The relative merits of atomic frequency standards

The relative merits of atomic frequency standards based upon resonances in hydrogen, rubidium, or cesium depend upon the particular application and the specific requirement for each of several performance factors combined with physical characteristics. While the properties of an ideal atomic frequency standard may be established, practical instruments depart from the ideal as the result of compromises in the apparatus design and construction. The resonance line sharpness is an important factor which is dependent upon the apparatus; however, others my have a greater influence upon the essential characteristics. These include instrumental offsets due to atomic collisions with neighboring atoms or walls and magnetic fields. The intensity of the resonance signal is also essential in the determination of merit. These factors are discussed in relationship to hydrogen maser rubidium gas cell and cesium beam atomic frequency standards and the merits of each are compared. The possible merits of frequency standards based upon thallium beams are also discussed; however, a lack of extensive operating experience limits the knowledge in this case.