Humans create big neutron amounts for isotope production essentially by uranium fission. Either in powerful reactors for electricity production, or in small reactors meant to preserve the excess neutrons, using highly enriched uranium and possibly heavy water.99
Mo is made by neutron irradiation of 235
I imagine special targets are inserted and removed, because 99
Mo must be extracted well before the main fuel is replaced.
As compared, particle accelerators give a smaller neutron flux, but under circumstances, they might be considered for the production of medical isotopes. A highly accelerated proton smashes on some unimportant heavy nucleus like lead, breaks it somehow, and neutrons are emitted which can then be absorbed by a target material.
Historically, alpha radioactive materials were mixed with beryllium which consists of two alphas loosely hold by a very fuzzy neutron. The collision breaks the kernel and frees the neutron. The tiny flux achieves nearly nothing.
Just D-T or D-D fusion in a fusor makes neutrons. The flux is too tiny for use.
I have proposed a reduced tokamak or stellarator that burns only deuterium in a D-D reaction as a neutron source. The flux is much smaller than at a fission reactor, but caring design could let it produce enough 99
Mo and other nuclides for medical useshttps://www.chemicalforums.com/index.php?topic=92021.0
I still have to explain some day how 98
Mo shall capture the neutrons efficiently. That would be a very nice use of miniature tokamaks, a first commercial use, much easier than electricity production.