Detection of unexploded ordnance by PGNAA based borehole-logging
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Detection of unexploded ordnance by PGNAA based borehole-logging John Kettler • Eric Mauerhofer • Marco Steinbusch
Received: 20 August 2012 / Published online: 14 September 2012 Ó Akade´miai Kiado´, Budapest, Hungary 2012
Abstract The performance of a borehole-logging system, based on prompt-gamma-neutron-activation-analysis (PGNAA), for explosive detection was studied by Monte-Carlo simulations. The prompt gamma of nitrogen, which is a constituent of common explosive, was used to identify the unexploded ordnance (UXO). Our results show that the minimum counting time depends on the soil moisture, the cladding thickness and the explosive composition. In conjunction with the standard detection by magnetometry, the PGNAA is a promising analytical technique for definitive identification of deep buried UXOs. Keywords PGNAA Borehole-logging Explosive Prompt gamma MCNP UXO Abbrevitations PGNAA Prompt gamma neutron activation analysis UXO Unexploded ordnance
Introduction During the Second World War about 2 million tons of bombs were dropped on military, industrial and urban area
J. Kettler (&) E. Mauerhofer M. Steinbusch Institute of Energy and Climate Research, Nuclear Waste Management and Reactor Safety, Research Centre Ju¨lich GmbH, Ju¨lich, Germany e-mail: [email protected] J. Kettler Institute of Nuclear Fuel Cycle, RWTH-Aachen University, Aachen, Germany
of Germany. However not all bombs exploded, due probably to a dysfunction the detonator and the percentage of unexploded ordnance (UXO) is estimated to range between 5 and 15 % of the total amount of dropped bombs corresponding to 100,000–300,000 tons of bombs. More than 67 years after the end of World War II, UXOs represent still a danger for the population and their detection is routine in Germany. Each year, more than 2,000 tons of American and British aircraft bombs and all sorts of munitions ranging from German hand grenades and tank mines to Russian artillery shells are recovered in the whole part of Germany. While near surface UXOs are easy to detect and to recover, the location of UXOs buried at depths larger than 3 m requires sophisticated techniques and their baring is time and cost consuming. The detection of deep buried UXOs is commonly achieved by boreholelogging magnetometry, which is based on the measurement of the perturbation of the earth magnetic field through ferrous material i.e. the bomb cladding [1]. Hereby the position of an UXO can be determined with an accuracy of about 20 cm, but not its orientation and inclination in the soil. However, the borehole-logging magnetometry has a major disadvantage in that the discrimination between UXOs and other non-hazardous ferromagnetic metallic objects like pipelines cannot be performed since the presence of explosive cannot be assessed by this technique. Thus, a prerequisite to avoid the time and cost-intensive baring of non-hazardous artefacts is the direct detection of the explosive in the deep buried UXO. Explosives may be assayed non-destructively by prompt-gamma-neutron-act
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