A theory of low source start-up based on the Pál-Bell equations

To carry out the calculations, we use the Pál-Bell backward formalism (Pázsit and Pál, 2008) and apply it to the point model in order to make comparisons with the earlier work of Hurwitz. We also extend the study to include space and energy dependence which are found to have a not insignificant influence on the results. The usefulness of the Gamma distribution is explored and its accuracy assessed. Tables and figures are given to illustrate the conclusions.