The measurement of the energy spectrum of ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}$ nuclei emitted in the spontaneous radioactivity of ${}_{}{}^{223}{}_{}{}^{}\mathrm{Ra}$ and ${}_{}{}^{224}{}_{}{}^{}\mathrm{Ra}$ has been carried out, using thin and intense sources (480 MBq for ${}_{}{}^{223}{}_{}{}^{}\mathrm{Ra}$ and 3550 MBq for ${}_{}{}^{224}{}_{}{}^{}\mathrm{Ra}$). The sources were obtained by implanting mass-separated beams into Al and vitreous C catchers. The measurement was performed with a superconducting solenoidal spectrometer. Our discovery, previously reported, of fine structure in the energy spectrum of ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}$ emission from ${}_{}{}^{223}{}_{}{}^{}\mathrm{Ra}$, which is analogous to the one known for α emission, is confirmed. Only 13% of the branching ratio in ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}$ decay leads to the ground state of the residual nucleus, while 81% to the first excited state. For ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}$ emission from ${}_{}{}^{224}{}_{}{}^{}\mathrm{Ra}$, a lower limit of 2 for the hindrance factor has been measured for the transition to the first excited state in the residual nucleus. Also, a precise identification in Z with an E×ΔE telescope has been performed for the radiation from the ${}_{}{}^{223}{}_{}{}^{}\mathrm{Ra}$ source. Our measurements of fine structure in ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}$ emissions open this field to nuclear structure studies.

• Received 28 March 1991

DOI:https://doi.org/10.1103/PhysRevC.44.1424