Induced release of the high energy densities stored in
isomeric nuclear states may be important in the development of
ultrashort wavelength lasers. Such a release could compensate the
spontaneous power density radiated from the laser medium at
threshold. The most promising candidate for such a role seems to
be the 31-yr isomeric nucleus of Hf-178 that stores 1.3 GJ/g in
the electromagnetic excitation of its constituent protons and
neutrons. Successful studies of the induced release of energies
from such isomeric states have required an extension of techniques
for nuclear resonance spectroscopy using synchrotron radiation
(SR) that had previously been applied only to ground state
materials. In 2004, monochromatic X-rays from the SPring-8 SR
source were used to identify one of the excited nuclear states
that mediates the induced decay of the 31-yr isomer of Hf-178.
That ``trigger level'' was found to lie at 2457.20(22) keV. It was
excited when an isomeric nucleus absorbed an incident X-ray
photon. We found that one branch of its subsequent decay
consisted of a strong electromagnetic transition to the ground
state of the nucleus. The energy of the ฮณ-photon emitted
was equal to the energy of the trigger level. Proximity in energy
of that level to the energy of 2446.06 keV stored by the isomer
makes it easy to induce a release of the stored energy and
encourages prospects for the development of a gamma ray laser.