Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

The wind energy ressources of a selected saxon area ( 64 km x 48 km ) has been investigated in detail. The region can be characterized by a mean height of 200 m a.s.l. with complex surface profil. Based on measuring data of three stations WASP calculations with a grid step of 0.25 km has been performed for the whole region. The data are compared with calculation results of the mesoscale KAMM model. These calculations based on the geostrophic wind data of the Czech station Prague and used a 1.0 km and a 2.5 km grid ( coresponding 60 and 120 wind clusters ). The ressource maps ( mean wind velocity and power density ) calculated by both methods show corresponding high wind potential in the investigated area. Differences in the absolute values are explained by the features of the used programmes.

In ein mit Erdgas betriebenes konventionelles Fernwärmesystem (Anschlußleistung 2,1 MW) wurde eine Solarkollektoranlage mit einer Bruttofläche von 100 m² integriert. Die Kollektoranlage diente vorrangig der Erzeugung von Brauchwarmwasser für eine Schule, solare Überschüsse wurden in den Rücklauf des Fernwärmesystems eingespeist. Ein umfangreiches Meßprogramm ermöglichte Effizienzuntersuchungen des Systems.
Der jährliche Nettoertrag des Solarsystems lag bei 280 kWh/m² bei einem Systemnutzungsgrad von 26%. Beide Kennziffern wurden durch hohe Rücklauftemperaturen (58°C) im Nahwärmenetz negativ beeinflußt. Weitere Untersuchungen galten dem Betrieb der eingesetzten Schichtspeicher (Reihenschaltung). Bei Ausschöpfung der in dem Vorhaben deutlich gewordenen Optimierungspotentiale können in künftigen Anlagen Nettoerträge von 350 kWh/m² und solare Wärmegestehungskosten unter 30 Pf./kWh erreicht werden.

Vom Zentrallager der Plus-Warenhandelsgesellschaft in Ottendorf-Okrilla (Sachsen) wird seit 1992 eine hybride Wind-Photovoltaik-Anlage zur Erzeugung von Elektroenergie betrieben. Die Anlage besteht aus einer 60-kW-Windkraftanlage des Typs TW 60 und einer Phtovoltaikanlage mit einer Spitzenleistung von 3,18 kW. Letztere zeichnet sich durch einige Besonderheiten (Orientierung des Generators, Master-Slave-Betieb der Wechselrichter) aus. Das Betriebsverhalten der Anlagen wurde über einen längeren Zeitraum untersucht.

Im Jahr 1995 erreichte die Photovoltaikanlage mit 689 Vollastbetriebsstunden etwa die Ergebnisse anderer Photovoltaikanlagen in Sachsen. Mögliche höhere Erträge werden durch die gewählte Orientierung des Generators verhindert. Die Master-Slave-Schaltung der Wechselrichter arbeitete ohne Probleme. Ihre Effektivität wurde durch die nicht optimale Abstimmung von Generator- und Wechselrichterleistung beeinträchtigt.

A neural-network approach has been developed for localizing leakages and estimating the leak rate in pressurized plants with complicated three-dimensional structures. Results are presented from experiments with simulated leaks at a VVER-440 reactor vessel head. As features for characterizing the occurrence and the location of a leak, RMS values of acoustic emission sensors and coherence values and power spectra of microphone signals were used. Three-layer perceptron networks were found to be best suited for leak localization and for estimation of leak rates. However, the estimation of leak rates required an additional neural network because a different normalization procedure was necessary for extracting features from the RMS values of the acoustic emission sensors. Perceptron networks with continuously valued outputs corresponding to the coordinates of the leak positions were useful for classifying even positions which had not been offered during training.

Im Rahmen eines Programms des Bundesministeriums für Umwelt, Naturschutz und Reaktorsicherheit zur Zusammenarbeit mit den MOE-Staaten und der GUS auf dem Gebiet der kerntechnischen Sicherheit hat das Forschungszentrum Rossendorf, Institut für Sicherheitsforschung, im Verbund mit dem technischen Überwachungsverein TÜV Rheinland, Institut für Kerntechnik und Strahlenschutz, die einvernehmlich spezifizierten "technischen Mittel für ein System zur verbesserten betrieblichen Überwachung" an das Kernkraftwerk Saporoshje, Ukraine, geliefert und in Betrieb genommen. Im vorliegenden Bericht (Textteil) werden die Lieferungen und Leistungen nach Art und Umfang (Beschaffenheit, Abnahmeprüfung, Übergabe und Inbetriebnahme der technischen Mittel und die für das ukrainische Fachpersonal durchgeführten Schulungsmaßnahmen) bis zur Aufnahme des Probebetriebes am 30. November 1995 beschrieben. Dem Bericht ist ein Anhang A mit Vorschlägen zur Gestaltung der automatisch arbeitenden Überwachungssoftware und ein Anhang B mit wissenschaftsorganisatorischen Details beigefügt.

Abstract
Extended calculations of the deuteron's static properties, based on the numerical solution of the Bethe-Salpeter equation,.are presented. A formalism is developed, which provides a comparative analysis of the covariant amplitudes in various representations and nonrelativistic wave functions. The magnetic and quadrupole moments of the deuteron are calculated in the Bethe-Salpeter formalism and tlie role of relativistic corrections is discussed.

Abstract
We consider the mass of the one-loop hedgehog soliton of the bosonized SU(2) Nambu & Jona-Lasinio model embedded in hot nuclear matter mimiced by a gas of constituent quarks. We prove that the proper-time regularized and self-consistently determined soliton in a heat bath obeys Poincare's invariance up order V². At ifinite temperature and chemical potential, we show that the inertial mass obtained in the perturbative pushing approach coincides with the total internal energy of the soliton.

By measuring the fast particles emerging from a proton-nucleus interaction the number of participants can be determined. This might be the key quantity for understanding subthreshold particle production.

The results on epitaxial crystallization of Si by mega-electron-volt heavy-ion-beam irradiation recently published by Nakata can be understood in the framework of the "point defect diffusion model". It is not necessary to consider inelastic electronic scattering effects in order to explain the decrease in the normalized crystallization rate with increasing nuclear deposited energy.

A neutron double-crystal diffractometer (DCD) with a position sensitive detector for a simultaneous measurement of the whole scattering range was realized. In this arrangement the angular dependence of the intensity distribution is transformed into a positional one by an elastically bent perfect analyzer (second) crystal set in a completely asymmetric diffraction geometry. The DCD may be used for the study of neutron beams scattered, diffracted, refracted or reflected in small angles. By tuning the curvature of the analyzer in the momentum transfer a range from 2x10-1 nm-1 is available. At present this DCD is used for small-angle neutron scattering investigations as well as for experiments with neutron optical components.

The report gives an overview on the scientific work of the Institute of Safety Research in 1994.

The temperature dependence of the ion beam induced interfacial amorphization process (IBIIA) in silicon has been investigated at temperatures above 80 K using Rutherford Backscattering Spectroscopy/Channeling (RBS/C) and Cross-Sectional Transmission Electron Microscopy (XTEM). Three regimes are observed. Above temperatures of about 320 K there is strong temperature dependence of the IBIIA rate (thermal regime). At lower temperatures the rate moves towards a saturation value (transition regime). Below approximately 150 K IBIIA is nearly temperature independent (ballistic regime). This low temperataure regime can be explained by an athermal transport of point defects like in ballistic mixing processes.

Surface Light Scattering Spectroscopy of the Gallium Liquid-Vapor Interface
Vladimir Kolevzon
Abstract
High frequency capillary waves at liquid Ga surface have been studied by means of quasielastic light scattering spectroscopy. The observed frequencies and damping constants of waves differed greatly from classical theoretical treatment of liquid Ga surface as that of a simple liquid. This effect was explained due to the presence of the surface layer, possessing visco-elastic properties extracted, for the first time, from the fit of experimental spectra with an appropriate theoretical form. Negative value of the surface dilational viscosity has been derived for all wavenumbers studied. At high wavenumbers q the wave dispersion behavior is best likely linked to the weak coupling between dilational and capillary modes, while at low and moderate q the experimental data resemble to the mixed oscillations. This behavior is consistent with an influence of diffusion and adsorption on the waves propagation.

Six different types of boron nitride films were investigated by polarized infrared reflection spectroscopy. Films with a highly cubic, mixed cubic and non-cubic, and exclusively non-cubic phase composition were synthesized using ion beam assisted deposition. Additionally, post-deposition argon ion irradiated cubic and non-cubic boron nitride films as well as nitrogen implanted boron sample were analyzed. Using this technique, besides the cubic phase, two different non-cubic modifications, layered anisotropic and amorphous, could be distinguished. A preferentional orientation of the normal axis of the sp2-bonded basal planes parallel to the substrate surface was observed.

Die 40-kWp-Photovoltaikanlage ist die größte netzgekoppelte PV-Anlage in Sachsen. Trotz nichtoptimaler Lage (Abschattungen im Winter) erreichte die Anlage im Jahr 1995 einen Ertrag von fast 700 kWh/kWp und liegt damit im Durchschnitt der Erträge anderer sächsischer Anlagen. Bewährt hat sich die Master-Slave-Schaltung der Wechselrichter. Der Strombedarf der Kirntzschtalbahn wird durch die Anlage zu knapp 30% gedeckt.

Durch das FZR werden an 50 PV-Anlagen in Sachsen mehrjährige Untersuchungen zum Betriebsverhalten durchgeführt. Das Untersuchungsprogramm umfaßt die technische Überprüfung des Anlagenzustandes und die Messung der Kennlinien des PV-Generators und der eingesetzten Wechselrichter. Ferner erfolgt eine monatliche Analyse der erreichten Energieerträge. Die ersten Ergebnisse dieser Untersuchungen sind im Beitrag zusammengefaßt.

In order to improve the operational surveillance of a VVER-1000 unit of the Ukrainian nuclear power plant Zaporosh´ye a technical monitoring system has been specified. The system will enable the state regulatory and supervisory bodies to survey the unit operation independently of operators to assess its safety status, and to impose appropriate conditions. Due to its up-to-date configuration the system provides early indication of any operational incident and emission of radioactive materials connected. Based on the system an immediate warning in mergency situations is possible as well as an effective emergency management. For this purpose 49 different operational parameters of the unit, 18 radiological parameters of the unit and the plant site and 6 meteorological parameters are monitored.
The monitoring concept and its technical realization are described.

Results of a small break loss of coolant accident experiment, conducted on the PMK-2 integral type test facility are presented. The experiment simulated a 1% break in the cold leg of a VVER-440-type reactor. The main phenomena of the experiment are discussed and in case of selected events a more detailed interpretation with the help of measured void fraction, obtained by a special measurement device is given. Two thermohydraulic computer codes, RELAP5 and ATHLET, are used for post test calculations. The aim of the presented calculations is to investigate the code capability for modeling natural circulation phenomena in VVER-440-type reactors. Therefore the results of the experiment and both calculations are compared. Both codes predict most of the transient events well, with the exception that RELAP5 fails to predict the dry-out-period in the core. In the experiment the hot and cold leg loop seal clearing is accompanied by natural circulation instabilities, which can be explained by means of the ATHLET calculation.

Abstract
The guiding centre appraximation for the motion of charged particles in axially symmetric magnetic and electric fields is formulated and stopping as well as small angle scattering on a multicompenent plasma are included. The developed code has been applied to the design of a 14-MeV neutron source according to the concept of the Budker Institute Novosibirsk. It is demonstrated that the self-interaction of injected D and T ions by stopping, scattering and induced internal Fields has to be taken into account, if the injected power exceeds a few megawatt.

The dependence of the mechanical properties on the depth position in the unirradiated state and after irradiation up to neutron fluences of approximately 5x1018 and 70x1018 cm-2 (E > 0.5 MeV) is tested on a forging made out of VVER 440 reactor pressure vessel (RPV) steel 15CrMoV. The near-surface position shows a higher strength and a lower transition temperature than the positions greater than 1/4 wall thickness. Irradiation does not change these differences in a significant manner. The testing of specimens from the 1/4 depth position withi the surveillance programme, as normally laid down in the legal rules relating to nuclear power plants, results in a conservative safety assessment against brittle failure up to the EOL fluence. On taking into account fluence attenuation, the flux effect, etc., the toughness gradually increases from the inside to the outside of the wall after longer RPV operating times.

With the aim of obtaining a general insight into the technetium/S-unprotected MAG3 system, the reactions of technetium with the unprotected MAG3 ligand, both at c.a.- and n.c.a.-level, were investigated. Based on a profound knowledge of the reaction route and the Tc-MAG3 complexes, sources of by-products were identified and eliminated as far as possible. Only a small percentage (< 5%) of intermediate Tc-MAG3 complexes occurs, but this may increase by improper handling of the kit, such as insufficient reaction time. In conclusion, two kinds of impurity may occur in the Tc/MAG3 kit: One is derived from impurities in the ligand (MAG3 disulphide), which can be excluded by careful preparation and storage. The other is caused by insufficient reaction time according to the scheme (Fig. 3) during the labelling procedure. Its content can be minimized by optimization of the reaction time. A reaction time of at least 10 minutes gives about 98% of the renal agent.

Zur Verbesserung der betrieblichen Überwachung eines WWER-1000-Reaktors im ukrainischen Kernkraftwerk Saporoshje wurde ein technisches Informationssystem entworfen. Dieses System soll die Staatliche Aufsichtsbehörde in die Lage versetzen, den Reaktorbetrieb unabhängig vom Betreiber zu beobachten, den Sicherheitszustand der Anlage zu erfassen und nötigenfalls Auflagen zu erteilen. Durch eine moderne Ausrüstung soll das System eine Früherkennung von betrieblichen Störungen und Unfällen sowie der damit verbundenen Emission radioaktiver Substanzen ermöglichen. Auf dieser Grundlage soll sowohl eine rechtzeitige Warnung als auch ein effektives Störfall-Management möglich werden. Zu diesem Zweck werden 49 betriebliche Parameter, 18 radiologische Parameter und 6 meteorologische Parameter kontinuierlich überwacht. Das Überwachungskonzept und die technische Realisierung werden vorgestellt.

Boron doped crystalline superlattices grown by low-temperature molecular beam epitaxy have been used by Stolk et al. to study the diffusion of self-interstitials I in Si. After 40 keV Si+ ion implantation and subsequent annealing, stationary interstitial profiles are found at 670 °C for periods t ~1 h, demonstrating that the penetration depth of interstitials is limited by trapping at hitherto unidentified impurities. In addition, the high
interstitial supersaturation causes B de-activation in the near-surface region. We show that both these effects, the trap-limited interstitial diffusion and the enhanced B clustering, can be explained, if the transient de-activation of boron is modeled by the first-order reaction I + B_s ->B_i. Boron atomic and electrical profiles as well as self-interstitial profiles are computed which are in good agreement with the experimental results.

Abstract
The trapping effect is investigated close to the elastic threshold. The nucleus is described as an Open quantum mechanical many-body system embedded in the continuum of decay channels. An ensemble of compound nucleus states with both discrete and resonance states is investigated in an energy-dependent formalism. It is shown that the discrete states can trap the resonance ones and also that the discrete states can directly influence the scattering cross section.

Abstract
Within an effective one- boson exchange parametrization of the T matrix of NN interactions we calculate cross sections for the reactions pp → ppγ and pn → pnγ for proton incidence energies in the order of 1 GeV. Besides bremsstrahlung processes we consider photons from ∆ decays and contributions from the η → γγ process, where the η is excited via the N₁₅₃₅ resonance. At beam energies above 700 MeV the ∆ decay channiel dsminates for large photon energies, while above the η threshold the η decay photons ähsw up only in a narrow window. The low energy photons stem frorn pure bremsstrahlunig processes.

Abstract

The role of the massive photon decay via intermediate states of electron-electron-holes and proton-proton-holes into neutrino-anti-neutrino pairs in the course of neutron star cooling is investigated. These reactions may ba operative in hot neutron stars in the region of proton pairing. The corresponding contribution to the neutrino emissivity is calculated. It varies with the temperature as T^3/2e^−m_γ/T for T < m _γ, where m_γ is an effective photon mass in superconducting matter. Estimates show that this process appears as strong cooling channel of neutron stars at temperatures T ≈ ( 10⁹ - 10¹⁰) K.

Die technische Überprüfung von bisher 30 netzgekoppelten Anlagen ergab keine gravierenden Mängel. Einzelne technische Schwächen von eingesetzten Komponenten wurden identifiziert. Zur energetischen Bewertung der Anlagen wurde ein PC-gestützter PV-Anlagen-Analysator entwickelt und erprobt. Ein optimales Verfahren zur Umrechnung gemessener PV-Generator-Kennlinie auf STC-Bedingungen existiert noch nicht.

The code DYN3D/M2 was developed for steady-state and transient analysis of reactor cores with hexagonal fuel assemblies. The new version DYN3DR contains a method for neutron kinetics solving the two group neutron diffusion equation by a nodal method for cartesian geometry. The thermal-hydraulic model FLOCAL simulating the two phase flow of coolant and the fuel rod hehaviour is used in the two versions. The fundamentals of the neutron kinetics are described. The accuracy of the code is demonstated by comparisons with the results of rod ejection benchmarks for PWR with rectangular fuel assemblies. The developed algorithm of neutron kinetics are suitable for using parallel processing. The speedup of neutronic calculation is demonstrated for a steady state solution of diffusion equation.

Asymmetry of the Dielectron Emission Rate in an
Isospin-Asymrnetric Pion Medium
T.I. GULANOVA,¹ A. I. TITOV
Bogoliubov Theoretical Laboratory, Joint Institute for Nuclear Research,
141980 Dubna, Russia
B. Kämpfer
Research Center Rossendorf, Institute for Nuclear and Hadron Physics,
PF 510119, 01314 Dresden, Germany
Institute for Theoretical Physics, Technical University Dresden,
Mommsenstr. 13, 01062 Dresden, Germany

Abstract

The dielectron emission by pion annihilation in an isospin-asymmetric pion gas at finite temperature is considered. Due to the differente between the longitudinal and tramverse parts of the in-medium p meson self-energy a specific asymmetry of the rates is caused for electron pairs with relative momenta perpendicular or parallel to the total pair momentum. This asymmetry may be considered as a sensitive signal of in-medium-modifications of the p properties.
¹Permanent- address: Physical and Technical Institute of Uzbek Academy of Sciences, 700084 Tashkent,
RepubIic Uzbekistan

Zusammenfassung
Dargestellt wird ein in sich geschlossenes 3D-Modell zur Berechnung der ortsabhängigen Übertragungsfunktionen für stochastische Schwingungen der Regel- und Brennelemente in Reaktoren vom Typ WWER-440 unter Berücksichtigung der heterogenen Brennstoffbeladung realer Spaltzonenkonfigurationen. Basis sind die nodalen Bilanz-Gleichungen zur Berechnung der stationären Neutronediußverteilung in der Eingruppen-Diffusionsnäherung für 3D-Nodes in Hexagonal-Z-Geometrie. Die Absorberteiie eines WWER- 440-Regelelements werden durch entsprechende Randbedingungen für die Diffusionsgleichun im neutronenphysikalischen Reaktormodell erfaßt. Die Modellierung der Rauschquellen erfolgt auf der Grundlage einer Sweigruppen-Diffusionsnäherung. Die Neutronenflußdichteschwankungen werden dabei durch Störungen bei der Kickstreuung thermischer Neuttonen in "Absorber-Nodes" bzw. durch stochastische Schwankungen der Zweigruppen-Wirkungsquerschiiitte an den radialen Nodegrenzen der 'Brennstoff-Nodes" beschrieben. Zur Berechnung der Ubertragungsfunktionen für die Schwankungen der Neutronenflußdichte werden die nodalen Bilanz-Gleichungen in der Prompt-Response-Approximation verwendet. Die Kopplung der Zweigruppen-Quellmodeiie für Brennstoff- und Absorberteil eines Regelelements an das nodale Eingruppen-Übertragungsmodel erfolgt im Sinne der modifizierten Eingruppen-Diffussionsnäherung.
Anhand numerischer Berechnungen werden wesentliche Charakteristika der Übertragungsfunktionen für
Regelelementschwingungen in Dwckwasserreaktoren vom Typ WWER-440 diskutiert.

The German 1000 roofs PV programme, in which more than 2000 roof-mounted grid connected PV systems are now operating, provides invaluable information on the operational performance of the installed PV systems, the PV users and their consumption behaviour. The Institut für Solarenergieforschung (ISFH) and the Forschungszentrum Rossendorf (FZR), responsible for the organization of the 1000 roofs programme in the Federal States of Lower Saxony and Saxony, have been analysing the monitored performance and consumption data of more than 300 PV systems operating since 1991. The purpose of this work is to examine the relationship between PV system yield and electricity consumption for the realized projects and to take advantage of the first-hand information on the PV users consumption behaviour for future PV applications.

Im Report werden die im Rahmen des Bund-Länder-1000-Dächer-Photovoltaik-Programmes in Sachsen erzielten Ergebnisse dargestellt. Insgesamt wurden auf Dächern von Ein- und Zweifamilienhäusern in den Jahren 1992 - 1994 150 netzgekoppelte Anlagen mit einer Gesamtleistung von 523 kWp errichtet. Dabei kamen Module und Wechselrichter von jeweils acht verschiedenen europäischen Herstellern zum Einsatz. Die beteiligten Fachfirmen erwarben ein breites Know-how zur Auslegung und Installation der Anlagen sowie zur architektonischen und bautechnischen Einbindung der Photovoltaikgeneratoren auf Dächern von Einfamilienhäusern. Entsprechende Ergebnisse werden zusammenfassend vorgestellt.
Die Ergebnisse des begleitenden Meßprogrammes werden im Detail diskutiert. Erstmals werden quantitative Zusammenhänge zwischen der solaren Energieproduktion und dem Eigenbedarf von Haushalten ermittelt. Der jährliche Elektroenergiebedarf von Haushalten kann durch dachmontierte PV-Anlagen unter mitteleuropäischen Bedingungen voll gedeckt werden. Die mögliche jährliche Energieproduktion einer Photovoltaikanlage in Sachsen beträgt 750 kWh/kWp, die weitere Minimierung der anlagenbedingten Verluste ist Gegenstand weiterführender Untersuchungen.

Spherical shell-model calculations have been performed in the configuration space ( s_1/2h_9/2i_13/2)
and (p_1/2p_3/2f_5/2i_13/2) for protons and neutrons, respectively, in order to interpret the sequences of strong dipole transitions found in neutron-deficient Pb isotopes. Regular dipole bands are found if several high-j protons and high-j neutron holes are interacting with neutrons in the low-spin (fp) orbitals. The calculated B(M1) values are in the order of several µ_N ²
for the deltaJ=1 transitions, and the crossover E2 transitions are very weak. The mechanism generating the dipole bands is found to be the same as in the tilted axis cranking mean-field description.

A Cobalt-Neodymium Liquid Alloy Ion Source (LAIS) is investigated with respect to ist cluster emission behaviour. Clusters and molecular ions were found. The influence of the source emission current on the cluster emission intensity and also on the cluster mass distributationis studied. The Co-Nd LAIS was used for writing patterning (implantation, sputtering) in a mass-selecting Focused Cluster Beam (FCB) system. Theoretical estimations were carried out concerning the use of the FCB for direct deposition at landing energies of about 100 eV / atom. First experimental results of cobalt FCBs are presented.

Invariant cross sections for the production of π^±, K ^±, p and d in pBe interactions at 14.6 GeV/c are well reproduced by calculations carried out in the framework of the Rossendorf collision model.

In den letzten Jahren war in Sachsen eine dynamische Entwicklung bei der Nutzung der Wind- und Sonnenenergie zu Erzeugung von Elektroenergie zu verzeichnen. Derzeit sind in Sachsen etwa Windenergieanlagen mit einer Leistung von insgesamt 20 MW und netzgekoppelte Photovoltaikanlagen mit einer Leistung von knapp 600 kW in Betrieb. Die Windenergienutzung befindet sich derzeit an der Schwelle zur Wirtschaftlichkeit (Stromgestehungskosten etwa 17 Pf/kWh), bis zum Jahr 2000 kann mit einer installierten Leistung bis zu 200 MW gerechnet werden. Demgegenüber ist Strom aus Photovoltaikanlagen noch um den Faktor 10 zu teuer.

A method for detecting and localizing leaks at complicated three-dimensional topolo-gies by measuring the leak induced structure-borne sound and by applying fuzzy pattern classification procedures has been developed. The sound patterns necessary to train the fuzzy pattern classifier are generated with simulated leaks at the original structure. RMS-values of acoustic emission sensors are used as features for char-acterizing the occurrence and the location of a leak. Fuzzy pattern classification is applied for check and calibration of the sensor lines and for leak localization as well. Several types of neural networks and the fuzzy pattern classification are compared concerning the capabilities of classification.

Analysis of hard two-photon correlations
measured in heavy-ion reactions at intermediate energies

H.W.Barz^1,2, B.Kämpfer^1,2, GY. Wolf^3,4, W. Bauer⁵

¹Institut für Kern- und Hadronenphysik, FZ Rossendorf,
PF 510119, 01314 Dresden, Germany
¹Institut für Theoretische Physik, TU Dresden,
Momrnsenstr. 13, 01062 Dresden, Germany
³GSI Darmstadt, PF 110552, 64220 Darmstadt, Germany
⁴KFKI RMKI Budapest, POB. 49, H-1525 Budapest, Hungary
MSU Michigan, East Lansing, MI 48824, USA

Abstract

Recently reported measurements of hard photon correlations in the reactions ³⁶Ar On ²⁷Al at 95 A*MeV, ⁸⁶Kr on ^natNi at 60 A*MeV, and ¹⁸¹Ta on ¹⁹⁷Au at 39.5 A*MeV are analyzed. A Boltzmann-Ühling-Uhlenbeck transport model is used to describe the photon production by individual nucleon-nucleon collisions. In the lighter systems we find the best agreement with data when taking into account only the photons from first chance collisions of nucleons or photons produced during the Passage of the nuclei, while the model predicts also a considerable late-time emission of photons which leads to a depletion of the calculated correlation function. The accuracy of the present data daas not allow firm conclusions on the reliability of this late time evolution. Our inveatigatiions do not support a recently reported interference pattern in the heavy Ta + Au system.