ORTEC Fission Meter FM-P3, Руководство пользователя

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9
2.
MODES OF OPERATION
2.1
Data Acquisition Modes
The Fission Meter has three data collection modes: Mobile Search, Static Search, and Characterization Data
Collect (“Reachback”).
2.1.1 Mobile Search Mode
Mobile Search Mode is a survey mode that allows you to monitor total neutron count rate and the Feynman
variance moment, Y2F. These two monitoring parameters have their own “strip chart” showing parameter
values with respect to time; and a “barometer” that
gives instantaneous values against an alarm threshold,
based on standard deviations. This mode is designed to identify slightly elevated count rates in a search area,
as well as significant neutron sources. If a significant neutron source is present (as indicated by an obviously
elevated count rate), the strip chart can help you maximize the count rate and localize the source.
Once a source is localized, you should switch to Characterization Data Collect Mode to obtain more detailed
data for Triage support. Bear in mind that even when the strip chart count rate is maximized, the source could
still be a significant distance away, behind various walls and barriers. To maximize detection efficiency, the
Characterization Data Collect measurement should be performed as close to the source as possible. Because
of this, it might be necessary to continue Mobile Search Mode into other rooms or locations to better localize
the source.
If the Mobile Search results in a Count Rate or Y2F Alarm , but the count rate is only slightly elevated and
source localization is unsuccessful, this could indicate the presence of a non-cosmic neutron source or just
an elevated background count rate (such as the ship effect). In this case, you should place the Fission Meter
in a fixed location and switch to Static Search Mode. In the Static Search Mode, Feynman moments are
examined more closely to help you and Triage determine the source of the neutron count rate by partitioning
the count rate into cosmic and non-cosmic fractions.
If an object is already suspect, you can skip this mode and move directly to the Static Search or
Characterization Data Collect mode.
2.1.2 Static Search Mode
The Static Search Mode can be used to verify the presence or absence of a non-cosmic source of a strength
comparable to or less than the typical background neutron count rate. In Static Search Mode, the Feynman
moments are examined more closely to enable partitioning of the total count rate into cosmic and non-
cosmic fractions. The Feynman moments are distinct for cosmic source neutrons and non-cosmic source
neutrons (including fission and Poisson sources). This allows the total count rate to be separated into a cosmic
source fraction and a non-cosmic source fraction. The ratio of cosmic to non-cosmic neutrons is displayed on
the bar graph at the top of the screen.
Static Search Mode is used where a non-cosmic source is suspected, due to information such as a mobile
search
Count Rate Alarm or Y2F Alarm , but when localization of the source in Mobile Search Mode has been
unsuccessful.