Entrance channel effects on the quasifission reaction channel in Cr plus W systems

Background: Formation of a fully equilibrated compound nucleus is a critical step in the heavy-ion fusion reaction mechanism but can be hindered by orders of magnitude by quasifission, a process in which the dinuclear system breaks apart prior to full equilibration. To provide a complete description of heavy-ion fusion it is important to characterize the quasifission process. In particular, the impact of changing the neutron richness on the quasifission process is not well known. A previous study of Cr + W reactions at a constant 13 % above the Coulomb barrier concluded that an increase in neutron richness leads to a decrease in the prominence of the quasifission reaction channel. Purpose: The dynamics of quasifission for reactions with varying neutron richness was explored at a constant excitation energy, closer to the interaction barrier than the previous work, to see if the correlation between neutron richness and quasifission is valid at lower energies. Methods: Mass distributions were measured at the Australian National University for eight different combinations of Cr + W reactions, using the kinematic coincidence method. To eliminate the effect of differing excitation energies, measurements were made at beam energies chosen to give 52 MeV of excitation energy in all the compound nuclei. Results: A curvature parameter, describing the shape of the mass distributions, was determined for the fission-like fragment mass distributions for each reaction, and compared to various reaction parameters known to influence quasifission. Conclusions: The present work demonstrates that, at energies near the interaction barrier, the beam energy with respect to the barrier is as important as neutron-richness effects in determining the quasifission characteristics in these Cr + W reactions involving statically deformed target nuclei, and both are important considerations for future heavy and superheavy element production reactions.This work is supported by the National Science Foundation under Grants No. PHY-1102511 and No. IIA-1341088, by the U.S. Department of Energy under Grant No. DE-FG02-96ER40975 with Vanderbilt University, and the Australian Research Council Grants No. DP160101254, No. DP170102318, No. DP140101337, No. FL110100098, No. DP130101569, No. FT120100760, and No. DE140100784. This material is based upon work supported by the Department of Energy National Nuclear Security Administration through the Nuclear Science and Security Consortium under Award No. DE-NA0000979

Unified State Model theory and application in astrodynamics

The Unified State Model is a method for expressing orbits using a set of seven elements. The elements consist of a quaternion and three parameters based on the velocity hodograph. A complete derivation of the original model is given in addition to two proposed modifications. Both modifications reduce the number of state elements from seven to six by replacing the quaternion with either modified Rodrigues parameters or the Exponential Map. Numerical simulations comparing the original Unified StateModel, the Unified State Model with modified Rodrigues parameters, and the Unified State Model with Exponential Map, with the traditional Cartesian coordinates have been carried out. The Unified StateModel and its derivatives outperform the Cartesian coordinates for all orbit cases in terms of accuracy and computational speed, except for highly eccentric perturbed orbits. The performance of the Unified State Model is exceptionally better for the case of orbits with continuous lowthrust propulsion with CPU simulation time being an order of magnitude lower than for the simulation using Cartesian coordinates. This makes the Unified State Model an excellent state propagator for mission optimizations.Aerospace Engineerin