This natural radioactivity became a basis for a mistaken claim of the discovery for element 87 (the next alkali metal after caesium) in 1925.
ðɪs nˈætʃɚɹəl ɹˌeɪdɪoʊæktˈɪvᵻɾi bɪkˌeɪm ɐ bˈeɪsɪs fɚɹə mɪstˈeɪkən klˈeɪm ʌvðə dɪskˈʌvɚɹi fɔːɹ ˈɛlɪmənt ˈeɪɾi sˈɛvən ðə nˈɛkst ˈælkəlˌaɪ mˈɛɾəl ˈæftɚ sˈiːsiəm ɪn nˈaɪntiːnhˈʌndɹɪd twˈɛnti fˈaɪv.