14C in uranium and thorium minerals: a signature of cluster radioactivity?

Various uranium and thorium minerals have been analysed with accelerator mass spectrometry to determine their C-14 content. It is found that, whenever the contribution from secondary reactions such as the B-11(alpha, p)C-14 is sufficiently low, the C-14 Concentration is consistent with that expected from C-14 (spontaneous) cluster radioactivity from radium isotopes of the uranium and thorium natural series.