Quick citation help/punctuation question. Would I use another period?

I have a sentence that needs APA style citing and I’m a little perplexed on how to use the period. I cited the sentence below and I would appreciate any insight on if I cited it correctly. If not, would I delete the period after the parentheses and leave it as is?

It was then noted that if other elements were exposed to these neutrons that new radioactive elements emerged (Walker, n.d.). A uranium nucleus that has absorbed a neutron splits and releases energy into two parts.