CHAPTER 2 - EFFECTS OF SMALL CHANGES IN BURST HEIGHT ON THE AMOUNT OF LOCAL FALLOUT 1. When fallout models are used in hypothetical nuclear war studies, the weapons usually are assumed to detonate either as true air bursts, in which case no local fallout is assumed; or as true surface bursts, in which case about two-thirds of the total amount of radioactivity, as normalized to one hour after the detonation, is assumed to be deposited in local fallout. In an actual attack on a city some incoming enemy weapons are likely to impact on a building rather than directly on the ground, especially if they arrive along a non-vertical pathway such as one that would be followed by an incoming ICBM. If such weapons are fuzed to detonate on contact, the detona- tions therefore could occur some distance above the ground, Presumably for this reason, the amount of radioactivity in local fallout would be reduced compared to that of a true surface burst of the same type weapon. The material of Chapter 2 can be used to estimate how much the local fallout would be reduced due to this "height-of-burst" effect, 2. If Curve B of Figure 2 of the Fallout Subcommittee's report applies to the building height vs local fallout production phenomena as suggested in the report, an equation can be derived which, when corrected for ground roughness and instrument response, is as follows: -2 a. where: Ky = e/ 965 ~ 1.599 x 10 “A (R/hr)/(kt/sq mi) at 1 hour _ . 1/3 @ } = scaled height of burst = h/w @ h is height in feet of building where detonation @ wis in kilotons of total yield occurs @ i is any positive value equal to or less than 100 @® - for }, values greater than 100, the Ky value for 4 = 100 applies. b. To illustrate, assume that h = 400 feet (i.e., about a 40-story building) and that the total yield, all of which is due to fission, is 1-MT. Then \ = 400/ 3 1000 = 40. In which case Ky = e699 = 1017 (R/hr)/(kt/sq mi). 2 I b re r4 ~ PY ies II-7