A comparison of measurements and predictions for the April 15 and April 18, 2001 solar proton events

Two energetic solar particle events (SPE) occurred during the week of April 15, 2001 resulting in exposure to the crew aboard the International Space Station (ISS). The radiation environment on the ISS is monitored with a tissue equivalent proportional counter (TEPC) which measures a time-resolved record of the accumulated dose and dose rate during the course of the event. In addition to TEPC measurements, the flight control radiological support team uses an in-house developed solar particle event – real time (SPERT) code to estimate the progress of crew exposures during an SPE. The TEPC measurements during these two events and corresponding calculated results from the SPERT code are compared. The timing of high dose rate intervals from SPERT is in excellent agreement with measured TEPC data. The accumulated dose and peak dose rate per pass are more difficult to assess due to uncertainties in shield distributions and directionality of the source term. However, using a standard shield file, the total accumulated exposure projected using SPERT was approximately two thirds of the total dose measured by the TEPC (900μG) for the April 15, 2001 and April 18, 2001 events.