Variations in Organ Doses Resulting from Different Solar Energetic Particle Event Spectrum Parameterizations

Calculations of solar energetic particle event (SPE) doses typically utilize SPE proton spectra parameterized with either an exponential in rigidity (momentum per unit charge) or a Weibull form in energy. In this work we report organ doses calculated using these two different parameterizations of proton spectra of four large solar energetic particle events. They are the SPEs of August 4, 1972, August 12, 1989, September 29, 1989 and October 19, 1989. The variations in predicted doses to critical organs introduced by the use of these two parameterizations for these large events could be a factor in evaluating the effectiveness of spacecraft shielding. Events similar to the largest SPEs observed during the space age could deliver large organ doses and the potential for an acute radiation syndrome response in interplanetary crews. The BRYNTRN transport code in conjunction with the CAM human geometry model are used to calculate the dose to the skin, ocular lens, and bone marrow (BFO) behind aluminum shielding thicknesses ranging from 1 to 10 g/cm². The largest variation in dose for the two parameterizations is for the BFO behind 10 g/cm² of aluminum shielding for the August 1972 event. The estimated doses are 21.1cGy and 6.9 cGy for the rigidity and energy parameterizations respectively - approximately a factor of three difference in the BFO dose. In general, however, the doses for all organs and shield thicknesses for all events studied are within 20% for the two parameterizations.