Valence electronic structure of Mn in undoped and doped lanthanum manganites from relative K x-ray intensity studies

Relative $K$ x-ray intensities of $Mn$ in $Mn$, $MnO_{2}$, $LaMnO_{3}$ and $La_{0.7}B_{0.3}MnO_{3}$ ($B$ = $Ca$, $Sr$, and $Ce$) systems have been measured following excitation by 59.54 keV $\gamma$-rays from a 200 mCi $^{241}$Am point-source. The measured results for the compounds deviate significantly from the results of pure $Mn$. Comparison of the experimental data with the multiconfiguration Dirac-Fock (MCDF) effective atomic model calculations indicates reasonable agreement with the predictions of ionic model for the doped {manganites except} that the electron doped $La_{0.7}Ce_{0.3}MnO_{3}$ and hole doped $La_{0.7}Ca_{0.3}MnO_{3}$ compounds show some small deviations. The results of $MnO_{2}$ and $LaMnO_{3}$ deviate considerably from the predictions of the ionic model. Our measured $K\beta/K\alpha$ ratio of $Mn$ in $La_{0.7}Ca_{0.3}MnO_{3}$ cannot be explained as a linear superposition of $K\beta/K\alpha$ ratios of $Mn$ for the end members which is in contrast to the recent proposal by Tyson et al. from their $Mn$ $K\beta$ spectra.Comment: 14 pages, 4 figures. to appear in NIM-B.Please send an e-mail for figure

Search for a heavy neutrino in the &#946;-decay of <SUP>35</SUP>S

Recent experimental evidence suggests that the neutrino (strictly, an antineutrino) emitted in the &#946;-decay of tritium is a mixture of two mass eigen states |<SUB>v1</SUB> and |<SUB>v2</SUB> where |<SUB>ve</SUB>=cos&#952; |<SUB>v1</SUB> + sin&#952; |<SUB>v2</SUB> with m<SUB>v1</SUB>&lt;50 eV and m<SUB>v2</SUB>=17.1&#177;0.2 keV and sin<SUP>2</SUP>&#952; =0.03. This conclusion is based on the observation of a 'kink' in the Fermi-Kurie plot of the electron energy spectrum at an energy 17.1 keV below the end point. Such an observation, if confirmed, will have far-reaching consequences in cosmology and particle physics. In the experiment reported here, a search was made for such an admixture in the &#946;-decay of <SUP>35</SUP>S. We fail to confirm the presence of mixing of neutrinos with mass 17.1 keV and place an upper limit on such an admixture of 0.6% (90% confidence level)