Characterization ofRu107,Ru108,Rh107, andRh108

The mass number of ${\mathrm{Rh}}^{107}$ (21.7±0.4 min) has been confirmed by alpha bombardments of ${\mathrm{Ru}}^{104}$ at selected energies, by fastneutron bombardment of ${\mathrm{Pd}}^{108}$, and by chemical identification; and the mass number of ${\mathrm{Rh}}^{108}$ (16.8±0.5 sec) has been established by the nature of its $\gamma$ radiations. The mass numbers of the two precursors ${\mathrm{Ru}}^{107}$ (4.2±0.3 min) and ${\mathrm{Ru}}^{108}$ (4.5±0.2 min) have thereby also been established. The main radiations associated with these species are as follows (energies in keV): ${\mathrm{Ru}}^{107}$ $\beta$ groups of 2100±300 and 3150±300, $\gamma$ rays of 195 (14%, coincident with the 2100 $\beta$), 370 (∼6%, coincident with the 195 $\gamma$), 480 (weak, seen only in coincidence with the 195 $\gamma$), 860 (7%, coincident with the 195 $\gamma$), 930 (4%), 1030 (4%), and 1290 (4%); ${\mathrm{Ru}}^{108}$ $\beta$ groups 1150±100 and 1320±100, a $\gamma$ of 165±3 (28%, coincident with the 1150 $\beta$); ${\mathrm{Rh}}^{107}$ $\beta$ groups 840±40, 940±70, 1140±50, and 1200±50 keV, $\gamma$ rays of 115 (0.5%), 285 (∼3%, seen only in coincidence with the 390 $\gamma$), 307 (73%, coincident with the 1200 $\beta$), 365 (∼2%, coincident with the 307 $\gamma$), 390 (11%, coincident with the 1140 and 840 $\beta$ groups), 470 (1%), 570 (2%, coincident with the 940 $\beta$), and 675 (3%, coincident with the 840 $\beta$), and $\gamma$ coincidence-sum lines at 680 (∼3%), 880 (very weak), and 1140 (≤0.5%); ${\mathrm{Rh}}^{108}$ $\beta$ of 4500±600 keV, $\gamma$ rays of 430 (43%), 510 (10%, partly coincident with the 430 $\gamma$), 620 (22%, coincident with the 430 $\gamma$), 1520 (5%), and 2000 (≤3%). No 940 $\gamma$ from the ${\mathrm{Pd}}^{108}$ 940 level could be detected ($\gamma$ rays follow $\beta$ transitions to the 940 level. All $\gamma$ rays above 115 in the four species are in fast coincidence with $\beta$ rays. There are other $\gamma$ rays associated with these species, especially for ${\mathrm{Ru}}^{107}$ and/or ${\mathrm{Rh}}^{108}$ above 1500. No evidence was found for isomers of ${\mathrm{Pd}}^{107}$, ${\mathrm{Rh}}^{107}$, ${\mathrm{Pd}}^{108}$, or ${\mathrm{Rh}}^{108}$ from decay of 21.7-min ${\mathrm{Rh}}^{107}$ or 16.8-sec ${\mathrm{Rh}}^{108}$. No ${\mathrm{Rh}}^{107}$ or ${\mathrm{Rh}}^{108}$ isomers could be isolated. However a $\gamma$ ray of 21 keV, presumed to be $K$ x rays of rhodium, appears in the short-lived ruthenium spectrum, with an intensity 5 to 8% relative to ${\mathrm{Ru}}^{107}$; this is attributed to a short-lived (${\mathrm{Rh}}^{107}$ isomer formed in >8% of the ${\mathrm{Ru}}^{107}$ disintegrations. The following decay paths are proposed: decay of ${\mathrm{Ru}}^{107}$ ($Q^{\beta }=3200\mathrm{}$) proceeding to ${\mathrm{Rh}}^{107}$ excited levels of 1290 (4%), 1030 (11%), 930 (4%), 675 or 1530 (${\mathrm{Rh}}^{107}$ ($Q^{\beta }=1510\mathrm{}$) proceeding to ${\mathrm{Pd}}^{107}$ levels of 1140 (∼0.2%), 675 (may be more than one level, 7%), 570 (2%), 470 (1%), 390 (8%), and 307 (71%), and to ground state (0 to 17%); decay of ${\mathrm{Ru}}^{108}$ (presumably 0+, $Q^{\beta }=1320\mathrm{}$) proceeding to ${\mathrm{Rh}}^{108}$ levels of 165 (0+ or 1+, 28%) and ground state (1+, 72%); decay of ${\mathrm{Rh}}^{108}$ (1+, $Q^{\beta }=4500\mathrm{}$) proceeding to ${\mathrm{Pd}}^{108}$ levels of 2000 or higher (≤3%), 1520 or higher (≥5%), 1050 (0+, 22%), 940 (2+, 0 to 5%), and 430 (2+, ∼17%), and to ground state (0+, 51%). Interpretations of these schemes are presented.