American Society for Nondestructive Testing (ASNT) Radiographic Testing Practice Test

The term that describes the unsharpness caused by geometrical factors in radiography is known as a "prenumbral shadow." When radiographic images are produced, the geometry of the image formation can lead to areas of unsharpness around the edges of a radiographic profile. This occurs due to the spreading of radiation as it travels from the source to the film or detector, resulting in softer transitions around the boundaries of an object.

Prenumbral shadows arise primarily from the finite size of the radiation source and the positioning of the source relative to the object and the film. Specifically, if the radiation source is not point-like, it will cause variation in the exposure at the edge of an object, leading to a gradation of density rather than a sharp boundary, creating a shadow that lacks clear definition.

The other terms listed have different meanings. Vignetting refers to a gradual darkening of the image at the corners compared to the center, which is not directly related to geometrical unsharpness. Diffraction blur describes the spreading of light waves when they encounter an edge, which is a more optical phenomenon rather than geometrically induced unsharpness. Image distortion typically involves warping or bending of the image, which may relate to the positioning of