Natural background radiation and X-ray radiation for the baggage check in an airport affect the photographic properties of silver halide imaging materials. The new mechanism of latent image formation by these ionizing radiations was proposed in the previous report on the basis of the experimental results by using ⁶⁰Co-γ-ray and 80kVp-X-ray irradiation in octahedral AgBr emulsions. The Experiments were extended to spectrally sensitized emulsions to clarify the scope and limitation of the proposed mechanism. It was found that the sensitivities of spectrally sensitized emulsions for these ionizing radiations could be also predicted quantitatively from the characteristic curve for visible-light radiation except the emulsions with extremely low quantum sensitivity.