# State-of-the-Art Mobile Radiation Detection Systems for Different Scenarios
## 4 Mobile Radiation Detection Systems
### Gamma Imaging
#### 4.3.1 Compton Cameras
The 3D structural model of the working environment can be obtained by photogrammetry software or by using 3D-LiDAR (can measure the distances to the objects), while the position and posture of the imaging system can be obtained by a SLAM function. [PERSON] et al. [22] described the development of a novel handheld Compton camera with only 1 kg and 10 cm\({}^{2}\) size (Figure 12). The camera is composed by 10 mm thick plates of 50 \(\times\) 50 mm\({}^{2}\) CeGAGG as scatter and absorber, as well as features a wide field of vision (180\({}^{\circ}\)) and an improved sensitivity (approximately 1% for 662 keV gamma-rays). Using the 3D position-sensitive scintillators together with large-area monolithic MPPC arrays, it was possible to reconstruct a gamma image in 30 s (integration time) for a \({}^{137}\)Cs source with approximately 6 \(\mu\)Sv/h. The resultant angular resolution was 14\({}^{\circ}\) (FWHM). The first commercial portable Si/CdTe Compton camera was manufactured by [PERSON] et al. [194] (ASTROCAM) and tested for hotspot detection and evaluation of decontamination effectiveness nearby Fukushima (in the 20 km zone). The camera weights 10 kg  
Figure 11: Examples of Compton cameras coupled to UAVs: (**a**) Unmanned helicopter with Compton camera composed by two arrays of Ce-doped Gd-Al-Ga-garnet (CeGAGG) scintillation crystals [178], reprinted by permission of the publisher (Taylor & Francis Ltd, [[http://www.tandfonline.com](http://www.tandfonline.com)]([http://www.tandfonline.com](http://www.tandfonline.com))). (**b**) Multi-rotor UAV with two stages of CeGAGG crystals mounted in a gimbal. Reproduced, with permission, from Reference [186]; published by Taylor & Francis, 2018, under the terms of the [[https://creativecommons.org/licenses/by-nc-nd/4.0/CC](https://creativecommons.org/licenses/by-nc-nd/4.0/CC)]([https://creativecommons.org/licenses/by-nc-nd/4.0/CC](https://creativecommons.org/licenses/by-nc-nd/4.0/CC)) BY-NC-ND 4.0 license. and the efficiency can be improved for a specific application by changing the number of detectors (scalability). In this camera, Si is used as the scatter, and CdTe is the absorber, wherein the former allows a smaller Doppler broadening effect, and the latter a good absorption, due to the high atomic numbers (48 and 52) and high density (5.8 g/cm\({}^{3}\)). The energy resolution is 2.2% at 662 keV, with an angular resolution of 5.4\({}^{\circ}\) (FWHM), and the exposure time used during the tests was 30 min. Particular attention must be paid when intense hotspot is near the camera because it can be difficult to detect the furthest of hotspots. To avoid this situation, the camera must be raised to some high point; doing this, it is possible to observe hotspots 20-30 m away from the camera. Another portable semiconductor-based Compton camera was developed by [PERSON] et al. [195] for spectroscopy and imaging in nuclear power plants. The Polaris-H is a 4\(\pi\) Compton camera based on a 3D-position-sensitive pixelated CZT detector (energy resolution better than 1.1% at 662 keV) with a total mass of 4 kg and an autonomy of 5 h.