In the past much noteworthy experimental work has been done about the decay of RaC to RaC'. The y-energies and intensities have been measured by E 1 1 i s 1) and later workers 2). A considerable amount of information about the level scheme of RaC' has been gathered by Rutherford and coworkersS) from its long range a-particles. Less is known about the continuous r-spectrum; the last measurements of L a t y s h e v and coworkers 4) indicate two r-transitions of energies 3.17 MeV and 1.65 MeV, the first having an intensity of about 20%.
It is, however
, not yet known with certainty whether the highest โข energy r-transition is followed by y-rays or not. Ellis assumes that it reaches the 608 keV level in RaC' known from the long range a-particles. Bothe and Mayer-LeibnitzS) investigated this question with coincidence experiments between y-rays and magnetically analysed electrons. Their experiment was not quite conclusive: if the published error, in their coincidence rate was a mean error, the limit of error corresponds to a maximum ~/-energy of 600 keV following the 3.17 MeV transition.
We have made some coincidence-absorption experiments in a normal fl--7 coincidence arrangement with G.M. counters. This arrangement was calibrated with 22Na, 38K, eยฐCo and 198Au. The result for the highest energy electrons is shown in fig. . The background to be substracted was determined by measuring an absorption curve with the active sample covered by 16Q0 mg/cm 2 Be. The coincidence counting rate was (--15 ยฑ 35). 10 -6 coincidences per ~-particle with energy > 1.7 MeV. This means that if the 3.17 MeV r-transition is followed by an E2 y-ray, as is normal for the deexcitation of the first excited state in an even-even nucleus,