1
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Helium : Francisco, Rudy,
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2017
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1
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2
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Helium-3 and helium-4 : Keller, W. E.
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1969
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1
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3
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Helium 4 : Galasiewicz, Zygmunt M.
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1971
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1
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5
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Helium, child of the sun : Seibel, Clifford W.,
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1968
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1
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8
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Helium or hydrogen in the balloon? -- : Grimvall, Göran.
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2007
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1
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9
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Helium stewardship (2013) : United States.
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2013
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1
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