## 4 Experimental Data and Processing Result Analysis of Combined Logging  
To effectively apply the conversion coefficient \(A_{k}\) and background response \(B_{k}\) for uranium quantification in field production logging, it is essential to construct saturated ore layer model wells that closely match the formation-rock layer composition, logging conditions, and borehole structure of field production wells. These model wells--referred to as standardized model wells--include equilibrium and disequilibrium uranium-series standardized uranium model wells, as well as standardized zero-value model wells. They are generally classified into at least two major types: sandstone-type standardized model wells and hard-rock-type standardized model wells. To validate the uranium quantification method proposed in this study, verification experiments were conducted using a self-developed combined logging tool that combines natural \(\gamma\)-ray energy spectrum logging and prompt neutron time spectrum logging (Figure 1). These experiments were carried out at the Nuclear Industry Radiological Survey Metering Station in Shijiazhuang, Hebei Province, using standardized model wells. For the sandstone-type standardized model wells, the logging results included measured profiles from four central sections of saturated ore layers, encompassing both natural \(\gamma\)-ray energy spectrum logging data and prompt neutron time spectrum logging data. Figure 3a shows the natural \(\gamma\)-ray energy spectrum within the central region of the measurement point, covering the energy range of 0-3 MeV. Figure 3b displays the prompt neutron time spectrum within the same region, spanning a time range of 0-800 \(\upmu\)s. It should be noted that the count rate for the natural \(\gamma\)-ray total logging is derived from the \(\gamma\)-ray energy spectrum curve, with the low-energy scattered \(\gamma\)-rays below 0.4 MeV excluded. The count rate for the prompt neutron time spectrum logging is obtained from the epithermal neutron time spectrum curve, with neutron counts below 128 \(\upmu\)s--primarily from source neutrons--excluded. Additionally, the epithermal neutron count rate curve is normalized using the thermal neutron count rate curve. The curves labeled NU-1-E to NB-4-E represent the epithermal neutron curves, while NU-1-T to NB-4-T denote the thermal neutron curves. Figure 3: (**a**) Natural \(\gamma\)-ray spectrum in center. (**b**) Prompt neutron time spectrum in center. To determine the calibration parameters, including the conversion coefficient \(A_{k}\) and background response \(B_{k}\), this study utilized a standardized zero-value model well (No. NB-4), where concentrations of radioactive elements (uranium, thorium, and potassium) were negligibly low. The logging count rates (\(\gamma\)-ray count rates and epithermal neutron count rates) measured in this well were employed to determine \(B_{k}\), as listed in Table 1. Additionally, a disequilibrium uranium-series standardized uranium model well (No. NU-3) was selected, characterized by negligibly low thorium and potassium concentrations but significantly higher uranium and radium concentrations than the zero-value well. Using its measured count rates and \(B_{k}\), the conversion coefficient \(A_{k}\) was derived and is also listed in Table 1. The radium content is expressed as the uranium content at radioactive equilibrium, with both uranium and radium content units unified as \(\times 10^{-4}\) eV (equivalent uranium). To validate the feasibility of the uranium quantification methodology and calibration parameters, this study arbitrarily selected two disequilibrium uranium-series standardized uranium model wells (No. NU-1 and NU-2), both exhibiting negligibly low concentrations of other radioactive elements (such as thorium and potassium).