Determining the uncertainty of Eγ

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

What are reasonable Δ[math]\displaystyle{ \theta_n }[/math] and Δ [math]\displaystyle{ P_n }[/math]?

[math]\displaystyle{ P_n }[/math] is determined by time of flight.

Knowns:

[math]\displaystyle{ m_n }[/math] = 939.565 ± 2.8x[math]\displaystyle{ 10^(-4) }[/math] [math]\displaystyle{ MeV/c^2 }[/math]