CHAPTER 17 end i I= iN Jy Mev/cm2 -sec ay (17-0) H = the gamma intensity per unit area (energy flux density) at the point of measurement, P where 2 = the effective free mean path, plotted on Fig. 17-11 4 from Ref.50. (The effective mean free path ig figure that takes into account buildup factor. reproduced an empirical N= islie aV, and represents the ratio of (1) the dose rate at P due to the given source, to (2) the dose rate that would be measured at a point within an infinite volume with the same source density. (In the expression for N, all distances are expressed in units of effective mean free path.) on the water surface, OfN#0.5. For points (The 0.5 value corresponds to a base surge with a semi-infinite volume.) *three types of buildup factor, corresponding of epectra (photons, energy flux, or dose rate) to the three types may be defined by the equation expressing the ratio of total (scattered and unscattered) to unscattered numbers of photons, energy flux, or dose rate. rate (or dose) buildup factor is: By s The dose diu + digs u where dy, represents the dose (rate) from unscattered radiation and dig represents the dose (rate) from scattered radiation. 17-49