Yes the thick mucous is the first stage of dry mouth and we all experience it usually late in the rad sessions so he is right on course. This typically lasts a few weeks and can/will get pretty disgusting. I walked around with a Styrofoam cup in my pocket and constantly spit all day. At night I would awaken with a mouth full of that crap and have to run to the nearest sink. Sometimes it even invoked a bout of nausea. When he leaves this period he will be left with dry mouth, the severity of which will be the result of the amount of radiation damage to his saliva glands. Most of us recover a great % of our saliva but his patience will be tested as that can take every bit of 2 years.