By using chromatographically separated, carrier-free sources, the electromagnetic spectra of RaD and RaE have been investigated from 4 to 60 kev with an argon-methane gas proportional spectrometer. No gamma rays or $L$ x-rays were detected in the decay of RaE. Aside from the principal 46.5-kev transition, no gamma rays (<0.2% of the 46.5-kev photons) were observed in the decay of freshly-purified RaD. However, when equilibrium mixtures of RaDEF, from spent radon seeds less than 2 years old, were examined through aluminum absorbers of thickness sufficient to eliminate pile-up peaks (20 to 26 kev) from the $L$ x-rays (10 to 16 kev), a broad peak at about 31 kev appeared; it was established conclusively that in reality this is external beta-bremsstrahlung of RaE, whose low-energy region has been attenuated selectively so as to give the appearance of a gamma-ray peak.

A chromatographic column separation of millicurie quantities of carrier-free RaD and RaE from each other, as well as from RaF and macro amounts of gold and mercury impurities, is described. The time required for separation is less than 2 hours.

• Received 16 April 1956

DOI:https://doi.org/10.1103/PhysRev.103.651