are known. Calculations can be made to estimate what the reading will be at some future time or was at some selected previous time by using the ete? fission product decay law. tion of this law for this purpose. Figure 6 is a graphical presentaBy drawing connecting lines to the points of same intensity readings calculated to the same time-dose-rate relationship, isodose rate lines or contours can be constructed. For planning purposes, before fall-out is completed and the true contour patterns are known, smooth, idealized contours are generally constructed, calculated for some specific time following detonation such as H+l hour or H+2 days, etc. For this purpose, since the ultimate wind struc- ture is not known at the time the contours are drawn, a basic simplification is made in that a single wind of constant velocity is assumed to act on the bomb cloud. For cases in which the wind shear is not exces- sive, this approximation does not introduce serious errors. Frequently, isodose contours are also constructed to indicate the integrated dose over a certain period of time, as for example up to H+50 hours. The family of curves included in Figure 6 is a graphic representation of several H+] hour radiation dose rates, in roentgens per hour, with time after detonation plotted sgainst dose rate. Using these curves, one can calculate the dose rate at any hour after the burst if the H+l hour dose rate is known. Also the H+1 hour dose rate can be calculated from the actual measured dose rate at any particular time. Dose and dose rate contour lines are drawn in such a manner that the boundaries represent the minimum quantity for the area enclosed. An example of a family of idealized contours for a 20 KT land surface burst is presented in Figure 7. The intensity is greatest at some point on the mid-line, becoming gradually less as one proceeds periph- erally. Locations of high radiation intensity, or “hot spots" as they are called, are not indicated on most contours. Additional examples of contour areas and downwind extents for an assumed 15 knot wind condition and for a number of different yields are given in Table l. 39