Kr and Xe isotopes from spontaneous fission of 248Cm and 250Cf: Comparison with noble gases in carbonaceous chondrites

Relative yields of Kr and Xe isotopes from the spontaneous fission of ²⁴⁸Cm and ²⁵⁰Cf have been determined mass spectrometrically. The yields are as follows: ⁸³Kr/⁸⁴Kr/⁸⁵Kr/⁸⁶Kr = 0.223/0.458/0.596/ ≡ 1.00 and 0.306/0.582/0.793/ ≡ 1.00;¹³¹Xe/¹³²Xe/¹³⁴Xe/¹³⁶Xe = 0.486/0.819/1.075/ ≡ 1.00 and 0.343/0.506/0.851/ ≡ 1.00 from ²⁴⁸Cm and ²⁵⁰Cf, respectively. The Xe yields from ²⁴⁸Cm agree with an earlier determination by Leich et al. 24]. Neither of these yield patterns matches that of “fissiogenic” Kr and Xe in carbonaceous chondrites and hence ²⁴⁸Cm and ²⁵⁰Cf are ruled out as progenitors of the meteoritic Kr and Xe. In general, none of the spontaneously fissioning nuclides of actinide elements can be identified as a possible progenitor. Even the mixtures of actinides, including a combination of ²⁴⁸Cm and ²⁵⁰Cm, are unsuitable. The origin of “anomalous” Kr and Xe in carbonaceous chondrites must then be traced either to the spontaneous fission of a superheavy element or to peculiarities in specific nucleosynthetic reactions.