Radioactivity

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Across
  1. 4. Particles with two protons + two neutrons
  2. 8. Natural radiation in the environment
  3. 10. Number of decays per second
  4. 11. Atom with lost electron
  5. 13. Negative particle
  6. 14. Charge on atoms
Down
  1. 1. Protons and neutrons found here
  2. 2. Number of protons in a nucleus
  3. 3. Atoms each with same number of protons
  4. 5. Gas with one proton in nucleus
  5. 6. Time for half the atoms to decay
  6. 7. Total number of protons and neutrons
  7. 9. High energy electromagnetic radiation
  8. 12. particle with positive charge