High-Resolution Measurements of Low-Energy Conversion Electrons

Measurements of low-energy internal conversion electrons have been performed with high energy resolution in some N = 105 odd and odd-odd nuclei using a semi-circular spectrograph associated to a specific tape transport system. These experiments aimed to answer the following questions~: \begin{itemize} \item Do M3 isomeric transitions exist in $^{183}$Pt and $^{181}$Os, isotones of $^{184}$Au~? \item Are the neutron configurations proposed to describe the isomeric and ground states of $^{184}$Au right or wrong~? \item Does it exist an isomeric state in $^{182}$Ir, isotone of $^{181}$Os, $^{183}$Pt and $^{184}$Au~? \item What are the spin and parity values of the excited states of $^{182}$Ir~? \end{itemize} In $^{183}$Pt, the 35.0 keV M3 isomeric transition has been clearly observed and the reduced transition probability has been determined. The deduced hindrance factor is close to that observed in the neighbouring odd-odd $^{184}$Au nucleus. This confirms the neutron configurations previously proposed for the isomeric and ground states in $^{184}$Au. In $^{181}$Os, only a limit of the intensity of the M3 transition could be extracted from the electron spectrum. This leads to an hindrance factor higher than in $^{183}$Pt or $^{184}$Au, but consistent with the value previously known in $^{179}$W. To study this variation of the hindrance factors in $^{179}$W, $^{181}$Os and $^{183}$Pt, we have performed, in $^{181}$Os, electron measurements with good detection efficiency using a cooled Si(Li) detector in order to observe the M3 transition that has a very weak intensity.\\ \\In $^{182}$Ir, internal conversion electrons have been measured from 2 keV to 190 keV. Multipolarities of 27 transitions have been precisely determined. In particular, a 25.7 keV E2 transition has been observed, which indicates that the first excited state is not an isomeric state but the first member of the doubly-decoupled band built on the ground state. Another measurement with a cooled Si(Li) detector associated to a mini-orange spectrometer has been performed to determine the multipolarities of the higher-energy transitions. Moreover, to determine if an isomeric state similar to the one observed in $^{184}$Au exists also in $^{182}$Au, electron- and $\gamma$-spectroscopy measurements have been undertaken. All this will allow the determination of the spin and parity of the excited states of $^{182}$Ir, the building of the $^{182}$Au level scheme and then the comparison with the predictions of microscopic models, which will provide information on the proton-neutron coupling mode and on the V$_{pn}$ interaction in doubly-odd nuclei.