  The cosmic dispersion in the abundances of the heavy elements strontium and
barium in halo stars is well known. Strontium and barium are detected in most
cool, metal-poor giants, but are these elements always detectable? To identify
stars that could be considered probable candidates for lacking these elements,
I examine the stellar abundance data available in the literature for 1148 field
stars and 226 stars in dwarf galaxies, 776 of which have metallicities lower
than [Fe/H]<-2.0. Strontium or barium have been detected in all field, globular
cluster, and dwarf galaxy environments studied. All upper limits are consistent
with the lowest detected ratios of [Sr/H] and [Ba/H]. The frequent appearance
of these elements raises the intriguing prospect that at least one kind of
neutron-capture reaction operates as often as the nucleosynthesis mechanisms
that produce lighter elements, like magnesium, calcium, or iron, although the
yields of heavy elements may be more variable.
