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With the improvement of stellar models, the scenarios for the various processes of element formation beyond the iron peak could be localized and characterized with increasing confidence. While many questions concerning the origin of the heavy elements have been answered, new problems emerged and represent a continuing challenge. Their solution depends to a large extent on the quality of the underlying nuclear physics data. New facilities and more sophisticated techniques allow to reduce the uncertainties and to push the experimental limits towards more exotic nuclei, thus assisting the theoretical extrapolation to the drip lines. The current experimental efforts and further data needs are discussed for the various processes with emphasis on the interaction between models, experiments and nuclear theory.

We outline the role of multidimensional hydrodynamics coupled to large nuclear networks in the case of core silicon burning in massive stars. Using an implementation of the Piecewise Parabolic Method (PPM) of solving the Euler equations for mass, momentum, and total energy, we examine the differences and similarities between a 1-D hydrostatic stellar evolution model and a 2-D hydrodynamical model at two resolutions. We find that 2-D models exhibit significantly less vigorous convection than 1-D hydrostatic models, and that the core compensates for the lack of energy production by increasing temperatures and densities through contraction. Equilibration between the Si-burning and convective timescales appears to occur. Including an 123 isotope network from Y e to 66 Ge to the hydrodynamic code leads to similar global behaviors as the 2-D model with the simplified burning algorithm used in the 1-D models. However, significant inhomogeneity in iron peak isotope composition occurs, which could have important consequences to energy losses via electron captures onto G-T resonances and the local energetics which drive convective silicon burning.

A brief review is presented of the observational and theoretical evidence for the production of iron peak nuclei in explosive nucleosynthesis, for which, under proton-rich conditions, nuclei of mass A = 56 are synthesized predominantly as 56Ni. Guided by the pioneering hydrodynamic studies of Stirling Colgate and his collaborators, it has now been firmly established that the timescale on which nuclear burning proceeds in the wake of a supernova shock wave is too short to permit any significant change (increase) in the total ratio of neutrons to protons. This guarantees dominance of the isotope 56Ni in the iron peak nuclei emerging from explosive/supernova environments, and holds important implications for the light curves of both Type I and Type II supernovae. Current models of nucleosynthesis in supernovae predict interesting and distinguishing abundance patterns that are found to be consistent with the stellar abundance determinations of halo and disk stars in our Galaxy.

Simple modification are described to reduce the microscope copper peak by 90% while maintaining use of the copper sample holder. The peak-to-background ratio shows a modest improvement. The iron peak becomes hidden in background being less than one standard deviation high.

Selective labeling of compounds containing one element in two or more chemical environments with Mossbauer inactive Fe-56 and with Mossbauer active Fe-57 isotopes has been used to study the nature of the three iron environments in Prussian blue type compounds. The effect of the intersititial ion in Prussian blue upon the nitrogen bonded and carbon bonded irons was studied by exchanging interstitial K+ with cations from Group IA, Group IIA, and including NH4+, H+, and Al+3. For the interstitial Group IA precipitates, the isomer shift values became more positive as the electronegativities decreased and the ionic radii increased. The Cs Prussian blue data were significantly different for both iron environments, giving very broad peaks with a distinct shoulder on the carbon hole active iron peak. This shoulder was found to be due to nitrogen hole iron indicating that the large cesium interstitial iron distorted the lattice in such a way as to permit exchange of the carbon and nitrogen hole irons. This isotope labeling technique is inexpensive and should be widely applicable to Mossbauer studies for atoms in multiple environments in which there is no exchange.

A stack of Lexan detectors from the Apollo 17 mission has been analyzed to obtain Z measurements of sufficient accuracy to resolve the iron peak into its isotopic components. Within this distribution several peaks are present. With the centrally located, most populated peak assumed to be 56Fe, our measurements imply that the abundances of 54Fe and 58Fe are appreciable fractions of the 56Fe abundance. This result is in agreement with those of Webber et al. and Siegman et al. but in disagreement with the predictions of Tsao et al.

A systematic study of LEXAN response to mass differences for Z = 26 ions is presented. Over thirty iron tracks from Berkeley Heavy Ion accelerator have been characterized by a single parameter, namely its mean residual range. A semiempirical function relating etch-rate to restricted energy loss has been fitted to the experimental points and subsequently used to establish a charge and mass scale. It is concluded that an isotopic resolution better than σ A ≃ 2 cannot be achieved with non-sensitized LEXAN.

The effect of Ar ion bombardment on Standard Reference Material 470: Glass K-411 with a composition of (Fe, Ca, Mg)1.9Si2O6, was studied by means of XPS. Results show Fe to be most sensitive to ion induced damage, while no effect on the main photoelectron peaks of Ca, Si and O was observed. The oxygen, however, developed a small peak at lower BE (∼ 5.5 eV) of the main O 1 s peak on sputtering. This peak was correlated to an iron peak, Feβ, which developed also on sputtering, and the resultant oxide is believed to exist as a separate surface phase. O was found to be sputtered selectively with respect to Ca and Si which keep a constant atomic ratio. Mg could not be studied in the present composition.