MEASURING LOW MAGNETIC FIELDS
VARIAN ASSOCIATES INC PALO ALTO CA
Pagination or Media Count:
A theoretical investigation was made of the ways of measuring small changes in the earths magnetic field by means of paramagnetic resonance methods. The effects of line shape, sensitivity of the apparatus, geometry, and the chemical and physical properties of the sample were also studied. All of these considerations indicated the desirability of a paramagnetic substance in which the line width is narrow. The advantage of a narrow line width are given and include 1 symmetry of the line shape about resonance, and 2 the perturbations on the shape of the line which result from geometric effects motion of the probe relative to the earths field. The perturbations are generally proportional to the line width, and the narrower widths imply smaller perturbations for a given effect. The use of a simple cross-coil probe was found to be impractical because of very serious directional effects. The effects may be minimized by the use of 2 cross-coil systems in series. The directional effects in single coil systems are not serious and are due to chiefly to sensitivity changes in the apparatus. The study indicated that a magnetic air- borne detector employing paramagnetic resonance can be designed to detect changes in the earths field of the order of 0.1 gamma which will be insensitive to changes in orientation with respect to the direction of the field provided that certain conditions are meet. These conditions include the possibility of making samples of solutions of metal-in-ammonia 100 cc or more in volume which have 1 line widths of about 3000 gamma 2 low electrical conductivity and long life and 3 the ability to withstand the internal pressure of the liquid ammonia.
- Electricity and Magnetism
- Magnetic and Electric Field Detection and Detectors