Joseph Odeurs

Recovery of radiation damage in platinum, studied by Mössbauer spectroscopy

Abstract Mossbauer effect measurements are reported with sources of radioactive 133Xe implanted in platinum at 100 and 300 K. Information about the nearby environment of an implanted probe atom is obtained through the hyperfine interaction of the daughter nucleus 133Cs with its surroundings. The sources are subjected to an isochronal annealing sequence in order to study the recovery of the radiation damage in platinum. Five different components are visible in the Mossbauer spectra. Those are associated with substitutional Xe atoms and Xe atoms which have trapped one, two, three and four or more vacancies. Vacancy trapping at the Xe impurities occurs around 300 and 400 K. We ascribe this to the free migration of divancies and monovacancies, indicating that this recovery stage in platinum is due to vacancy migration. Around 550 K dissolution of interstitial clusters is observed and around 700 K vacancy loops start dissolving.

Rare gas matrix isolation of 57Co by the ion implantation technique

Abstract Implantation of 57 Co in solid Xe has been studied by Mossbauer spectroscopy. The results show that this technique provides a valuable alternative to matrix isolation obtained by the co-evaporation method.

Induced transparency for gamma radiation via nuclear level mixing

A significant reduction of absorption of single gamma photons has been observed using the Mössbauer spectra of 57Fe in a FeCO3 crystal. The absorption deficit can be ascribed to partially destructive interference for absorption because of two indistinguishable absorption paths. The necessary coherence is created by means of level mixing produced by a suitable combination of a magnetic dipole and electric quadrupole interaction.

Nuclear level mixing-induced interference in FeCO3

We present a detailed description and a consistent explanation of the transparency observed in the Mossbauer absorption spectra at a nuclear level mixing in FeCO3. We develop a model for scattering in this nuclear Λ system in a Maxwell–Schrodinger approach, taking into account multiple scattering and polarization effects. It is shown that the level mixing scheme not only yields an expected Stark splitting, but, due to the unequal relaxation rates and transition strengths, an additional interference term is present. Therefore, this scheme is equivalent to the Λ scheme considered for EIT in quantum optics. The interference in the absorption of the gamma radiation can be destructive, leading to a partial transparency, but can also be constructive. Both types of interference are present in the observed spectra.

Time-integrated synchrotron Mössbauer spectroscopy

A new hyperfine interaction technique, time-integrated synchrotron Mössbauer spectroscopy, is presented. This technique uses synchrotron radiation to measure hyperfine splittings of nuclear levels in the energy domain. A comprehensive theoretical description is given, several simulations are presented and some experimental results are discussed. Time-integrated synchrotron Mössbauer spectroscopy can open new perspectives, especially in the study of nuclear resonances that are not accessible with conventional Mössbauer spectroscopy or time-differential synchrotron Mössbauer spectroscopy.

Dose dependence of the substitutional fraction of Xe implanted in Fe

By means of the nuclear orientation technique a systematic study of the behaviour of xenon implanted in iron has been done. Strong evidence for the dose dependence of the substitutional fraction is shown. Radiation damage during implantation is obviously the cause of this phenomenon. By means of a general mathematical model one can describe what happens during implantation. A physical two-site model derived from the general one enabled us to explain the dose dependence of the substitutional fraction. At the same time, the dependence of the substitutional fraction on other parameters as temperature and ion flux appears in the equations.

Aspects of EIT with gamma radiation

Abstract We have observed the effect of electromagnetically induced transparency (EIT) in a nuclear system. A series of Mössbauer measurements was performed on a single crystal of natural FeCO3. When the condition of nuclear level crossing is fulfilled, a clear reduction in absorption or transparency is seen at the point of level crossing. This reduced absorption cannot be ascribed to saturation effects because of the specific geometry of the experiment. We present an explanation in terms of level mixing by a small non-axial component of the electric field gradient. It can be shown that such a scheme is equivalent, at least in principle, with the schemes considered for EIT in quantum optics.

Enhanced resolution in Mössbauer spectroscopy

Using a resonant detector in Mossbauer spectroscopy can result in a spectral linewidth that is 1.46 , where is the linewidth of the excited-state nuclear level. As is well known, the minimum linewidth obtained in conventional Mossbauer experiments is 2 . The quantum mechanical calculation using a nuclear resonant detector, which predicts this result, is presented. The fundamental equations describing the system are solved by means of perturbation theory in the frequency domain. The model system is taken to consist of a source nucleus, an absorber nucleus, and the resonant-detector nucleus. As noted, the minimum linewidth obtained in a Mossbauer spectrum taken under these conditions is found to be appreciably smaller than the linewidth obtained in a conventional Mossbauer set-up. Thus the conversion-electron, resonant-detector scheme may be used to advantage in experiments requiring the highest possible energy resolution.

Model for the site populations of heavy-ions implanted in metals in the case where all defects are immobile

Abstract Heavy impurities implanted in metals may occupy different sites. In general a substitutional site is possible, as well as sites associated with defects. The interaction of the impurities with the defects produced during the slowing down process is thought to be the reason for the population of the different sites. The incoming atoms are interacting with the correlated damage—interaction with the own damage cascade—and with the uncorrelated damage. The correlated interaction is responsible for the major part of the landing behaviour of the impurities, only the uncorrelated interaction describes the transitions between different sites. With these ideas the evolution of the site populations may be described by means of a set of differential equations. We have solved the equations for the case where all defects are immobile. In order to do so we have introduced spontaneous trapping volumes around every defect configuration. The solutions of these equations produce the evolution of the site population...

Slow gamma photon with a doublet structure: Time delay via a transition from destructive to constructive interference of collectively scattered radiation with the incoming photon

Single gamma photon propagation in a dense absorptive medium with two widely spaced resonances is experimentally studied. After an initial fast decay, a revival of the photon amplitude in the form of a bump, exceeding the probability amplitude of the incident photon, is observed. The irradiation time of this bump delays approximately by the lifetime of the excited nuclei in the absorber. This effect is explained by the interference of the incoming radiation with the collectively scattered radiation, the phase of which is modulated with the frequency of the doublet splitting. Initially, the destructive interference changes to a constructive one, distinguishing the storage and retrieval stages of the photon propagation in a dense medium, i.e., the collective absorption and collective re-emission processes.