Nuclear Fusion Question Please Help its for a science project.?

Okay I've looked all over the internet, but I can't find anything that tells me why protium fusion can't happen. Look I know it involves that protium the most abundant isotope of hydrogen in the universe doesn't have a neutron. However what I don't understand is why can't they just add neutrons to the vacuum chamber containing the protium and then start the nuclear fusion process. Won't the plasma that's created collide the neutrons with the protium atoms also fusing the into deuterium. I'm trying to build a nuclear fusor and there aren't many out there, but its been done before so I know its not impossible. I just want to understand why this can't be done. Please I've researched so much on my spare time and I have not found any explanation of why this can't be done. Thank You for your help.