This paper presents the design and test results of a low-power radiation detection system. When paired with a scintillation-based detector, the design forms a compact, portable unit suitable for use in long-duration radiation monitoring applications. The system consists of two distinct modules. The first is a low-power detector power supply (DPS) used to generate multiple high voltages necessary to bias a photomultiplier tube (PMT), which is controlled and regulated by a 0.35 μm controller chip. The second is a 0.13 μm low-power multichannel analyzer (MCA) chip with an integrated microcontroller and event-driven charge-sensitive front-ends with 10-bit ADCs used to acquire and analyze the energy spectrum of the radiation. The MCA interfaces with the DPS through a digital interface, allowing it to tune the PMT voltage to compensate for temperature and time variations in the detector. Both modules were fabricated and tested to verify low-power functionality, consuming 2.4 mW when sensing radiation events at 1000 counts/sec (cps).