Suppose we have isolated a nucleus from a helium atom. If we treat the two protons and two neutrons as equal spheres, how would the protons and neutrons be arranged if the shape of a nucleus took the form of a tetrahedron? 

So you are asking about the shape of an alpha particle?

Have you tried Google?

https://www.google.co.uk/search?source=hp&ei=dACwW4mHEbDjsAeqs6uQBg&q=shape+of+alpha+particle&oq=shape+of+alpha+particle&gs_l=psy-ab.3..33i22i29i30k1l9.1106.6636.0.6978.23.17.0.0.0.0.258.2536.0j8j5.13.0....0...1c.1.64.psy-ab..10.13.2522...0j0i131k1j0i22i30k1.0.5dp2kSUXfxs

13 hours ago, studiot said:

Have you tried Google?

Ah. I was trying to find something like that by using words like "structure". The word "shape" never occurred to me! Well done.