infinite source thickness
For a specified @R05048@, the minimum thickness of a flat preparation of a @R05077@ material where the @I03072@ of the specified radiation at the surface does not increase when the thickness is increased by adding more of similar @R05077@ material.
PAC, 1982, 54, 1533. (Glossary of terms used in nuclear analytical chemistry (Provisional)) on page 1544 [Terms] [Paper]