Advanced UXO Discrimination using Magnetometry: Understanding Remanent Magnetization
Draft final technical rept. 2004-2009
SKY RESEARCH INC ASHLAND OR
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The use of apparent magnetic remanence to prioritize the digging order at sites contaminated by unexploded ordnance was investigated. A mobile device for measuring the magnetic remanence of field samples was constructed and deployed to two field sites and to make before firing and after impact measurements of 81 mm mortars at a test facility. Results from the field sites indicated that most, but not all, excavated ordnance items had small remanent magnetization, suggesting that shock demagnetization occurs. The controlled firing tests proved that shock demagnetization occurred and also demonstrated that initially demagnetized rounds acquire a remanent magnetization in the direction of the inducing field at the time of impact. Shock demagnetization of highly magnetized 81 mm mortars was not sufficient to guarantee the success of a ranking scheme based on apparent remanence, so we conclude that the method should not be used if 100 recovered of detected UXO is required. Apparent remanence does provide an efficient ranking scheme for recovery of 95 of UXO. Measurements of the magnetic viscosity of steel samples revealed that magnetic remanence is stable on time-scales of at least 1000 years and is not a significant factor that needs to be considered from a discrimination perspective.
- Ammunition and Explosives
- Electricity and Magnetism