In option a, the process of annihilation and pair production is still possible and mostly observed by the photons emitted from the unstable nucleus (radioactive nucleus).
Thus, option a is correct.
In option b, as with the help of heat light nuclei can be produced but they destroy immediately.
Hence, option b is not correct.
In option c, the photons emitted from the nucleus do have very large energy and can easily ionize an atom.
Hence, option c is correct.
In option d, the photons can ionize the atoms.
Hence, option d is incorrect.
In option e, the photons can ionize the atoms.
Thus, option e is incorrect.
Hence, options a and c are correct.