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