Talk:Gamma ray logging

"These elements are used for two reasons, first they have a radioactive half life similar to the age of the earth, so even relatively old material (shale and clay) continue to emit radiation. Second, these three elements are more common in shales than in sand, which means an area with a lower gamma ray count is likely to be a sand."
 * The above is not accurate. Gamma detectors are affected by whatever gamma sources are in the rock, and these are the decay chains that are present in geologic materials.  Plazak 19:48, 6 April 2007 (UTC)