TM 5-6635-386-12&P
object of the same mass will produce a major loss of
energy or slowing down.
The only atom which can markedly slow down a fast
neutron, and which we would likely see in soil, IS
hydrogen. The hydrogen nucleus is the same mass as
the neutron and slows down the neutron Immensely
compared to collisions with other nuclei. The greatest
loss of energy in any collision is when two similar mass
objects collide.
A simple analogy is that of a golf ball colliding with a
bowling ball. The golf ball would rebound with little loss
of energy. The golf ball colliding with BB’s (electrons
floating around a nucleus) would push them aside.
However, two golf balls colliding would produce a strong
loss of energy in each of them, or a transfer of energy
from one to the other.
This is what happens when a fast neutron hits a
hydrogen atom. The neutron is markedly slowed down.
A few collisions with hydrogen atoms reduces a fast
neutron to the slow or "thermal" energy at which the
moisture detectors in the soil tester can "see" the slow
neutron.
Thus, the moisture channel is in reality a "Hydrogen
Analyzer" and is responsive to any form of hydrogen
present whether it be in the form of water, or of some
organic matter. It is possible to measure water on a
construction site because the only form of hydrogen we
normally see on a soil site is free water, the very feature
we are trying to measure. However, bound water within
the mineral matrix, organic matter, roots, or asphalt in an
asphalt
pavement
would
also
provide
hydrogen
moderation and the neutron tester would "read" it
accordingly. If we know the quantity of extraneous
hydrogen, we can account for it in calibration and the
tester can still be used for moisture determination.
Neutron radiation is emitted by any alpha producing
source when mixed with
Beryllium.
CPN
uses
Americium/Beryllium (AmBe) source in its soil testers.
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
