X RAYS IN, GAMMA RAYS OUT. A laser is a machine for pumping energy (electrical, light, chemical, etc.) into a medium (liquid, gas, solid, etc.) whose atoms subsequently relax in a concerted way, producing coherent light. One of the obstacles to creating an x-ray or gamma laser is the inability to pack enough energy into the medium and have it sit there long enough until it can be extracted under the right circumstances. One candidate medium for the job is isomeric hafnium. In nuclear physics isomers are nuclei that have the same number of neutrons and protons but differ in that for one nucleus one or more nucleons (protons or neutrons) are placed in an excited state. Physicists at the University of Texas at Dallas (Carl Collins, 972-883-2864, cbc@utdallas.edu) and their colleagues in Russia, Romania, Ukraine, and the US begin with a sample (prepared at Los Alamos) of a metastable (31-year lifetime) isomer of Hf-178 with 4 participating nucleons, possessing a stored energy of 2.5 MeV. Then, like a transistor triggered by the merest of gate signals, the isomer material can, with the input of some x rays (amounting to only 1.6% of the output energy), produce induced gamma emission (IGE); thus x ray energy is stockpiled in the Hf and later extracted at higher gamma-ray energy. The emitted rays are not coherent, however, so this is not yet an example of gamma lasing. IGE research also has astrophysical implications since isomer states are expected to behave differently in gamma-intense environments such as supernovas. (C.B. Collins et al., Physical Review Letters, 25 January 1999; see http://www.utdallas.edu/research/quantum.)