1 / 17

Coherent and Incoherent Processes in Nuclear Reactions

Study of pre-equilibrium emission and extra yield in nuclear reactions at varying energies through Sez.-CT data. Analysis of GDR, binary processes, and collective versus microscopic incoherent contributions. Detailed exploration of molecular dipole and statistical models. Investigation of multifragmentation and degree of coherence in hot sources. Unveiling new observables related to dipolar γ-ray emission dynamics. Unified understanding of pre-equilibrium phenomenon via dynamical ComD calculations.

coleenhall
Download Presentation

Coherent and Incoherent Processes in Nuclear Reactions

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Sez.-CT GDR pre-equilibrium emission 40Ca+48Ca,46Ti at 25 MeV/A M.Papa et al EPJ A4 (1999) 69 F.Amorini et al PRC 58 (1998) 98 S.Tudisco EPL 58 (5), 811(2003) M.Papa et al, PRC 68., 034606 (2003) F.Amorini et al PRC 69, 014608(2004) Fusion-Incomplete Fusion Dissipative binary processes Extra yield at 10 MeV

  2. GDR pre-equilibrium emission 40Ca+48Ca,46Ti at 10 MeV/A M.Papa et al, submitted to PRC Dissipative binary processes study of kinematical coincidence

  3. Z=14-22 Elab<160 MeV 40Ca+46Ti 40Ca+46Ti 40Ca+48Ca γ-2f γ-1f •Accurate selection of events for which, different quantities measured for the two systems look very similar.

  4. CoMD calculations TKEL-angular and charge distrib. b-window→ pre-eq γ Yield Calculated dynamical pre-eq yield able to explain the extra-yield

  5. Sez.-CT How we can generate the coherent contribution? A simple picture the “Molecular Dipole” The average ensemble in an harmonic mean field The initial conditions for the GDR mode At the contact D1≈D2 ≈0 n p N1/Z1≠N2/Z2 if M.Papa et al EPJ A 4 69 (1999) and ref.there in If Y=0 NO coherent contribution

  6. Sez.-CT • Incoherent contribution • Collective • Microscopicincoherent Coherent contribution (ensemble average) Statistical models Mean field approach Fully N-body dynamical approach for 1000 fm/c an unified description M.Papa et al, PRC 68., 034606 (2003)

  7. Sez.-CT Υ-ray average multiplicity in semi-classical approximation The Larmor formula Fourier Transform Formal analogy with scattering amplitude theory- quite general way to define statistical processes.

  8. Sez.-CT b=0 fm E/A 25 MeV Langevin prediction for the total system • Prediction in the loc. Time equil. hypothesis • Prediction according to a full CoMD approach g~12 M.Papa et al, PRC 68(2003) 034606

  9. Sez.-CT We have also high energy bremsstrahlung contribution We have to study the local time spectral properties of the  yield • We need to define T at long time • We need to separate the • incoherent Microscopic contribution

  10. Sez.-CT High energy results Multifragmentation of the hot source

  11. Sez.-CT   50 MeV/A b=0 fm M.Papa et al, PRC 68(2003) 024612  obtained from the fit procedure Very small Coherent contribution or

  12. Something is changed in the fundamental properties of the formed hot sources…. Degree of collectivity-Degree of coherence as function of t

  13. A new observables related to the properties of the dipolar γ-ray emission in different reaction mechanisms have been measured. - Φch represents the ratio between the average and fluctuating dynamics. For N-body approaches able to evaluate the two contributions in a self consistent way, this parameter should be rather robust with respect some model ansatz: semi-classical approximation, occupation numbers……. - On the other hand and we can expect that Φch can depend on the dynamics (Forces) governing the equilibration Process. From the experiments Фch(12MeV)=0.6±0.15 10 MeV/A Binary. proc. Фch(10 MeV)=0.3±0.07 25 MeV/A Inc. fusion.proc.

  14. c(0,tm) c(0,tf) ch(0,tf) Collectivity and Coherence for the total system limiting energy for the collective motion-GDR quenching M.Papa et al, PRC 68(2003) 024612, Black: collectivity long times rather smooth behaviour 40Ca + 48Ca Central Collisions Red: collectivity short times, it contains the ambiguity related to the experimental selections of 1 equilibrated source *10 Green:Coherence, high sensitivity related to the natural time selection performed by the dynamics through memory effects.

  15. γ-Pre-equilibrium effects and “Isospin-Equlibration” non diffusive mechanism-”quasy resonant mechanism” M.Papa et al Sub. to PRC Invariant with respect to secondary statistical emission processes

  16. Sez.-CT Conclusive remarks • An unified description of the pre-equilibrium phenomenon (fluctuating-average dynamics) has been obtained in a fully dynamical approach by means of ComD calculations. • The fluctuations predicted by the model are in agreement with Cascade calculations at 25 MeV/A and for long time by using g≈12. The fluctuations on the collective motion show marked non-equilibrium features at short time. This effect is able to describe the GDR quenching. • The degree of coherence φch rapidly change when the multifragmentation processes set in. (much more than the • degree of collectivity φc) • 3. In the explored incident energy range, (8-25 MeV/A) the dynamical pre-equilibrium extra-yield seems to be strictly related to the isospin equilibration process throgh a “quasy-resonant” mechanism.

More Related