Romualdo de Souza

1. Nuclear Chemistry- Studying the Behavior of Microscopic Droplets • General Overview (What & Why) • Particle Accelerator Labs (Where) • Experimental Tools (How) • Experimental Results • Outlook (RIA) • Other Physical Chemistry at IUB Romualdo de Souza

2. I. General Overview Why study nuclei? • Necessary to understand the formation of the elements – nucleosynthesis • Important in understanding the properties of astrophysical objects such as neutron stars ( a giant nucleus with a radius of ~ 0.6 km)  nuclear equation-of-state. • Important in understanding the thermodynamic properties of small, finite systems (strong ties to the study of atomic clusters). Basic facts about nuclei • Nuclei behave like microscopic drops of liquid (fairly incompressible yet deformable). • Nuclei are small (R= 1-10 x 10-15 m);104 times smaller than an atom; requires measuring instruments of a comparable size to measure them e.g. other nuclei • Nuclei are positively charged so one has to overcome the mutual repulsion between two nuclei (Coulomb repulsion) i.e. Particle accelerators are required. Romualdo de Souza

3. Nucleosynthesis • Fe is the most tightly bound nucleus • Fusion of lighter nuclei releases energy • Fission of heavier nuclei releases energy How are heavier nuclei formed if they are not at the thermodynamic minimum ? Supernova explosions Romualdo de Souza

4. Nuclear Equation-of-state In order to understand supernova explosions, neutron stars, and the behavior of nuclei we need to understand the nuclear equation-of-state. Nuclei within the spinodal region are unstable against density fluctuations and disintegrate into many fragments. Nuclear matter at high excitation is prepared by colliding two nuclei. Romualdo de Souza

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6. Reconstructing a collision Collision of a nucleus with a light-ion (Z<3) or a heavy-ion (Z>2) converts kinetic energy of relative motion into intrinsic excitation i.e. heats the nucleus. From the debris – the fragmentation pattern we need to determine what happened • identity of all the particles • number of clusters (Z>2) • number of light particles Z=1,2 • energy of all the particles • angles of all the particles Romualdo de Souza

7. Particle accelerators around the U.S. Brookhaven National Laboratory Lawrence Berkeley National Laboratory Oakridge National Laboratory TAMU Cyclotron Facility I.U. Cyclotron Facility

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9. Collisions of Mercury Drops* Plateau-Rayleigh instability Liquid cylinder of length radius R is unstable against wavelengths  > 2R Strongly Damped Collision Strongly damped + neck emission and re-absorption Strongly Damped + neck emission • Unstable shapes subject to Plateau-Rayleigh instabilities may be formed due to destabilizing forces. • Coulomb repulsion • Angular momentum *Thanks to G. Poggi Romualdo de Souza

10. Cold spectator fragments Abrasion-Ablation model Hot participant zone Characterize collision by looking at the forward going fragment Energy is essentially linear with Z Since A  Z and E  Av2 This means the velocity is essentially constant. Unit Z resolution from Z=2 to Z=45 Romualdo de Souza

11. little or no velocity damping of projectile-like fragment (PLF) • limited mixing of protons and neutrons from projectile and target • geometry (impact parameter) governs breakup—volume instability (T,) Abrasion-Ablation model Cold spectator fragments Hot participant zone • breakup is a surface instability • deformation/stretching are the governing factors Plateau-Rayleigh instability Romualdo de Souza

12. Particle identification through the interaction of radiation with matter Large Area Silicon Strip Array (LASSA) Incident charged particle 65 m Si 500 m Si 6cm CsI(Tl) Photodiodes Romualdo de Souza

13. Si-Si identification Si-CsI(Tl) identification Two dimensional E-E spectrum provides Z,A identification LASSA provides isotopic resolution for Z  9 Romualdo de Souza

14. Experimental Setup 114,106Cd + 98,92Mo at Elab/A=50 MeV LASSA 9 telescope array (7°lab58°) Miniball/Miniwall 4 array BEAM Si-CsI Ring Counter (2.1°lab4.2°) Target foil Measure: • Number of charged particles in each collision (Nc) • Number of clusters/IMFs in each collision (NIMF) • Z,E, of all particles detected • Z,A,E, of all particles detected in LASSA Romualdo de Souza

15. Increasing v Two fragments in the Ring Counter Romualdo de Souza Velocity of the smaller fragment exceeds velocity of the larger fragment Velocity of the larger fragment exceeds velocity of the smaller fragment Increasing v

16. Z-velocity correlations for fragments in Si-CsI Ring Counter (2.1°lab4.2°) • Large fragments (projectile-like) are observed at forward angles at near beam velocity. • The velocity of the forward going fragment is independent of its size except for the smallest fragments. • Smaller fragments (Z<10) are also observed at lower velocities. Beam velocity Romualdo de Souza

17. Increasing v Increasing v Charge anti-correlation indicates binary decay of a common parent Quite different decay pattern observed Size of smaller fragment is independent of size of larger fragment Binary decay of a PLF* Size of smaller fragment is peaked at Z=6 Neck fragmentation Romualdo de Souza

18. Increasing v Increasing v Velocity of the heavy fragment depends on whether it precedes or trails the lighter fragment and the size of the smaller fragment When VH>VL And ZL < 9, Relative velocity of the fragment pair depends on Nc  NOT a two stage process. Velocity of the center of mass of the fragment pair is independent of the velocity order or size of ZL Vrel is independent of Nc two stage process. (Vrel consistent with fission systematics) Romualdo de Souza

19. Dependence of relative yield and relative velocity on the size of the smaller fragment Relative yield is peaked at Z=6 3-5 times more fragment yield for neck fragmentation process as compared to binary decay of PLF* Neck fragmentation is associated with a much larger vrel than binary decay (Coulomb expectation). Where does this extra energy come from? Romualdo de Souza

20. Outlook: Study this process by tagging the isospin (N/Z). Preliminary Conclusions • Neck fragmentation is an effective means for producing fragments in peripheral collisions of projectile and target nuclei. • The relative velocity is significantly larger than allowed by Coulomb considerations alone suggesting a stretching of the nuclear matter as the fragments are produced.  Interrupted mixing of two finite quantum fluids (N/Z)light clusters (N/Z)target (N/Z)projectile (N/Z)heavy clusters Romualdo de Souza

21. Acknowledgements Indiana University, Bloomington Washington University, St. Louis T. Bredeweg B. Davin R. Molina H. Xu Y. Larochelle T. Lefort L. Beaulieu A. Caraley V.E. Viola R.T. deSouza R.J. Charity L.G. Sobotka Michigan State University T.X. liu X.D. Liu W.G. Lynch R. Shomin W.P. Tan M.B. Tsang A. Vander Molen A. Wagner H.F. Xi C.K. Gelbke Romualdo de Souza

22. G. Martyna J. Zwanziger understand and develop materials, with special focus on glassy and partially ordered solids structural and dynamical properties of biochemical and catalytic materials P. Ortoleva D. Clemmer spontaneous generation of patterns in nature structures of large low-symmetry molecules in the gas phase; protein structure