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Background: The formation of superheavy elements by fusion of two massive nuclei is severely inhibited by the competing quasifission process. Purpose: Through extensive mass-angle distribution measurements, we map out the systematic dependence of quasifission characteristics as a function of the identity of the colliding nuclei. Methods: The Australian National University's Heavy Ion Accelerator Facility and CUBE spectrometer have been used to measure mass-angle distributions for 42 reactions forming heavy elements. Beam energies above their respective capture barriers were used to minimize the known influence of nuclear structure effects. Results: Different mappings of mass-angle distribution characteristics (including timescales) over the nuclear landscape show a systematic dependence on entrance channel and compound nucleus fissilities. Conclusions: The results provide an empirical baseline to assess effects of nuclear structure at lower beam energies, and motivate the testing and validation of complete dynamical models of heavy element fusion through comparison of mass-angle distributions.

The quasi-fission mechanism hinders fusion in heavy systems through breakup within zeptoseconds into two fragments with partial mass equilibration. Its dependence on the structure of both the collision partners and the final fragments is a key question. Our original approach is to combine an experimental measurement of the fragments' mass-angle correlations in 40 Ca+ 238 U with microscopic quantum calculations. We demonstrate an unexpected interplay between the orientation of the prolate deformed 238 U with quantum shell effects in the fragments. In particular, calculations show that only collisions with the tip of 238 U produce quasi-fission fragments in the magic Z = 82 region, whilst collisions with the side are the only one which may result in fusion.In the late 70's, Heusch and collaborators measured fission characteristics in heavy-ion collisions which could not be reconciled with the statistical decay of a compound nucleus [1]. Later, the angular anisotropy of the fission fragments was found to be much larger than that predicted by the statistical model in some reactions [2,3], which was taken as a clear signature for an out-ofequilibrium process.The origin of these characteristics is understood to be a process known as quasi-fission. Here the dinuclear system fissions before reaching the stage of an equilibrated compound nucleus [3]. Quasi-fission thus results in fusion hindrance in reactions forming heavy nuclei [4][5][6]. In fact, this is by far the dominant mechanism suppressing the formation of super-heavy elements. The understanding of this process is thus crucial in order to optimise the formation of new heavy and superheavy nuclei.Since the discovery of quasi-fission, important progress has been made thanks to extensive experimental studies [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24]. Correlations between the mass and the angles of the fragments show that quasi-fission often takes place before a full rotation of the di-nuclear system, that is, with typical contact times between the fragments of 5 to 10 zs [7,8,17]. The characteristics of the entrance channel -in particular, the deformation [10,11,[13][14][15] and shell structure [21] of the collision partners as well as the fissility of the system [19,22] and its energy [15,20] were shown to play an important role. Shell effects could also favor the production of fragments in the vicinity of magic nuclei [12,15,16,[24][25][26].The complex interplay of all these variables that have been identified by experiments dictates quasi-fission characteristics and probability, and hence the suppression of fusion. To understand the dynamics at play, in particular the inter-dependency of these variables, it is necessary to perform theoretical calculations. Classical dynamical models have been developed where the system is described as a viscous fluid evolving through a family of parametrised shapes [27][28][29][30][31][32]. Despite their ability to reproduce some experimental observables, these approaches require parameters, such as t...

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