1. A radiation measuring apparatus comprising: at least one scatterer detector functioning as a scatterer that scatters an electromagnetic radiation from a measurement object; at least one absorber detector functioning as an absorber that absorbs the electromagnetic radiation; and a processing unit, wherein each of the scatterer detector and the absorber detector comprises: a semiconductor substrate; and a plurality of pixel electrodes arranged in a matrix on a first main surface of the semiconductor substrate, wherein the plurality of pixel electrodes are arranged such that a distance between centers of two neighbor pixel electrodes is smaller than a mean free path of a recoil electron generated in Compton scattering of the electromagnetic radiation, wherein the processing unit extracts events based on signals obtained from the scatterer detector and the absorber detector, and specifies an incidence direction of the electromagnetic radiation based on a recoiling direction to which a recoil electron recoils, to each of the extracted events, in each of which the Compton scattering has occurred in either of the scatterer detectors, the recoil electron generated in the Compton scattering in either of the scatterer detectors recoils to a direction having an in-plane component of the semiconductor substrate in an inside of the scatterer detector in which the Compton scattering has occurred, and photoelectric absorption has occurred in which the photon scattered in the Compton scattering is absorbed in either of the absorber detectors, wherein the scatterer detector further comprises a plurality of back electrodes arranged on a second main surface which is opposite to the first main surface of the semiconductor substrate, wherein each of the plurality of back electrodes of the scatterer detector is arranged to be opposite to more than one of the plurality of pixel electrodes of the scatterer detector, wherein a number of the plurality of back electrodes is less than a number of the plurality of pixel electrodes in each of the scatterer detectors, wherein the radiation measuring apparatus further comprises: a first signal processing section configured to generate first pixel electrode measurement data from a first analog signal read from the plurality of pixel electrodes of the scatterer detector; a temporary storing area provided to temporarily store the first pixel electrode measurement data; a second signal processing section configured to generates back electrode measurement data from a second analog signal read from the plurality of back electrodes of the scatterer detector; and a data processing section, wherein the data processing section reads from the temporary storing area, pixel electrode measurement data which are selected the first pixel electrode measurement data according to the back electrode measurement data, to transfer to the processing unit, wherein the processing unit carries out extraction of the event and specification of the incidence direction of the electromagnetic radiation based on the selected pixel electrode measurement data.