## 4 Results and Discussion
These results are perfectly consistent, considering the uncertainties, with the experimental ones provided in literature and/or stated by the manufacturer, which are 16 \(\pm\) 4% for RAD7, 6 \(\pm\) 1% for RaMonA, and 27 \(\pm\) 3% for Radim3A. A further study has been performed to simulate, by Geant4+COMSOL, two different versions of RaMonA system, called Ramonino and Ramonello, used in diffusion mode respectively as the reference monitor in the Rn exposure facility of Universities of Naples and Campania, and referred to the ENEA (National Metrology Institute of Ionizing Radiation Metrology in Italy) respectively [29; 30; 31; 32; 33]. Ramonino and Ramonello consist of 190 \(\pm\) 4 cm\({}^{3}\) and 300 \(\pm\) 5 cm\({}^{3}\) hollow hemispherical metallic chambers with silicon surface barrier detectors, having a 50.0 \(\pm\) 0.4 mm\({}^{2}\) and 100 \(\pm\) 1 mm\({}^{2}\) circular active area, on the bottom, respectively [28]. The basis of the hemispherical chamber of both systems has a hole for the detector (insulated in a plastic holder). A high voltage of 1500 V is applied to the metallic chamber of both systems, to electrostatically collect \({}^{222-220}\)Rn ionized daughterson the detector. Experimentally, the measurement systems have a \({}^{218-216}\)Po detection efficiency of: 0.0108 \(\pm\) 0.0003 cps\(\cdot\)L\(\cdot\)Bq\({}^{-1}\) for Ramonino, and 0.0275 \(\pm\) 0.0008 cps\(\cdot\)L\(\cdot\)Bq\({}^{-1}\) for Ramonello [28]. Considering the volume of the two measurement chambers, Ramonino and Ramonello have 6.0 \(\pm\) 0.2% and 9.0 \(\pm\) 0.3% of \({}^{218-216}\)Po detection efficiencies. In addition, in this case, the simulated efficiencies of Ramonimo and Ramonello, i.e., 6 \(\pm\) 1% and 8 \(\pm\) 2%, by Geant4+COMSOL agree within uncertainty with the experimental ones. No figures of the Ramonino and Ramonello systems are shown because they are in [28] and, also, have geometries similar to those of RAD7 and Radim3A and, therefore, from the simulation point of view they would have been similar and brought only an overload of repetitive figures. Based on all previous considerations, a new Rn monitoring device (Ramonetto) has been designed and realized to be used in diffusion mode as new improved reference monitor in the Rn exposure facility of Universities of Naples and Campania. It consists of a 1072 \(\pm\) 3 cm\({}^{3}\) hollow hemispherical metallic mesh chamber with a silicon PIN photodiode detector, having a 784 \(\pm\) 2 mm\({}^{2}\) square active area, on the bottom (insulated in a plastic holder). A voltage of 2500 V is applied to the metallic chamber to electrostatically collect \({}^{222-220}\)Rn ionized daughters on the detector. The measurement system has a high \({}^{218-216}\)Po detection efficiency of: 0.25 \(\pm\) 0.03 cps\(\cdot\)L\(\cdot\)Bq\({}^{-1}\), and 24 \(\pm\) 3% considering the volume of the measurement chamber. Again, the efficiency of the new device is consistent with the simulated one of 23 \(\pm\) 4% by Geant4+COMSOL. The experimental efficiency of Ramonino, Ramonello and Ramonetto were obtained using \({}^{222}\)Rn + \({}^{220}\)Rn mixed atmospheres realized by calibrated sources of a pylon RNC-RN-1025 \({}^{226}\)Ra for \({}^{222}\)Rn, and \({}^{232}\)Th salts for \({}^{220}\)Rn [28]. Figure 3a shows Ramonetto measurement system. It is worth mentioning that to choose  
Figure 1: Schematic view of the Geant4 and COMSOL simulations of the three main worldwide commercial \({}^{222-220}\)Rn measurement system RAD7 (**a**), RaMonA (**b**) and Radim3A (**c**). For Geant4 are shown the 3D geometry and simulation of the primary starting particles source; for COMSOL are shown the simulated electric potential spatial distributions and electric field flow lines. the right high voltage value to be applied to the chamber walls of Ramonetto, experimental and simulated tests have been carried out on the \({}^{218}\)Po counts per seconds (cps) versus the applied voltage value. As seen in Figure 3(a.1), the value of 2500 V has been chosen since the maximum cps saturation is reached.