- See Example 2.6.4:Use Electrostatics to estimate how small a gold nucleus must be to backscatter
a 5.5 MeV alpha particle.*
This brought up a new problem. The atomic size was known from several types of experiments.
Ifelectrons orbit around the atomic nucleus, according to Maxwell’s equations, they should
radiate energyas they accelerate. This radiation is not observed and the ground states of atoms
are stable.
In Quantum Mechanics, thelocalization of the electron around a nucleus is limited because
of the wave nature of the electron. For hydrogen, where there is no multi-body problem to make
the calculation needlessly difficult, the energy levels can be calculatedvery accurately. Hydrogen
was used to test Quantum Mechanics as it developed. We will also use hydrogen a great deal in this
course.
Scattering of the high energyαparticles allowed Rutherford to“see” inside the atomand deter-
mine that the atomic nucleus is very small. (He probably destroyed allthe atoms he “saw”.) The
figure below shows Rutherford’s angular distribution in his scattering experiment along with several
subsequent uses of the same technique, with higher and higher energy particles. We see Rutherford’s
discovery of thetiny nucleus, the discovery ofnuclear structure, the discovery of a point-like
proton inside the nucleus, the discovery ofproton structure, the discovery ofquarks inside
the proton, and finally the lack of discovery, so far, of anyquark structure.