Magnitude of the energy for interference maxima

[soul]

Homework Statement

Consider a crystal with planar spacing 3.2 A⁰. What order of magnitude of energies would
one need for (a) electrons, (b) helium nuclei (mass = 4*proton mass) to observe up to three
interference maxima?

Homework Equations

2d.sinx = n.lambda (I)
lambda = h / p (II)
E = (1/2)mv2²

The Attempt at a Solution

To solve this question, I thought I must first find the wavelength and can use other equetions that I wrote above. Actually, I don't know how I can use them but since in the question, mass is important, I thought an equation with mass can work.

 

[BigJDubs]

So I tried to solve this question by using equations (I) and (II). Firstly, I set equation (I) as 2d.sinx = nh/p and solved for sine as sine = nh/(2dp). Then, I used equation (II) as h/p = lambda and found the wavelength as lambda = nh/(2dp). Finally, I used equation E = (1/2)mv22 and substituted the wavelength that I found above as v = 2dp/nh. Then, I found energy for electrons as E = (1/2)*(9*10^-31)*((2*3.2*10^-10)/(nh))^2 and for helium nuclei as E = (1/2)*(4*1.67*10^-27)*((2*3.2*10^-10)/(nh))^2 However, I am not sure if this is right or wrong. Could you please check it for me? Thanks in advance.