| 11. | It was U-235, a fissionable isotope of uranium.
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| 12. | The older a sediment is, the more isotopes it acquires.
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| 13. | Astatine-218 was the first astatine isotope discovered in nature.
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| 14. | Fourteen isotopes of berkelium were identified with mass numbers 238 252.
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| 15. | All these isotopes are characterized by high rates of spontaneous fission.
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| 16. | Five other isotopes have half-lives longer than a day.
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| 17. | No other isomer or isotope of gold has three decay paths.
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| 18. | The isotope was successfully produced in 2010 by the same team.
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| 19. | The atomic number defines the stable isotope, such as fluorine.
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| 20. | The isotopes of scandium range from 36 Sc to 60 Sc.
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