X ray diffraction investigation of Pu-Ce and Pu-Ce-Ga alloys stabilized inthe delta-phase

In the actinides series (progressive filling of the 5f-sub shell), Pu inter links the light actinides with delocalized 5f electrons, and the heavy acti nides with localized 5f electrons. At this boundary, delta -Pu is a high te mperature allotrope with an intermediate 5f behaviour. It reaches stability at room temperature by alloying with deltagen solutes like Al, Ga, Am, Ce. X-Ray Diffraction showed that the 5f electrons of delta Pu tend to delocal ize in the Pu-Al and Pu-Ga alloys (Ga and Al atoms am smaller than delta -P u atoms) whereas they tend tp localize in the Pu-Am alloys (Am atoms am big ger than delta -Pu atoms). Ce atoms, also bigger than delta -Pu atoms, are expected to induce a similar behaviour as Am atoms. However, in the Pu-Ce a lloys, Ce atoms exhibit an allotropic transformation (gamma -Ce-alpha -Ce) caused by the lattice strains: a delocalization of the 4f electrons of Ce i nvolves a reduction of its atomic volume and disturbs the investigation of the 5f electrons behaviour. In this work, some Pu-Ce and Pu-Ga-Ce alloys we re studied and showed a cooperative deltagen effect of Ga and Ce. This resu lt, together with previous studies in literature, indicates that the mechan ism of the delta phase stabilization by Ce and Am are not equivalent. It se ems that the localization of the 5f electrons of Pu by Ce alloying is uncer tain. Photoemision measurements are planned in order to confirm this hypoth esis.