Abstract: Method and apparatus for enabling fluid material contained in a package to be examined in a non-destructive manner to see whether there is any unacceptable alteration in the material. This examination is accomplished by shaking the package so that the package and its contents vibrate at the natural resonance frequency thereof, exposing the package to an irradiation of ultra-soft X-ray beams while the package is vibrating at the resonant frequency, either immediately after the package contents begin to be agitated by shaking or immediately after the vibration is stopped and it ceases to be agitated, detecting the strength of X-rays transmitted through the package and its contents, coverting the transmitted X-rays to a corresponding analog signal, and determining any alteration by comparing the analog signal against the refernece signal previously obtained in the same manner as described above for a like package with unaltered contents.