## 2 X-ray Detectors
### Muonic Atom X-ray Spectroscopy (MAXRS)  
Muonic atom X-ray spectroscopy (MAXRS) is based on sample exposure to a collimated muon beam and the detection of characteristic X-rays, emitted following the implantation/formation of muonic atoms inside the target. Muon mass is 200 times bigger than electron mass, thus characteristic muonic X-rays have energies much higher than those of the corresponding characteristic X-rays generated in electronic transitions. Although they are referred to as muonic X-rays, they actually have energies detectable by detectors normally used for \(\gamma\)-ray spectroscopy. Thus, by using high-energy muon beams, we can probe elements well inside the sample (up to several millimeters depth) and the EM radiation generated even deeply inside the sample can easily emerge out thanks to its higher energy (i.e., less self-absorption). Elements can be detected inside the samples with very limited (if any) sample activation, differently from what happens with neutron irradiations for PGNAA analysis, where materials can be probed in depth, thanks to the use of neutrons, but with remarkable indeed activation. The MAXRS technique can be used for CH applications as it enables non-destructive analyses. Using intense double pulsed muon beams at the RIKEN-RAL facility, MAXRS can be used to discover the provenance of raw materials, the manufacturing processes, the past trading patterns and/or the persistence of particular past cultural traditions. The main features of the MAXRS technique are:  
* Non-invasive, simultaneous, multi-elemental analytical technique;
* High-energy characteristic X-rays emission (small autoabsorption also for low Z elements);
* Potentially applicable for all elements (from Li to U);
* External analyses possible (no vacuum system required);
* Suitable for a wide variety of samples;
* Depth profiling possible by changing muon beam momentum/energy;
* 2D mapping;
* Very high specificity (energy and temporal signatures);
* Negligible radioactivation;
* Complementary technique to other non-invasive analytical techniques for bulk (PG-NAA) or surface analysis (PXE, XRF,... ). This technique, still under development, has already been employed on a wide range of materials, including Japanese coins [140], different animal tissues ([141; 142; 143] and ancient Chinese mirrors [144]. Very recently, the negative muons at J-PARC were used to examine extra-terrestrial material and meteorites [145]. In a proof-in-principle experiment [146], a new instrument was setup, built, and installed on port 4 of the RIKEN-RAL facility. After detector calibration, standard samples (Au standards, Bronze Standards, and pure elements) were measured. Since then, this instrument has been upgraded to look at archaeological artifacts, such as Roman and Islamic coins, Bronze Age artifacts and ancient swords [147] and, within INFN-CHNet, for the in-depth analysis of archaeological finds (fragments of votive bronze boats from the Nuragic age). Results have pointed out the use of lead as an additive in the Cu and Sn alloy, especially in some particular junction areas (bow of the ships) [148]. The MAXRS detection setup of INFN-CHNet makes use of two beam hodoscopes, originally developed for the FAMU experiment at RAL. These detectors are based on single-clad square 1 mm or 3 mm PMMA Bicron BCF scintillating fibers, arranged along x/y coordinates, and read at one extreme by ASD RGB SiPM from Advansid or S12752-025P SiPM from Hamamatsu. They are designed to deliver position, shape, and timing information for the low-energy Riken-RAL muon beam, with a fiducial area of 96 \(\times\) 96 mm\({}^{2}\) and 32 \(\times\) 32 mm\({}^{2}\), respectively. A picture of the 1 mm pitch detector is shown in Figure 6[149; 150]. Considering that the used SiPMs have been selected in order to have similar breakdown voltages as shown in Figure 7, a simple readout scheme was developed, giving the same supply voltage to all SiPMs.