TM 5-6635-386-12&P
object of the same mass will produce a major loss of
neutron to the slow or "thermal" energy at which the
energy or slowing down.
moisture detectors in the soil tester can "see" the slow
neutron.
The only atom which can markedly slow down a fast
neutron, and which we would likely see in soil, IS
Thus, the moisture channel is in reality a "Hydrogen
hydrogen. The hydrogen nucleus is the same mass as
Analyzer" and is responsive to any form of hydrogen
the neutron and slows down the neutron Immensely
present whether it be in the form of water, or of some
compared to collisions with other nuclei. The greatest
organic matter. It is possible to measure water on a
loss of energy in any collision is when two similar mass
construction site because the only form of hydrogen we
objects collide.
normally see on a soil site is free water, the very feature
we are trying to measure. However, bound water within
A simple analogy is that of a golf ball colliding with a
the mineral matrix, organic matter, roots, or asphalt in an
bowling ball. The golf ball would rebound with little loss
asphalt pavement would also provide hydrogen
of energy. The golf ball colliding with BB's (electrons
moderation and the neutron tester would "read" it
floating around a nucleus) would push them aside.
accordingly. If we know the quantity of extraneous
However, two golf balls colliding would produce a strong
hydrogen, we can account for it in calibration and the
loss of energy in each of them, or a transfer of energy
tester can still be used for moisture determination.
from one to the other.
Neutron radiation is emitted by any alpha producing
This is what happens when a fast neutron hits a
source when mixed with Beryllium.
CPN uses
hydrogen atom. The neutron is markedly slowed down.
Americium/Beryllium (AmBe) source in its soil testers.
A few collisions with hydrogen atoms reduces a fast
1-4. PANEL CONTROLS
Refer to Keyboard (Fig. 1-1) - Each Touchkey is outlined below.
CLEAR
=
Stops count in progress. Stores this count and does not reset the display to zero.
Cancels any other prior program keys (D or M-ONLY).
Pushing a display touchkey will produce a display of the stored count. Note that the
tester will go through its normal, rapid shutdown "beep" to alert the operator that the
tester was stopped deliberately and not automatically.
LOCK
=
Interlocks TEST and STANDARD to prevent accidental field actuation of either o'
these two functions. LOCK by itself will do nothing.
STD
=
When pressed simultaneously with LOCK, will erase all four memories and will
initiate a 4 Minute count into all four memories. This provides a check on the
performance of the memories. The stored readings are normalized to the 1/4
minute time base for ease of operator computation. STD by itself will do nothing.
The two STANDARD memories will be retained for future recall. Pushing any of the
4 OPERATION buttons will erase the standard count stored in the D-DATA and M-
DATA memories and they will count normally.
TEST
=
When pressed with any DISPLAY key, will light all 8's to test the display and the
display command system. When pressed alone, it displays a random number
which should be discarded.
1-4
