Is there a threshold wavelength above which no constructive interference is observed? Select the correct answer. Is there a threshold wavelength above which no constructive interference is observed? Select the correct answer. There is no threshold wavelength, since the constructive interference appearance depends only on the angle the x rays are incident on the crystal and the spacing between the atomic places. There is a threshold wavelength equal to the double path length difference for photons reflected from adjacent atomic planes. There is no threshold wavelength, since the constructive interference appearance depends only on the angle the x rays are incident on the crystal. There is a threshold wavelength equal to the double spacing between the atomic planes.