h = 6.626*10^(-34); e = 1.602*10^(-19)*10^3; 
    me = 9.109*10^(-31); c = 3*10^8; 
    d = 3.14*10^(-10);
Ekin = 40*e

λe = 
      h/(2*me*Ekin*(1 + Ekin/2/me/c^2))^(1/2)

λp = h*c/Ekin

θ = ArcSin[λe/2/d]

0.009579919775179463`*180/π

θ = ArcSin[λp/2/d]

0.04941596801187158`*180/π