RADIATION PROTECTION WITHIN A THE SHORTER-TERM BIOLOGICAL HAZARDS OF A FALLOUT FIELD $7] GAMMA RADIATION (MR/HR) 16 tb coNcRETE LEVEL GROUND SLABS Topen PORGH SECTION Am~A Frieure 4.-—Section View, speaker said seems to be quite correct, in that surface roughness affects readings in this way. Wehave observed that sometimes the reading will rise to as large a height as 30 feet before beginning to fall if the surface is rough enough. The shape of the curves he showed seem to be in agreement with our experimental and theo- retical work. Mr. Gravuson. This is approached by a thick slab calculation, such as you get over water, where the material is distributed in depth, and then any slant distances are highly preferentially absorbed and the source seems to be almost a monodirectional plane source. Mr. Hottann (AEC). On the other hand, youhave an increase of something of the order of 4 or 5 mr per hourin the indoor curve. It seems as though this would haveto be reflected. This would be added onto the doses outdoors as you went up and would give you a departure from the theoretical curve, wouldn'tit? Mr. Graveson. I am sorry I didn’t quite INSIDE @+ QUTSIDE (OPEN FIELD) STATION 4 STATION 3 4 STATION | Th true plane calculation. Therefore, the irregu- larities could not he serious to give this type of result. The small irregularitics could, and itis 6. possible did contribute. gL ‘r 3} r 0 follow what you meant by your question, Would you rephrase it? Mr. Houianp. I assume that the theoretical , curve for the decrease of dose rate with height does not include this effect of irregularities? Mr. Graveson. It as such does not. It isa [. 2 GAMMA J 4 at 1 5 Qo 6 GAMMA RADIATION (MR/HR) VERTICAL RADIATION FIG-5 Figure 5.—Vertical Radiation Profile. ! \ 15 RADIATION (MR/HR) ite) PROFILE STANDARD HOUSING STRUCTURE 17 Mr. Hownann. If they were of the magnitude shown which is of the order of several—I don’t remember the exact magnitude-—many r per hour increase, it seems to me they would have shown up on that curve, and particularly since those readings were taken indoors the same effect would probably be larger if existed outdoors. In other words, I am trying to pointto the other indication. There must have been contamination on the roof. Mr. Gravison. Onthe other hand,if we had contamination on the roof, which would match these readings, the contamination density would have been 3 or § times higher than the contamination density on the ground. I am not in a very strong position here. J am just saying I am presenting some measurements whieh I think are verv interesting. Dr. Werner. Are there any further comments on this? Mr. Recuen (Publie Health Service). I have a feeling on this that what was missing was 4 theoretical curve for the indoor type of measurement where you have an uncontaminated slab under the measuring instrument. Mr. Graveson. The theoretical curve we derived was based on the simplest case, that of a smooth plane. This neglected unevenness of the surface. When the major radiation contributionis from outsidea clean area, this is not applicable. The Theory for thick slab source is under examination.