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.