The investigated dual-range photon detector consists of an SDD which is optically coupled with a lanthanum bromide crystal. In contrast to similar configurations investigated by Fiorini et al. [6], the SDD side, not the scintillator side, points to the radiation source. Low-energy gammas or X rays are therefore absorbed in the bulk silicon and the SDD acts as a high-resolution detector on its own (Figure 1, left). siswitch detectors operate on this basis [CsI(TI) scintillator plus photodiode) [7], as well the dual-range photon detectors with CsI(TI) scintillators and photodiode [8] or SDD readout [9]. The proposed detector configuration combines for the first time a fast scintillator and a slow silicon detector. However, the pulse shape discrimination is successfully applied due to the long time required to collect the charge in the SDD, when the charge carriers are formed opposite to the anode (geometry effect). t Fig. 1: Scheme of the dual-range photon detector (DRPD) and illustration of the underlying detection modes. Low-energy gammas or X rays are absorbed in the SDD (l). The absorption process generates a local cloud of charge carriers. Electrons drift towards the anode (drift time to). The anode (A) signal is delayed just by to but shows a steep rise if the electron cloud arrives at the anode. Energetic gamma radiation mostly passes the SDD but might be absorbed in the scintillator (2).The SDD detects scintillation light. Photoelectrons are generated along the crystal-SDD contact zone. The superposition of contributions representing different drift paths and drift times results in a shallow anode signal. Pulse shape discrimination (PSD) separates the distinct detection mechanisms.This process is referred as to direct detection (SDD mode). More energetic radiation mostly passes the silicon layer but may be absorbed in the scintillator.The SDD then acts as an efficient photo detector for the scintillation light of those events. The scintillation flash illuminates the full contact area of SDD and crystal. The '1 (2) A '1 (1) qr toC, Abstract-Homeland security applications demand compact, high resolution detectors for gamma and X rays identification. Most commercial instruments use scintillating crystals or CdZnTe detectors. The identification performance is therefore intrinsically linked with the progress in developing crystals with a very high light output (LaBr3Ce or SrI 2 ) and with the manufacturing of the CdZnTe detectors. A new detector concept is proposed, which essentially improves on the existing resolution limits. It combines two distinct detection mechanisms in a compact, state-of-the-art solid-state detector, providing complementary information in different but overlapping energy ranges. The dual-range detector consists of a LaBr3(Ce3+) scintillator coupled to a silicon drift detector (SDD). The SDD serves as a high-resolution X-rayon its own, and in parallel as a light readout device for the LaBr3(Ce31 scintillator ensuring best possible resolution at higher energies.