Prior to the Bethe-Bloch formula, this man derived a classical expression for the stopping power which is proportional to the log of the ratio of maximum to minimum impact parameter.
Prior to the Bethe-Bloch formula, this man derived a classical expression for the stopping power which is proportional to the log of the ratio of maximum to minimum impact parameter. He's the first namesake of the theorem which states that for confined classical systems, magnetic susceptibility will be zero. He's the first namesake of a condition which states that the phase space integral of p dq equals n times h, implying that allowed orbits have action which is an (*) integer multiple of Planck's constant. Electron charge times h bar over two times electron mass is equal to a unit of magnetic moment named for him, and he names another unit which is equal to h bar over electron mass times speed of light times the fine structure constant. For 10 points, name this Danish physicist whose radius describes the distance between the proton and electron in the ground state. 
Prior to the Bethe-Bloch formula, this man derived a classical expression for the stopping power which is proportional to the log of the ratio of maximum to minimum impact parameter.
Niels Bohr [with van Leeuwan, and Sommerfeld, respectively] 