Mystery Spherical Source

This dummy source is a 3/8" diameter metal sphere (non-magnetic), with a hole drilled through the center. The hole is threaded. There are no markings on it of any kind. An XRF analysis reveals that the major constituents are nickel, chromium, molybdenum and cobalt. It was probably made radioactive by irradiation with neutrons rather than by filling an interior cavity with a radioactive material. My guess is that it is some sort of brachytherapy source, but that is pure speculation.