A radiation image forming apparatus, comprising: a plurality of Compton cameras arranged annularly to surround a region in which a specimen is placed, wherein each of the plurality of Compton cameras includes a plurality of radiation detection devices and detection modules, wherein the plurality of radiation detection devices is configured to detect an electron generated by a track of a recoil electron generated by Compton scattering and configured to output a detection signal configured to specify a position of a pixel that has detected the electron and a time when the pixel has detected the electron, and wherein the detection modules are configured to detect an incident position of scattered Y rays generated by the Compton scattering, wherein the plurality of radiation detection devices each comprises a first radiation detection device and a second radiation detection device, wherein the first radiation detection device includes a first pixel electrode portion including a plurality of first pixel electrodes, and the second radiation detection device includes a second pixel electrode portion including a plurality of second pixel electrodes, wherein the first radiation detection device and the second radiation detection device share a chamber into which a gas is introduced, and a first insulating member provided in the chamber, wherein the first radiation detection device is provided on a first surface of the first insulating member, and the second radiation detection device is provided on a second surface located on an opposite side to the first surface of the first insulating member, and the second radiation detection device annularly surrounding the outer circumference of the first radiation detection device and the first radiation detection device being arranged to annularly surround a region in which a specimen is placed. a plurality of Compton cameras arranged annularly to surround a region in which a specimen is placed, wherein each of the plurality of Compton cameras includes a plurality of radiation detection devices and detection modules, wherein the plurality of radiation detection devices is configured to detect an electron generated by a track of a recoil electron generated by Compton scattering and configured to output a detection signal configured to specify a position of a pixel that has detected the electron and a time when the pixel has detected the electron, and wherein the detection modules are configured to detect an incident position of scattered Y rays generated by the Compton scattering, wherein the plurality of radiation detection devices each comprises a first radiation detection device and a second radiation detection device, wherein the first radiation detection device includes a first pixel electrode portion including a plurality of first pixel electrodes, and the second radiation detection device includes a second pixel electrode portion including a plurality of second pixel electrodes, wherein the first radiation detection device and the second radiation detection device share a chamber into which a gas is introduced, and a first insulating member provided in the chamber, wherein the first radiation detection device is provided on a first surface of the first insulating member, and the second radiation detection device is provided on a second surface located on an opposite side to the first surface of the first insulating member, and the second radiation detection device annularly surrounding the outer circumference of the first radiation detection device and the first radiation detection device being arranged to annularly surround a region in which a specimen is placed.