We propose a spectrometer that employs a single room temperature semiconductor detector that can perform both gamma and neutron spectroscopy. The proposed detector is based on the novel mercurous halide materials, Hg2X2 (X=I, Cl, Br). The mercurous halides are new wide band-gap semiconductor detector materials that can provide radiation detection with low cost, high performance and long term stability. Despite years of research, no explored room temperature semiconductor detection candidates can satisfy all three features simultaneously. At Brimrose, we have successfully developed the growth procedures for high quality Hg2X2 crystals for long wavelength infrared (LWIR) imaging systems. Recently, we have been able to engineer our growth process toward gamma radiation detection and have demonstrated initial encouraging detector response from Hg2I2 to both gamma and alpha particle incident radiations. The focus will be on the material engineering aspect of the detector material itself (i.e., crystal growth and post growth processing), as well as on the detector fabrication and system design. The proposed mercurous halides-based nuclear instrument can be used onboard NASA's orbiters and landers for space planetology. Specifically, it can be used to determine surface and sub-surface composition of planetary bodies via both gamma spectroscopy and neutron spectroscopy.