PIONEER aims to probe high energy BSM physics via high precision measurements of rare pion decay. The technology required to do this sits at the frontiers of technological capabilities and is actively being developed around the world. The detector needs to measure both highly energetic yet very light positrons and the more massive, less energic pions/muons. Additionally, it needs to measure decays on the scale of nanoseconds and allow for reconstruction of particle tracks of less than a millimeter in length. While low-gain avalanche diodes (LGADs) have been identified as a promising device for the needs of PIONEER, the large dynamic range of energies that need to be detected introduces challenges that must be understood and characterized to achieve the desired precision. In this talk, I will discuss how CENPA's own tandem van de graaf was used to characterize the response of LGADs to heavy particles and how we will use these characterization to improve analyses and precision for PIONEER.