| 11. | It is an area of concentrated thorium, a radioactive element.
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| 12. | Among the actinides, thorium and uranium are the easiest to isolate.
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| 13. | As a result, thorium salts have a weak tendency to hydrolyse.
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| 14. | Small addition of fluoride ions catalyses dissolution of thorium dioxide in acids.
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| 15. | Thorium precipitates out of solution as hydroxide and is removed.
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| 16. | Thorium is weakly radioactive : all of its known isotopes are unstable.
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| 17. | Thorium only occurs as a minor constituent of most minerals.
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| 18. | Half of this thorium produced is used in gas mantles.
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| 19. | Thorium tetrafluoride is used as an antireflection material in multilayered optical coatings.
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| 20. | Because of their uranium and thorium content, some zircons undergo metamictization.
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