[loarake]

Are you sure you're not mixing up neutrons and protons? Here are some typical depth dose curves from google images(http://www.nap.edu/books/11976/xhtml/images/p20014b2bg205001...). Neutrons, being neutral particles, don't exhibit the Bragg Peak (large increase in energy deposition at the end of the particle's track) that you get for heavy charged particles.

[privong]

I was pretty sure neutrons beahved that way (recalling from a course I took in grad school), but it has been a few years, and I do not have references handy. I am not entirely sure what the y-axes are, on the plot you linked, so I am not sure how it correponds to what I was saying.

[tjradcliffe]

The do not. Protons have a quite definite range, and can be controlled in the way you suggest. This is because they lose energy primarily by scattering (much lighter) electrons out of their path. This means protons have relatively straight paths and the dynamics of the electromagnetic interaction gives an energy deposition curve that is sharply peaked at the end.

Neutrons slow down via interaction with nuclei (all of which except hydrogen are heavier) so they lose energy slowly and scatter all over the place. They have no definite range (search for "fermi age theory" to get a rough idea of the distribution) and can't be meaningfully beamed (unless they are ultra-cold, which is not relevant to fusion power.)

I've made a longer comment above that goes into neutron physics in a little more detail.