ˈɛstᵻməts ʌvðɪ ˈeɪdʒ ʌv ɹˈeɪn dɹˈɑːps hɐvbɪn əbtˈeɪnd fɹʌm mˈɛʒɚɹɪŋ ðɪ ˌaɪsətˈɑːpɪk ɐbˈʌndəns ʌv ɹˈeɪdɑːnz ʃˈɔːɹtlˈɪvd dᵻkˈeɪ pɹˈɑːdʒəni ɪn ɹˈeɪnwɔːɾɚ.
Estimates of the age of rain drops have been obtained from measuring the isotopic abundance of radon's short-lived decay progeny in rainwater.