Fig. 1. Experimental flowchart

Fig. 2. Pulse samples of neutron and gamma rays

Fig. 3. Intercepted pulse waveform (a) and baseline adjustment (b), smoothing filtering (c), and amplitude normalization (d)

Fig. 4. Diagram of the KPCA-ELM model structure

Fig. 5. Specific algorithm flowchart of the KPCA-MPA-ELM model

Fig. 6. Contribution rate and cumulative contribution rate of the first 10 principal component features

Fig. 7. Fitness change curve of the MPA-ELM

Fig. 8. Confusion matrix of the 3 000 test samples of the KPCA-ELM model

Fig. 9. Confusion matrix of the 3 000 groups of the test samples of the KPCA-MPA-ELM model

Fig. 10. Comparison of the classification accuracy of four models

Fig. 11. CCM discrimination result chart (color online)

Fig. 12. PGA discrimination result chart