In the residual fit, TD-prompt is fit first to capture most of the signal, TD-slow1 is fit next followed by TD-slow2 (Figure ). In the simultaneous fit, both TD-prompt and TD-slow1 are adjusted simultaneously to capture the TOF distributions, and the remaining portion is fit with TD-slow2 (see Figure , Supplementary Material). The residual fitting method provides an upper bound to the flux of TD-prompt and a lower bound to the flux of TD-slow1, while the simultaneous fitting method provides a lower bound to TD-prompt and an upper bound to TD-slow1. We found that the residual fitting process was more robust, as the activation energies obtained from the simultaneous fit were inconsistent with the expected trends. Attempts to perform the residual fitting method in reverse -i.e., fit the slow signal first and then fit the remaining signal with a MB distribution did not capture the rising portion of the TOF distribution and always resulted in an underprediction of the total flux. After the fitting of the TD component of a TOF distribution was complete, the IS component was obtained by subtracting the total thermal component (TD-prompt+TD-slow1+TD-slow2) from the total TOF distribution. The IS component in the TOF distributions of FiberForm was negligible; however, a non-negligible IS component (~10-15 %) was seen for vitreous carbon. Previous analysis suggested that this signal arose from a complicated thermal process on the surface or uncertainties in the surface temperature measurement . The angular distribution of the IS component in vitreous carbon appears to have thermal characteristics with a cosine-power distribution; therefore, the IS flux from vitreous carbon was added to the TDprompt flux.