Laura Francalanza Collaborazione EXOCHIM INFN Sezione di Catania - LNS

Competition between fusion-evaporation and multifragmentation in central collisions in 58 Ni + 48 Ca reaction at 25 AMeV . Laura Francalanza Collaborazione EXOCHIM INFN Sezione di Catania - LNS. OUTLINE. 58 Ni+ 48 Ca reaction at 25 A MeV The CHIMERA multidetector at INFN-LNS (Catania)
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Competition betweenfusion-evaporation and multifragmentation in central collisions in 58Ni + 48Ca reactionat 25 AMeV Laura FrancalanzaCollaborazione EXOCHIMINFN Sezione di Catania - LNSOUTLINE
  • 58Ni+48Ca reaction at 25 A MeV
  • The CHIMERA multidetector at INFN-LNS (Catania)
  • Selection of centrality
  • Competition between reaction mechanisms: “fusion-evaporation” and “multifragmentation”.
  • Comparison with dynamical + sequential evaporative model.
  • Conclusions and perspectives.
  • 58Ni+48Ca a 25 A MeVThe experiment was performed by the ISOSPIN NUCL-EX collaboration and it was realized by means of the CHIMERA apparatus, located at LNS – INFN (Catania).An ion beams of 58Ni was accelerated on a thin target 48Ca by the LNS Superconducting Cyclotron, and the reaction products were collected by the 1192 telescopes of CHIMERA multidetector.It was devoted to study the competition between reaction mechanisms for central collisions in the Fermi energy domain.RELEVANT ISSUES:Enhancement in the number of the emitted IMFs (fragments with Z≥3) with respect to low energy domain; predominance of fusion mechanism for small impact parameter and competition with prompt multifragmentation.CHIMERABEAMTARGET1192 telescopes30°176°1°
  • 9 rings in the angular range 1°≤θ≤30° (forward part)
  • 17 rings between 30°≤θ≤176 °(sphere)
  • High granularity
  • Efficiency in angular coverage up to 94% 4π
  • IDENTIFICATION TECHNIQUESE(Si)-E(CsI)Z for charged particles that punch through silicon detector.Z and A for ions up to Z<9.(Pd)18x18mm2PSD in CsI(Tl)Z and A for light particles10cmSiCsI(Tl)E(Si)-TOFA for particles stopped in Si.Z for particles that punch through Si.300mE(Si)-Rise TimeZ for particles stopped in silicon detector. (NEW)vPAR= component of velocity parallel
  • to beam direction
  • A= Mass (amu) of each reaction product
  • COMPLETE EVENTSAproj = 58 umaZproj = 28Atarget = 48 umaZtarget = 20vproj ≈ 6.5 cm/nsvCM≈ 3.8 cm/nsMinimum value : 70%Maximum value : 105%11.5%
  • Relevant presence of fragments with properties like PLF and TLF.
  • Contribution of reaction products with parallel velocity close to centre of mass velocity.
  • 0.7 ≤ ZTOT / (Zproj + Ztarget) ≤ 1.050.7 ≤ pTOT / (pproj + ptarget) ≤ 1.05SELECTION OF CENTRAL COLLISIONSTKE = Σi EkiniDISSIPATIONCENTRALITYThe inclination of the main axis of the ellipsoid with respect to beam direction defines the flow angle,ϑflow, that gives information about event shape.NOTE: An increasing in ϑflow values results in a selection of more dissipative events.CENTRAL EVENTSCentral = 6.16% Complete< MIMF > = 2 (IMF : Z ≥3)< MCP > ≈ 6-7 (LP : Z<3)
  • ϑflow selection method
  • ϑflow 60°c)a)c)b)Large number of PLF and TLF, indicative for peripheral collisions.PLF and TLF contributions are progressively reduced.Emissions from peripheral collisions vanished; vpar spectrum is more and more centered on the CM velocity: strong evidence for a fusion-evaporation residue.A (amu)a)b)vpar (cm/ns)QUALITATIVE CHARACTERIZATIONMIMF≈ 1-2MLCP≈ 4-5A1≥ 50 amuMIMF = 1 : 43.5% amount< MIMF > = 1-2 (IMF : Z ≥3)< MLP > ≈ 4-5 (LP : Z<3)Abig (amu)MIMF≥ 3MLCP≈ 4a)A1< 50 amuMIMF up to 6< MIMF > = 3b)Two classes of emitted fragments, concerning their mass.vPARbig (cm/ns)Mass and longitudinal velocity of the heaviest fragment Event by event analysis, in order to disentangle between events that show this heavy residue (fusion-evaporation meachanism) and ones that don’t show this feature: good candidates for prompt multifragmentation process?MIMFQUALITATIVE CHARACTERIZATIONA1 (amu) A2 (amu)A1≥ 50 amuMIMF = 1 : 43.5% amount< MIMF > = 1-2 (IMF : Z ≥3)< MLP > ≈ 4-5 (LP : Z<3)A3 (amu) Abig (amu)a)A1< 50 amuMIMF up to 6< MIMF > = 3b)A1 (amu) A2 (amu)A3 (amu) vPARbig (cm/ns)
  • EVENTS a)
  • The biggest fragment, is accompanied with lighter reaction products. There is a strong difference in mass value between the first three emitted fragments, ordered according to decreasing masses.
  • EVENTS b)
  • Completely different nature of the emission pattern: the three biggest fragments show very similar mass values.
  • We can notice the sensitivity of the shape of mass distribution to MIMF:
  • Heavy residue, with A>50 amu, strongly decreases with increasing of MIMF.
  • The intermediate mass component is dominant for high values of MIMF.
  • A (amu)A (amu)A (amu)Comparison exp.-BNV-SIMON
  • We have compared mass distributions, multiplicity … for selected central events with those predicted by a two step mechanism: dynamical BNV calculation followed by the sequential de-excitation of a composite source (SIMON).
  • The source information were obtained from a BNV calculation, including a pre-equilibrium emission:
  • SOURCE’S MASS = 94 amu
  • E* = 400 MeV (± 50 MeV)
  • 0.45Experimental dataBNV – SIMON SimulationUNFILTERED0.40.3510.3PRELIMINARY RESULTS0.2510-10.20.15ZIMF ≥ 310-20.10.05010-302468101214161820020406080100120MIMFA (amu)Comparison exp.-BNV-SIMONExperimental dataBNV – SIMON b = 0SimulationUNFILTERED
  • Comparison between the mass distribution of the heaviest fragment, in each event.
  • Mass distribution for events with MIMF≥3 and MIMF≥4
  • SOURCE’S MASS = 94 amu
  • E* = 400 MeV (± 50 MeV)
  • b =0
  • 10-210-3020406080100120Abig (amu)Experimental dataBNV – SIMON Experimental dataBNV – SIMON 1MIMF ≥ 3MIMF ≥ 410-1SimulationUnfilteredSimulationUnfilteredA (amu)CONCLUSIONS
  • Main criterion for centrality selection: ϑflow.
  • Mass and velocity correlations for all emitted fragments have shown the presence of a broad component centered at vCM.
  • Low MIMF values are associated with emission of a heavy residue, while events with high values of MIMF show relevant presence of fragments with mass of intermediate values.
  • Preliminary comparisons of experiment with reaction simulation show quite good agreement with the assumption of theoretical sequential emission. However further analysis are needed in order to obtain definitive conclusions (IMF-IMF correlations, SMM calculations … )
  • PRELIMINARY RESULTSACKNOWLEDGEMENTSThanks to CHIMERA/EXOCHIM groupfor the help and support during the studyand toM. Colonna for her careful work in calculations.Thank you all for your attention!
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