Muon Attenuation Budgets for Internal Low-Density Zones in a Concrete Gravity Dam

This paper computes the muon attenuation, exposure and resolution budget for imaging a concrete gravity dam with cosmic-ray muons. Sight lines through 45 metres of mass concrete at a density of 2.35 grams per cubic centimetre present an opacity of 1.058e+04 grams per square centimetre (105.8 metres of water equivalent), which sets a minimum muon energy of 21.55 GeV and a transmitted vertical intensity of 0.5362 per square metre per second per steradian. For a detector of 1 square metres with the stated acceptance and efficiency, divided among 160 image elements, the stated feature produces a flux contrast of 0.3136 and reaches five standard deviations in 1.951 days of counting, while the target precision of 0.04 per image element requires 4.796 days. A deployment of 150 days delivers a per-element precision of 0.007153, corresponding to a thickness sensitivity of 0.3219 metres. The combined angular resolution is 15.58 milliradians, of which tracking contributes 1.768 milliradians and multiple scattering at the threshold momentum 15.48 milliradians. The budget is compared with published muography of the same class of target, for which muon imaging trials on dam and embankment structures have reported sensitivity to internal density variation and water-content changes in the dam body. Every number is computed by the accompanying script from the stated inputs. Computed, not measured.