1. Mapping timescales of quasifission Dr. Elizabeth Williams, Australian National University Humboldt Kolleg, ECT*, Trento, Italia, 1 September 2015

2. Outline  Quasifission and superheavy element formation  ANU’s quasifission mapping program  New technique: High angular momentum mass angle distributions E. Williams, Humboldt Kolleg, 1 September 2015

3. 40 Ca Quasifission 238 U TDHF calculation of 40 Ca+ 238 U reaction (Cedric Simenel, Aditya Wakhle) E. Williams, Humboldt Kolleg, 1 September 2015

4. Quasifission: P CN = 1 - P QF E. Williams, Humboldt Kolleg, 1 September 2015

5. The ANU Quasifission Program Aims to examine the dependence of quasifission probability and characteristics on collision variables (related to P CN ): Compound nucleus fissility (Z 2 /A); Coulomb repulsion in the entrance channel (Z 1 Z 2 ); Angular momentum; Nuclear structure of the colliding nuclei: o deformation (alignment with projectile) o closed shells (magic numbers) in the colliding nuclei E. Williams, Humboldt Kolleg, 1 September 2015

6. Aim of the ANU Quasifission Program Ultimate goal: Reliable model including all relevant physics to predict P CN Model should allow direct comparison to experimental data Model should predict quasifission probability, since P CN = 1 – P QF E. Williams, Humboldt Kolleg, 1 September 2015

7. Means of creating this model  Start with experimental data  Define smooth trends in quasifission dynamics Fissility Coulomb repulsion Angular momentum  Then take into account the influence of shell effects on quasifission outcomes Magicity Collective structure Valence nucleon number  Work closely with theorists to develop models that provide insight into the physics driving quasifission probabilities E. Williams, Humboldt Kolleg, 1 September 2015

8. Means of creating this model  Start with experimental data  Define smooth trends in quasifission dynamics Fissility Coulomb repulsion Angular momentum  Then take into account the influence of shell effects on quasifission outcomes Magicity Collective structure Valence nucleon number  Work closely with theorists to develop models that provide insight into the physics driving quasifission probabilities E. Williams, Humboldt Kolleg, 1 September 2015

9. The MAD Map Identifying smooth trends in quasifission dynamics E. Williams, Humboldt Kolleg, 1 September 2015

10. How do we identify smooth trends in quasifission dynamics experimentally? Minimize shell effects – high E * Minimize effects of angular momentum – low E/V b Compromise: choose E/V b = 1.05-1.10 o Effects of spherical magic numbers attenuated by E * o Effects of deformation alignment averaged out o Angular momentum not too high (but still relevant to SHE production) E. Williams, Humboldt Kolleg, 1 September 2015

11. The MAD Map R. du Rietz, E. Williams et al., PRC 88 (2013) 054618 Z = 6Z = 28 Projectile Z Z = 82 Z = 92 Z = 102 Z = 112 Target Z Hg NoNo Ti

12.  (deg.) Miminal mass-angle correlation Strong mass-angle correlation 160 o 20 o Scission R. Bock et al., NP A388 (1982) 334 J. Toke et al., NP A440 (1985) 327 W.Q. Shen at al., PRC 36 (1987) 115 B.B. Back et al., PRC 53 (1996) 1734 10 203040 10 203040 MADs: Mass equilibration and rotation Slide courtesy of D. J. Hinde

13. Quasisim: A simple Monte Carlo model for quasifission timescales Ingredients: Reaction timescale determined by: Angular velocity ω = L/I  Angular momentum L  moment of inertia I Center-of-mass scattering angle θ c.m. θ i,f : ½ Coulomb deflection angles for the initial and final trajectories  Angle of rotation of the dinuclear system during reaction: Δθ = π-θ i -θ f -θ c.m  t rxn = Δθ/ω Mass equilibration: 1-exp(t rxn / τ m ), τ m ~ 5.2 zs [1] J. Tōke et al. Nucl. Phys. A 440, 327 (1985) [2] R. du Rietz et al. PRL 106, 052601 (2011) E. Williams, Humboldt Kolleg, 1 September 2015

14. QF Timescales 5x10 -21 s 10x10 -21 s >> 10x10 -21 s 186 W Experimental MAD Simulated MAD R. du Rietz et al. PRL 106 (2011) 052701 MAD1MAD2MAD3

15. MAD Classes: Distinguishing features E. Williams, Humboldt Kolleg, 1 September 2015 ClassMass distributionMass-angle correlation? MAD 1 ( < 5 zs)Minimum at M r =0.5Yes MAD 2 ( ~ 10 zs)Maximum at M r =0.5; Significantly wider than that predicted for fusion-fission Yes MAD 3 ( >> 10 zs)Maximum at M r =0.5; may be slightly wider than that predicted for fusion-fusion No For MAD class 3, quasifission can be identified using other observations (e.g. angular anisotropies in comparison to Standard Model predictions).

16. Class 1Class 2Class 3 MADs for reactions in this energy regime (E/V B ~ 1.05 – 1.10) show a smooth evolution from long to short timescales as a function of entrance channel parameters. Primarily fusion- fission E. Williams, Humboldt Kolleg, 1 September 2015

17. Class 1Class 2Class 3 MADs for reactions in this energy regime (E/V B ~ 1.05 – 1.10) show a smooth evolution from long to short timescales as a function of entrance channel parameters.  Based on entrance channel quantities (charge product, effective fissility, etc.) and compound nucleus properties, can we predict which MAD class a given reaction is likely to conform with? Primarily fusion- fission E. Williams, Humboldt Kolleg, 1 September 2015

18. R. du Rietz, E. Williams et al., PRC 88 (2013) 054618 Smooth trends: Coulomb repulsion

19. Smooth trends: Fissility W. J. Swiatecki, Phys. Scr. 24, 113 (1981) Compound nucleus fissility Effective fissility

20. R. du Rietz, E. Williams et al., PRC 88 (2013) 054618 Smooth trends: Fissility

21. What conclusions can we draw from the MAD Map?  Using Z p Z t and Z CN, or X eff and X CN, we can roughly estimate the average timescale of a given reaction at ~1.05-1.10 V B.  We can use the same parameters to determine whether quasifission is likely to dominate in a given reaction in this energy range.  We have observed a smooth evolution in the MADs as a function of two categories of reaction parameters; this smooth evolution provides a first test of future dynamic models of reactions. E. Williams, Humboldt Kolleg, 1 September 2015

22. Mapping MADs for high angular momentum collisions E. Williams, Humboldt Kolleg, 1 September 2015 A new method of extracting more from experimental data

23. Means of creating this model  Start with experimental data  Define smooth trends in quasifission dynamics Fissility Coulomb repulsion Angular momentum  Then take into account the influence of shell effects on quasifission outcomes Magicity Collective structure Valence nucleon number  Work closely with theorists to develop models that provide insight into the physics driving quasifission probabilities E. Williams, Humboldt Kolleg, 1 September 2015 MAD Map

24. The angular momentum degree of freedom This is a difficult thing to study directly:  Each observation represents the sum of many reaction outcomes, reflecting the angular momentum distribution of the reaction in question.  We cannot select out reactions corresponding to a single angular momentum (L) value. But can we restrict the angular momentum range we examine, using observations from complementary reactions? E. Williams, Humboldt Kolleg, 1 September 2015

25. Complementary reactions We’ll define complementary reactions based on fusion angular momentum distributions. E. Williams, Humboldt Kolleg, 1 September 2015 CCFULL [1] No coupling a = 1 fm r 0 = 1 fm V B reproduced 52 Cr + 198 Pt (E lab = 264.8 MeV; E*=42.9 MeV) [1] K. Hagino, N. Rowley, and A.T. Kruppa, Comp. Phys. Comm. 123 (1999) 143

26. Complementary reactions We’ll define complementary reactions based on fusion angular momentum distributions. E. Williams, Humboldt Kolleg, 1 September 2015 CCFULL [1] No coupling a = 1 fm r 0 = 1 fm V B reproduced 52 Cr + 198 Pt (E lab = 264.8 MeV; E*=42.9 MeV) [1] K. Hagino, N. Rowley, and A.T. Kruppa, Comp. Phys. Comm. 123 (1999) 143 54 Cr + 196 Pt (E lab = 272.2 MeV; E*=42.3 MeV)

27. Complementary reactions We’ll define complementary reactions based on fusion angular momentum distributions. E. Williams, Humboldt Kolleg, 1 September 2015 CCFULL [1] No coupling a = 1 fm r 0 = 1 fm V B reproduced 52 Cr + 198 Pt (E lab = 264.8 MeV; E*=42.9 MeV) [1] K. Hagino, N. Rowley, and A.T. Kruppa, Comp. Phys. Comm. 123 (1999) 143 54 Cr + 196 Pt (E lab = 272.2 MeV; E*=42.3 MeV)

28. Complementary reactions E. Williams, Humboldt Kolleg, 1 September 2015 52 Cr + 198 Pt (E lab = 264.8 MeV; E*=42.9 MeV) [1] K. Hagino, N. Rowley, and A.T. Kruppa, Comp. Phys. Comm. 123 (1999) 143 54 Cr + 196 Pt (E lab = 272.2 MeV; E*=42.3 MeV)

29. Complementary reactions E. Williams, Humboldt Kolleg, 1 September 2015 52 Cr + 198 Pt (E lab = 264.8 MeV; E*=42.9 MeV) [1] K. Hagino, N. Rowley, and A.T. Kruppa, Comp. Phys. Comm. 123 (1999) 143 54 Cr + 196 Pt (E lab = 272.2 MeV; E*=42.3 MeV)

30. Complementary reactions E. Williams, Humboldt Kolleg, 1 September 2015 54 Cr + 196 Pt  250 Nb; E*~42.6 MeV Subtract the two complementary distributions to isolate the high angular momentum component: 52 Cr + 198 Pt (E lab = 264.8 MeV; E*=42.9 MeV) 54 Cr + 196 Pt (E lab = 272.2 MeV; E*=42.3 MeV)

31. Class 1Class 2Class 3 Primarily fusion- fission E. Williams, Humboldt Kolleg, 1 September 2015 Cr Pt Complementary reaction: -Same reaction (and therefore, same CN), different E*. -Same CN and E*, different projectile / target combinations leading to the same MAD class.

32. High angular momentum MAD E. Williams, Humboldt Kolleg, 1 September 2015 How can we use this concept to extract high angular momentum MADs? 52 Cr + 198 Pt (E lab = 264.8 MeV) 54 Cr + 196 Pt (E lab = 272.2 MeV)

33. High angular momentum MAD E. Williams, Humboldt Kolleg, 1 September 2015 MAD1: 52 Cr + 198 Pt (E lab = 264.8 MeV) MAD2: 54 Cr + 196 Pt (E lab = 272.2 MeV) MAD 2’ - MAD 1’ = ΔMAD

34. High angular momentum MAD E. Williams, Humboldt Kolleg, 1 September 2015 High angular momentum MAD Corresponding angular momentum distribution 54 Cr + 196 Pt  250 Nb; E*~42.6 MeV

35. Cr + Pt reaction energies E. Williams, Humboldt Kolleg, 1 September 2015 ANU 14UD tandem accelerator + LINAC + CUBE CUBE CNReactionE lab (MeV)E/V B E* (MeV) 250 Nb 52 Cr + 198 Pt264.841.0342.9 54 Cr + 196 Pt272.151.0642.3 52 Cr + 198 Pt272.671.0649.1 54 Cr + 196 Pt278.221.0847.0 52 Cr + 198 Pt276.851.0852.4 54 Cr + 196 Pt284.291.1051.8 52 Cr + 198 Pt282.851.1057.2 54 Cr + 196 Pt288.681.1255.2

36. Preliminary Mass-Angle Distributions (elastics / recoils excluded) E. Williams, Humboldt Kolleg, 1 September 2015

37. Preliminary Loss of efficiency due to pulse height in back detector X-position delay line Detector effects E. Williams, Humboldt Kolleg, 1 September 2015

38. Preliminary Loss of efficiency due to pulse height in back detector X-position delay line Exclusion of events due to poor front detector timing resolution Detector effects E. Williams, Humboldt Kolleg, 1 September 2015

39. Preliminary Mass-Angle Distributions (elastics / recoils excluded) E. Williams, Humboldt Kolleg, 1 September 2015

40. Preliminary CCFULL (no coupling, a = 1 fm, r 0 = 1 fm, V B reproduced) K. Hagino, N. Rowley, and A.T. Kruppa, Comp. Phys. Comm. 123 (1999) 143 High Angular Momentum Mass-Angle Distributions What can we learn from this? E. Williams, Humboldt Kolleg, 1 September 2015

41. A first estimate of timescales Ingredients: Reaction timescale determined by: Angular velocity ω = L/I  Angular momentum L  moment of inertia I Center-of-mass scattering angle θ c.m. θ i,f : ½ Coulomb deflection angles for the initial and final trajectories  Angle of rotation of the dinuclear system during reaction: Δθ = π-θ i -θ f -θ c.m  t rxn = Δθ/ω Mass equilibration: 1-exp(t rxn / τ m ), τ m ~ 5.2 zs [1] J. Tōke et al. Nucl. Phys. A 440, 327 (1985) [2] R. du Rietz et al. PRL 106, 052601 (2011) E. Williams, Humboldt Kolleg, 1 September 2015

42. Preliminary Moment of inertia – TDHF (tip collision): K. Vo-Phuok E. Williams, Humboldt Kolleg, 1 September 2015

43. Cr + Pt: Summary of findings Preliminary High angular momentum mass angle distributions have been extracted for reactions leading to 250 No Simple model suggests quasifission timescales decrease with increasing angular momentum Next steps:  Improve the model, cross check with TDHF  Apply method more broadly E. Williams, Humboldt Kolleg, 1 September 2015

44. Means of creating this model  Start with experimental data  Define smooth trends in quasifission dynamics Fissility Coulomb repulsion Angular momentum  Then take into account the influence of shell effects on quasifission outcomes Magicity Collective structure Valence nucleon number  Work closely with theorists to develop models that provide insight into the physics driving quasifission probabilities E. Williams, Humboldt Kolleg, 1 September 2015 MAD Map High angular momentum MADs

45. Entrance channel magicity, isospin: C. Simenel et al., PLB 710 (2012) 607 N/Z ratio: K. Hammerton et al., PRC 91 (2015) 041602 Shell effects: G. Mohanto et al., ANU, in preparation Additional measurements

46. Collaborators E. Williams, Humboldt Kolleg, 1 September 2015 Heavy Ion Accelerator Facility (HIAF) E. Williams, D.J. Hinde, C. Simenel, M. Dasgupta, A. Wakhle, I.P. Carter, K.J. Cook, D.Y. Jeung, D.H. Luong, G. Mohanto, C.S. Palshetkar, E. Prasad, D.C. Rafferty and R. du Rietz (ANU) The ANU Accelerator and Technical Staff Research made possible by the Australian Research Council Grants and Fellowships DP110102858, DP110102879, DP130101569, FL110100098, FT120100760, and DE140100784.

47. Thank you!

48. E. Williams, Humboldt Kolleg, 1 September 2015

49. ANU Experiments E. Williams, Humboldt Kolleg, 1 September 2015  Hinde et al., PRC 53 (1996) 1290  Rafiei et al., PRC 77 (2008) 024606  Thomas et al., PRC 77 (2008) 034610  Hinde et al., PRL 100 (2008) 202701  Hinde et al., PRL 101 (2008) 092701  du Rietz et al., PRL 106 (2011) 052701  Lin et al., PRC 85 (2012) 014611  Simenel et al., PLB 710 (2012) 607  Williams et al., PRC 88 (2013) 034611  du Rietz et al., PRC 88 (2013) 054618  Wakhle et al., PRL 113 (2014) 182502

50. Designed to study two-body fission. Composed of two large-area multiwire proportional counters (MWPC). MWPCs are position sensitive in X,Y coordinates. Position resolution: ~ 1mm Relative positions of the MWPCs can be adjusted to suit the experimental aims. Pulsed beam allows time-of- flight measurement. Resolution ~1 ns Angular coverage ~ 1.2π sr Hinde et al., PRC 53 (1996) 1290 Rafiei et al., PRC 77 (2008) 024606 Thomas et al., PRC 77 (2008) 034610 Williams50 The ANU CUBE detector

51. Hinde et al., PRC 53 (1996) 1290 Rafiei et al., PRC 77 (2008) 024606 Thomas et al., PRC 77 (2008) 034610 Position and time-of-flight information provide: -scattering angle θ C.M. in the center of mass frame, -differential cross sections, and -angular anisotropies. Williams The ANU CUBE detector 51

52. V1V1 V2V2 V 1cm V 2cm Hinde et al., PRC 53 (1996) 1290 Rafiei et al., PRC 77 (2008) 024606 Thomas et al., PRC 77 (2008) 034610 Kinematic coincidence: Position and time-of-flight information allow us to determine the mass ratio M R of the two fission fragments: M R1 = A F1 /(A F1 +A F2 ) = V 2cm /(V 1cm +V 2cm ) Williams The ANU CUBE detector 52