Determining the uncertainty of Eγ

To determine the uncertainty in Eγ we pick an angle for the neutron within [[math]\theta_n[/math], [math]\theta_n + Δ \theta_n[/math]] and a momentum of the neutron between [[math]P_n[/math], [math]P_n + Δ P_n[/math]]. What are reasonable Δ[math]\theta_n[/math] and Δ [math]P_n[/math]?