Which statement about the beam uniformity coefficient is true?

• A. It is a unitless quantity with a value of 1 or greater
• B. It has units of W/cm2
• C. SP/SA Factor
• D. It is always less than 1

Answer: (C)

The key idea is that the beam uniformity coefficient is defined by a specific ratio called the SP/SA factor. This is a dimensionless measure that compares the peak signal within the beam (SP) to the average signal across the beam (SA). It is this precise SP/SA ratio that quantifies how uniform the beam is: values near 1 indicate a very flat, uniform beam, while values above 1 reflect hotspots or nonuniformities.

Labeling it as the SP/SA factor is the standard way this property is described in this material, which is why that option is the correct one. The other statements mix in aspects like units (the coefficient isn’t expressed in W/cm2) or describe a general unitless property without naming the standard SP/SA descriptor, and since the beam’s peak cannot be smaller than its average, the notion that it’s always less than 1 is incorrect.