Posted on January 19, 2016January 26, 2016 by Steve Norris LESSON 1 – HISTORY OF X-RAYS TOPIC 1_6 MATERIAL GROUPS BASED ON ATOMIC Z NUMBER Lesson Progress 0% Complete https://rcexraytraining.com/rce/wp-content/uploads/2016/01/Topic-1_6.mp3 Previous Topic Back to Lesson