Gamma rays are high energy photon keV and above from nuclear or subatomic processes, e.g., anihilation (e+e- → γγ) or decay (e.g., πo → γγ).
Photons interact with charged particles, e.g., electrons, positrons, protons, and nuclei.
Gamma rays will not be detered by electric or magnetic fields, but they will interact with charged particles within those fields.
In radiation shielding, particular for shielding against gamma rays, one would use high Z materials because high-Z means high electron density. Electrons interact with photons via the photoelectric effect or Compton scattering. In the case of nuclei, gamma rays of energy greater than 1.022 MeV initiate pair production, and at higher energies, photoneutron emission, photodissociation (d+γ → p + n) or photofission/spallation.