Abstract: A method and apparatus for adding minute quantities of radioactive material to frac material, acid material, cement squeezes, or the like, being pumped underground which includes providing a filler material or carrier having a minor portion of radioactive material distributed evenly therethrough, providing a lead shielded container having a variable volume chamber for the filler having the radioactive material and progressively decreasing the chamber volume at a predetermined rate to meter outflow of the filler with radioactive material from the container and into the line carrying the material being pumped underground. The rate of metering is such as to provide the desired concentration of radioactive material relative to the flow rate of material being pumped underground. The filler with the radioactive material is preferrably a solid plug and a grinder is used to progressively grind material at a selected rate from the leading end of the plug into particles of selected size.