Abstract: Self-Powered Neutron Detectors (SPNDs) are crucial components for measuring neutron flux inside reactor cores. Due to their unique response mechanism, SPND signal currents are typically small and exhibit a delayed response. Furthermore, research on SPND sensitivity currently lacks experimental data obtained within reactors. This study focuses on Rhodium-SPNDs (Rh-SPNDs). By developing amplification circuitry for weak currents and implementing algorithms to process the delayed signals, a fast-response system for Rh-SPNDs was developed, reducing the detector's signal response time from several hundred seconds to approximately 3 s. Sensitivity irradiation tests were conducted on the Rh-SPNDs in the Minjiang Test Reactor (MJTR). The experimental results show that as the reactor power increased, the temperature in the test section also gradually rose, reaching 42.4 °C at full power. The output current of the Rh-SPNDs increased with rising reactor power, with higher currents observed on the "sunny side" (facing the core) compared to the "shady side". Finally, the thermal neutron sensitivity of the Rh-SPNDs was calculated. The thermal neutron sensitivities for the three SPNDs were: 1.66×10⁻²⁰, 1.68×10⁻²⁰ and 1.44×10⁻²⁰ A·(n·cm⁻²·s⁻¹)⁻¹, respectively.