Feasibility of Sea-level Cosmic-Ray Muon-Capture SNM Detection

The first part of this report argues the average time between signal events for X-rays from negative muon capture on SNM is from a few to a few 10's of minutes, depending on how sophisticated one care's to make the detector. The second part of this report argues that the recoil proton background in the energy resolution window can be orders of magnitude larger than the expected signal. How could one evade this result? Firstly, one could conceive of a very highly segmented muon counter (or electromagnetic calorimeter) system to actually detect a stopping muon. This would be extraordinarily expensive for a large area and volume of a cargo container. There are also quite a few assumptions we applied to make the calculations tractable. For instance, we assumed the detector was fully efficient for a neutron recoil. probably something like 25% or 50% is more appropriate. However, probably the biggest uncertainty is the neutron energy spectrum. The Boehm et al. paper discusses the range of spectrum parameterizations, some of which are considerably softer and will lower the high-energy proton yield. This outcome is certainly possible. However, given the difference between signal and background rates, it would take a considerable change in detector parameters and particle yields to change the basic conclusion that this technique does not appear promising