X-rays trigger gamma rays from hafnium isomer

X-rays trigger gamma rays from hafnium isomer

Prospects for a gamma-ray laser--commonly thought to be impossible due to the cubic dependence of subthreshold spontaneous emission power on frequency--have brightened. Physicists at the University of Texas at Dallas (UTD) describe development of an isomer of hafnium as a potential gamma-ray laser gain medium. With four of its nucleons in an excited metastable state, the isomer has a 31-year half-life and emits cascades of gamma rays when perturbed by soft x-rays. A single 40-keV photon triggers a gamma cascade with energy totaling 2.5 MeV, a 60X enhancement in energy. Produced by a process called proton spallation, the isomeric hafnium is capable of storing 1.3 GJ of releasable energy per gram.

Obtaining a sample of the material from Los Alamos Scientific Laboratory (Los Alamos, NM), the UTD physicists teamed with researchers from five countries to experimentally trigger gamma-ray production. According to Carl Collins at UTD, the cross section of the hafnium is so large that the team was able to use an ordinary dental x-ray machine as the triggering source. As of yet, the emitted gamma rays are not coherent. Contact Carl Collins at cbc@utdallas.gifdu.

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