Elementary particle quarks—now considered elementary particles. And within a molecule, the electron's three degrees of freedom (charge, spin, orbital) can separate via the wavefunction into three quasiparticles (holon, spinon, orbiton). Yet a free electron—which is not orbiting an atomic nucleus and lacks orbital motion—appears unsplittable and remains regarded as an elementary particle. Around 1980, an elementary particle's status as indeed elementary—an "ultimate constituent" of substance—was mostly discarded for a more practical outlook, embodied in particle physics' Standard Model, what's known as science's most experimentally successful theory. Many elaborations upon and theories beyond the Standard Model, including the popular supersymmetry, double the number
Atomic recoil recoil, when momentum transfers to the atomic nucleus as whole. In some cases, quantum effects can forbid momentum transfer to an individual nucleus, and momentum is transferred to the crystal lattice as a whole (see Mössbauer effect). Atomic recoil Atomic recoil is the result of the interaction of an atom with an energetic elementary particle, when the momentum of the interacting particle is transferred to the atom as whole without altering non-translational degrees of freedom of the atom. It is a purely quantum phenomenon. Atomic recoil was discovered by Harriet Brooks, Canada's first female nuclear physicist. If the transferred momentum