Ground Roughness Effects on the Energy and Angular Distribution of Gamma Radiation from Fallout

Abstract

This report is published in the interest of providing information which may prove of value to the reader in his study of effects data derived principally from nuclear weapons tests and from experiments designed to duplicate various characteristics of nuclear weapons. This document is based on information available at the time of preparation which may have subsequently been expanded and re-evaluated. Also, in preparing this report for publication, some classified material may have been removed. Users are cautioned to avoid interpretations and conclusions based on unknown or incomplete data. LEGAL NOTICE This report was prepared as an account of Government sponsored work. Neither the United States, nor the Commission, nor any person acting on behalf of the Commission: A. Makes any warranty or representation, expressed or Implied, with respect to the accu racy, completeness, or usefulness of the information contained In this report, or that the use of any information, apparatus, method, or process disclosed in this report may not infringe privately owned rights; or B. Assumes any liabilities with respect to the use of, or for damages resulting from the use of any information, apparatus, method, or process disclosed in this report. As used in the above, *'person acting on behalf of the Commission" includes any em ployee or contractor of the Commission, or employee of such contractor, to the extent that such employee or contractor .of the Commission, or employee of such contractor prepares, disseminates, or provides access to, any information pursuant to Ms employment or contract with the Commission, or his employment with such contractor.

Environmental and Fallout Gamma Radiation Protection Factors Provided by Civilian Vehicles

“…The energy and angular exposure rate distributions above fallout fields have been measured (HUDDLESTON et al, 1965) and calculated (SPENCER, 1962). The radioisotope 6oCo can be used to simulate fallout radiation fields for shielding studies, provided the correct angular distribution is produced on the outside of the shield (BURSON and FRENCH, 1970).…”

Building Protection Against External Ionizing Fallout Radiation

“…While this report is focused on isolated buildings, it is worth noting that roughness in the earth's surface also provides protection -due in large part to the reduction of direct radiation [9], [30], [35]. The corresponding protection factors range from PF = 1.5 for natural, small-scale (≤ 0.125 m) roughness, PF = 3 at the centers of large 300 m (1,000 ft) hills and valleys, and potentially larger for congested urban areas…”

“…where DR = dose rate at point P (rad s -1 ) Ψ = conversion from photon flux to dose rate (rad photon -1 cm 2 ) SC = surface contamination (photon cm -2 s -1 ) B(FP) = buildup factor (dimensionless) FP = number of mean free path lengths (dimensionless) 30 dA = (infinitely small) area of point A (cm 2 ) s = distance from points A to P, also called the slant range (cm) h = height of point P (cm) r = distance from the center of fallout disk to point A (cm) µ = mass attenuation coefficient (cm 2 g -1 ) ρ = air density (g cm -3 ) 29 The dose rate scales with s 2 since it depends on the surface area of an expanding sphere. 30 The mean free path is the average distance radiation will travel in a straight line. For the radiation energies considered here (0.5 to 3 MeV), this corresponds to a distance of ~100 to ~250 m in air.…”

“…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].…”

“…𝑅𝑒𝑙𝑎𝑡𝑖𝑣𝑒 𝐷𝑜𝑠𝑒 𝑅𝑎𝑡𝑒 𝑔𝑟𝑜𝑢𝑛𝑑,𝑛𝑜 𝑏𝑢𝑖𝑙𝑑𝑖𝑛𝑔 (𝜃, ℎ) = mid-section bone marrow dose rate for 1 h old fallout as interpolated from Table D1 values 39 (Sv m 2 Bq -1 s -1 sr -1 ) 39 Spencer [27] calculated the dose rate above an infinite, flat, uniformly contaminated plane of 1.12 hr old fission fallout as a function of incidence angle and height. Additional calculations on 28 h, 40 h, and 131 h old fission fallout indicate that there is some, but limited change in the relative angular dose rate -which is neglected in the PFscreen calculation [26], [27], [30]. After deposition, the absolute dose rate due to fallout radiation decreases rapidly, t -1.2 [54].…”