## 4 Experimental Data and Processing Result Analysis of Combined Logging
Utilizing the saturated ore layer equations for uranium and radium content (Equation (3)), the uranium and radium contents of these saturated ore layers were derived based on the measured logging count rates and calibration parameters \(A_{k}\) and \(B_{k}\) listed in Table 1, with the results summarized in Table 2.  
Table 2 demonstrates that for sandstone-type standardized model wells with low thorium and potassium concentrations, the combined logging methodology combining natural \(\gamma\)-ray total logging and prompt neutron time spectrum logging developed in this study achieves accurate uranium and radium quantification. The absolute error of uranium content is within \(\pm 0.002\%\) eV, with a relative error of within \(\pm 2.5\%\), fully meeting the requirements specified in the _exploration specifications on in situ leaching sandstone type uranium deposits_ [12]. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \begin{tabular}{c} **Standardized** \\ **Model Wells** \\ \end{tabular} & \begin{tabular}{c} **Uranium or Radium** \\ **(10\({}^{-4}\) eV)** \\ \end{tabular} & \begin{tabular}{c} **Nominal Content** \\ **(10\({}^{-4}\) eV)** \\ \end{tabular} & \begin{tabular}{c} **Measurement Count** \\ **Rates (cps)** \\ \end{tabular} & \begin{tabular}{c} **Calculated Results of** \\ **the Scale Parameters** \\ \end{tabular} \\ \hline NB-4 & \begin{tabular}{c} Uranium \\ Radium \\ \end{tabular} & \begin{tabular}{c} 0.01 \\ 0.01 \\ \end{tabular} & \begin{tabular}{c} 0.66 \\ 47.09 \\ \end{tabular} & \begin{tabular}{c} \(B_{1}=0.66\) cps \\ \(B_{2}=47.09\) cps \\ \end{tabular} \\ \hline NU-3 & \begin{tabular}{c} Uranium \\ Radium \\ \end{tabular} & \begin{tabular}{c} 9.83 \\ 9.01 \\ \end{tabular} & \
\begin{tabular}{c} 35.56 \\ 2492.04 \\ \end{tabular} &
\begin{tabular}{c} \(A_{1}=3.55\) cps\(/10^{-4}\) eV \\ \(A_{2}=271.36\) cps\(/10^{-4}\) eV \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Logging data and calibration parameter determination results for standardized model wells. Without applying prompt neutron time spectrum logging to correct the uranium-radium-radon balance coefficient \(K_{P}\), the calculated \(K_{P}\) values are 0.87 for NU-1 and 0.92 for NU-2. The radium contents derived from the natural \(\gamma\)-ray total logging are consistent with those presented in Table 2. Based on these radium contents and the corresponding \(K_{P}\) values, the inferred uranium contents are shown in Table 3. By comparing the results in Table 3 with those in Table 2, it can be observed that for Borehole NU-1, the combined logging method performs better than the traditional natural \(\gamma\)-ray total logging method. However, in Borehole NU-2, the natural \(\gamma\)-ray total logging yields slightly better results. Overall, both methods provide essentially consistent results for uranium quantitative interpretation, while the combined logging method offers the advantage of faster on-site interpretation. As shown in Table 1, the conversion coefficients for radium and uranium quantification are \(A_{2}=271.36\,(\mathrm{cps}/10^{-4}\,\mathrm{eU})\) and \(A_{1}=3.55\,(\mathrm{cps}/10^{-4}\,\mathrm{eU})\), respectively. This signifies that a saturated one layer with 0.01% uranium content generates a natural \(\gamma\)-ray total count rate of 271.36 cps but only an epithermal neutron count rate of 3.55 cps--a difference approaching two orders of magnitude. The experimental results indicate that the count rate of the prompt neutron time spectrum logging is relatively low. In order to reduce statistical fluctuation errors, the maximum logging speed of this method falls significantly short of the 2-4 m/min standard required by the _exploration specifications on in situ leaching sandstone type uranium deposits_[12]. Accordingly, this study proposes a method in which, for the entire uranium-bearing layer, the summed logging count rates of both logging methods are calculated separately. This cumulative value inherently exhibits minimal statistical fluctuations.