"An area of oak-pine wood was selected East of Upton, and a tower was constructed that could raise and lower a canister from underground that contained radioactive source material, allowing for controlled dosage levels that emanated in a radius from the tower. The canister contained Cesium-137, which would emit ionizing gamma radiation without making the surrounding area radioactive itself."

They said specifically that it were a cesium-137 source. I think the commentator is fair in pointing out that this finding is ultimately quite odd.