Dependence of the propagation of ultra-heavy cosmic ray nuclei on first ionization potential

Over 2000 Ultra Heavy (Z ≥ 65) cosmic ray ions with energies over 3 GeV/n have been recorded in the UHCRE, of which a total of 205 have already been located, measured and positively identified as Ultra Heavy (UH) ions by our group. The histogram of UH elemental abundances in the Earth's neighbourhood is obtained and the UH cosmic ray source abundances may be determined by means of an appropiate propagation model. This model describes the travel of UH ions from their sources to near the Earth, through the insterstellar medium (ISM). In our case, a dynamical Leaky Box (DLB) model has been used for propagation studies. Due to the nature of the transport equations corresponding to this model, it is necessary to assume given source abundances, perform the transport calculation to near the Earth, and to compare the result with the experimental measurements. A 'trial and error' procedure is applied until the source abundances giving the best agreement between the calculated and measured abundances near the Earth are found. Among all variables on which the transport equation depend, this work focuses on the effect of the First Ionization Potencial (FIP) on the propagation process. Although a better agreement between propagated and measured abundances is found when a correction for the effect of FIP is used for lighter cosmic ray nuclei, it has been found that the UHCRE experimental results are better reproduced when no FIP correction is assumed.