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--*. -F u r t h e r E v i d e n c e f o r t h e N o n e x i s t e n c e of P a r t i c le -Stab le T e t r a n e u t r o n s S e a r c h f o r T e t r a n e u t r o n s Using a R e c o i l P r o t o n D e t e c t o r S . C i e r j a c k s , G. M a r k u s , W . M i c h a e l i s , W. P ö n i t z

An electrostatic model, according to which the electronegativity of an atom is identified with the electrostatic force between the effective nuclear charge and an electron at a distance equal to the relative radius of the atom, is used to calculate a nonempirical electronegativity scale for the first 54 elements. The relative radius is calculated from the free-atom wave function by use of the density contour approach, while intergration of the radial density from the nucleus to the relative radius yields the effective nuclear charge. In contrast to the empirical methods, the nonempirical electrostatic method is not only applicable to all elements, but treats all elements equally. In addition to correlating well with empirical scales, the proposed model is consistent with the major conclusions of the density functional approach of Parr and his co-workers. In particular, the model is easily extended to yield valence state electronegativities.

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The level structure of 169Yb has been studied by radiative capture of thermal neutrons in 168Yb. High resolution measurements of the gamma-ray spectrum have been performed using a Ge(Li) anti-Compton spectrometer in the low-energy region and a Ge(Li) pair spectrometer for the high-energy transitions. The target was Yb 2 0 S enriched to 19.5 % in 168Yb thus corresponding to a cross section contribution of (97.5~~:~) %for 168Yb. More than 300 gamma lines have been detected in the spectrum. The high accuracy of the data allows the application of Ritz' combination principle to excitation energies up to 1.5 MeV. The results c1early demonstrate the presence of remarkab1e band-mixing effects. The analysis suggests the following spectroscopic interpretation (bandhead energies and dominant structure): 0 keV, i+ (633)