Lach et al., Eur Phys J. A12, 381 (2001)

GDR feeding of SD states in 143Eu Experiment @ LNL: 165 MeV 37Cl + 110Pd  147Eu* G. Benzoni et al., Phys. Lett. 540B, 199 (2002) Setup: Euroball HECTOR SD feeding of the SD states in 143Eu by the low energy GDR component spher ND

c) GDR decay to high-spin isomeric states 96 MeV 18O + 198Pt → 216Rn* E*=56MeV, Lmax=39h gating on isomers choosing nuclei at highest spins surviving fission Setup: Hector + Helena Catcher Ge BGO isomer

Isomer gated GDR high-energy γ-rays gated on isomer gate on time GDR width for 216Rn small increase of deformation for highest spin - nucleus remains almost spherical up to the fission limit M. Kmiecik et al. PR C70, 064317 (2005)

Idea – to apply described methods in experiments using nuBall + PARIS Study: GDR decay to states of different deformation in evaporation residues Obtain information on: feeding of these states by GDR corelation between shape of hot nucleus and deformation of evaporation residues

Example 1 - shape coexistence P. Möller et al., Phys. Rev. Lett. 103, 212501 (2009) 72-78Kr prolate oblate β=0.3-0.4 38 ns oblate 18.8 ns prolate oblate prolate prolate oblate E. Bouchez et al., Phys. Rev. Lett. 90, 082502 (2003) 11 ps 61 ps

Possible reactions 16O @ 90 MeV on 66Zn,64Zn → 80Sr*,82Sr* → 76Kr, 78Kr 32S @ 144 MeV on 46Ti → 78Sr* → 74Kr 32S

GDR gated on transitions between states of different deformation E. Clement et al., Phys. Rev. C 75, 054313 (2007) gating on low-energy γ-transitions 76Kr oblate prolate result: GDR strength → nuclear shape

γ-transitions yield gated on GDR energy E. Clement et al., Phys. Rev. C 75, 054313 (2007) 76Kr gating on high-energy γ-rays oblate result: transitions yield as a function of GDR energy → GDR feeding of low energy structures prolate

74,78Kr isotopes 74Kr 78Kr oblate prolate oblate prolate E. Clement et al., Phys. Rev. C 75, 054313 (2007) 74Kr F. Becker et al., Nucl. Phys. A 770, 107 (2006) 78Kr oblate prolate oblate prolate

Example2 - shape isomer – 188Pt S. Mukhopadhyay et al., Phys. Lett. B 739, 462 (2014) 188Pt near prolate triaxial β =0.18and γ=−6° β=0.16 and γ=−40°

Available reaction 176Yb (18O @ 82 MeV, 4n) 188Pt

GDR decay to different deformation structures GDR in CN (192Pt) triaxial β=0.16 γ=−40° how the states of different deformation are populated by high energy gammas from GDR decay near prolate β =0.18and γ=−6°

gating on time Example of time spectrum measured by FATIMA gate on triaxial deformation gate on (mostly) prolate deformation result: GDR strength function delivering information on shape of hot nuclei decaying to given final deformation oblate triaxial prolate

Experimental set-up measured: nu-ball array: 24 clover Ge detectors at 90 degrees ~4.5% efficiency at 1MeV 36 LaBr3 detectors from Fatima - 5% efficiency PARIS clusters - 2% (at 23 cm) efficiency for 15 MeV gamma rays measured: low energy discrete transitions: energy time multiplicity high energy γ-rays

The PARIS PHOSWICH 10 ns risetime Single pulses HAMAMATSU Mixed signal

First PARIS cluster – already used in the experiment at IPN Orsay

Conclusions nuBall array together with PARIS clusters can be used for measurement of GDR high-energy gamma decay from compound nucleus in coincidence with low energy gamma transitions or/and with isomers Possible regions of interest are: a) shape coexistence in Kr isotopes; and b) shape isomers around A≈190 Such experiments will allow us to: trace shape evolution from hot nuclear system to specific cold nuclear structures and study the feeding of states of different deformation by high-energy γ–rays from GDR decay

Deadlines: Abstract submission: May 27, 2016 Registration closes: July 10, 2016 http://zakopane2016.ifj.edu.pl