Radioisotope Decay Rate Based Counting Clock

Abstract

Precise timing and frequency sources are vital in a wide range electronic-based systems such as communication networks and global positioning systems. These applications constantly demand reductions in size, weight and power (SWaP) while improving the precision of time or frequency references. Historically, clocks based on electromagnetic oscillations of atoms have provided the most precise method of timing events lasting longer than a few minutes.These oscillations are so precise that in 1967 the unit of time the second – was redefined to be the time taken for a Cs atom in a particular quantum state to undergo exactly 9,192,631,770 oscillations. While the long-term precision of atomic clocks is unsurpassed, the size and power required to run these devices has prevented their use in a variety of areas, particularly in those applications requiring portability or battery operation. The NIST 17 F-1 primary standard, for example, occupies a large optical table and requires many hundreds of watts to operate. The state-of-the-art in compact commercial atomic frequency references are Rb vapor-cell devices with volumes near 100 cm³ that operate on a few tens of watts of power and cost about 1–3 thousand dollars.The long-term stability of atomic clocks including is based onthe ability to interrogate a fundamental time constant – the hyperfine resonance frequency of ground level transitions¹. It is thus natural to extend this idea of interrogating other time constants to realize clocks with good long-term stabilities.