Scaling of muon remote sensing signals

Few hundred MeV muon beams can penetrate vessels, detect nuclear materials, and differentiate between them from distances of several hundred meters. A companion report provides point estimates of the beam and detector parameters required to do so. This note varies the most sensitive parameters to examine performance over a range of scenarios. In the process it examines the results of the IDA analysis of muon interrogation, finding no serious discrepancies in the cases and parameters it examined, although some parameters are admittedly somewhat arbitrary. This note concentrates on the sensitivity of performance to beam size and to signature path length in targets, i.e., the sizes of the targets and vessels. The main results are shown in the figures. The companion report provides a useful framework for analysis, although it concentrates on a few, perhaps atypical examples. This note uses that framework to explore the beam and standoff requirements for a wider range of engagements. It primarily studies the impact of beam radius and area at varying and constant and fixed dose, and varying vessel thickness. The first two figures show quite distinct variations of signal gammas, background levels, and signal to noise ratios, but their main result is that the signal to noise ratios greater than unity essential for practical application can be achieved at beam radii up to about 1 m. Imposition of required dose limits in Fig. 2 has little impact on that result. The third figure indicates that adequate signal to noise ratios are achievable for thicknesses up to 4-5 m. Those ranges could be improved by smaller beams and other improvements, but exploring them in detail should probably await the improvement of the elements of the model that are stressed for thicker vessels.