Question: who discovered that the number of protons for each element’s atoms is unique
[{'answer': 'James Chadwick', 'provenance': [{'wikipedia_id': '673', 'title': 'Atomic number', 'start_paragraph_id': 21, 'start_character': 50, 'end_paragraph_id': 21, 'end_character': 64, 'bleu_score': 1.0, 'section': 'Section::::History.:The discovery of the neutron makes "Z" the proton number.\n'}]}, {'provenance': [{'wikipedia_id': '673', 'title': 'Atomic number', 'start_paragraph_id': 21, 'start_character': 0, 'end_paragraph_id': 21, 'end_character': 402, 'bleu_score': 0.9716239638199891, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 11833786450611772557}, 'section': 'Section::::History.:The discovery of the neutron makes "Z" the proton number.\n'}]}]