ðə fˈækt ðæt ɹˈeɪdɑːn ɪz pɹˈɛzənt ɪn ˈɪndoːɹ ˈɛɹ hˈæzbiːn nˈoʊn sˈɪns æt lˈiːst ðə nˈaɪntiːnhˈʌndɹɪd fˈɪfti z ænd ɹᵻsˈɜːtʃ ˌɪntʊ ɪts ɪfˈɛkts ˌɔn hjˈuːmən hˈɛlθ stˈɑːɹɾᵻd ɪnðɪ ˈɜːli nˈaɪntiːnhˈʌndɹɪd sˈɛvənti z.
The fact that radon is present in indoor air has been known since at least the 1950s and research into its effects on human health started in the early 1970s.