To get a clearer picture, physicists in recent years have inverted the traditional setup: By aiming a beam of nuclei, or ions, at a target of protons, scientists can not only directly measure the knocked out protons and neutrons, but also compare the original nucleus with the residual nucleus, or nuclear fragment, after it has interacted with a target proton. But protons are also more complex, and made of quarks and gluons, the interactions of which can muddy the final interpretation of the nucleus itself. Scientists also use beams of protons instead of electrons to probe nuclei, as protons are comparably larger and more likely to hit their target. To increase this probability, beams are loaded with ever-higher electron densities. The probability that an electron will hit a nucleus is relatively low, given that a single electron is vanishingly small in comparison to an entire nucleus. While electron scattering is a precise way to reconstruct a nucleus’ structure, it is also a game of chance. Researchers measure the energy of the electron beam before and after this interaction to calculate the original energies of the protons and neutrons that were kicked away. When an electron hits a nucleus, it knocks out protons and neutrons, and the electron loses energy in the process. Particle accelerators typically probe nuclear structures through electron scattering, in which high-energy electrons are beamed at a stationary cloud of target nuclei. Hen’s co-authors include Jullian Kahlbow and Efrain Segarra of MIT, Eli Piasetzky of Tel-Aviv University, and researchers from Technical University of Darmstadt, the Joint Institute for Nuclear Research (JINR) in Russia, the French Alternative Energies and Atomic Energy Commission (CEA), and the GSI Helmholtz Center for Heavy Ion Research in Germany. “That gets us closer to understanding such exotic astrophysical phenomena.” “We’ve opened the door for studying SRC pairs, not only in stable nuclei but also in neutron-rich nuclei that are very abundant in environments like neutron star mergers,” says study co-author Or Hen, assistant professor of physics at MIT. The results, published today in Nature Physics, demonstrate that inverse kinematics may be used to characterize the structure of more unstable nuclei - essential ingredients scientists can use to understand the dynamics of neutron stars and the processes by which they generate heavy elements. These are pairs of protons or neutrons that briefly bind to form super-dense droplets of nuclear matter and that are thought to dominate the ultradense environments in neutron stars. The team used this “inverse kinematics” approach to sift out the messy, quantum mechanical influences within a nucleus, to provide a clear view of a nucleus’ protons and neutrons, as well as its short-range correlated (SRC) pairs. The experiment is an inversion of the usual particle accelerators, which hurl electrons at atomic nuclei to probe their structures. Physicists at MIT and elsewhere are blasting beams of ions at clouds of protons -like throwing nuclear darts at the speed of light - to map the structure of an atom’s nucleus.
0 kommentar(er)
