An experiment shows that an acoustic field can govern the polarization state of gamma photons emitted in resonant nuclear transitions. The result opens a route to manipulating gamma radiation with conventional mechanical tools, something previously achieved only with magnetic fields or suitable crystals.

The polarization of gamma photons from excited nuclei is a valuable probe of nuclear structure and fundamental symmetries, but controlling it actively is delicate: the energies involved are on the order of keV to MeV, far beyond what ordinary optical modulators can handle. The work exploits the coupling between lattice vibrations and resonant nuclear levels, so that an acoustic wave induces a controllable anisotropy in the emission.

In the setup used, a piezoelectric transducer excites ultrasonic waves in the emitting crystal while the angular distribution and polarization of the resonant gamma radiation are measured. By varying the amplitude and frequency of the acoustic excitation, the researchers observe reproducible changes in the degree of linear polarization of the photons, in agreement with the phonon-nucleus coupling model.

The practical interest is twofold. On the one hand, it allows tunable polarized gamma beams to be generated without superconducting magnets or specialized gamma optics, simplifying nuclear spectroscopy setups. On the other, it turns acoustic control into a tool for studying the environment of the emitting nuclei, since the polarization response reflects the dynamics of the lattice in which they are embedded.