Reference Radiographs are nondestructive testing standards universally accepted because of their high reliability in accept-reject actions.
Guide for Equivalent Pentrameter Sensitivity Between X-rays and Cobalt-60 (8 radiographs - 6 x-rays, 2 Co-60)
Adjunct to E592 Guide to Obtainable ASTM Equivalent Penetrameter Sensitivity for Radiography of Steel Plates 1/4 to 2 in. (6 to 51 mm) Thick with X Rays and 1 to 6 in. (25 to 152 mm) Thick with Cobalt-60