3. SOFTWARE GUIDE
15
Figure 15. Static Search Mode.
The
Neutron Partition
bar shows the instantaneous ratio of non-cosmic (yellow) to cosmic (green) neutrons.
The corresponding, color-coded message bar shows additional data and statistics on the measurements.
3.3.2
Counting in Static Search Mode
To count in this mode, unfold the panels, turn the thin sides toward the object, and “clamshell” them as
closely and completely as possible around it (Figure 16).
You can either manually control the length of the acquisition with the
Start
and
Stop
buttons, or tap
Settings
and set a
Dwell Time
, in minutes (Figure 17). To return to manual control, set the dwell time to zero or exit
and re-enter Static Search Mode.
During the count, the software tells you to continue counting (see Figure 15). If a consistently high and
statistically valid reading is obtained for either or both of the non-cosmic fractions, a red message bar saying
to “send the log file to home” is displayed, as shown in
Figure 18. If you receive this message, go back to the
main screen (
) and switch to Characterization Data Collect Mode to acquire data according to the
instructions in Section 3.4.
So that neutron events can be accurately characterized as cosmic or non-cosmic, it is important for the system
to have accurate information about the shape of the background neutron distribution. This distribution can
scale up and down depending on exact location, just as the reported cosmic count rate is not constant but
will change depending on exact location. However, the shape of the background count distribution is
consistent for a given environment. Environmental properties that affect this shape include altitude, latitude,
and surrounding materials (generally high-Z materials) subject to spallation interactions with cosmic rays.
The Fission Meter is supplied with a “universal”
background; alternatively
, you can collect a “local”
background as described in the next paragraph.
3.3.2.1
C
REATING A
L
OCAL
B
ACKGROUND
F
ILE
The first step in characterizing the local neutron background is to collect approximately 2 hours of background
data in the Static Search Mode with no neutron sources present. Once the data collection has stopped, the
software will automatically save a real-time data file. This file can then be used as a background file. The
Settings screen for the Static Search Mode allows you to use of universal or local background information.
