THE MAGNESIUM FREQUENCY STANDARD

We report a complete description of a frequency standard based on the P-3(1) - P-3(0) Mg-24 transition at 601 GHz; in particular the metasta ble atomic source, the Ramsey-type interaction region, the submillimet ric frequency synthesizer and the frequency-control loop are described both theoretically and experimentally. The main experimental results concerning the operation of the atomic beam, the Ramsey signal intensi ty and width versus some important parameters and the signal-to-noise ratio, with and without optical pumping, are reported and compared wit h theoretical predictions. The clock transition frequency has been mea sured with respect to UTC (IEN) with an uncertainty of +/- 1 x 10(-12) ; at present the frequency instability reaches the value of 2 x 10(-13 ) for counting times of 3 000 s and the repeatability the level of 3 x 10(-13). The accuracy budget is also reported and discussed as are po ssible improvements of the present prototype.