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

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

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

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

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

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

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

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

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

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 = 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

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

 (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) MADs: Mass equilibration and rotation Slide courtesy of D. J. Hinde

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, (2011) E. Williams, Humboldt Kolleg, 1 September 2015

QF Timescales 5x s 10x s >> 10x s 186 W Experimental MAD Simulated MAD R. du Rietz et al. PRL 106 (2011) MAD1MAD2MAD3

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).

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

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

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

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

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

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 ~ 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

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

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

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

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 Pt (E lab = MeV; E*=42.9 MeV) [1] K. Hagino, N. Rowley, and A.T. Kruppa, Comp. Phys. Comm. 123 (1999) 143

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 Pt (E lab = MeV; E*=42.9 MeV) [1] K. Hagino, N. Rowley, and A.T. Kruppa, Comp. Phys. Comm. 123 (1999) Cr Pt (E lab = MeV; E*=42.3 MeV)

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 Pt (E lab = MeV; E*=42.9 MeV) [1] K. Hagino, N. Rowley, and A.T. Kruppa, Comp. Phys. Comm. 123 (1999) Cr Pt (E lab = MeV; E*=42.3 MeV)

Complementary reactions E. Williams, Humboldt Kolleg, 1 September Cr Pt (E lab = MeV; E*=42.9 MeV) [1] K. Hagino, N. Rowley, and A.T. Kruppa, Comp. Phys. Comm. 123 (1999) Cr Pt (E lab = MeV; E*=42.3 MeV)

Complementary reactions E. Williams, Humboldt Kolleg, 1 September Cr Pt (E lab = MeV; E*=42.9 MeV) [1] K. Hagino, N. Rowley, and A.T. Kruppa, Comp. Phys. Comm. 123 (1999) Cr Pt (E lab = MeV; E*=42.3 MeV)

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

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.

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 Pt (E lab = MeV) 54 Cr Pt (E lab = MeV)

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

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

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 Pt Cr Pt Cr Pt Cr Pt Cr Pt Cr Pt Cr Pt Cr Pt

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

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

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

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

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

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, (2011) E. Williams, Humboldt Kolleg, 1 September 2015

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

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

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

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

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 DP , DP , DP , FL , FT , and DE

Thank you!

E. Williams, Humboldt Kolleg, 1 September 2015

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

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) Thomas et al., PRC 77 (2008) Williams50 The ANU CUBE detector

Hinde et al., PRC 53 (1996) 1290 Rafiei et al., PRC 77 (2008) Thomas et al., PRC 77 (2008) 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

V1V1 V2V2 V 1cm V 2cm Hinde et al., PRC 53 (1996) 1290 Rafiei et al., PRC 77 (2008) Thomas et al., PRC 77 (2008) 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