# 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
also used other sensors as a stereovision system to generate terrain maps and a gimbal camera with laser rangefinder to geo-locate points of interest. After the Fukushima accident, several lightweight (50-500g) spectrometers started to be available as commercially off-the-shelf (COTS), like CZT semiconductor, CsI, and CsI(Tl) scintillation detectors [18]. In Table 5, some characteristics of COTS detectors are presented. Recently, Saint Gobain made available compact SiPM-based scintillators, such as: (i) NaI(Tl) with an energy resolution between 7.5-8.5% at 662 keV (depends on the crystal size), (ii) NaIL (NaI(Tl+Li) a dual mode detector for gamma radiation and thermal neutrons, and (iii) LaBr\({}_{3}\):Ce with an energy resolution of 4% at 662 keV for a crystal with 3.81 cm (diameter) \(\times\) 3.81 cm (length), and (iv) enhanced LaBr\({}_{3}\):Ce with an energy resolution of 3.5% at 662 keV for a crystal with 3.81 cm (diameter) \(\times\) 3.81 cm (length) [157]. They feature temperature gain compensation, low voltage operation (5 V, with a power consumption \(<\)150 mW), and are tested according to ANSI N42.34. [PERSON] et al. (2014) [152] implemented a compact, lightweight, and small volume CZT detector (1 cm\({}^{3}\) GR1, Kromek) coupled to a small UAV (multi-rotor) for monitoring, assessment, and mapping radiation anomalies. The payload consisted in a gimbaled system (to ensure sensors are perpendicular to the ground surface) with a CZT and a single-point laser rangefinder (AR2500, Acuity) to obtain high precision heights. A similar setup was used by [PERSON] et al. [158; 159; 160] (Figure 8a) to obtain high-resolution radiation mapping of legacy uranium mines, verify the effectiveness of various remediation methods, and to investigate contaminant migration in FDNPP post-disaster scenario including 3D mapping (using a software to visualize 3D spatial data). Due to the flight characteristics of the UAV (heights between 1-15 m and speeds between 1-1.5 m/s), it was possible to monitor elevations of land and infrastructure, allowing to measure not only the radiation fields but also to identify the radionuclides present. In general, this detection system showed the following advantages: low operation and maintenance cost (compared to fixed-wing), fast deployment, and accomplish autonomous missions. However, some limitations were identified, like the platform low autonomy (30-35 min), the strong weather dependence, and the small volume size sensors (payload limitation), compared to high altitude fixed-wing platforms. As future work, the use of a 3D-scanning LiDAR system (32 lasers) is referred for monitoring and contamination mapping of structures, such as buildings and waste material storage. Recently, [PERSON] et al. [164] used a SIGMA-50 CsI(Tl) scintillation detector (with SiPM) coupled to a multi-rotor to assess the remediation efforts (contaminant distribution) in a Fukushima waste storage area (Figure 8b). Despite the better energy resolution of CZT (used in previous works [158; 159; 160]) compared to CsI(Tl) (2-2.5% vs \(<\)7% at 662 keV), the latter detector was chosen because of its larger volume (32.8 cm\({}^{3}\)) and correspondingly higher efficiency, which allowed obtaining the mapping of lower radiation intensity areas. For high resolution mapping at NORM sites, particularly decommissioned uranium mines, a lightweight gamma spectrometer coupled to a multi-rotor was proposed [158; 140]. While [PERSON] et al. [158] proposed a CZT to scan the area at 5-15 m AGL and speed 1.5 m/s, [PERSON] et al. [140] suggested lower altitudes and speeds (1-2 m height and 0.2-0.23 m/s) using a GM for a first monitoring (hotspot identification) and only after the use of a CZT for hotspot inspection (energy spectra obtained at 10-20 cm from the ground--platform landed). The latter is related to the FRIENDS project, which consists of using a combination of sensors coupled in a fleet of drones (autonomous and cooperative navigation) with the goal of monitoring and mapping in real time areas with high concentrations of NORMs.