Illustration of several background components for mono-energetic transmission measurements, from reference [13], which used a D(d,n)³H reaction and a gas cell generator. In this diagram, ϕ represents the portion of the flux that is not attenuated by the sample and β represents the room return background. The third component of the background, neutrons produced anywhere but the gas cell or solid target, are represented by γ₁, γ₂, and ζ. In-scattering is not represented in this diagram.