## 2 X-ray Detectors
These systems can reach active areas as large as 500 mm\({}^{2}\)[7]. This solution, however, leaves some dead space between detector elements and has a quite large diameter (45 mm) without a passage for the beam. This configuration does not allow the optimization of the detector solid angle and makes it necessary to have the detector far from the beam impact point on sample. On the other side, single or multiple SDD arrays allow covering wide solid angles, much wider than in the previous configuration, minimizing dead space between detector elements. In addition, these detectors have dedicated electronics for each element and thus allow achieving high statistics in a short acquisition time with a very-high count rate. To give an example, using a 0.9 \(\upmu\)s peaking time, while conventional SDDs typically afford a maximum output count rate (OCR) of approximately 100 kcounts/s, a complete multi-element SDD array can result in an OCR as high as 8 Mcounts/s [8], while maximizing the collection solid angle. However, at present, they are not as widespread as expected, due to their high cost. In this regard, it is worth mentioning MAIA, a sensor array of 384 diodes, 1 \(\times\) 1 mm\({}^{2}\), built on high-resistivity silicon, which is 400 \(\upmu\)m thick, arranged symmetrically around a central (with a diameter of 2.4 mm) hole for the beam, which has been developed mainly for earth sciences problems [9,10]. Large spectroscopic detector arrays based on the pn-CCD (Charge Coupled Device) architecture are also available,offering hundreds of thousand 75 \(\upmu\)m pixels with energy resolution as good as 145 eV at Mn\({}_{\text{K}\alpha}\)[11]. As already mentioned, SDDs have excellent energy resolution when compared to all the other ED detectors. However, there are cases where lines overlap, thus limiting the capacity of the X-ray based analytical techniques; see, e.g., the S K lines (2308 eV) and the Pb M lines (2346 eV). X-ray Superconductive Detectors (SD) may allow overcoming many of these problems, due to their superior energy resolution, typically below 20 eV and which can be as low as few eV [12]. These systems are very expensive, cumbersome, heavy and of big dimensions, but are nevertheless appealing for their high resolution. SDs are not very common in the community working with techniques exploiting X-ray detection, but they have started to be used. Since 2010, some applications of high-resolution PIXE have been presented [13; 14; 15; 16]. Very recently, an application to a problem of interest in CH has been presented. Quantitative speciation of chemical elements in cultural heritage samples is a challenging issue, of great interest for example for unravelling forgeries. In PIXE with SDDs, the determination of chemical species is in principle not possible, due to insufficient energy resolution, but high-resolution PIXE, based on state-of-the-art X-ray Microcalorimeter Spectrometers (XMSs), has demonstrated to be able to study chemical speciation [17]. SDDs allow for simultaneous detection of all the elements from Na (Z = 11) up. Element detection is accomplished using either K or L lines, depending on energy. SDDs active elements have a typical thickness of approximately 500 \(\upmu\)m, which corresponds to 100% detection efficiency for X-ray energies below 10 keV (-1.5 10\({}^{-7}\) transmission). The efficiency decrease for high-energy X-ray detection is due to the decrease in the X-ray absorption with increasing energy. However, quite recently (see below for example the Ardesia description), 100% detection efficiency beyond 10 keV has been achieved, thanks to the development of innovative SDD detectors with thickness increased up to 1000 \(\upmu\)m (-1.5 10\({}^{-7}\) transmission). The decrease in detection efficiency below 1 keV is due to the absorption of low-energy X-rays in the path from the emission point to the detector active area.