弱磁场中质子的自由进动和一个野外测磁场的实验

本文报导了我们在弱场中进行的核矩预极化和核矩自由进动的实验和分析。主要研究了极化磁场衰减过程中核矩的运动、讯号的绝对强度,并观察到探头转动对讯号频率的影响,指出了这是测核磁矩正负号的最直接的方法。此外,弱磁场中质子自由进动现象在高空磁场测量、地质探矿、石油开采等方面都有重要的实际应用,本文的结果对解决这些应用中的具体问题是有帮助的。为了检验全套仪器在野外工作时的性能,以及观察周围大体积的磁性物质对讯号频率的影响,我们在野外进行了一系列的测磁实验,获得了肯定的结果。测磁的相对精密度达到1×10^-5。

AN EXPERIMENTAL STUDY OF PROTON FREE PRECESSION IN A WEAK MAGNETIC FIELD AND ITS APPLICATION TO FIELD WORK

A Packard-Varian type experiment was done, in which the free precession of proton magnetic moment about a very weak magnetic field was observed, by first lining up the protons in an aqueous sample with a separate magnetic field and then allowing them to execute the free precession. In out experiment the studies on the non-adiabatic process of withdrawing the polarizing field, the absolute value of the signal strength and the reduction of sample size to minimize the effect of inhomogeneity of the magnetic field were emphasized. The effect of rotating the sample coil upon the measured signal frequency was also noted, and it is pointed out that this is the most direct way to determine the sign of the nuclear magnetic moment.The phenomenon of proton free precession in weak magnetic field has important practical applications in earth's magnetic field measurement at high altitudes, in geological prospecting, and in petroleum recovery from oilfield rocks. The present studies may be helpful in solving the problems likely to occur in these applications.In order to check the performance of the entire experimental set-up for field works, and especially to investigate the influence of magnetic substances in surroundings on the signal frequency, a series of experiments was carried out on a lake. Affirmative results were obtained. The relative accuracy of the measurement of the precessional signal frequency, which in turn determines the magnetic field strength, is 1×10^-5.