# State-of-the-Art Mobile Radiation Detection Systems for Different Scenarios
## 4 Mobile Radiation Detection Systems
### Radiation Detection and Gamma Spectrometry  
Radiation detection systems can be divided into three classes: gas-filled detectors, scintillation detectors, and solid-state detectors [100]. Due to their good sensitivity and energy resolution, scintillation detectors and solid-state detectors are used for radiation dose rate measurements and for gamma spectrometry. Gas-filled detectors, like the Geiger-Muller (GM) detector, are used to obtain the radiation dose rate. Some critical characteristics that measure the effectiveness of a radiation detector are: the energy resolution, correlated with the intensity of the light yield, counting efficiency which is related to the crystal ability to attenuate photons which depends on the incident gamma energy and is proportional to both the density and the atomic number of the material, and inherent dead time [16; 43]. Scintillation detectors may be gaseous, liquid, or solid, organic (plastics, liquids) or inorganic. Their operating principle is based on the interaction of the incident radiation with the scintillator material and the conversion of the resulting light into electrical signals by a photodetector. Since inorganic scintillators exist in the form of a high \(Z\) crystal and a high light output, they are normally used for spectroscopy purposes (even for low energy radiation). In the same way, their high density offers good detection efficiency. Examples of inorganic scintillators are the alkali halides (e.g., NaI, CsI), oxides, such as the Bismuth Germanate (BGO), or lanthium halides (e.g., LaB, LaC). A summary of some typical characteristics of common inorganic scintillators is given in Table 3. LaBr3[Ce+Sr] is a recent scintillating crystal featuring enhanced energy resolution (light yield) and photoelectron yield in comparison to the standard LaBr3 [101]. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Scintillator** & **NaI(TI)** & **CsI(TI)** & **LaBr3[Ce]** & **LaBr3[Ce+Sr]** & **BGO** & **CeGAGG** & **Ref.** \\ \hline Density & 3.67 & 4.51 & 5.08 & 5.08 & 7.13 & 6.63 & [43; 100; 101] \\ \hline Effective atomic number & 49.7 & 54 & 45.2 & & 74 & 50.5 & [102; 103] \\ \hline \(\Delta E/E\) \% at 662 keV & \textless{}7.5 & 6.5–8 & 2.6 & 2.2 & 16 1  & 5.2 & [101; 104; 105; 106; 107] \\ \hline Wavelength of max emission [nm] 2  & 415 & 550 & 380 & 385 & 480 & 520 & [100; 101; 106] \\ \hline Photoelectron yield [\% & NaI(TI)] (for \(\gamma\)-rays) & 100 & 45 & 165 & \textgreater{}190 & 20 & – & [101] \\ \hline Light yield (photons/keV) & 38 & 54 & 63 & 73 & 8–10 & 46 & [101; 104] \\ \hline Primary decay time (ns) & 250 & 1000 & 16 & 25 & 300 & 90 & [101; 104] \\ \hline Hygroscopic & yes & slightly & yes & yes & no & no & [101; 104; 106] \\ \hline Self activity & no & no & yes & yes & no & no & [101; 104] \\ \hline \hline \end{tabular}  
* Energy resolution (%) at 511 keV. 2 The emission wavelength (emitted light) should match the quantum efficiency of the photomultiplier (PMT) or silicon photomultiplier (SiPM).  
\end{table} 
Table 3: Resume of the inorganic scintillation crystal main characteristics. Since organic scintillators have low Z, Compton scattering is the main reaction, and photoelectric effect becomes dominant for low energies, typically below 20 keV. Their low density and low light output (e.g., SGC BC-400 plastic scintillator has a factor of four less light output than the inorganic scintillator NaI) makes them less efficient; however, this can be offset if large volumes of plastic scintillator are used (e.g., in RPM or waste monitors) due to their low price. Therefore, plastic detectors are normally used for gross counting gamma-rays above 100 keV. Other relevant characteristics are the ruggedness, very short decay time (a few ns), and the possible use for charged particles and neutrons detection.