Systems, devices, processes, and algorithms for adaptively filtering a signal output from a radiation detector and adaptively sampling the signal. A count rate of events detected by the radiation detector is estimated by a processing unit. An RC time constant of the filter and a sampling rate of an analog-to-digital converter are adjusted based on the estimated count rate. Events are continuously detected by the radiation detector and counted by the processing unit while the adjustable parameters (the RC time constant and the sampling rate) of the filter and the analog-to-digital converter are adjusted on the fly (in real time) to optimize an energy resolution of the detected events, while reducing degradation due to pile-up effects and improving efficiency of the analog-to-digital converter. The filter can be implemented through analog filters, digital filters, or a combination thereof.