# State-of-the-Art Mobile Radiation Detection Systems for Different Scenarios
## 4 Mobile Radiation Detection Systems
### Radiation Detection and Gamma Spectrometry
#### 4.2.2 Airborne Survey
On the other hand, a small and low-cost multi-rotor platform can be used for source localization and contour mapping in all-terrain and confined spaces (e.g., mountain or urban areas) and for lower sources activities [171]. [PERSON] et al. [172] implemented a 14 \(\times\) 14 mm\({}^{2}\), 256 \(\times\) 256 pixel matrix CMOS detector, known as Timepix, coupled to a multi-rotor. Despite the implementation of a single Timepix detector to source localization and mapping (e.g., in security and nuclear disaster mitigation), the development of a Compton camera made by two Timepix3  
Figure 9: Examples of detection systems coupled to unmanned fixed-wing aircraft: **(a)** UAV with two SIGMA-50 CsI(Tl) scintillation detectors. Reproduced, with permission, from Reference [67]; published by Frontiers, 2020, under the terms of the [[https://creativecommons.org/licenses/by/4.0/CC](https://creativecommons.org/licenses/by/4.0/CC)]([https://creativecommons.org/licenses/by/4.0/CC](https://creativecommons.org/licenses/by/4.0/CC)) BY 4.0 license. **(b)** Ranger UAV with a GM, NaI(Tl) and a CZT detection system. Reproduced, with permission, from Reference [170]. **(c)** Patria MASS Mini UAV with a CsI detector (in the fuselage) a radioactive particle air sampler (on top). Reproduced, with permission, from Reference [170]. detectors coupled to MAV in order to localize weak gamma-ray sources is expected. The high mobility of an MAV allied to the lightweight Compton camera data will allow full autonomous localization of radioactive sources. The use of a UAV for multiple source localization and contour mapping (e.g., for fast emergency response) was also proposed by [PERSON] et al. [173; 174]. When considering multiple sources, each of them contributes in a cumulative manner for a given hotspot, which differs from the situation in which each source is considered individually. To agile the process, a region of interest (ROI) is first considered and then the source localization is based on two methods: Hough transform and the variational Bayesian. A multiple formation of UAVs was proposed for cooperative source seeking and contour mapping. While [PERSON] et al. [175] proposed the use of low-cost UAV formation (e.g., fixed-wing aircrafts) in four different scenarios, which included the study of a decentralized formation strategy to increase its robustness in the case of a communication failure (with the GCS) and different types of formations (circular and square), [PERSON] et al. [176] considered a circular formation of three multi-rotors to discover the radiation intensity gradient for low altitude and clustered environments (only feasible with this kind of platforms). The latter used a plug-and-play concept for the integration of the CZT detectors into the platforms. For the urgent detection of nuclear radiation, a multi-UAV system has several advantages compared to a single UAV system, mainly related to the use of low-cost, small, and lightweight platforms, which translates in more safety, flexibility, and endurance [177].