# 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  
After the Fukushima accident, there was a serious lack of information, not only regarding the identification of the radioactive materials released but also their distribution as a consequence of the plume's fall-out in neighboring regions [17]. Traditional airborne (manned aircrafts) measurements of radiation intensity, dose, and corresponding spatial distribution were performed at altitudes of 150-300 m. First, measurements were done by using NaI scintillation detectors to obtain an estimate of the ambient dose rate at 1 m height within an area of 80 km from the FDNPP [118]. [PERSON] et al. [150] described the use of manned helicopters to measure the ambient dose-rate and the deposition of radioactive cesium in the vicinity of FDNPP using large NaI detectors mounted either inside or outside the platform. The helicopters have the advantage of reaching difficult areas for humans, like forests and paddy fields [151]. Due to regulatory restrictions (manned aircrafts cannot fly below 150 m) and to avoid contamination and exposure risks to the crews, the flying altitudes were above 150 m, which resulted in poorer spatial resolution. Therefore, to obtain the necessary detection sensitivity, heavy, high volume, and expensive radiation detectors were necessary [152]. A more recent work reported on the use of several NaI detectors and a LaBr\({}_{3}\) installed in a manned helicopter to determine the influence of natural radionuclides (radon progenies, \({}^{214}\)Pb and \({}^{214}\)Bi) in aerial radiation monitoring for a better estimation of the deposition of artificial radionuclides in the vicinity of Fukushima [153]. [PERSON] et al. [154] described a detection system housed in a manned fixed-wing aircraft for air-sampling and ground contamination measurements in large areas, e.g., the aftermath of a nuclear or radiological accident. To accomplish that, a Sky Arrow 650 aircraft was modified (the aircraft nose), in order to accommodate the air sampling unit. To analyze the aerosol samples (collected in the filter), a GM and a BGO scintillator (1 cm\({}^{3}\)) next to the sampling line is used. However, since the BGO scintillator has poor energy resolution, an HPGe semiconductor (nitrogen cooled for 4 h) with a 60 mm (diameter) \(\times\) 35 mm (length) crystal size to radionuclides identification is also used. To measure the ground contamination (dose rate estimate), a large volume NaI(Tl) scintillation detector (\(400\times 100\times 100\) mm\({}^{3}\)) weighing 17.5 kg is used. One important condition for correct air sampling measurements is to guarantee the isokinetic condition, ie, the air streamlines and the airspeed must not be perturbed by any part of the airplane. Due to possible dose risks to the crew, in an emergency situation, the manned airplane can only measure environmental contamination in a far field situation, while near field situations can only be handled using an UAV or a network of UAV. The FDNPP accident marked the first use of UAVs to obtain the distribution of air dose rate and radioactive cesium in the ground (\({}^{134}\)Cs and \({}^{137}\)Cs) nearby the nuclear power plant. The use of unmanned helicopters allowed to carry a more reasonable payload weight and also perform measurements at lower altitudes (50-150 m) and speeds (8 m/s) than manned aircrafts, which allowed improved spatial resolution [78; 151; 155; 156]. While [PERSON] et al. [155] used an NaI(Tl) scintillating detector for the mapping of the radiation distribution and localization of hotspots, [PERSON] et al. [78; 151] and [PERSON] et al. [156] used three LaBr\({}_{3}\):Ce (6.5 kg) to measure the distribution and variation along the time of the air dose rate and a single LaBr\({}_{3}\):Ce to determine the ratio \({}^{134}\)Cs and \({}^{137}\)Cs, respectively. The choice of LaBr\({}_{3}\) was related to its higher efficiency and energy resolution compared to NaI crystals, allowing to distinguish the energy lines of the radioactive \({}^{134}\)Cs (796 keV) and \({}^{137}\)Cs (662 keV). [PERSON] et al.