Fig. 1. Schematic diagram of the active multiplicity method for measuring the total mass of uranium in yellow cake

Fig. 2. FH-NCM/S1 device model established by the MCNP program (a) 2D axis section view, (b) 3D axis section view

Fig. 3. Flow chart of MCNP and MATLAB joint simulation multiplicity analysis flow chart

Fig. 4. f_Di versus mass of ²³⁸U in the sample

Fig. 5. Diagram of the relationship between multiplicity count rates S/D/T and the change of sample mass

Fig. 6. Relationship between the calculated and actual values of the sample induced fission rate and multiplication with uranium content (a) Sample induced fission rate, (b) Simulated multiplication M and calculated net leakage multiplication M_L

Fig. 7. Actual and measured values of the corrected fission rate F and total mass of uranium m(a) Change of sample fission rate F and F_m′ with mass of ²³⁸U, (b) Calculated value and actual value of total uranium mass

Fig. 8. Relation diagram of the change of sample S/D rate with water content (a) Single rate S, (b) Double rate D

Fig. 9. Correction curve and double rate before and after correction(a) Correction curve fitting, (b) Double rate before and after correction

Fig. 10. Actual and measured values of total uranium mass in samples with different water contents