## 4 Conclusions  
From the Monte Carlo studies in this work, in comparing the LET spectra and secondary particles yield from the proton and neutron radiation, we found that 200 MeV proton radiation has the closest resemblance to the neutron radiation, which concurs with suggestions from NASA. However, even with this close proton radiation, several differences present between proton and neutron radiation are as follows: First, proton radiation produces high secondary particles yield for LET \(>\) 15 MeV-cm\({}^{2}\)/mg, and neutron hardly has LET \(>\) 10 MeV-cm\({}^{2}\)/mg. Second, the secondary particles distribution is broader for the case of proton radiation. Third, proton radiation produces more secondary particles with \(Z>\) 14 whilst neutron radiation produces more secondary particles with \(8<Z<14\). Fourth, the energy deposited from proton radiation is around 300 times higher than neutron in the same flux. Fifth, the presence of SiGe does not affect the secondary particles yield for proton radiation, but it is decreased for neutron radiation. This implies that the strengthen of radiation robustness with the addition of SiGe cannot be seen with proton radiation.  
In this study, we only focus on some commonly used monoenergetic protons in several testing protocols. As presented in the results, no monoenergetic proton can reproduce exactly the secondary particle LET and yield spectra to that of the LANSCE broad band neutron. However, it may be possible that mixing energies of protons can create better equivalence. Further study using range (energy) modulation technique to generate wider proton spectrum will be conducted to explore this possibility.  
As LET and secondary particles yield can affect SEE testing, how the above-mentioned five differences will affect the SEE testing results are as of yet unknown. The answers can only be known through either subsequent proton or neutron testing or SEE simulation on semiconductor devices with LET and secondary particles yield distribution as obtained from the Geant4 simulation. On the other hand, as proton radiation seems to be more stringent than neutron radiation, one may use proton radiation tests as a higher calling to the radiation robustness of integrated circuits, with the expense of possibly higher design and fabrication costs. All these future works will be necessary in order to ascertain the equivalence or acceleration of neutron and protons radiation for SEE testing.  
Conceptualization, C.M.T. and T.-C.C.; methodology, C.-J.T. and C.-C.-L.; Writing--original draft preparation, Y.C.; project administration, C.M.T.; writing--review and editing, C.M.T. and T.-C.C.; All authors have read and agreed to the published version of the manuscript.  
This research was funded by Taiwan Semiconductor Manufacturing Company JDP project. And Chang Gung Medical Re-search Program under projects CIRPDI10022, BMRP736, CIRPD2F0024, and CIRPD2I0012.  
This work was technically supported by the Particle Physics and Beam Delivery Core Laboratory of the Institute for Radiological Research, Chang Gung University/Chang Gung Memorial Hospital.  
All authors have no conflict of interest to the organizations mentioned in the paper.