Characterization of Ru 107 , Ru 108 , Rh 107 , and Rh 108

The mass number of ${\mathrm{Rh}}^{107}$ (21.7\ifmmode\pm\else\textpm\fi{}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\ifmmode\pm\else\textpm\fi{}0.5 sec) has been established by the nature of its $\ensuremath{\gamma}$ radiations. The mass numbers of the two precursors ${\mathrm{Ru}}^{107}$ (4.2\ifmmode\pm\else\textpm\fi{}0.3 min) and ${\mathrm{Ru}}^{108}$ (4.5\ifmmode\pm\else\textpm\fi{}0.2 min) have thereby also been established. The main radiations associated with these species are as follows (energies in keV): ${\mathrm{Ru}}^{107}$ $\ensuremath{\beta}$ groups of 2100\ifmmode\pm\else\textpm\fi{}300 and 3150\ifmmode\pm\else\textpm\fi{}300, $\ensuremath{\gamma}$ rays of 195 (14%, coincident with the 2100 $\ensuremath{\beta}$), 370 (\ensuremath{\sim}6%, coincident with the 195 $\ensuremath{\gamma}$), 480 (weak, seen only in coincidence with the 195 $\ensuremath{\gamma}$), 860 (7%, coincident with the 195 $\ensuremath{\gamma}$), 930 (4%), 1030 (4%), and 1290 (4%); ${\mathrm{Ru}}^{108}$ $\ensuremath{\beta}$ groups 1150\ifmmode\pm\else\textpm\fi{}100 and 1320\ifmmode\pm\else\textpm\fi{}100, a $\ensuremath{\gamma}$ of 165\ifmmode\pm\else\textpm\fi{}3 (28%, coincident with the 1150 $\ensuremath{\beta}$); ${\mathrm{Rh}}^{107}$ $\ensuremath{\beta}$ groups 840\ifmmode\pm\else\textpm\fi{}40, 940\ifmmode\pm\else\textpm\fi{}70, 1140\ifmmode\pm\else\textpm\fi{}50, and 1200\ifmmode\pm\else\textpm\fi{}50 keV, $\ensuremath{\gamma}$ rays of 115 (0.5%), 285 (\ensuremath{\sim}3%, seen only in coincidence with the 390 $\ensuremath{\gamma}$), 307 (73%, coincident with the 1200 $\ensuremath{\beta}$), 365 (\ensuremath{\sim}2%, coincident with the 307 $\ensuremath{\gamma}$), 390 (11%, coincident with the 1140 and 840 $\ensuremath{\beta}$ groups), 470 (1%), 570 (2%, coincident with the 940 $\ensuremath{\beta}$), and 675 (3%, coincident with the 840 $\ensuremath{\beta}$), and $\ensuremath{\gamma}$ coincidence-sum lines at 680 (\ensuremath{\sim}3%), 880 (very weak), and 1140 (\ensuremath{\le}0.5%); ${\mathrm{Rh}}^{108}$ $\ensuremath{\beta}$ of 4500\ifmmode\pm\else\textpm\fi{}600 keV, $\ensuremath{\gamma}$ rays of 430 (43%), 510 (10%, partly coincident with the 430 $\ensuremath{\gamma}$), 620 (22%, coincident with the 430 $\ensuremath{\gamma}$), 1520 (5%), and 2000 (\ensuremath{\le}3%). No 940 $\ensuremath{\gamma}$ from the ${\mathrm{Pd}}^{108}$ 940 level could be detected (3%), and less than one-third of the 510 $\ensuremath{\gamma}$ rays follow $\ensuremath{\beta}$ transitions to the 940 level. All $\ensuremath{\gamma}$ rays above 115 in the four species are in fast coincidence with $\ensuremath{\beta}$ rays. There are other $\ensuremath{\gamma}$ 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 $\ensuremath{\gamma}$ 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 (10 sec) ${\mathrm{Rh}}^{107}$ isomer formed in g8% of the ${\mathrm{Ru}}^{107}$ disintegrations. The following decay paths are proposed: decay of ${\mathrm{Ru}}^{107}$ (${Q}^{\ensuremath{\beta}}=3200$) proceeding to ${\mathrm{Rh}}^{107}$ excited levels of 1290 (4%), 1030 (11%), 930 (4%), 675 or 1530 (5%), 565 (\ensuremath{\sim}6%), and 195 (0 to 5%), and to ground state (74%), with the reservation that it is likely that some of these levels should be referred to the supposed isomeric level rather than to the ground level; decay of ${\mathrm{Rh}}^{107}$ (${Q}^{\ensuremath{\beta}}=1510$) proceeding to ${\mathrm{Pd}}^{107}$ levels of 1140 (\ensuremath{\sim}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+, ${Q}^{\ensuremath{\beta}}=1320$) proceeding to ${\mathrm{Rh}}^{108}$ levels of 165 (0+ or 1+, 28%) and ground state (1+, 72%); decay of ${\mathrm{Rh}}^{108}$ (1+, ${Q}^{\ensuremath{\beta}}=4500$) proceeding to ${\mathrm{Pd}}^{108}$ levels of 2000 or higher (\ensuremath{\le}3%), 1520 or higher (\ensuremath{\ge}5%), 1050 (0+, 22%), 940 (2+, 0 to 5%), and 430 (2+, \ensuremath{\sim}17%), and to ground state (0+, 51%). Interpretations of these schemes are presented.