From figure 6 and table 1, the feature values of most background spectra
were less than 0.05, as well as those in the range of (0.05, 0.2) but
they presented discontinuous phenomenon. The feature values of the
source contained spectra, with the dose rate increase, the part less
than 0.05 decreased sharply and the part larger than 0.2 increase
gradually. The feature values at the test position of 10 cm, although
the number of those feature values larger than 0.2 were less than the
position of 15cm. However, the whole feature values in the range of
(0.05,0.2) were larger than those at the position of 15 cm. In
certainly, it may because the statistic fluctuation which lead the
phenomenon.
In actual application, the false alarm is intolerable. Therefore, the
detection method should be on the premise of no false alarm, then rise
the accuracy of alarm. The detection method was as follows:
5-s consecutive feature valses were set as judge array J . AssumeNmax was the number of feature values larger
than 0.2 among J , Nmid was the number of
those in the range of (0.05,0.1) while Nmin was
the number of those less than 0.05. The detection method was shown in
table 2.