Abstract: A scintillation apparatus design is provided which eliminates the requirement of an optical window between the scintillator and the photosensitive device. The disclosed design provides significantly improved performance with a scintillator mounted directly to the photosensitive device. Improved light coupling between the scintillator and the photosensitive device is achieved. The present disclosure improves the light transmission to the photosensitive device (PSD) by direct coupling of the photosensitive device to the scintillator. By eliminating the need for an optical window, light loss due to the glass interface caused by the optical window likewise may be eliminated. The improvement of light transmission to the PSD improves the gamma ray energy resolution. The quality of the gamma spectroscopy is improved with this design. Furthermore, providing the means and method for evacuating the internal assembly significantly improves the reliability and lifespan of the detector assembly.