## 2 X-ray Detectors
### X-ray Detectors (XRDs)  
X-ray diffraction is a scattering-based technique aimed at the characterization of crystalline phases. XRD exploits Bragg's law to measure interplanar crystal distances and hence it needs the simultaneous and well-resolved determination/knowledge of radiation wavelength (or energy) and angle of scattering. In CH, XRD is used for qualitative and quantitative phase determination. Similarly to XRF, basic setups provide an averaged measurement over 'large' areas, but the development of X-ray optics has enabled micro X-ray diffraction typically combined with a scanning stage to perform X-ray diffraction imaging. Applications encompass paintings, manuscripts, ceramics, metallic alloys, fossils, studied to understand origin, counterfeiting, realization processes or degradation phenomena. A review on the application of XRD imaging for CH studies has recently been published by [PERSON] al. [113].  
Standard XRD setups use monochromators (or Kb filters) to perform angle scattering measurements at a well-defined known wavelength. When using single-element (0D) detectors, the monochromator is usually preferred on the diffracted beam to remove X-ray fluorescence, which is a source of background for XRD. For segmented detectors (1D: strips, 2D: pixels), a monochromator on the diffracted beam cannot be implemented and monochromatic sources are typically used. Hence, for XRD detectors, energy discrimination is not really necessary and X-ray counters are used. As single-element de  
Figure 4: XRF measurement of a graphite sheet with an excitation energy of 2100 eV performed at the DXR1 beamline (CPS = counts/s).  
tectors, scintillation detectors are often used. They may offer counting capabilities up to 1 Mounts/s. Position-sensitive detectors are most often based on solid-state semiconductor detectors segmented to define the point of detection. The advances in CMOS technology have allowed the fabrication of dedicated Application-Specific Integrated Circuits (ASICs) to analyze the charge collected by the sensors and convert the signal into the corresponding number of photons and in some cases energy. Preamplification of the signals, which used to be performed by either integrated or external JFET charge amplifiers, is now often accomplished by CMOS charge preamplifier ASICs. Charge preamplification can also be combined in a single ASIC. The coupling of segmented semiconductor sensors with multi-channel ASICs with matching pitch constitutes hybrid (pixel) detectors. Integration of a full signal analysis chain enabling energy resolution is not trivial and typically these detectors are used as photon counters (hybrid photon-counting detectors, HPCDs). Nowadays, they are the most used in XRD and, depending on the instrumental range, can go from 1D strips with only tens of channels to 2D detectors with 16 M pixels. Well known in this category are detectors based on the Medipix readout chips (the latest is Medipix3) developed under the auspices of CERN by the Medipix collaboration [114] and detectors based on chips developed at the Paul Scherrer Institut (PSI) [115].  
A curved position-sensitive detector based on a (curved) gas ionization chamber is commercially available and has recently been used to characterize Mayan green stones [116]. Recently, FBK fabricated a Si strip sensor for the development of a spectroscopic 1D detector, specifically designed for the combined analysis of X-ray diffraction and X-ray fluorescence. The paired-X project consortium has proposed this strip detector with spectroscopic capability and a novel concept of data analysis based on Rietveld refinement of an angle-energy map [117]. This methodology, developed for mineralogical characterization (EIT RawMaterials consortium funds), can be exploited for the characterization of CH artifacts, and in particular when scanning \(\upmu\)-XRD measurements are required and the XRD patterns have to be collected as quickly as possible.