Simplified approach to double jumps for fluorescing dipole-dipole interacting atoms

A simplified scheme for the investigation of cooperative effects in the quantum jump statistics of small numbers of fluorescing atoms and ions in a trap is presented. It allows the analytic treatment of three dipole-dipole interacting four-level systems which model the relevant level scheme of Ba+ ions. For the latter, a huge rate of double and triple jumps was reported in a former experiment and the huge rate was attributed to the dipole-dipole interaction. Our theoretical results show that the effect of the dipole-dipole interaction on these rates is at most 5% and that for the parameter values of the experiment there is practically no effect. Consequently it seems that the dipole-dipole interaction can be ruled out as a possible explanation for the huge rates reported in the experiment.Comment: 7 pages, 6 figures, typos corrected, to appear in EPJ D (as highlight paper

Cooperative quantum jumps for three dipole-interacting atoms

We investigate the effect of the dipole-dipole interaction on the quantum jump statistics of three atoms. This is done for three-level systems in a V configuration and in what may be called a D configuration. The transition rates between the four different intensity periods are calculated in closed form. Cooperative effects are shown to increase by a factor of 2 compared to two of either three-level systems. This results in transition rates that are, for distances of about one wavelength of the strong transition, up to 100% higher than for independent systems. In addition the double and triple jump rates are calculated from the transition rates. In this case cooperative effects of up to 170% for distances of about one wavelength and still up to 15% around 10 wavelengths are found. Nevertheless, for the parameters of an experiment with Hg+ ions the effects are negligible, in agreement with the experimental data. For three Ba+ ions this seems to indicate that the large cooperative effects observed experimentally cannot be explained by the dipole-dipole interaction.Comment: 9 pages, 9 figures. Revised version, to be published in PR

Validation of the burnup code MOTIVE with respect to fuel assembly decay heat data

The burn-up code MOTIVE is a 3D code for fuel assembly inventory determination developed at GRS in recent years. It modularly couples an external Monte Carlo neutron transport code to the in-house inventory code VENTINA. In the present publication, we report on the validation of MOTIVE with respect to full-assembly decay heat measurements of light water reactor fuel. For this purpose, measurements on pressurized water reactor and boiling water reactor fuel assemblies from different facilities have been analyzed with MOTIVE. The calculated decay heat values are compared to the measured data in terms of absolute and relative deviations. These results are discussed and compared to other published validation analyses. Moreover, the observed deviations between measurements and calculations are analyzed further by taking into account the results of the validation of nuclide inventory determination with MOTIVE. The influence of possible biases of calculated nuclide densities important to decay heat at the given decay times are investigated and discussed

Cooperative fluorescence effects for dipole-dipole interacting systems with experimentally relevant level configurations

The mutual dipole-dipole interaction of atoms in a trap can affect their fluorescence. Extremely large effects were reported for double jumps between different intensity periods in experiments with two and three Ba^+ ions for distances in the range of about ten wave lengths of the strong transition while no effects were observed for Hg^+ at 15 wave lengths. In this theoretical paper we study this question for configurations with three and four levels which model those of Hg^+ and Ba^+, respectively. For two systems in the Hg^+ configuration we find cooperative effects of up to 30% for distances around one or two wave lengths, about 5% around ten wave lengths, and, for larger distances in agreement with experiments, practically none. This is similar for two V systems. However, for two four-level configurations, which model two Ba^+ ions, cooperative effects are practically absent, and this latter result is at odds with the experimental findings for Ba^+.Comment: 9 pages, 5 figures, RevTeX4, to be published in Phys. Rev.

Blind Benchmark Exercise for Spent Nuclear Fuel Decay Heat

The decay heat rate of five spent nuclear fuel assemblies of the pressurized water reactor type were measured by calorimetry at the interim storage for spent nuclear fuel in Sweden. Calculations of the decay heat rate of the five assemblies were performed by 20 organizations using different codes and nuclear data libraries resulting in 31 results for each assembly, spanning most of the current state-of-the-art practice. The calculations were based on a selected subset of information, such as reactor operating history and fuel assembly properties. The relative difference between the measured and average calculated decay heat rate ranged from 0.6% to 3.3% for the five assemblies. The standard deviation of these relative differences ranged from 1.9% to 2.4%

Effekte der Atom-Laser Wechselwirkung auf ultrakalte Atome

Die Kontrolle und Beeinflussung von internen und translationalen atomaren Freiheitsgraden mit Hilfe der Atom-Laser Wechselwirkung ist ein entscheidendes experimentelles Werkzeug in modernen quantenoptischen Experimenten, das viele wichtige Anwendungen ermöglicht. Die vorliegende Arbeit befasst sich mit theoretischen Untersuchungen, die neue Einsichten in einige Experimente auf diesem Gebiet geben.Im ersten Teil der Arbeit werden kooperative Effekte in der Fluoreszenz dipol-dipol-wechselwirkender Atome in einer Falle untersucht. Die berühmten makroskopischen Quantensprünge können bei einem einzelnen Atom mit einem metastabilen Niveau auftreten, wenn dieses mit Licht bestrahlt wird: Phasen mit konstanter Intensität und Phasen ohne spontane Emission wechseln einander in zufälliger Weise ab. Wenn zwei oder mehr Atome in der Falle gespeichert sind, treten Dunkelphasen und Phasen einfacher und mehrfacher Intensität auf, entprechend der Überlagerung der Fluoreszenz der Einzelatome. Die Statistik dieser Leuchtphasen kann durch die Dipol-Dipol-Wechselwirkung in empfindlicher Weise beeinflusst werden. Die Arbeit befasst sich mit der theoretischen Beschreibung dieser Effekte, insbesondere in Bezug auf scheinbar widersprüchliche experimentelle Ergebnisse in diesem Zusammenhang. Als ein wesentliches Resultat wird gezeigt, dass die hohe Rate von Doppel- und Dreifachsprüngen, die bei drei gespeicherten Ba+-Ionen beobachtet wurde, nicht der Dipol-Dipol-Wechselwirkung zugeschrieben werden kann.Im zweiten Teil der Arbeit wird die mögliche Verwendung eines auf evaneszenten Wellen beruhenden Atomspiegels als Apparatur zur Messung von Eigenschaften atomarer Wellenpakete untersucht. Die zugrundeliegende Idee entstammt einem Experiment, in dem ein solcher Spiegel für die zeitliche Interferenz einer Wolke von lasergekühlten Atomen benutzt wurde, die aus einer magneto-optischen Falle fallen gelassen wurden. Es wird ein Modell zur Untersuchung der atomaren Wellenfunktion mit Hilfe eines solchen Spiegels angegeben, und die Ergebnisse verschiedener Messanordnungen werden untersucht. Als Hauptresultat wird gezeigt, dass mit einem solchen Spiegel das Betragsquadrat einer ausgedehnten Wellenfunktion abgetastet werden kann. Dies eröffnet eine realistische Mglichkeit diese sonst experimentell nur schwer zugängliche Größe zu messen

LOW TEMPERATURE EFFECTS ON PWR FUEL ASSEMBLY CRITICALITY CALCULATIONS

One of the parameters affecting the neutron multiplication factor keff of a system containing fissile material is the system temperature. Therefore, the effect of temperature on criticality safety analyses is an area of international interest. In this context, the Working Party on Nuclear Criticality Safety (WPNCS) of the OECD Nuclear Energy Agency (NEA) formed a subgroup to define and execute a code-to-code comparison benchmark to investigate the effect of temperature on keff for PWR fuel assemblies. Two configurations of a generic water-moderated PWR fuel assembly were analysed at different temperatures between 233 K and 588 K, and with different assembly burnups. Based on this benchmark, GRS performed an additional study to investigate the impact of the moderator densities, the neutron reaction cross sections and the thermal scattering data on keff separately. The benchmark results show the expected decrease of keff with temperature and a considerable jump in keff at the phase transition of the moderator. The additional investigation demonstrates that the jump in keff is mainly caused by the change of the moderator density due to the phase transition. The change of the thermal scattering data due to the phase transitions leads to a similar but smaller jump in keff. Furthermore, the actual impact of the different parameters on keff depend strongly on the considered fuel assembly configuration

LOW TEMPERATURE EFFECTS ON PWR FUEL ASSEMBLY CRITICALITY CALCULATIONS

One of the parameters affecting the neutron multiplication factor keff of a system containing fissile material is the system temperature. Therefore, the effect of temperature on criticality safety analyses is an area of international interest. In this context, the Working Party on Nuclear Criticality Safety (WPNCS) of the OECD Nuclear Energy Agency (NEA) formed a subgroup to define and execute a code-to-code comparison benchmark to investigate the effect of temperature on keff for PWR fuel assemblies. Two configurations of a generic water-moderated PWR fuel assembly were analysed at different temperatures between 233 K and 588 K, and with different assembly burnups. Based on this benchmark, GRS performed an additional study to investigate the impact of the moderator densities, the neutron reaction cross sections and the thermal scattering data on keff separately. The benchmark results show the expected decrease of keff with temperature and a considerable jump in keff at the phase transition of the moderator. The additional investigation demonstrates that the jump in keff is mainly caused by the change of the moderator density due to the phase transition. The change of the thermal scattering data due to the phase transitions leads to a similar but smaller jump in keff. Furthermore, the actual impact of the different parameters on keff depend strongly on the considered fuel assembly configuration