Complete the crossword, then click on "Check" to check your answer. If you are stuck, you can click on "Hint" to get a free letter. Click on a number in the grid to see the clue or clues for that number.

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Across: 1. Positively charged nucleon 4. Negatively charged 6. Experiment that told us the size of the nucleus 8. Process in which small nuclei come together 9. _______ decay of unstable nuclei 13. _____ Ray, electromagnetic wave associated with decay 14. Neutral nucleon 15. Element with different numbers of neutrons 17. Consists of nucleus and electrons 18. High speed Electron 19. Tiny part of the atom at the very centre

Down: 1. Early model of the atom 2. Isotope of hydrogen, mass number 2 3. Fission may cause a _____ _______ 5. Fissile isotope of mass number 239 7. Charged atom 8. Large nucleus splits by _____ 10. Energetic nucleus 11. Fissile metal, mass number 235 12. _____ particle, a helium nucleus 16. Isotope of hydrogen, mass number 3