Gaunt factor

The Gaunt factor (or Kramers–Gaunt factor) is a correction factor that accounts for the effect of quantum mechanics on an object's continuous x-ray absorption or emission spectrum. In cases where classical physics provides a close approximation to the true spectrum, the Gaunt factor is close to 1. When quantum physics becomes important, it becomes bigger or smaller than 1.¹

The Gaunt factor was named after the physicist John Arthur Gaunt, based on his work on the quantum mechanics of continuous absorption.² Gaunt used a 'g' function in his 1930 work, which Subrahmanyan Chandrasekhar named the 'Gaunt factor' in 1939.³ It is sometimes named the Kramers-Gaunt factor as Gaunt incorporated the work of Hendrik Anthony Kramers.