THE EVOLUTION OF OXYGEN AND IRON FLUENCE DURING SOLAR PARTICLE EVENTS AND THEIR CONTRIBUTION TO SKIN DOSE FOR EVENTS FROM OCTOBER 1997 TO DECEMBER 2005

Abstract

One of the primary concerns with space travel is the protection of astronauts from potentially lethal radiation. A major source of potentially lethal radiation is our own sun. During Solar Cycle 23 there were 97 detected Solar Particle Events (SPEs). In order to develop radiation protection guidelines and establish methods to protect astronauts the spectrum of particles emitted during a SPE must be understood. Data for oxygen and iron particle fluence was taken from the Solar Isotope Spectrometer. The fluence was sorted and formatted for each solar particle event. After determining the contribution to skin dose for oxygen, the time evolution of each event was analyzed. After analyzing the raw count data, a threshold was set that could be applied to each event. Using this threshold count rate as the starting point, each event was plotted and fitted with a smoothing polynomial function. The slope calculated from this function was then plotted against the previously calculated skin dose and a Weibull function was fitted to the data. The resulting plot provides a method to predict the cumulative dose due to the oxygen fluence over the first 24 hours of an event and thereby provide a warning of future high dose rate in time to achieve significant dose sparing for most events. For the ten events that delivered the highest oxygen dose, the dose sparing that could be achieved by taking shelter when the high dose rate was predicted was greater than 70 percent for all but one event. The one outlier achieved a dose paring of only 57 percent.