AL-26 IN THE EARLY SOLAR-SYSTEM

Until a few years ago, most scientists believed that the isotopic anom alies produced by the extinct radionuclides such as Al-26 and I-129 re lative to normal abundances are all of the order of 10(-4) despite the wide range in their mean lifetime and hence this anomaly range must b e the result of inhomogenious mixing of exotic materials with much lar ger quantities of normal solar system materials over a short time rath er than the result of free decay. Re-examination of the existing alumi num isotope data for the mineral inclusions of the carbonaceous chondr ite Murchison reveals, however, that the observed anomalies can be exp lained in a more straightforward manner as due to the formation of spa llation-produced aluminum and magnesium isotopes from Si-28 during the x-process nucleosynthesis, which must have occurred on the surface of an exploding supemova more than 5 billion years ago.