a self-gating pulse effect. Expansion of the molecule by Coulomb forces is not covered by the statistical treatment presented here, but is discussed further below.

The second term on the right-hand side of Eq. is sensitive to the atomic positions and accounts for the contrast in the average diffraction pattern. We can treat this information as the “signal" we aim to measure. The contribution each atom makes to the signal is proportional to $B(q)$, which is equal to the standard deviation of the diffraction in the merged 3D dataset divided by the number of atoms. The mean shot noise level, denoted by $\sigma_N$, is proportional to the square root of the intensity. We can estimate the mean shot noise level by considering the mean diffracted intensity in a shell of constant $q$, which can be derived by integrating Eq. and is proportional to $A(q)$. When the signal is compared to the noise, the proportionality constants have no influence on the interpretation, so we drop them for simplicity and write $$\sigma^2_N(q) =  A(q)  \;.
\label{eq:sigN}$$ In addition to shot noise, there is the damage noise due to the variations in how the damage manifests in each measurement. One contribution to the 