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.