Systems, methods, and devices relating to a sourceless X-ray downhole tool are provided. By way of example, such a downhole tool may include an X-ray generator, an X-ray detector, and data processing circuitry. The X-ray generator may emit some X-rays out of the downhole tool and some X-rays internally through the downhole tool. The X-ray detector may detect some of the X-rays that return to the downhole tool, as well as some of the X-rays that pass internally through the downhole tool. The data processing circuitry may gain-stabilize the X-ray detector based at least in part on the X-rays that passed internally through the downhole tool and were detected by the X-ray detector.