In Physical Review Letters, the researchers describe using “fully microscopic approaches” to observe and measure collisions of different kinds of nuclei. Their goal: quantify the energy and time these exchanges take in order to better understand how they affect quantum phenomena like dissipation, which is how, and how much, energy leaves a reaction.
The scientists modeled 13 pairs of nuclei and studied 600 kinds of interactions.
Since part of quantum mechanics involves how the physical interactions of particles cause them to behave erratically or otherwise, the relative magnitude of nuclear reactions can help researchers categorize the reactions by energy required and other parameters based on that timing. They found a tenfold difference in time—a zeptosecond versus 20 zeptoseconds, basically—between larger nuclear exchanges and smaller motions.
Colliding the pairs of nuclei made them break apart in a realistic way, and the size of the pieces (“fragments”) determined the speed and magnitude of the subsequent interaction. This is one reason the time frames were so broadly distributed: Sometimes what happened was just a tiny nick, and sometimes the two nuclei collided head on and exchanged much larger amounts of particulate.
“First, the protons and neutrons swap between the newly-united fragments, in order to equalise their neutron-to-proton ratio. Known as charge equilibration, the calculations showed this is the fastest process, taking only one zeptosecond,” Cosmosexplains.
Mass equilibration, with much more flow and exchange, took 20 times longer. And while these times varied greatly between different nuclear processes, the time didn’t vary by which element was at play. Any combination of element nuclei took the same time for the same process.
A project at Vienna University of Technology is using a similar methodology, combining an electron microscope with a supercomputer molecule simulation in order to understand what’s happening in a different kind of reaction: surface wear on metals. Both computer simulations involve powerful modeling of complex processes that are too tiny for scientists to meaningfully examine in realtime.