Asymmetry parameters in183W and182W using mice detection with a crystal monochromator

Using exceptionally high intensity Mössbauer sources (～ 1–100 Ci) of¹⁸²Ta and¹⁸³Ta, we have measured the Mössbauer effect for the 46.5 and 99.1 keV transitions of¹⁸³W and the 100.1 keV transition of¹⁸²W. Using a microfoil internal conversion electron (MICE) /1/ detector capable of operation at low temperatures, and a LiF crystal monochromator, we obtain effects of nearly 600% for the 46.5 keV transition and 3 1/2% and 6% for the other two cases, while standard transmission measurements typically yield much smaller signal-to-background ratios. With this technique we have measured the asymmetry term in the conversion electron spectra. To our present level of accuracy the results are in agreement with theoretical calculations of interference parameters /2/. Our results do not agree with earlier measurements /3/ on this transition, which are grossly at variance with theoretical calculations of the interference parameter.     

Quasielastic gamma-ray scattering from glycerol

The Mössbauer scattering instrument at the Missouri University Research Reactor (MURR) has been used to study the liquid dynamics of glycerol as a function of temperature. The measurements were made by observing the Mössbauer gamma rays from the 46.5-keV level in¹⁸³W scattered in the direction corresponding to the first liquid structure peak atQ=1.36 Å^–1. The widths of the Mössbauer velocity spectra were found to be quasielastically broadened by 3.1 eV at 24 °C up to 55 eV at 113 °C. The broadening varied quadratically with temperature above the melting point, but showed a linear dependence when plotted versus the absolute temperature divided by the viscosity. As discussed by Singh and Mullen, this latter dependence is expected in the continuous diffusion limit. The original analysis by Singwi and Söjlander was carried out for a diffusing Mössbauer ion, where the observed cross section is the Fourier transform of the self-correlation function. Our case requires the use of the paircorrelation function. Quantitative calculations as well as further experiments are needed.This work was performed with the support of the US Department of Energy under Grant Nos. DE-FG02-85ER45200 and DE-FG02-85ER45199.     

Phosphor und Phosphors?ure

Ohne Zusammenfassung     

Polymeric Antitumor Agents on a Molecular and on a Cellular Level?

“Chemistry has become a mature science, with all the advantages and handicaps of maturity: harvest is abundant, but many people think future and adventure are to be found elsewhere”^[1a]. This holds true—in 1981, the year of Hermann Staudinger's 100th birthday—for macromolecular chemistry, too. Where can the polymer chemists seek adventures? Unsolved problems in neighboring fields like medicine and molecular biology attract his zeal. Cancer chemotherapy is such a field. Can the polymer chemist help to solve its problems? Polymers may be pharmacologically active as such. If used as carriers, they may, due to their intrinsic properties, influence body distribution, excretion or cell uptake of the pharmaca they carry. Hence, there is a chance for new ways in therapy, including affinity chemotherapy using synthetic macromolecules. Our own body has a perfect biological system for affinity therapy: immune response to infection selectively attacks foreign cells, It is fascinating to observe what the immune system does to a tumor cell which could not escape immune surveillance (cf. Fig. 14). Can these specific cell-cell interactions be mimicked? What do we have to learn for an experimental approach to this adventure? Stable membrane and cell models can be synthesized, a first step towards this goal. Macromolecular chemistry is far from being able to offer satisfying solutions for a specific tumor therapy; striving for it, polymer chemists can learn lots of things. In order to do so, they will have to enter neighboring fields and they will have to be willing and able to cooperate.