Beam Resonance Measurements of Atomic Quadrupole Moments
The starting point for this work is the well-known multipole expansion of the interaction between a charge distribution and an externally applied electrostatic field. For an atom in a laboratory field the expansion converges rapidly since it is a power series in the ratio of the size of the atom to the dimensions of the electrodes producing the field. A further simplification occurs when the field is sufficiently weak that it can be treated in first order because then the odd order multipoles vanish for reasons of parity and time-reversal symmetry. In addition, the monopole term is zero because an atom has no net charge. It follows that not only is the quadrupole moment the first non-vanishing multipole moment for an atom, it is also the only one which it is possible to measure directly through its interaction with a laboratory applied field.
KeywordsQuadrupole Moment Electric Field Gradient Quadrupole Interaction Central Field Beam Resonance
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