Probing the birth of clusters in a warm and dilute nuclear medium with correlation functions

1. Colliding microscopic droplets (nuclei) what can we learn? or Probing the birth of clusters in a warm and dilute nuclear medium with correlation functions Theme : Aggregation Phenomena Studying the onset of structure Geller et al., Harvard Smithsonian • Large Scale Structure of the universe (anisotropies in initial conditions) Romualdo T. deSouza Indiana University

2. T. Neff et al On a very different scale … •  cluster structure of light nuclei Additional stability/binding of so called alpha cluster nuclei (12C, 16O, 20Ne, …) • Spontaneous cluster emission from heavy nuclei ( emission, 14C evaporation, etc) • Cluster formation in a dilute gas (Van der Waals clusters) Evolution of correlations in a dilute (sub-saturation density) medium Romualdo T. deSouza Indiana University

3. Q: How does one produce excited nuclear matter? A: collisions Ni + Mo at E/A = 11 MeV fusion Zp+Zt Zt,At Ap+At Zp,Ap Helium Isotopes Thermal Emission of nucleons and clusters • Maxwell Boltzmann distribution • Neutron, protons • α-particles, heavier clusters • Coulomb Barrier for charged particles Charity, et.al., PRC (2001) Statistical emission is generally characterized by the types of emitted particles, the number of emitted particles, their angular distribution, and their energy spectra.

4. What happens when we collide two more equal size nuclei at somewhat higher energies?

5. AMD: A microscopic picture • System: • 114Cd + 92Mo at 50 MeV/nucleon • 25000 events accumulated (34 - 68 years!) • Mass, charge, energy exchange • Binary nature of the collision • Transiently deformed nuclei • Early cluster production, t  90 fm/c 100 fm/c = 3 x 10-22 sec. Clusters are also statistically emitted as the excited reaction products de-excite! S. Hudan, R.T. de Souza and A. Ono, PRC (2005)

6. Beam Ring Counter 48 Projectile 114Cd + 92Mo at E/A = 50 MeV B. Davin et al., NIM A473, 302 (2001) Ring Counter : Si (300 m) – CsI(Tl) (2cm) 2.1lab 4.2 δZ/Z ~ 0.25 Mass deduced†

7. Si-E0.5/1.5 mm Si-DE 65mm Beam pixel 16/32 strips h. (back) 16/32 strips v. (front) Target Beam 114Cd + 92Mo at E/A = 50 MeV B. Davin et al., NIM A473, 302 (2001) LASSA : 0.8 Mass resolution up to Z=9 7lab 58

8. Experimental details 4x CsI(Tl) 6/4cm Beam 114Cd + 92Mo at 50 A.MeV LASSA : 0.8 Mass resolution up to Z=9 7lab 58  Detection of charged particles in 4p B. Davin et al., NIM A473, 302 (2001)

9. LASSA 4x CsI(Tl) 6cm Si-E 0.5 mm Si-DE 65 mm Pixel 16 strips h. (back) Target 16 strips v. (front) Beam Particle Identification: ΔE-E Technique Measure Z – atomic number A – mass number E – energy Θ,Φ – angles No 8Be

10. s b RP+RT TLF TLF PLF PLF Mid-Peripheral Peripheral Peripheral and mid-peripheral collisions Projectile-like fragment = PLF Target-like fragment = TLF projectile target Conventional wisdom: Central collisions lead to the highest excitation/single source • Large cross-section • PLF/TLF: • Well-characterized (Size, E*, J) • Selectable

11. Reaction Characteristics Emitting Source α-particles detected in LASSA PLF: 15<Z<46, 6.5<v<9.5 cm/ns Statistical Emission “Coulomb Ridge” color indicates yield in log-scale • Boltzmann Distribution • Shape & Yield are • Independent of Emission Angle •  Isotropic Emission Yanez et.al., PRC 68, 11602 (R) (2003)

12. KE spectra in PLF* frame selected on VPLF* Decreasing VPLF*, increasing dissipation, increasing excitation Emitting Source α-particles detected in LASSA PLF: 15<Z<46, 6.5<v<9.5 cm/ns Yanez et.al., PRC 68, 11602 (R) (2003) • Decay of PLF* dominated by a single exponential (statistical evaporation). • Pre-equilibrium emissions comprise at most 2% of the yield. • Systematic increase of exponential slope with decreasing VPLF* • 6He exhibits systematically higher slope parameters (temperatures)  emission from hotter sources possibly earlier in the de-excitation cascade.

13. KE spectra in PLF* frame selected on VPLF* 0 E ≤B* C*(E-B*)De-E/T B*<E<B+T (E-B*)De-E/T EB+T P(E) = Yanez et.al., PRC 68, 11602 (R) (2003) Decreasing VPLF*, increasing dissipation, increasing excitation • Decay of PLF* dominated by a single exponential (statistical evaporation). • Pre-equilibrium emissions comprise at most 2% of the yield. • Systematic increase of exponential slope with decreasing VPLF* • 6He exhibits systematically higher slope parameters (temperatures)  emission from hotter sources possibly earlier in the de-excitation cascade. B  Barrier parameter T Temperature parameter D  Barrier diffuseness parameter B* = (1-D)T + B ; C* = T/(DT)D

14. damping PLF*: velocity damping With increasing damping: • More emitted particles • Larger slope parameter • Lower ZPLF • Larger Zemitted • “Linear” increase of E*/A with damping • High E*/A reached compatible with limiting T R. Yanez et al., PRC68, 011602 (R) (2003)

15. The hot PLF* can decay by emitting both bound and unbound clusters. • How do we study these unbound clusters ? • If the unbound cluster is short-lived it will decay in the proximity of the emitting nucleus (Proximity decay) • Is there an observable difference between Proximity decay and decay in isolation (standard decay)?

16. 11.35 MeV 3.5 MeV 11.44 MeV 3.03 MeV 3.12 MeV =1.51 MeV gr. st. =6.8 eV 93 keV 8Be α + α Studying short-lived clusters Resonance Spectroscopy • Tool to measure the existence and properties of short-lived intermediates J. Pochodzalla et al., PRC 35, 1695 (1987) Inclusive analysis! • Relative Energy Determined by Quantum State

17. x100 x100 x10 …Back of the envelope scribbles • Maxwell-Boltzmann Distribution • Expect 8Be to be similar to other isotopes 20 MeV  2.2 cm/ns (0.073 c) 0.073c * 130 fm/c ~ 9fm Overestimate because 0.073c is asymptotic velocity  on average 8Be* decays closer than 9 fm!

18. Tidal effects:a manifestation of proximity decay July 16 – 22 1994: Comet P/Shoemaker-Levy 9 collided with Jupiter resulting in at least 21 discernable fragments with diameters estimated at up to 2 km. http://www2.jpl.nasa.gov/sl9/

19. Tidal Effects on the Mesoscopic scale Zsource Cluster Zsource Zsource Transverse  Higher Erel Longitudinal  Lower Erel For nuclei: Coulomb interaction

20. Tidal effects: gradient in the field • Change of the relative velocity • Transverse decay with higher relative energy • Longitudinal decay with lower relative energy Zsource • Decay angle dependence of the probability • Higher probability to decay transverse to the emission direction • Effect depends on: • Time spent in the field • Stronger effect when decaying close to the “source” • Field gradient

21. Isotropic emission forward of PLF* R. Yanez et al., PRC68, 011602 (R) (2003) Tidal effect: data selection 114Cd + 92Mo at 50 MeV/nucleon • Data selection: • 15  ZPLF 46 • 8  VPLF 9.5  E*/A = 2 – 4 MeV • 2  particles “forward” of PLF (  100)

22. Relative Energy Distribution • Observe peak at 3 MeV • Yield: • Sequential emission • (primary component) • Resonant Decay of 8Be* • Detector Acceptance: • finite geometrical coverage • decreased efficiency at low Erel LASSA Telescope

23. Assessing the Non-Resonant Decay α α Emitting Source Event i α Emitting Source Event j α • Primarily due to sequential emission of alphas • Construct Background from 2 alpha particles chosen from 2 different events α • Good description of yield for Erel ≥ 7 MeV • Excess yield ~ 3 MeV • Over-prediction at low Erel α

24. ΔVPLF* (cm/ns) Assessing the Non-Resonant Decay • Particle detection efficiency varies with ΔVPLF* • Restrict the difference of source velocity A.B. McIntosh et al. , PRL 99 132701 (2007)

25. 2nd approach: Simulation of Non-Resonant Decay Approach: Sequential αemission Coulomb trajectory calculation • Ingredients of the model: • Initial KE of α from experimental distribution • Z and Velocity of source • Intervening emissions • Time between emissions: • Results: • Sensitivity to the Final State Interaction • (t≥300fm/c) • Relative insensitivity to intervening emissions

26. Zresidue Zresidue Zresidue Cluster Longitudinal  Lower Erel Transverse  Higher Erel Dependence on Orientation

27. MC-RES: Modeling Proximity Resonant Decay • Approach: • 8Be* is emitted from a source • Propagate in the Coulomb field until 8Be* decays • Propagate the two daughter  in the Coulomb field • Filter the model results with the detector acceptance • Ingredients of the model: • Z and velocity of source: from experimental distributions • Lifetime of 8Be*: • Initial KE of 8Be*: • Relative velocities of α:

28. Coulomb Tidal Effect Trend: Consistent with experimental observation Magnitude: Over-predicts experimental observation Yellow band includes deformation towards mid-rapidity, spin of 8Be consistent with 2+ state, and changing inter-alpha separation (0.7 – 1.5 Moretto sys.)

29. Can it be Coulomb only? Consider the PLF to be deformed in the direction of emission (touching configuration) with Z1=6, A1 = 12 Z2=30, A2 = 64 Even more deformed shapes would manifest a weaker Coulomb tidal effect but would imply an unexpectedly large difference between saddle and scission configurations.

30. Can it just be the additional nuclear potential (nuclear tidal)? ZPLF = 30 APLF = 64

31. Other Nuclear Effects (stabilization) ln P(t) t (fm/c) E.H. Berkowitz NPA 60 555 (1964) 8Be is prevented from decaying while it is within some distance of the nuclear surface.

32. Proximity Decay A.B. McIntosh et al. , PRL 99 132701 (2007) Stabilization decreases Coulomb tidal effect A stabilization distance of 5 fm results in rough agreement with the experimental data 8Be* travels ~2-4 fm in approximately 200 fm/c

33. Conclusions • Clear observation of a proximity effect for decay of a short-lived nucleus • Magnitude of observed tidal effect suggests influence of: • A Nuclear tidal effect in addition to a Coulomb tidal effect • Stabilization of short-lived nucleus by the emitting source • Role of extremely deformed shapes • What we are doing – • Observed the interaction between the surface of the emitting nucleus and the emitted cluster • Comparable to taking an ultrasound image of a baby just before birth (structure of both cluster and surface must be modified)

34. The road ahead … Do two components really matter? Nuclei are two-component systems (neutrons and protons), the N/Z of the system affects the phase diagram. A pot still for distilling alcohol What are the properties (and structure) of nuclei far from  stability? Are present ideas on the nucleosynthesis of the heavy elements in supernova explosions valid? A 550 M$ facility to be built in the Midwest !

35. Future accelerator facilities for nuclear science (Radioactive Beams) Vary the neutron to proton ratio (N/Z) in nuclei • FAIR (Facility for Antiproton and Ion Research); Darmstadt, Germany UNDER CONSTRUCTION; $1.5 Billion • SPIRAL II, Grand Accelerateur National d’Ions Lourds; Caen France UNDER CONSTRUCTION; $200 Million FRIB • RIKEN, Japan (Near completion) • 4. Radioactive Beam Facility (U.S.) • Most likely locations – Argonne, IL / E.Lansing MI; $550 Million

36. Thanks to: Indiana University S. Hudan A.B. McIntosh R. Yanez B. Floyd C.J. Metelko V.E.Viola • Collaborators • R. Charity and L.G. Sobotka (Washington University) • M.B. Tsang and W.G. Lynch (Michigan State) • J. Toke and W.U. Schroder (University of Rochester) • S.J. Yennello (TAMU) • R. Roy, M-O. Fregeau, J. Moisan, J. Gauthier (Universite Laval) • Chbihi (GANIL) • M. Famiano (Western Michigan University) • W. Trautmann, C. Schwarz S. Bianchin (GSI) … and for financial support U.S. DOE National Science Foundation (MRI grants) Indiana University

37. Additional slides

38. Probing the birth of clusters in a warm and dilute nuclear medium with correlation functions 124,136Xe + 112,124Sn at E/A = 49.2 MeV GANIL Caen, France Simultaneous measurement of neutronsand charged particles • DEMON Neutron Detectors • 27 detectors cover 5°-165° • Time of Flight • Pulse-Shape Disc Romualdo T. deSouza Indiana University

39. Detection of charged particles: Forward Indiana Ring Silicon Telescopes (FIRST) and Large Area Silicon Strip Array (LASSA) Z=54 elastic

40. Characterizing mid-peripheral collisions FIRST+ LASSA T1 Si(IP)–Si(IP)–CsI(Tl)/PD 273m, 977m, 3cm 2.07  – 6.57 Z for Z=3-55 A for Z=4-14 LASSA Si(IP)–Si(IP)–CsI(Tl) 75m, 500m, 6cm 36.38  – 51.11 Z and A for Z=1-7 T2 Si(IP)–CsI(Tl)/PD 500m, 3cm 7.34  – 14.45 Z for Z=2-20 FIRST + LASSA = 752 Si segments and CsI(Tl)/PD detectors T. Paduszynski et al., NIM A547 464 (2005)