To provide an usage of a hard ray sensor which can detect any feeble hard ray, etc. at high resolution, for example, a method for accurately valuating such natural resources as crude oil or natural gas in the earth.

The implant valuation method is characterized by that it comprises a detection step wherein a radiation detector placed opposite a hard ray source radiating 1st hard rays is used to detect both 2nd hard rays which permeated the above implant among the above 1st hard rays and 3rd hard rays which have not permeated the implant, and a valuation step to valuate the implant on the basis of both the above 1st and second hard ray intensities detected by the radiation detector.