Bitumen swelling is first induced by radiation because of the presence of hydrogen gas bubbles generated by alpha and gamma radiolysis.
bɪtˈuːmɛn swˈɛlɪŋ ɪz fˈɜːst ɪndˈuːst baɪ ɹˌeɪdɪˈeɪʃən bɪkˈʌz ʌvðə pɹˈɛzəns ʌv hˈaɪdɹədʒən ɡˈæs bˈʌbəlz dʒˈɛnɚɹˌeɪɾᵻd baɪ ˈælfə ænd ɡˈæmɚ ɹˌeɪdɪoʊlˈaɪsiz.