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Pre-equilibrium a -particle emission as a probe to study a -clustering in nuclei

Pre-equilibrium a -particle emission as a probe to study a -clustering in nuclei. D. Fabris INFN Sezione di Padova on behalf of Nucl-ex collaboration. International Workshop on Nuclear Dynamics and Thermodynamics in Honor of Prof. Joe Natowitz

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Pre-equilibrium a -particle emission as a probe to study a -clustering in nuclei

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  1. Pre-equilibriuma-particleemissionas a probe tostudya-clustering in nuclei D. Fabris INFN Sezione di Padova on behalfofNucl-excollaboration International Workshop on Nuclear Dynamics and Thermodynamics in Honor of Prof. Joe Natowitz Texas A&M University, College Station, Texas August 19-22, 2013 D. Fabris College Station – August 2013

  2. Contents • Introduction • Previousresults : • 130, 250 MeV 16O + 116Sn • TheoreticalModel • Experimental set-up • Preliminaryresults: • 256 MeV16O + 65Cu • 304 MeV19F + 62Ni • Summary D. Fabris College Station – August 2013

  3. Nucleara-clustering Ikedadiagrams W. Von Oertzenet al. Phys. Rep. 432 (2006)43 • In 1968 Ikedasuggestedthata-conjugate nuclei are observedasexcitedstatesclosetodecaythresholdintoclusters • The interest in nuclearclusteringhasbeenpushedstrongly due to the studyofneutron-rich and exoticweakly-bound nuclei • Studyofnuclearstatesbuilt on clustersboundbyvalenceneutronsin theirmolecularconfigurations -> ExtendedIkedadiagram D. Fabris College Station – August 2013

  4. Inlight nuclei at the neutrondrip-line, clusteringmightbe the preferredstructural mode • Presentlythesestructures are mainlydescribedbytheory, butmustbeexperimentallyverifiedat the newradioactivebeamfacilities Particularlyinterestingistoconfirmtheexistenceofalphaclusterizationin nuclei through a new generation ofexperiments D. Fabris College Station – August 2013

  5. In a previouscampaign, aimedtostudy the dependence on the entrancechannelmass-asymmetryof the pre-equilibrium Light ChargedParticlesemission, the same CN hasbeenformedthrough64Ni + 68Zn and 16O + 116Sn reactions at differentbombardingenergies (5 MeV/u ÷ 16 MeV/u). • The comparisonof the data withHybridExcitonModelcalculationsshows up anextra yieldofalphaparticleswhichcan notbetakeninto account onlyby a pre-equilibriumcomponent, butseemstobeassociatedwith the a-cluster structureof the 16O beam. Idea to isolate cluster structureeffectsin thisrangeofenergies studying the pre-equilibriuma-particlesemission D. Fabris College Station – August 2013

  6. Previous work 250, 130 MeV16O + 116Sn Protons and a-particles in coincidencewithEvaporationResidues using GARFIELD apparatus • p, a-particles Energy spectrafordifferent qangularranges: 29° - 41°; 41° - 53°; 53° - 67°; 67° - 82° • The spectrahavebeencomparedwithcalculationsthatdescribe the evaporative plus the pre-equilibriumcontributionof the particlesemission. The Hybridexcitonmodelhasbeenusedwhichtakesinto account the angulardistributionsofnon-equilibriumprocesses . O.V.Fotinaet al. Int. Journ. Mod. Phys. E19 (2010) 1134 D.O.Eremenkoet al. PhysAtom. Nucl. 65 (2002) 18 O.V.Fotinaet al. Phys. Atom. Nucl. 73 (2010) 1317 D. Fabris College Station – August 2013

  7. TheoreticalModel • Evaporative (statistical) emission: Statisticaldecayof a CompoundNucleusisanalyzedusingmodified PACE2 Monte Carlo code , withlevel density parametrization [A.V.Ignatyuket al. Sov. J.Nucl. Phys. 29 (1979) 450] , decaycompetitionprobability (n, p, a, g or fission), kineticenergyofemittedparticles, bindingenergy, transmissioncoefficients, angularmomentum. • Insertionofnon-equilibrium stage in the fusionreaction • All the processprobabilities are calculatedwithin the Hauser-Feshbachmodel • Pre-equilibriumemission: The relaxationprocess in the nuclear system afterfusionreactionisdescribedby the Hybridexcitonmodelbased on Griffinmodel[J.J.GriffinPhys. Rev. Lett.17 (1966) 478]. The state ofnuclear system produced in the collisionisdeterminedby the excitonnumbern = p + h, wherepis the numberofvalenceparticlesover the Fermi energy and h the numberofholeslocated under the Fermi energy, and byexcitationenergyE*. • The excitonnumber can bedeterminedfrom the empirical trend [N.Cindroet al. Phys. Rev. Lett. 66 (1991) 868; E. BětákFizika B12 (2003) 11] • Clustering: Pre-formationprobabilityof cluster and excitonenergiesfor cluster/light ioninducedreactions[M. Blannet al. Phys Rev. C 62 (2000) 034604] For more detaileddescriptionofusingmethodseeO.V.Fotinaet al. Phys. Atom. Nucl. 73 (2010)1317 and ref. therein. D. Fabris College Station – August 2013

  8. Protonsspectra 130 MeV16O + 116Sn 250 MeV16O + 116Sn a-particlesspectra 130 MeV16O + 116Sn 250 MeV16O + 116Sn a-particlesspectraare notreproducedexpecially at the mostforwardangles • Exp • Pre-eq • Total D. Fabris College Station – August 2013

  9. Start conditionsPossible a clustering configurations in 16O nucleus ? 100-N% N% nO=16p+0(1)h nC=12p+0(1)h na=4p+0(1)h e12C e – clusters energy x – random number ea Courtesyof O. V. Fotina D. Fabris College Station – August 2013

  10. 250 MeV16O + 116Sn a-particlesspectra • ---No a-clustering in 16O • __10% a-clustering in 16O • __ 50% a-clustering in 16O • Exp D. Fabris College Station – August 2013

  11. Extra production ofa-particles at smallangles can beascribedtoalphaclusteringin the projectilenucleus(16O). • Aconfirmationof the existenceofalphaclusterizationin nuclei can beobtained in a model-independentway Comparing the secondaryalphaparticlesemitted in fusionreactionswherean a-cluster projectile(16O) andprojectilewithoutaclusterization(19F) are used. D. Fabris College Station – August 2013

  12. 16O + 65Cu Eb = 256 MeV(16 MeV/u)19F + 62Ni Eb = 304 MeV(16 MeV/u) • Twosystemswithsameprojectilevelocity->fromCabreraet al. systematics the pre-equilibriumemissionisalmostentirelydependent on the projectileenergy per nucleon[J. Cabreraet al. Phys. Rev. C68 (2003) 034613] • Light ChargedParticlesAngulardistributionand Energy spectrain coincidencewithEvaporationResidues • Set-up: GARFIELD 4papparatus at Legnaro National LaboratoryforFragments and Light ChargedParticlesidentification CN 81Rb* E*(16O) = 209 MeV E*(19F) = 240 MeV D. Fabris College Station – August 2013

  13. GARFIELD: geometry GARFIELD Scattering Chamber Length 6m Ø 3.2m 2 DriftChambers+ RCo TargetbetweenDriftchambers F.Gramegnaet al. NIM 389 (1997) 474 A. Moroni et al. NIM A556 (2006) 516 D. Fabris College Station – August 2013

  14. 2 DriftChambers + CsI(Tl) GARFIELD: geometry CsI(Tl) beam MSGS target Onlyone volume of gas forallsectors Double stage ΔE-E: Micro Strip Gas Counter(MSGC)+ CsI(Tl) telescopes (in total 180+180for the 2 chambers) 1 Sector = 4 microstrips + 4 CsI(Tl) Forward chamber = 24 sectors Backward chamber = 21 sectors ForwardChamberBackwardChamber 29°<q<83° 97°<q<147° 0°< f<70° 0°<f<360° 110°< f<360° Chargeresolution: from Z=1 to Z=28 Energy resolutionCsI(Tl) crystal : 3.0% for 5.5 MeV. Identificationthreshold: 0.8-1 MeV/u DetectionThreshold: fewtens of keV Angularresolutionq=1°, f=7.5°

  15. RING Counter (RCo) Three stage telescope in forwardangularregion: Ionizationchamber(IC), Strip Silicon Detector (Si), CsI(Tl). • Itisdivided in 8 Sectors: 8 independentIonizationChambers are working. • Eachsilicon detector, “Pie- shaped”, issegmentedinto8 independentannularstripson one side (for a total of 64 Strips). In the presentversionthey are nTDSilicon Reverse mounteddetectorsExploitation of the PulseShape Analysis based on Digital electronics. Improvement of the identification of fragmentsstopped in the detector. • The thirdstadiumconsistsof48 smallerCsI(Tl)crystals (6 per Silicon detector) goodgranularity for particlecorrelationfunctionstudies. RCo

  16. DSP: The digital way Electronics: system overview CsI(Tl) 24 x 4 = 96 21 x 4 = 84 tot 180 preamp Microstripdet. 24 x 4 = 96 21 x 4 = 84 tot 180 preamp Ancillarydet. (es. RCo) 8 x 1 I.C. 6 x 8 CsI(Tl) tot 108 pre 8 x 8 Si det Passive Splitter Analoguechain Digital chain Trigger Unit FAIR ADC FAIR TDC FAIR BUS DigitalSampling Processor 125MHz 12bit mounted on VMEmotherboard Storage On-line monitor G. Pasquali et al. NIM A570 (2007) 126 D. Fabris College Station – August 2013

  17. EvaporationResidues Detected in the Ring CounterIC-Si Dq = 8.6° ÷ 17° at P = 25 mbar CF4 Silicon Strip 256 MeV16O + 65Cu qgr =8.2° 304 MeV19F + 62Ni qgr =7.3° D. Fabris College Station – August 2013

  18. Detected in GARFIELD CsI(Tl) Dq= 29° ÷ 151° Light ChargedParticles <qC2> =133.1 <qC1> =74.6° <qC2> =119.9° <qC1> = 60.1° <qC2> =145.3° <qC2> =105.4° <qC1> = 46.9° <qC1> = 34.7° a-particles 3He, a <q> = 34.7° ÷ 145.3° Fast (ch) p, d,t Slow (ch) D. Fabris College Station – August 2013

  19. a, 16O+65Cu81Rb, EO=256 MeV (16 MeV/u); E*=208,9 MeV19F+62Ni 81Rb, EF=304 MeV (16 MeV/u); E*=239,9MeV( in lab) Unified Code, O.V.Fotina, Moscow State University D. Fabris College Station – August 2013

  20. ___ 16O + 65Cu ___ 19F + 62Ni ProtonspectrainLab PRELIMINARY 139°- 151° 127°- 139° 113°- 127° 98°- 113° 67°- 82° 53°- 67° 41°- 53° 29°- 41° Elab(MeV) D. Fabris College Station – August 2013

  21. ___ 16O + 65Cu PACE ___ 19F + 62Ni PACE ___ 16O + 65Cu ___ 19F + 62Ni Protonspectra in Lab 139°- 151° 113°- 127° 98°- 113° 127°- 139° 67°- 82° 53°- 67° 41°- 53° 29°- 41° Elab(MeV) D. Fabris College Station – August 2013

  22. ___ 16O + 65Cu ___ 19F + 62Ni aspectra in Lab PRELIMINARY 139°- 151° 127°- 139° 113°- 127° 98°- 113° 67°- 82° 53°- 67° 41°- 53° 29°- 41° Elab(MeV) D. Fabris College Station – August 2013

  23. ___ 16O + 65Cu PACE ___ 19F + 62Ni PACE ___ 16O + 65Cu ___ 19F + 62Ni aspectra in Lab 139°- 151° 127°- 139° 113°- 127° 98°- 113° 53°- 67° 67°- 82° 41°- 53° 29°- 41° Elab(MeV) D. Fabris College Station – August 2013

  24. PRELIMINARY CMSpectra at differentangles Proton in CM Alphain CM 16O + 65Cu 16O + 65Cu 19F + 62Ni 19F + 62Ni ECM ECM D. Fabris College Station – August 2013

  25. aspectra in Lab 67°- 82° 53°- 67° _ 10-2 _ PRELIMINARY 10-3 Experimental 41°- 53° _ 29°- 41° 10-1 _ 10-2 ___ 16O + 65Cu ___ 19F + 62Ni _ 10-2 _ 10-3 Calculated HybridExcitonModel _ 10-1 _ 10-2 D. Fabris College Station – August 2013

  26. Summary • ThePre-equilibriumparticlesemission in the systems256 MeV16O + 65Cu and 304 MeV19F + 62Ni hasbeenstudiedto probe the a-clusterstructure in nuclei • PreliminaryresultsofProtons and Alphaparticles in coincidencewithEvaporationResidueshavebeenextracted • Protons : The comparisonwith PACE calculationsshows a smallPre-equilibriumcomponent, verysimilarfor the twosystems • Alpha: • Experimentalspectra are similarfor the two system, but the Pre-equilibriumcomponentisbiggerfor the 19F + 62Ni system, notexpectedfrompreviousstudies • A first comparisonwithHybridExcitonModelcalculationsshowsanunderstimationofPre-equilibriumalpha in both system (forward and backward) and the shapesof the spectra are similarto the onewhere the cluster isincluded D. Fabris College Station – August 2013

  27. Outlook • PreliminaryresultsseemNOTtoconfirmthe predicteddifferencebetween the twosystems • An overproductionofalphaparticles, at the mostforwardangles, byrespect the HybridExcitonModelpredictionsisconfirmed. • Thisoverproductionhastobeexplaned… Whatnext • Toextractenergyspectraforallparticlesp, d, t, 3He, aalsofor the most • forwardanglesof the RCo. • Tostudypossibleangular and energycorrelationsevents-by-events. • Tomake more selectivecoincidenceswithevaporationresidues, as a function • oftheirenergies and of the detectedangles. • Tocomplete the HybridExcitonModelcalculationsforallparticles and forall • the measuredangles. D. Fabris College Station – August 2013

  28. NUCL-EX collaboration V.L. Kravchuk1, F. Gramegna2, M. Cinausero2, T. Marchi2, D. Fabris3, M. Bruno4, M. D’Agostino4, G. Baiocco4, L. Morelli4, G. Vannini4, G. Casini5, S. Barlini5, M. Bini5, S. Carboni5, A. Olmi5, G. Pasquali5, S. Piantelli5, G. Poggi5, O.V. Fotina6, S.A. Goncharov6, D.O. Eremenko6, O.A. Yuminov6, Yu.L. Parfenova6, S.Yu. Platonov6, V.A. Drozdov6, M. Degerlier7 1National Research Center “Kurchatov Institute”, Moscow, Russia 2Laboratori Nazionali di Legnaro, Legnaro (PD), Italy 3INFN sezione di Padova, Padova, Italy 4Dipartimento di Fisica, Universita’ di Bologna and INFN sezione di Bologna, Bologna, Italy 5Dipartimento di Fisica, Universita’ di Firenze and INFN sezione di Firenze, Firenze, Italy 6Skobeltsyn Institute of Nuclear Physics, Moscow State University, Moscow, Russia 7University of Nevsehir, Science and Art Faculty, Physics Department, Nevsehir, Turkey D. Fabris College Station – August 2013

  29. 1983 1984 1987 Thankyou JOE !!!....

  30. Spares

  31. PRELIMINARY Proton in CM ECM (MeV) ___ 16O + 65Cu ___ 19F + 62Ni Alpha in CM ECM (MeV) D. Fabris College Station – August 2013

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