Production and Decay Properties of Protactinium Isotopes of Mass 222 to 225 Formed in Heavy-Ion Reactions

Four $\alpha$-decay chains initiated by ${}_{}{}^{225}{}_{}{}^{}\mathrm{Pa}$, ${}_{}{}^{224}{}_{}{}^{}\mathrm{Pa}$, ${}_{}{}^{223}{}_{}{}^{}\mathrm{Pa}$, and ${}_{}{}^{222}{}_{}{}^{}\mathrm{Pa}$ were produced by the bombardment of thallium, lead, and bismuth targets with beams of ${}_{}{}^{22}{}_{}{}^{}\mathrm{Ne}$, ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$, ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$, ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$, ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, ${}_{}{}^{15}{}_{}{}^{}\mathrm{N}$, and ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$ at the Berkeley heavy-ion linear accelerator. The reaction products were transported from the reaction cell by the helium-jet technique and their decay was measured with a semiconductor detector. Energy values, excitation functions, half-lives, and genetic relationships of individual peaks were determined. Two new techniques based on the use of a time-to-amplitude converter were developed for the measurement of μsec half-lives of daughter products, and five half-lives in the μsec range were measured.

These new $\alpha$ data help to determine the trends in $\alpha$-decay energies for isotopes of odd-$Z$ elements, particularly in the poorly defined region just above the 126-neutron shell. This allows more accurate predictions of $\alpha$-decay properties of many unknown nuclei. Some anomalous behavior of the apparent $\alpha$-decay energies for nuclei with 133 and 135 neutrons is pointed out.