An Experimental Evaluation of Roof Reduction Factors Within a Multi-Story Structure

Abstract

Fallout contamination deposited on the roof of a structure is, in many cases, the source of the primary radiation component of the total dose obtained at any point within the structure. Experiments have been performed in which the doses from a souice of radiation present on a roof were measured in many locations within a multi-story building. This report presenis the results of these experiments for roof ancG floor mass thicknesses of 48.6 and 97. 2 psf. Comparisons of the experimentally measured gamma doses with those determined theoretically have been shown throughout this report. Agreement between experiment and theory has, in general, been found to be good. ii FOREWORD This report presents results of an experimental evaluation of radiation attenuatioti and distribution caused by simulated fallout from the roof of a multi-story structure with floors of varying mass thicknesses. The experiment was performed during the period August 1965-1966 by the CONESCO Division of Flow Corporation at the Protective Structures Development Center (PSDC), Fort Belvoir, Virginia. This work was conducted for the Office of Civil Defense through the PSDC, Joint Civil Defense Support Group (JCDSG), Office of the Chief of Engineers, and was accomplished under Subtask 1117A Contract DA-18-050-ENG-3407, Work Order No. OCD-PS-65-17 and Contract DACA 31-67-C-0018, Work Order No. (OCD) DAHC 20-67-W-01l 1,

Building Protection Against External Ionizing Fallout Radiation

“…where R = radius of the fallout disk (cm) PF(h,R) = protection factor (dimensionless) 32 Within 100 m of the ground, the protection factors have limited dependence on photon energy over the energy range of interest (varies less than 2x). 33 These theoretical prediction of dose rate and protection factors are consistent with prior estimates, see Figure C3 and Table C3. 34 31 8 mean free path lengths correspond to a slant range of ~1,250 m, e.g., ~800 m above a disk of 1 km radius, for 1 h old fallout radiation.…”

“…Radiation from roof contamination can likewise be blocked (scattered) by ceilings, floors, and the roof -with heavier structures providing more protection. Figure A19 illustrates these effects with a roof source atop a multistory concrete structure with two different roof and floor thicknesses (5 m effective radius) [33]. The relative importance of ground and roof sources depends on the specific building construction and detector location within the building.…”

“…A 3-story experimental test building (80 m 2 footprint) was studied using Co-60 roof and ground sources, see Figure B5 [33], [36], [45]. The PFscreen building models were developed using reported building attribute values for 17 different configurations.…”

“…34 31 8 mean free path lengths correspond to a slant range of ~1,250 m, e.g., ~800 m above a disk of 1 km radius, for 1 h old fallout radiation. 32 Protection factor = the ratio of the dose rate at height 1 m to the dose rate at height h. 33 There is minimal (< 10%) variation of protection factor with energy at a location 1 m above the ground for a disk radius ranging from 3 to 300 m. 34 In this figure, "NBS42" = [27]; "Theory" = Appendix C results; "Huddleston 1965" = [30].…”

“…Appendix C; "Zahringer 1998" = [28]; "Bursen 1970" = [29]; "Huddleston 1965" = [30]; "Bursen 1963" = [31]; "Breslin 1963" = [20]; "Schumchyk 1966" = [32]; "ARA 2016" = personal communication (Andy Li; Tyler Dant; Kevin Kramer); "Spring 1967" = [33].…”