THE PROTON PRECESSION MAGNETOMETERThe proton precession magnetometer is most commonly used for terrestrial magnetic surveys. This magnetometer only measures the total amplitude (size) of the Earth's magnetic field. Usually these types of measurements are called total field measurements. The proton precession magnetometer is so named because it uses the precession of rotating protons or hydrogen atom nuclei in a hydrocarbon fluid sample to measure the total magnetic intensity. The sensor component is a cylindrical container filled with a liquid rich in hydrogen atoms surrounded by a coil. Kerosene, alcohol and water are the commonly used liquids. When the switch closes, a direct current from the battery is directed through the coil, producing a relatively strong magnetic field in the liquid-filled cylinder. The hydrogen nuclei (protons) behave like tiny rotating dipole magnets and align themselves in the direction of the applied field (i.e. along the axis of the cylinder). When opening the switch, the power to the coil is cut off, since the earth's magnetic field generates torque on the aligned and rotating hydrogen cores, they begin to precede in the direction of the total field terrestrial. As the protons precess, the precession produces a time-varying magnetic field that induces a small alternating current in the coil such that the frequency of precession of the nuclei equals the frequency of the alternating current. Proton precession measures the frequency of the oscillating field and since it is equal to the proton precession frequency, it can be used to determine the strength of the external field. the constant of proportionality which relates frequency to field intensity is a well-known atomic constant. The gy...... middle of paper ...... exhibits the pattern generally common to a small magnet, as shown below in Figure 1. The direction of the field lines at the equator are horizontal while at the north and south magnetic poles they are vertical. This geometry is important in the interpretation of magnetic anomalies. The total intensity of the Earth's field is not perfectly asymmetrical with respect to the geographic north pole, for example the north magnetic pole in the north. Canada is more than 1,000 miles from the geographic pole. The Earth cannot be represented exactly by a single bar magnet, but it has many higher order poles and anomalous features on a very large scale due to the unknown characteristics of the generating mechanism in the Earth's core. As shown in Figure 1, the solar wind or constant flow of particles and electric currents from the sun distort the field lines. The deviation from the asymmetric field is the abnormal set of characteristics in the