Radiation detector and radiation detection system

A radiation detector comprising a plurality of pixels configured to output pixel signals in accordance with incident radiation and an A/D converter configured to A/D-convert the pixel signals,

• wherein the A/D converter includes a comparator configured to compare the pixel signal with a signal threshold and is configured to operate in a plurality of modes,
• the plurality of modes includes a first mode of performing A/D conversion of the pixel signal by using a first reference signal in a case where the pixel signal is smaller than the signal threshold and performing A/D conversion of the pixel signal by using a second reference signal in a case where the pixel signal is larger than the signal threshold,
• the first reference signal is a signal that temporally changes in a first voltage range, and the second reference signal is a signal that temporally changes in a second voltage range,
• an upper limit value of the first voltage range is smaller than a lower limit value of the second voltage range, and
• the signal threshold is set between the upper limit value and the lower limit value.