THE RAREST NATURALLY OCCURRING ISOTOPE, tantalum-180, is rare because it is bypassed in the two processes that produced most of the heavy elements we dig out of the ground here on Earth: the so called s process (slow neutron capture in stars) and the r process (rapid neutron capture in supernova explosions). What little Ta-180 that is produced (in stars or in reactors) is quite robust; its halflife is more than 10¹⁵ years. Ta-180 is also unique in being the only naturally occurring isomer; it is essentially a nucleus in a perpetual excited state. A group of German physicists (Peter Mohr, 011-49-615-116-3221, mohr@ikp.tu-darmstadt.de), essentially working with the world's supply of this priceless substance, about 7 milligrams, try to jar the tantalum nuclei out of their customary states by shooting them with gamma photons, thus re-creating stellar conditions. They observed that depending on the temperature the Ta-180 halflife varied over a range of more than 10¹⁷! This rules out the nucleosynthesis of Ta-180 within the "canonical" s process; however, in a more realistic version of the theory, the tantalum can survive if it rapidly mixes with cooler layers of the star. (Belic et al., Physical Review Letters, 20 December 1999; Select Article.)