—
Secon
pas APS
(HPGe) detector having a surface area of 19 em? and a thickness of
1.6 cm.
aclu 6
The detector was suspended from a retractable pneumatic boom
740 cm above ground.
The boom was mounted to the rear of the Thiokol
IMP - a small, lightweight, tracked vehicle--modified and equipped to be
a fully self-contained, mobile, data-acquisition and reduction system.
Quantitative data can be obtained from in situ measurement by
combining a theoretical calculation of the flux at the detector as a
function of source and source distribution with an experimental calibration of the detector response to a given incident flux.
The un-
scattered flux of game rays of energy E at a height h above a smooth
-alr-ground interface resulting from en emitter distributed in the soil
(Fig. 2) is given by:
«
a S exp
PL go
[-(u_h sec 6 + 2% sece )7
a
47 (h sece
+ 2 sec 6)?
2> rdrdz,
(1)
where
S, = the source activity per unit volune (
.
Va,
¥o = the air and soil
tetal
photons),
Cm
ang
Sec
lineéar attenuetion
coefficients (cn!).
This expression assumes a source distribution that varies only with
depth.
For fallout activity the distribution after a period of time can
be reasonably approximated by an exponentia] distribution given by
s
= sf «7%
(2)