## 3 Results and Discussions
### LET Difference between Neutrons and Protons  
To examine if protons can be used to replace neutrons for SEE testing, the most important consideration is the equivalence of the LET spectrum as LET is a key determining parameter for the SEE. Figure 3 shows the LET spectra of the structure without SiGe being irradiated by protons and neutrons. Figure 3: Linear energy transfer (LET) spectra in a structure without silicon-germanium (SiGe) irradiated by 63, 105, 150, 200, and 230 MeV proton and LANSCE neutron. The LET spectra of the examined geometry irradiated with LANSCE neutron and selected monoenergetic protons were plotted in Figure 3. The largest visible difference in the LET spectra is below 1 MeV-cm\({}^{2}\)/mg, where protons generated 1000 times more events than neutrons did. Due to the low LET, this visible difference has minimal impact on single event effects, whilst it could cause the total ionization dose (TID) effects under prolonged radiation exposure. However, the cross section of the SEE can be altered by TID as described by [PERSON] et al. [19] and [PERSON] et al. [20]. We further compared the LET spectra of 200 MeV proton and the LANSCE neutron for LET larger than 1 MeV-cm\({}^{2}\)/mg. The differential fluence was in good agreement in LETs between 1 to 10 MeV-cm\({}^{2}\)/mg but was slightly deviated in LETs larger than 10 MeV-cm\({}^{2}\)/mg. This phenomenon can be explained with the help of Figure 4, in which the LET was plotted for several major secondary particles. In parentheses, the first symbol represents incident particles and the second symbol represents particles that contribute to the LET. For example, (n, He) means that the helium is generated by the LANSCE neutron. In the LETs between 1 to 10 MeV-cm\({}^{2}\)/mg, events were mainly caused by helium ions, which were mostly due to the elastic interactions of high-energy particles, regardless of whether they were neutrons or protons. For LETs more than 10 MeV-cm\({}^{2}\)/mg, 200 MeV protons gave a higher differential fluence than the LANSCE neutron because protons generate more heavy secondary ions such as aluminum and magnesium. The LANSCE neutron produces very few of these secondary particles because most of the LANSCE neutron shown in Figure 1 is less than 10 MeV which is below the threshold energy of these nuclear interactions. The LET spectra from the studied structure irradiated by lower proton energy are rarely used, but we included them in our work (see Figure 5). In these low-energy proton irradiations, the differential fluence in LET is 10,000 times higher than neutrons for LET lower than 0.5 MeV-cm\({}^{2}\)/mg and five times higher for LETs between 1 to 10 MeV-cm\({}^{2}\)/mg. On the other hand, for LETs larger than 10 MeV-cm\({}^{2}\)/mg, low-energy protons give less events. Therefore, from the above results, our further evaluation will focus on the protons with energy higher than 63 MeV. Figure 4: The LET contribution from He, Mg, and Al generated by the 200 MeV proton and the LANSCE neutron. In parentheses, the first symbol represents incident particles and the second symbol represents particles that contribute to the LET. In comparison to the results from [PERSON] et al. [21], the LET distribution in our work was much wider because the simulation of all secondary particles was performed in our study, which means that both the ionization energy loss and the nuclear interactions were simulated. Therefore, our simulations are expected to be more accurate, but it is time-consuming (takes 2-3 days per energy per condition in a computer with Intel I9-9900k CPU working at 4600 MHz and two dual channels 8 GB RAM working at 3000 MHz). The uncertainty in our simulation for the LET spectra shown in Figures 3 and 4, is quantified using the coefficient of variation (C\({}_{\rm v}\)). We found that the C\({}_{\rm v}\) is less than 10% for LETs lower than 6 MeV-cm\({}^{2}\)/mg. However, if the LET is greater than 40 MeV-cm\({}^{2}\)/mg, C\({}_{\rm v}\) is between 30% and 70%, due to the small number of events with these LETs.