The composition and the chemical states of components of Zircaloy-4 (zirconium alloy) surfaces were studied in the temperature range between room temperature and 500°C. Each sample was kept at constant temperature (25, 100, 200, 300, 400, 500°C) for up to 16 hours. The changes of composition and chemical states of the Zircaloy-4 surface during heating were monitored by x-ray photoelectron spectroscopy (XPS). Originally, the components form well-defined layers elucidated by angle-resolved x-ray photoelectron spectroscopy (ARXPS). In contrast to depth profiling using ion sputtering, ARXPS is nondestructive. However, it is applicable for layers of up to a few nanometres thickness only.The experiments showed a decomposition of the ZrO, coverage above 200 "C accompanied by oxygen diffusion into the bulk. These processes lead to the reduction of ZrO, to metallic zirconium on the surface at 300°C and higher temperatures. The oxygen diffusion into the bulk was indicated by A M depth profiles. The layered structure observed up to B heating temperature of 200°C could not be seen at higher temperatures. After Zr metal appears at the surface during the heating process, a reaction with the adsorbed hydrocarbons takes place, leading to the formation of zirconium carbide. Though the depth resolution of an AES depth profile does not permit identification of layers with thicknesses in the nanometre region, the temperature-depeadent behaviour of oxygen is reflected by its AES profiles, showing features in accordance with the results from ARXPS, especially with respect to the fact that well-defined layers vanish above 200 "C. INTRODUCTIONSurface processes between structural materials and fission products in a nuclear reactor are of importance in many fields of reactor safety considerations during normal operation as well as in the case of an accident.In particular, aggressive gaseous fission products, such as molecular iodine or volatile iodine compounds, may severely attack structural materials. In addition, although the quantity of gaseous iodine released in the case of an accident was found to be much less than had been previously adopted, it is of interest to get information on possible retention mechanisms for fission iodine in the (case of a core meltdown accident. '-Surface analytical methods have been widely applied to investigate such mechanisms as well as to study the resistivity of structural and fuel material in the presence of aggressive media under operational conditions. Observation of stress corrosion cracking of the fuel cladding material Zircaloy in the presence of gaseous iodine above a critical concentration at elevated temperatures, ' which may lead to reduced mechanical stability of the fuel cladding tubes, gave rise to the question of what the basic processes of this effect were.Since the attack of iodine on the Zircaloy starts from the surface, the surface analytical methods XPS and AES are suitable for use in the investigation of such processes because the information depths of these methods are only a fe...

A delayed fission activity with a half-life of (55 _+ 7)s and a production cross section of (5_+ 1)nb has been observed in the irradiation of 237Np with 104 MeV a particles. It is tentatively assigned to the electron capture decay of 232Am followed by fission of 232pu with a probability of (1 3 +4 ] 10_2 . A barrier height of (5.3 +0.4) MeV is extracted for " -0.8/ 232pu exceeding theoretical barrier heights by about 2MeV. Systematic deviations between experimental and theoretical barrier heights previously observed in particular for U and Th isotopes are now also established for neutron deficient Pu isotopes indicating severe defects in the procedure of calculating static fission barriers.The heights of double humped fission barriers [1] in actinide nuclei have generally been determined by measuring fission probabilities as a function of excitation energy [2]. If resonance structures due to the potential well between the barrier peaks occur the analysis of such data yields information on both barriers. Additional information on the outer barrier has been derived from fission isomeric lifetimes. The heights of the inner barriers E A show a systematic deviation from calculated values [3], particularly evident for Th isotopes. The limited number of available targets has, however, restricted this comparison to nuclei along the stability line. In this paper a new method is proposed to derive fission barriers of nuclei far off the stability line by simple cross section measurements exploiting fidelayed fission [4,5]. Using this technique barrier heights of neutron deficient Pu nuclei have been found to be about 2MeV higher than expected theoretically, thus providing further evidence for severe deviations between calculated and experimental barrier heights, hitherto called "Th-anomaly". The probability for fission following fi or electron capture decay of a precursor nucleus Qa ~f(Q~ -E) S~(E) _ FI_ (E)dEJ;+~z g,,=~pz =o e~(1)is a sensitive function of the fission barrier parameters. Here, the product of the integrated Fermi function f and the fl-strength function S~ accounts for the population of excited states in the daughter nucleus, and the ratio FI describes the competition between fission and 7-cascades leading to the ground state. The main energy dependence of the integrand in (1) is essentially determined by the barrier parameters (heights EA, E B and curvature energies hCOa, hOB) and the Q~-value for the electron capture decay which is rather reliably predicted by mass formulae.

Miniaturized photoacoustic and photothermal sensors have been developed for non-destructive in situ control of the state of patinated copper and bronze monuments. For calibration purposes, various systematic surface and microanalytical studies have been carried out, including x-ray photoelectron spectroscopy (XPS) studies of artificially patinated copper and bronze substrates. In order to prevent patina sample damage by x-ray-induced reduction of cupric sulphates, it has been found necessary to perform XPS measurements at liquid nitrogen temperature. In this way reliable qualitative and semi-quantitative analyses of copper and bronze patina could be accomplished. The XPS analyses have been successful in detecting partial chemical transformations of patina films upon artificial weathering. The acid weathering procedure applied, which was thought to imitate a very aggressive industrial atmosphere with rapidly changing relative humidity, produced less basic cupric sulphates such as chalcanthite both in pure antlerite and brochantite films and in mixed patina films.

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