The Confinement of Particles in Fields

The development of atomic standards based on quantum resonance in neutral atoms confined by diffusion through a buffer gas, or collisions with inert walls, culminated in the hydrogen maser, a standard of astonishingly high stability. However, as explained in the last chapter, for certain applications the hydrogen maser suffers from two deficiencies: First, its lack of portability due to its size and the need for elaborate magnetic shielding, and second, a wall shift that limits its absolute accuracy, and disqualifies it as a primary standard.