Existence of GZK neutrinos ( ultra high energy neutrinos ) have been justified although the flux is very low .
A new method is desired to use a huge mass of a detector medium to detect them .
A fundamental study of radar method was carried out to measure microwave reflection from electromagnetic energy deposit by X-ray irradiation in a small rock salt sample .
The reflection rate of 1 \times 10 ^ { -6 } was found at the energy deposit of 1 \times 10 ^ { 19 } eV which was proportional to square of the X-ray intensity suggesting the effect to be coherent scattering .
The decay time of the reflection was several seconds .
This effect implies a large scale natural rock salt formation could be utilized like a bubble chamber irradiated by radio wave instead of visible light to detect GZK neutrinos .