Is it expensive?
Do you mean transmutation of one element into another? Typically this uses a target material which is inserted into a tube that moves the target into the middle of a reactor so it can be neutron activated.
Yes exactly. Does this process change the number of protons in the atom for it's known that the atomic number characterizes the element.
Yes, if you add one or more neutrons to a nucleus it might undergo beta decay and become a different element.
It is not expensive to generate "some" new nuclei, but it is expensive to produce macroscopic amounts. In addition, you usually get a composition of some stable and some radioactive isotopes. For a practical application, you might have to separate them, which is expensive, too.
To put "not expensive" in perspective here, you still need the reactor or particle accelerator. This is not a workroom table experiment.
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