## 3 Gamma-Ray Detectors
### Gamma-Ray Detectors--PIGE  
The Particle-Induced Gamma Ray Emission (PIGE) technique is based on the detection of the prompt gamma rays emitted by the nuclei of the target atoms in nuclear reactions caused by ion beams. With MeV ion beams (typically protons with energies in the (1-3 MeV) energy range for IBA analyses), PIGE is typically limited to \(Z<15\)-20, because heavier elements need higher beam energies for the projectiles to interact with the target nuclei. For a given atom/nucleus, gamma rays have higher energies than X-rays and absorption in the target depth probed by the beam particles is normally negligible, which makes the PIGE technique ideally suited for detection/quantification of low \(Z\) elements [160]. In CH applications, PIGE often complements PIXE, because it enables obtaining information about the low \(Z\) elements, non-detectable by PIXE because their X-rays have too low energy to be detected or are absorbed before reaching the detector(s). Examples of the complementary use of the PIXE and PIGE techniques are quite common; see, for example, [161, 162]. However, production cross sections for gamma rays are much smaller than those for X-rays, which makes the sensitivity of PIGE generally worse than that of PIXE [163, 164, 165, 166, 167]. A recent development, interesting for PIGE measurements, has been proposed in [168]. Following this approach, considering the detailed angular dependence of the gamma ray production cross sections, when a specific element is under study, the detector is set in the position where the gamma-ray yield has its maximum. In this way, a gain in the intensity up to 70% can be achieved. This approach enables lowering the limit of detection, minimizing the measurement time and the radiation dose delivered to the sample. In PIGE measurements, semiconductors detectors are normally used, and, though the first application in the CH field exploited Ge(Li) for obsidian characterization [169], recently only HPGe are applied [170]. Additionally, CdTe detectors are used for high-energy X-ray/low-energy gamma-ray detection, thanks to their compactness and low weight. CdTe detectors with the same configuration (form factor, footprint, and front-end electronics) of SDDs have been presented. They can be used both for low-energy gamma rays (e.g., F gamma rays) and for high-energy X-rays. For example, a 3 \(\times\) 3 mm\({}^{2}\) CdTe detector with FWHM = 850 eV@122 keV line of \({}^{57}\)Co and FWHM = 290 [EMAIL_ADDRESS] keV line of \({}^{55}\)Fe is commercially available (to be compared with ER down to 480 eV and 165 eV respectively for the most performing low-energy HPGe detectors). Their DE is higher than that of HPGe, for the same thickness, due to the higher \(Z\) of both Cd and Te with respect to Ge. However, being typically available in small dimensions and thickness, CdTe detectors have good DE only for photons with energies up to a few hundreds of keV (10% DE @ 300 keV). These CdTe detectors can be configured to use the same power supply, preamplifier, cooling, and mechanics of SDDs. A detection setup based on SDDs and CdTe detectors in the same configuration described above is going to be installed on the abovementioned MACHINA beamline, thus enabling an extremely compact, lightweight, and low-cost detection system, of crucial importance for a transportable apparatus. In CH applications, the PIGE technique is most often applied for the study of glasses [171, 172, 173, 174]. Interesting studies concerning rock and minerals have also been reported [175, 176], as well as about ivory and bones [177, 178, 179]. Most often the exploited reaction is based on the inelastic scattering, typically (p,p\({}^{\prime}\)\(\gamma\)). The elements more frequently detected by the PIGE techniques are F (exploiting the \({}^{19}\)F(p,p\({}^{\prime}\gamma\))\({}^{19}\)F reaction where gamma rays at 110 and 197 keV are emitted) and Na (\({}^{23}\)Na(p,p\({}^{\prime}\gamma\))\({}^{23}\)Na reaction where 440 keV gamma rays are produced).