The ultra heavy elements in the cosmic radiation

The concept that nuclei of all of the elements in the periodic table were accelerated to relativistic energies in the primary cosmic rays was confirmed by the discovery of the presence of nuclei significantly heavier than iron. These "ultra heavy" nuclei must all have been synthesized in endothermic reactions, occurring predominately in the final stages of stellar evolution. Determination of the relative abundances of these nuclei should provide new insights into the nuclear processes in some of the most energetic events in the life cycle of stars. The very low abundances of these nuclei relative to those of the exothermic lighter nuclei have made progress difficult. In addition, the effects of apparent preferential acceleration mechanisms and of propagation through the interstellar medium have distorted the source abundances. The history of the original discovery of the presence of these nuclei will be followed by a summary of the present state of knowledge of the observed abundances. The effects of acceleration biases and of interstellar propagation will be discussed. Finally some of the possibilities for further advances will be outlined.