The Born-Oppenheimer approximation, which allows approximate decomposition of atomic wavefunctions, depends on the relative "slow" motion of these entities. The subclass of mesons known as pions mediates the attractive forces within it, which is sometimes known as the residual strong force. This entity's discovery disproved J.J. Thomson's Plum Pudding model and came about by the unexpected scattering of decaying radium by gold foil in the Rutherford Experiment. For 10 points, name this region of the atom which can split or merge in its fission 
The Born-Oppenheimer approximation, which allows approximate decomposition of atomic wavefunctions, depends on the relative "slow" motion of these entities. The subclass of mesons known as pions mediates the attractive forces within it, which is sometimes known as the residual strong force. This entity's discovery disproved J.J. Thomson's Plum Pudding model and came about by the unexpected scattering of decaying radium by gold foil in the Rutherford Experiment. For 10 points, name this region of the atom which can split or merge in its fission or fusion, also known as an alpha particle in the context of helium that consists of protons and neutrons.
The Born-Oppenheimer approximation, which allows approximate decomposition of atomic wavefunctions, depends on the relative "slow" motion of these entities.
atomic nucleus