This project is demonstrating the use of an array of muon detectors, combined with gravity and seismic data, to map out subsurface density variations temporally and spatially (Figure 1). Beyond development and deployment of miniaturized muon tracking detectors for use in standard boreholes, the project is developing a rapid and efficient inversion method that takes into account not only the different muon paths, but also the data generated by other techniques, such as seismic and gravity.

The project team is designing and building a prototype muon borehole detector. Once built, the detector is to undergo a series of tests at the surface and underground both at PNNL and Los Alamos National Laboratory. Next, the borehole muon detector is encapsulated in a housing suitable for insertion into a borehole, the electronics and other systems re-designed to fit the housing requirements. Finally, the unit’s operation is to be verified in the laboratory and then at various depths in the borehole.

A working version of a chain of 10 to 25 detectors is envisioned as necessary to track the small changes in muon flux expected in real subsurface conditions. Ultimately, a chain of detectors will be installed and monitored in a borehole close to a reservoir for one year and the data will be recorded and analyzed.