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Syclone Portable Gamma-Ray Spectrometer, Revision 10
system testing for special applications.
c) PEAK THRESHOLD – Selections are 2.0, 2.5,
This parameter is essentially a "sensitivity" setting for Nuclide Identification.
During Nuclide Identification, a spectrum is taken then a Peak Analysis engine is used to
select significant peaks. This engine suppresses backscatter peaks etc and other
spurious peaks during its action and then defines a list of all peaks found. For each peak
the error on that peak is computed and the amplitude of the peak is determined in
Standard-Deviation (SD) units.
The PEAK THRESHOLD setting is then used to remove low amplitude peaks. So if 3.0 is
selected (the default value) then any peak 2.9 SDs or below is eliminated before the peak
list is used for Nuclide Identification.
This parameter is useful in some applications where low amplitude peaks need to be
excluded for special application. However if this value is set too low then some spurious
peaks may occur so the default setting of 3.0 usually gives the best results.
d) BASE DOSE THRESHOLD – Selections are 10, 15,
This "NaI Dose Limit" normally set at 20µR/h (200nSv/h) is used to show that the
radiation level is clearly above the background level indicating some source is present
and is used as explained below.
After NUCLIDE IDENT, if NO PEAKS are found or a peak is found that is not in the library
and the Dose Rate is BELOW the NaI DOSE LIMIT setting the following messages
displays:
UNKNOWN SOURCE – (and Shielded Source) The Syclone has a wide selection of
radioactive isotopes in its internal library. If after analysis, the isotope or the residual
signal/ gamma peak cannot be identified, and the Dose Rate ≤ Base Dose Threshold
the screen displays "UNKNOWN SOURCE".
If the analysis results are such that the Dose Rate ≤ Base Dose Threshold radiation, and
no gamma-peaks found then the Syclone shall display "BACKGROUND" as the system is
seeing the local background.
Furthermore, the results may contain peaks with no Isotope Identification, scattered
radiation with no Isotope Identification, or a combination of an identified isotope and strong
peaks with no Isotope Identification and if the Dose Rate > Base Dose Threshold. These
all may indicate the presence of a SHIELDED SOURCE.
Note: If the isotope cannot be identified, retrieve the stored spectrum and follow your
predefined operating protocol, or call the RadComm Help desk (see
who will direct the call to the appropriate person for further analysis.
e) NUCLIDE THRES – Selections are 3, 5,
The "NUCLIDE THRESHOLD" = 7SDs as default. In NUCLIDE IDENT the PEAK
THRESHOLD parameter is normally set at 3.0SDs to determine whether a peak is used
in NUCLIDE IDENT. The Peak Analysis engine produces a list of all peaks found and any
peak below this setting (3SDs) are NOT used for NUCLIDE IDENT. This works very well
for multi-peak isotopes but many complex spectra can easily produce aberrant peaks
because of Pile-Up etc. and these can easily be misconstrued as being present whereas
in fact they are scattering effects etc. The parameter NUCL THRES requires the SUM of
all the peaks in an ID to exceed the default setting (7SDs).
For example, if you have an analysis producing 3 peaks A=5SDs, B=6SDs and C=3SDs
and Isotope X requires A+B. Then in this case A+B = 11SDs which is above the 7SD
default setting, so identification of isotope X is displayed. In the case where isotope Y
requires only 1 peak and this is B, then since B=6SDs and this value is below the 7SDs
limit, isotope Y is NOT identified. The net effect of this is that single peak identification is
RadComm – Proprietary
3.0
, 3.5, 4.0, 4.5, 5.0 (SD units)
20
, 30, 40, 50
7
, 8, 9, 10, 11, 12, 15 (SD units)
Page 40
5.0 MANUAL MODE
(µR/h units)
Appendix
Revision Date: March 3, 2016
Z)
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