discover of the neutron, what happen to 2+ charge
Corrected: "James Chadwik identified the neutron by exposing a Beryllium foil to  α-rays (He+2) and showing that the previously discovered emitted collision product were massive neutrally charged particles." The experimental set-up he used (see:http://rspa.royalsocietypublishing.org/content/royprsa/136/830/692.full.pdf) did not determine where any electrons came from, so while electrical charge can be assumed to balance, he couldn't claim any direct knowledge of the source or fate of any electrons in his experiment. For us, today, balancing a nuclear reaction's charge distribution on both sides of the arrow is simply "bookkeeping", it implies facts that were not as well supported in 1932 as they are today. He avoided the temptation to over-interpret his experimental data.