Final answer:
In a longitudinal UT scan with the beam perpendicular to the entry surface, diffracted wave signals will not be shown because the waves are sent directly into the material without encountering obstructions that would cause diffraction.
So option (B) is correct.
Step-by-step explanation:
The correct answer to the question is B) not. A longitudinal ultrasonic testing (UT) scan with an incident beam perpendicular to the entry surface will not show diffracted wave signals since the beam is directed in such a way that allows it to continue straight into the material. The phenomenon that usually causes beams to spread out is known as diffraction. However, when a beam of ultrasonic energy is introduced perpendicularly to a flat surface, it typically does not exhibit diffraction within the material unless some flaws or edges cause diffraction. Diffraction occurs when waves encounter an obstacle or a slit that is comparable in size to the wavelength of the waves, which is not the case in a standard longitudinal UT scan.
Diffraction is a fundamental property of wave behavior, but it is not always evident in every scenario. In the context of a longitudinal UT scan, where the waves are sent straight into a medium without encountering any such obstructions, the ultrasonic waves propagate through the material without showing a diffracted pattern.