An experiment was performed in which neutrons were shot through two slits spaced 0.10 mm apart and detected 3.5 m behind the slits. The following figure shows the detector output. Notice the 100 μm scale on the figure. To two significant figures, what was the speed of the neutrons?
Δy = λL/d (spacing between maxima)
λ = h/mv (de Broglie λ)
m= 1.67*10^-27 Kg
The Attempt at a Solution
The spacing between the maxima appears to be 100*10^-6 m in the figure, so:
(Δy*d)/L = λ = ((100*10^-6 m)*(0.1*10^-3 m))/3.5 m = 2.85714*10^-9 m = de Broglie λ
v = h/(mλ) = (6.626*10^-34 J.s)/((1.67*10^-27 Kg)*(2.85714*10^-9 m) = 138.9 m/s
This answer is incorrect. Can someone please give me a hint as to what I'm doing wrong?