Michael Barabas - Academia.edu (original) (raw)

Papers by Michael Barabas

Research paper thumbnail of Aufbau und Weiterentwicklung von optischen Verfahren zur Messung von Gasblasen in Wasser; Messungen von Blasendichtespektren in Wind/Wasser-Kanälen in Marseille und Heidelberg

Ein optisches Blasengrößenmeßgerät (nach Th. Wais, 1983), das die von Luftblasen in Wasser reflek... more Ein optisches Blasengrößenmeßgerät (nach Th. Wais, 1983), das die von Luftblasen in Wasser reflektierten Anteile eines Laserstrahls registriert (Reflexionsprinzip), wurde am linearen Wind/Wasser-Kanal in Marseille (I.M.S.T.) eingesetzt. Für Messungen am zirkularen Windkanal in Heidelberg wurde ein anderes optisches Blasengrößenmeßgerät aufgebaut, das die Minderung der Lichtintensität eines Laserstrahls durch Luftblasen registriert (Lichtstreutechnik). Für beide Techniken wurde eine elektronische Schaltung entwickelt, die die von den Luftblasen erzeugten Impulse erkennen und in digitalisierter Form im Rechner abspeichern kann. Bei verschiedenen Windgeschwindigkeiten (10-13.1 m/sec) und in verschiedenen Tiefen wurden Blasendichte als Funktion des Radius gemessen. Die Ergebnisse wurden mit anderen Kanalmessungen und mit einer theoretischen Ableitung der Blasendichte verglichen.

Research paper thumbnail of Temperature experiments on mollusc samples: an approach to ESR signal identification

International Journal of Radiation Applications and Instrumentation. Part A. Applied Radiation and Isotopes, 1989

Powdered mollusc samples, which were irradiated with 7 rays at room temperature, were analysed by... more Powdered mollusc samples, which were irradiated with 7 rays at room temperature, were analysed by ESR spectrometry at different temperatures ranging from 293 to ~ 100 K. Gamma-ray irradiations, sometimes preceded by a thermal treatment at 180°C, were also performed at 77 K and at 140-180°C. From these experiments and from a study on non-powdered samples, it is concluded that the mollusc ESR spectrum is principally due to five paramagnetic species with the following values: (1) g = 2.0057; (2) gll = 2.0033 and g± = 2.0031 (the narrow g = 2.0032 line); (3) gtl = 2.0017 and g± = 2.0020 (the g = 2.0019 line); (4) g = 2.0007; (5) g~ = 2.0032, g2 = 2.0016 and g3 = 1.9973 (CO~-).

Research paper thumbnail of Environmental Distribution and Long-term Dispersion of Reactor 14CO2 Around Two German Nuclear Power Plants

Health Physics, Feb 1, 1988

Carbon-14 data on atmospheric CO2 as well as on plant material (tree leaves and wheat) from the v... more Carbon-14 data on atmospheric CO2 as well as on plant material (tree leaves and wheat) from the vicinity of two German boiling water reactors (Philippsburg and Isar/Ohu) are reported. Atmospheric CO2 samples taken routinely with an integration time of one or two weeks 1.75 km downwind of the Philippsburg reactor (900 MW electrical power) show a maximum 14C excess concentration of delta 14C (excess) = 300 +/- 7%, corresponding to 12.7 mBq m-3 (STP air). The long-term average excess amounts to delta 14C (excess) = 47 +/- 3%, corresponding to 2.0 mBq m-3 (STP air). The concentrations observed with plant material at the same sampling site range between delta 14C (excess) = 0% and 120%, corresponding to 0 and 27 mBq (g carbon)-1. With the meteorological dispersion parameters actually measured at the nuclear power plants, the dispersion factors for the various sampling sites and for the individual periods of sampling were calculated on the basis of a one-dimensional Gaussian plume model. With the observed 14C excess concentrations and the dispersion factor, a "theoretical" (i.e. calculated) reactor 14C source strength is then determined. For the Philippsburg reactor, which is situated in the flat Rhine valley, the "theoretical" and the observed yearly mean 14C emissions compare rather well (within a factor of 2). A significant systematical deviation from the model was found in the concentration decrease with source distance: the decrease predicted between the 1.75-km and 3.25-km distances is steeper than actually observed. The 14C excess concentrations found in tree leaves around the Isar/Ohu reactor (907 MW electrical power) at 1-2 km distance fall into the same range as observed at Philippsburg. In the hilly terrain at this reactor site, the model calculations agree well with the observed values up to a distance of 1 km if the relative elevation of the sampling site is taken into account by introducing a "reduced stack height" in the model calculations. This method fails in predicting the concentrations at distances greater than 1 km from the source.

Research paper thumbnail of The nature of the paramagnetic centres at g = 2.0057 and g = 2.0031 in marine carbonates

International Journal of Radiation Applications and Instrumentation. Part D. Nuclear Tracks and Radiation Measurements, 1992

A number of ESR signals appears regularly in marine carbonates with characteristic properties (g-... more A number of ESR signals appears regularly in marine carbonates with characteristic properties (g-factor, line width, symmetry). In this study we try to clarify the nature of the signals at g = 2.0057, 2.0031, and 2.0036 which are relevant for ESR dating. Especially the knowledge of the nature of the centre with g = 2.0057 may enable one to obtain reliable age information from this signal. Our approach was to synthesize carbonate powders (with different Mg/Ca ratios) doped with varying concentrations of SO:ions (or other sulphur compounds). On irradiation the samples with a Mg/Ca ratio > 0.1 showed very intense, isotropic ESR signals at g = 2.0057 and 2.0031. The intensity of both signals was found to be related to the SO:-concentration. By measuring the corresponding HFS components from natural "S (X-band and Q-band) we could unambiguously assign these signals to SO; (g = 2.0057) and SO; (g = 2.0031) radicals. The number of radicals related to the isotropic signals have been shown to be positively correlated to the Mg content of the carbonates. At low Mg content an axial signal (gper = 2.0036; gwr = 2.0021) arises, probably also originating from SO;. Experiments at various cavity temperatures indicate that the isotropic signals are due to rapid tumbling radicals (room temperature), thus generating motional narrowed lines. At lower temperatures (<-100°C) the tumbling of the radicals will be blocked and the corresponding anisotropic species can be detected exclusively. Comparing the properties (g-factor, line width, MW saturation, temperature behaviour, response to irradiation and annealing) of Ihe ESR signals in question with those in natural carbonates we deduce that they originate from the same paramagnetic centres in both cases.

Research paper thumbnail of The nature of the paramagnetic centres at g = 2.0057 and g = 2.0031 in marine carbonates

International Journal of Radiation Applications and Instrumentation. Part D. Nuclear Tracks and Radiation Measurements, Jul 1, 1992

A number of ESR signals appears regularly in marine carbonates with characteristic properties (g-... more A number of ESR signals appears regularly in marine carbonates with characteristic properties (g-factor, line width, symmetry). In this study we try to clarify the nature of the signals at g = 2.0057, 2.0031, and 2.0036 which are relevant for ESR dating. Especially the knowledge of the nature of the centre with g = 2.0057 may enable one to obtain reliable age information from this signal. Our approach was to synthesize carbonate powders (with different Mg/Ca ratios) doped with varying concentrations of SO:ions (or other sulphur compounds). On irradiation the samples with a Mg/Ca ratio > 0.1 showed very intense, isotropic ESR signals at g = 2.0057 and 2.0031. The intensity of both signals was found to be related to the SO:-concentration. By measuring the corresponding HFS components from natural "S (X-band and Q-band) we could unambiguously assign these signals to SO; (g = 2.0057) and SO; (g = 2.0031) radicals. The number of radicals related to the isotropic signals have been shown to be positively correlated to the Mg content of the carbonates. At low Mg content an axial signal (gper = 2.0036; gwr = 2.0021) arises, probably also originating from SO;. Experiments at various cavity temperatures indicate that the isotropic signals are due to rapid tumbling radicals (room temperature), thus generating motional narrowed lines. At lower temperatures (<-100°C) the tumbling of the radicals will be blocked and the corresponding anisotropic species can be detected exclusively. Comparing the properties (g-factor, line width, MW saturation, temperature behaviour, response to irradiation and annealing) of Ihe ESR signals in question with those in natural carbonates we deduce that they originate from the same paramagnetic centres in both cases.

Research paper thumbnail of ESR dating of the quaternary deep-sea sediment core RC17-177

Quaternary Science Reviews, 1992

The deep-sea sediment core RC17-177 from the west equatorial Pacific was dated with ESR using the... more The deep-sea sediment core RC17-177 from the west equatorial Pacific was dated with ESR using the signal at g = 2.0036 of 234 2 231 foraminifera. The measured dose rate parameters were: U-, Th-and K-concentrations, U-3°'I'h-and Pa-excess (initial values were assumed to be constant), average water content (derived from carbonate content) and a k,~-factor of 0.1 + 0.02 (own experiment). The ESR-signal growth curves on y-irradiation have been fitted by single exponential saturation functions. However, significant deviations from a single exponential form have been observed for larger y-doses. Agreement between ESR ages from the signal at g = 2.0036 and those from an independent 6180 stratigraphy was observed up to 800 ka. The existence of outliers could be explained by variable initial Th-excess or water content at different depths. On the contrary, the signal at g = 2.0006 delivered ADs (and corresponding ages) that are far too small due to a low thermal stability.

Research paper thumbnail of Influence of the Mg-content on ESR-signals in synthetic calcium carbonate

International Journal of Radiation Applications and Instrumentation. Part A. Applied Radiation and Isotopes, 1989

Carbonate crystals doped with various concentrations of Mg2+-ions have been grown by a gel-diffus... more Carbonate crystals doped with various concentrations of Mg2+-ions have been grown by a gel-diffusion method. An increase of the Mg/Ca-ratio to more than about 1 caused a phase change in the crystal lattice from calcite to aragonite. The properties of the ESR-signals of the synthetic carbonates were studied and compared with natural marine carbonates. The following results were derived: (a) In the presence of Mg2+-ions the synthetic carbonates display the same ESR-signals as natural calcites of marine origin with similar properties (thermal stability, radiation sensitivity). (b) The saturation value of the signal at g = 2.0006 in synthetic calcites was found to be strongly related with the Mg-content in the crystals. (c) The signal at g = 2.0036 (axial symmetry) which is present in calcite was not influenced by the Mg-concentration. Its saturation value decreases when the crystal phase changed from calcite to aragonite and in complement the signal at g = 2.0031 appeared. (d) The signals at g = 2.0057 and g = 2.0031 are most probably not of organic origin.

Research paper thumbnail of Basic ESR studies on recent corals

Quaternary Science Reviews, 1992

Experiments on recent corals (Acropora palmata, Barbados) were carried out to study the dating re... more Experiments on recent corals (Acropora palmata, Barbados) were carried out to study the dating relevant properties of the characteristic ESR signals. Highly resolved signal growth curves (55 aliquots of a sieve fraction 125-250 ~tm) were obtained by y-irradiation in small steps up to 20 kGy. The signal growth curve of the "dating signal" at g = 2.0006 can only he approximated by a single exponential saturation function in a certain dose range. Thus, ADs derived with this function tend to be overestimated. A better analytical description by two different functions was tested. Isothermal annealing experiments were carried out at various temperatures before and after irradiation with a definite y-dose respectively. The thermal decay of the dating signal is not 1st order. Furthermore, the decay process is strongly influenced by the decay of the traps themselves. The behaviour of the signals at g = 2.0057 and g = 2.0031 was compared with that of the dating signal. A surprising result was the growth of the signal at g = 2.0057 with y-irradiation.

Research paper thumbnail of An analytical model for the growth of ESR signals

International Journal of Radiation Applications and Instrumentation. Part D. Nuclear Tracks and Radiation Measurements, 1988

We have developed an analytical model for the time-and dose-dependency of ESR signals in calcite.... more We have developed an analytical model for the time-and dose-dependency of ESR signals in calcite. The model describes well the observed natural growth and the growth by artificial irradiation of ESR-signals (g = 2.0034 and g = 2.0006) in deep-sea foraminifera. The model shows how to derive the archeological dose from the artificial growth curve of ESR signals. Applying the model we have determined the lifetime of the signal at g = 2.0006 to be about 350 ka at 2°C. The thermal decay of the traps responsible for that signal was shown by heating experiments.

Research paper thumbnail of General properties of the paramagnetic centre at g = 2.0006 in carbonates

Quaternary Science Reviews, 1992

The ESR-signal at g = 2.0006 ('dating'-signal) in carbonates has characteristic properties that d... more The ESR-signal at g = 2.0006 ('dating'-signal) in carbonates has characteristic properties that do not depend on the origin nor on the crystal modification of the carbonate. It is shown how the dating signal is identified even in complex spectra by taking advantage of these properties. Independent methods of identification have been applied: Q-band measurements and computersimulations. These methods reveal the presence of this signal in aragonitic molluscs. Signals that often superimpose the dating signal have been analyzed. A probable model for the paramagnetic centre that is responsible for the signal is a rapid rotating COe-signal. This model is discussed and compared with the experimental findings. Systematic observations of the occurrence of the signal in different natural carbonates and comparisons with synthetic calcites show that the Mg/Ca ratio is the main factor that determines the density of the traps related to this signal.

Research paper thumbnail of Second interlaboratory-comparison project on ESR dating

Applied Radiation and Isotopes, 1993

Research paper thumbnail of Dose-response and thermal behaviour of the esr signal at g = 2.0006 in carbonates

Quaternary Science Reviews, 1992

Growth curves of the ESR dating signal at g = 2.0006 on irradiation have been carefully examined.... more Growth curves of the ESR dating signal at g = 2.0006 on irradiation have been carefully examined. They revealed that a description by a single exponential saturation function is only a good approximation in the dose range smaller than 1 kGy. In this dose range the saturation dose, Do, for carbonates was found to be between 400 and 800 Gy. The systematic deviations from this function and statistical uncertainties limit the reliable AD range to about 250 Gy. Expanded functions and models that explain the observed deviations are given. The usual way of determining the thermal life time of ESR signals (isothermal annealing and Arrhenius plot) is critically discussed and additional specific complications (trap decay, different components of the signal) of the signal at g = 2.0006 are shown. A different method of detecting long term fading was used, in which the natural signal growth is compared with artificial growth curves on y-irradiation. Evaluation of measurements from the sediment core RC17-177 revealed a thermal stability lower than previously assumed for foraminifera. The data fit best with the assumption that the dating signal contains a component (about 50%) that has a very low thermal stability (with a lifetime of about 50 ka at 2°C). Annealing experiments indicate that this may be the case in other carbonates as well. This would drastically limit the dating applicability of the signal at g = 2.0006.

Research paper thumbnail of German Nuclear Power Plants

Carbon-14 data on atmospheric C02 as well as on plant material (tree leaves and wheat) from the v... more Carbon-14 data on atmospheric C02 as well as on plant material (tree leaves and wheat) from the vicinity of two German boiling water reactors (Philippsburg and Isar/Ohu) are reported. Atmospheric C02 samples taken routinely with an integration time of one or two weeks 1.75 km downwind of the Philippsburg reactor (900 MW electrical power) show a maximum 14C excess concentration of AI4C (excess) = 300 -C 7%0, corresponding to 12.7 mBq m-3 (STP air). The long-term average excess amounts to AI4C (excess) = 47 & 3%0, corresponding to 2.0 mBq m-3 (STP air). The concentrations observed with plant material at the same sampling site range between AI4C (excess) = 0% and 120%0, corresponding to 0 and 27 mBq (g carbon)-’. With the meteorological dispersion parameters actually measured at the nuclear power plants, the dispersion factors for the various sampling sites and for the individual periods of sampling were calculated on the basis of a one-dimensional Gaussian plume model. With the observ...

Research paper thumbnail of Aufbau und Weiterentwicklung von optischen Verfahren zur Messung von Gasblasen in Wasser; Messungen von Blasendichtespektren in Wind/Wasser-Kanälen in Marseille und Heidelberg

Ein optisches Blasengrößenmeßgerät (nach Th. Wais, 1983), das die von Luftblasen in Wasser reflek... more Ein optisches Blasengrößenmeßgerät (nach Th. Wais, 1983), das die von Luftblasen in Wasser reflektierten Anteile eines Laserstrahls registriert (Reflexionsprinzip), wurde am linearen Wind/Wasser-Kanal in Marseille (I.M.S.T.) eingesetzt. Für Messungen am zirkularen Windkanal in Heidelberg wurde ein anderes optisches Blasengrößenmeßgerät aufgebaut, das die Minderung der Lichtintensität eines Laserstrahls durch Luftblasen registriert (Lichtstreutechnik). Für beide Techniken wurde eine elektronische Schaltung entwickelt, die die von den Luftblasen erzeugten Impulse erkennen und in digitalisierter Form im Rechner abspeichern kann. Bei verschiedenen Windgeschwindigkeiten (10-13.1 m/sec) und in verschiedenen Tiefen wurden Blasendichte als Funktion des Radius gemessen. Die Ergebnisse wurden mit anderen Kanalmessungen und mit einer theoretischen Ableitung der Blasendichte verglichen.

Research paper thumbnail of The Age of the Holstein Interglaciation: A Reply

Quaternary Research, 1988

Research paper thumbnail of General properties of the paramagnetic centre at< i> g</i>= 2.0006 in carbonates

Research paper thumbnail of Influence of the Mg-content on ESR-signals in synthetic calcium carbonate

International Journal of Radiation Applications and Instrumentation. Part A. Applied Radiation and Isotopes, 1989

Carbonate crystals doped with various concentrations of Mg2+-ions have been grown by a gel-diffus... more Carbonate crystals doped with various concentrations of Mg2+-ions have been grown by a gel-diffusion method. An increase of the Mg/Ca-ratio to more than about 1 caused a phase change in the crystal lattice from calcite to aragonite. The properties of the ESR-signals of the synthetic carbonates were studied and compared with natural marine carbonates. The following results were derived: (a) In the presence of Mg2+-ions the synthetic carbonates display the same ESR-signals as natural calcites of marine origin with similar properties (thermal stability, radiation sensitivity). (b) The saturation value of the signal at g = 2.0006 in synthetic calcites was found to be strongly related with the Mg-content in the crystals. (c) The signal at g = 2.0036 (axial symmetry) which is present in calcite was not influenced by the Mg-concentration. Its saturation value decreases when the crystal phase changed from calcite to aragonite and in complement the signal at g = 2.0031 appeared. (d) The signals at g = 2.0057 and g = 2.0031 are most probably not of organic origin.

Research paper thumbnail of General properties of the paramagnetic centre at< i> g</i>= 2.0006 in carbonates

Research paper thumbnail of Basic ESR studies on recent corals

... Electron spin resonance (ESR) dating of stalagmites of the Caune de l'Arago at Tautavel.... more ... Electron spin resonance (ESR) dating of stalagmites of the Caune de l'Arago at Tautavel. ... 135–138. Y. Yokoyama, JP Quaegebeur, R. Bibron, C. Leger, HV Nguyen and G. Poupeau, Electron spin resonance (ESR) dating of stalagmites of the Caune de l'Arago at Tautavel. ...

Research paper thumbnail of Dose-response and thermal behaviour of the esr signal at g = 2.0006 in carbonates

Quaternary Science Reviews, 1992

Growth curves of the ESR dating signal at g = 2.0006 on irradiation have been carefully examined.... more Growth curves of the ESR dating signal at g = 2.0006 on irradiation have been carefully examined. They revealed that a description by a single exponential saturation function is only a good approximation in the dose range smaller than 1 kGy. In this dose range the saturation dose, Do, for carbonates was found to be between 400 and 800 Gy. The systematic deviations from this function and statistical uncertainties limit the reliable AD range to about 250 Gy. Expanded functions and models that explain the observed deviations are given.

Research paper thumbnail of Aufbau und Weiterentwicklung von optischen Verfahren zur Messung von Gasblasen in Wasser; Messungen von Blasendichtespektren in Wind/Wasser-Kanälen in Marseille und Heidelberg

Ein optisches Blasengrößenmeßgerät (nach Th. Wais, 1983), das die von Luftblasen in Wasser reflek... more Ein optisches Blasengrößenmeßgerät (nach Th. Wais, 1983), das die von Luftblasen in Wasser reflektierten Anteile eines Laserstrahls registriert (Reflexionsprinzip), wurde am linearen Wind/Wasser-Kanal in Marseille (I.M.S.T.) eingesetzt. Für Messungen am zirkularen Windkanal in Heidelberg wurde ein anderes optisches Blasengrößenmeßgerät aufgebaut, das die Minderung der Lichtintensität eines Laserstrahls durch Luftblasen registriert (Lichtstreutechnik). Für beide Techniken wurde eine elektronische Schaltung entwickelt, die die von den Luftblasen erzeugten Impulse erkennen und in digitalisierter Form im Rechner abspeichern kann. Bei verschiedenen Windgeschwindigkeiten (10-13.1 m/sec) und in verschiedenen Tiefen wurden Blasendichte als Funktion des Radius gemessen. Die Ergebnisse wurden mit anderen Kanalmessungen und mit einer theoretischen Ableitung der Blasendichte verglichen.

Research paper thumbnail of Temperature experiments on mollusc samples: an approach to ESR signal identification

International Journal of Radiation Applications and Instrumentation. Part A. Applied Radiation and Isotopes, 1989

Powdered mollusc samples, which were irradiated with 7 rays at room temperature, were analysed by... more Powdered mollusc samples, which were irradiated with 7 rays at room temperature, were analysed by ESR spectrometry at different temperatures ranging from 293 to ~ 100 K. Gamma-ray irradiations, sometimes preceded by a thermal treatment at 180°C, were also performed at 77 K and at 140-180°C. From these experiments and from a study on non-powdered samples, it is concluded that the mollusc ESR spectrum is principally due to five paramagnetic species with the following values: (1) g = 2.0057; (2) gll = 2.0033 and g± = 2.0031 (the narrow g = 2.0032 line); (3) gtl = 2.0017 and g± = 2.0020 (the g = 2.0019 line); (4) g = 2.0007; (5) g~ = 2.0032, g2 = 2.0016 and g3 = 1.9973 (CO~-).

Research paper thumbnail of Environmental Distribution and Long-term Dispersion of Reactor 14CO2 Around Two German Nuclear Power Plants

Health Physics, Feb 1, 1988

Carbon-14 data on atmospheric CO2 as well as on plant material (tree leaves and wheat) from the v... more Carbon-14 data on atmospheric CO2 as well as on plant material (tree leaves and wheat) from the vicinity of two German boiling water reactors (Philippsburg and Isar/Ohu) are reported. Atmospheric CO2 samples taken routinely with an integration time of one or two weeks 1.75 km downwind of the Philippsburg reactor (900 MW electrical power) show a maximum 14C excess concentration of delta 14C (excess) = 300 +/- 7%, corresponding to 12.7 mBq m-3 (STP air). The long-term average excess amounts to delta 14C (excess) = 47 +/- 3%, corresponding to 2.0 mBq m-3 (STP air). The concentrations observed with plant material at the same sampling site range between delta 14C (excess) = 0% and 120%, corresponding to 0 and 27 mBq (g carbon)-1. With the meteorological dispersion parameters actually measured at the nuclear power plants, the dispersion factors for the various sampling sites and for the individual periods of sampling were calculated on the basis of a one-dimensional Gaussian plume model. With the observed 14C excess concentrations and the dispersion factor, a &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot;theoretical&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot; (i.e. calculated) reactor 14C source strength is then determined. For the Philippsburg reactor, which is situated in the flat Rhine valley, the &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot;theoretical&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot; and the observed yearly mean 14C emissions compare rather well (within a factor of 2). A significant systematical deviation from the model was found in the concentration decrease with source distance: the decrease predicted between the 1.75-km and 3.25-km distances is steeper than actually observed. The 14C excess concentrations found in tree leaves around the Isar/Ohu reactor (907 MW electrical power) at 1-2 km distance fall into the same range as observed at Philippsburg. In the hilly terrain at this reactor site, the model calculations agree well with the observed values up to a distance of 1 km if the relative elevation of the sampling site is taken into account by introducing a &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot;reduced stack height&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot; in the model calculations. This method fails in predicting the concentrations at distances greater than 1 km from the source.

Research paper thumbnail of The nature of the paramagnetic centres at g = 2.0057 and g = 2.0031 in marine carbonates

International Journal of Radiation Applications and Instrumentation. Part D. Nuclear Tracks and Radiation Measurements, 1992

A number of ESR signals appears regularly in marine carbonates with characteristic properties (g-... more A number of ESR signals appears regularly in marine carbonates with characteristic properties (g-factor, line width, symmetry). In this study we try to clarify the nature of the signals at g = 2.0057, 2.0031, and 2.0036 which are relevant for ESR dating. Especially the knowledge of the nature of the centre with g = 2.0057 may enable one to obtain reliable age information from this signal. Our approach was to synthesize carbonate powders (with different Mg/Ca ratios) doped with varying concentrations of SO:ions (or other sulphur compounds). On irradiation the samples with a Mg/Ca ratio > 0.1 showed very intense, isotropic ESR signals at g = 2.0057 and 2.0031. The intensity of both signals was found to be related to the SO:-concentration. By measuring the corresponding HFS components from natural "S (X-band and Q-band) we could unambiguously assign these signals to SO; (g = 2.0057) and SO; (g = 2.0031) radicals. The number of radicals related to the isotropic signals have been shown to be positively correlated to the Mg content of the carbonates. At low Mg content an axial signal (gper = 2.0036; gwr = 2.0021) arises, probably also originating from SO;. Experiments at various cavity temperatures indicate that the isotropic signals are due to rapid tumbling radicals (room temperature), thus generating motional narrowed lines. At lower temperatures (<-100°C) the tumbling of the radicals will be blocked and the corresponding anisotropic species can be detected exclusively. Comparing the properties (g-factor, line width, MW saturation, temperature behaviour, response to irradiation and annealing) of Ihe ESR signals in question with those in natural carbonates we deduce that they originate from the same paramagnetic centres in both cases.

Research paper thumbnail of The nature of the paramagnetic centres at g = 2.0057 and g = 2.0031 in marine carbonates

International Journal of Radiation Applications and Instrumentation. Part D. Nuclear Tracks and Radiation Measurements, Jul 1, 1992

A number of ESR signals appears regularly in marine carbonates with characteristic properties (g-... more A number of ESR signals appears regularly in marine carbonates with characteristic properties (g-factor, line width, symmetry). In this study we try to clarify the nature of the signals at g = 2.0057, 2.0031, and 2.0036 which are relevant for ESR dating. Especially the knowledge of the nature of the centre with g = 2.0057 may enable one to obtain reliable age information from this signal. Our approach was to synthesize carbonate powders (with different Mg/Ca ratios) doped with varying concentrations of SO:ions (or other sulphur compounds). On irradiation the samples with a Mg/Ca ratio > 0.1 showed very intense, isotropic ESR signals at g = 2.0057 and 2.0031. The intensity of both signals was found to be related to the SO:-concentration. By measuring the corresponding HFS components from natural "S (X-band and Q-band) we could unambiguously assign these signals to SO; (g = 2.0057) and SO; (g = 2.0031) radicals. The number of radicals related to the isotropic signals have been shown to be positively correlated to the Mg content of the carbonates. At low Mg content an axial signal (gper = 2.0036; gwr = 2.0021) arises, probably also originating from SO;. Experiments at various cavity temperatures indicate that the isotropic signals are due to rapid tumbling radicals (room temperature), thus generating motional narrowed lines. At lower temperatures (<-100°C) the tumbling of the radicals will be blocked and the corresponding anisotropic species can be detected exclusively. Comparing the properties (g-factor, line width, MW saturation, temperature behaviour, response to irradiation and annealing) of Ihe ESR signals in question with those in natural carbonates we deduce that they originate from the same paramagnetic centres in both cases.

Research paper thumbnail of ESR dating of the quaternary deep-sea sediment core RC17-177

Quaternary Science Reviews, 1992

The deep-sea sediment core RC17-177 from the west equatorial Pacific was dated with ESR using the... more The deep-sea sediment core RC17-177 from the west equatorial Pacific was dated with ESR using the signal at g = 2.0036 of 234 2 231 foraminifera. The measured dose rate parameters were: U-, Th-and K-concentrations, U-3°'I'h-and Pa-excess (initial values were assumed to be constant), average water content (derived from carbonate content) and a k,~-factor of 0.1 + 0.02 (own experiment). The ESR-signal growth curves on y-irradiation have been fitted by single exponential saturation functions. However, significant deviations from a single exponential form have been observed for larger y-doses. Agreement between ESR ages from the signal at g = 2.0036 and those from an independent 6180 stratigraphy was observed up to 800 ka. The existence of outliers could be explained by variable initial Th-excess or water content at different depths. On the contrary, the signal at g = 2.0006 delivered ADs (and corresponding ages) that are far too small due to a low thermal stability.

Research paper thumbnail of Influence of the Mg-content on ESR-signals in synthetic calcium carbonate

International Journal of Radiation Applications and Instrumentation. Part A. Applied Radiation and Isotopes, 1989

Carbonate crystals doped with various concentrations of Mg2+-ions have been grown by a gel-diffus... more Carbonate crystals doped with various concentrations of Mg2+-ions have been grown by a gel-diffusion method. An increase of the Mg/Ca-ratio to more than about 1 caused a phase change in the crystal lattice from calcite to aragonite. The properties of the ESR-signals of the synthetic carbonates were studied and compared with natural marine carbonates. The following results were derived: (a) In the presence of Mg2+-ions the synthetic carbonates display the same ESR-signals as natural calcites of marine origin with similar properties (thermal stability, radiation sensitivity). (b) The saturation value of the signal at g = 2.0006 in synthetic calcites was found to be strongly related with the Mg-content in the crystals. (c) The signal at g = 2.0036 (axial symmetry) which is present in calcite was not influenced by the Mg-concentration. Its saturation value decreases when the crystal phase changed from calcite to aragonite and in complement the signal at g = 2.0031 appeared. (d) The signals at g = 2.0057 and g = 2.0031 are most probably not of organic origin.

Research paper thumbnail of Basic ESR studies on recent corals

Quaternary Science Reviews, 1992

Experiments on recent corals (Acropora palmata, Barbados) were carried out to study the dating re... more Experiments on recent corals (Acropora palmata, Barbados) were carried out to study the dating relevant properties of the characteristic ESR signals. Highly resolved signal growth curves (55 aliquots of a sieve fraction 125-250 ~tm) were obtained by y-irradiation in small steps up to 20 kGy. The signal growth curve of the "dating signal" at g = 2.0006 can only he approximated by a single exponential saturation function in a certain dose range. Thus, ADs derived with this function tend to be overestimated. A better analytical description by two different functions was tested. Isothermal annealing experiments were carried out at various temperatures before and after irradiation with a definite y-dose respectively. The thermal decay of the dating signal is not 1st order. Furthermore, the decay process is strongly influenced by the decay of the traps themselves. The behaviour of the signals at g = 2.0057 and g = 2.0031 was compared with that of the dating signal. A surprising result was the growth of the signal at g = 2.0057 with y-irradiation.

Research paper thumbnail of An analytical model for the growth of ESR signals

International Journal of Radiation Applications and Instrumentation. Part D. Nuclear Tracks and Radiation Measurements, 1988

We have developed an analytical model for the time-and dose-dependency of ESR signals in calcite.... more We have developed an analytical model for the time-and dose-dependency of ESR signals in calcite. The model describes well the observed natural growth and the growth by artificial irradiation of ESR-signals (g = 2.0034 and g = 2.0006) in deep-sea foraminifera. The model shows how to derive the archeological dose from the artificial growth curve of ESR signals. Applying the model we have determined the lifetime of the signal at g = 2.0006 to be about 350 ka at 2°C. The thermal decay of the traps responsible for that signal was shown by heating experiments.

Research paper thumbnail of General properties of the paramagnetic centre at g = 2.0006 in carbonates

Quaternary Science Reviews, 1992

The ESR-signal at g = 2.0006 ('dating'-signal) in carbonates has characteristic properties that d... more The ESR-signal at g = 2.0006 ('dating'-signal) in carbonates has characteristic properties that do not depend on the origin nor on the crystal modification of the carbonate. It is shown how the dating signal is identified even in complex spectra by taking advantage of these properties. Independent methods of identification have been applied: Q-band measurements and computersimulations. These methods reveal the presence of this signal in aragonitic molluscs. Signals that often superimpose the dating signal have been analyzed. A probable model for the paramagnetic centre that is responsible for the signal is a rapid rotating COe-signal. This model is discussed and compared with the experimental findings. Systematic observations of the occurrence of the signal in different natural carbonates and comparisons with synthetic calcites show that the Mg/Ca ratio is the main factor that determines the density of the traps related to this signal.

Research paper thumbnail of Second interlaboratory-comparison project on ESR dating

Applied Radiation and Isotopes, 1993

Research paper thumbnail of Dose-response and thermal behaviour of the esr signal at g = 2.0006 in carbonates

Quaternary Science Reviews, 1992

Growth curves of the ESR dating signal at g = 2.0006 on irradiation have been carefully examined.... more Growth curves of the ESR dating signal at g = 2.0006 on irradiation have been carefully examined. They revealed that a description by a single exponential saturation function is only a good approximation in the dose range smaller than 1 kGy. In this dose range the saturation dose, Do, for carbonates was found to be between 400 and 800 Gy. The systematic deviations from this function and statistical uncertainties limit the reliable AD range to about 250 Gy. Expanded functions and models that explain the observed deviations are given. The usual way of determining the thermal life time of ESR signals (isothermal annealing and Arrhenius plot) is critically discussed and additional specific complications (trap decay, different components of the signal) of the signal at g = 2.0006 are shown. A different method of detecting long term fading was used, in which the natural signal growth is compared with artificial growth curves on y-irradiation. Evaluation of measurements from the sediment core RC17-177 revealed a thermal stability lower than previously assumed for foraminifera. The data fit best with the assumption that the dating signal contains a component (about 50%) that has a very low thermal stability (with a lifetime of about 50 ka at 2°C). Annealing experiments indicate that this may be the case in other carbonates as well. This would drastically limit the dating applicability of the signal at g = 2.0006.

Research paper thumbnail of German Nuclear Power Plants

Carbon-14 data on atmospheric C02 as well as on plant material (tree leaves and wheat) from the v... more Carbon-14 data on atmospheric C02 as well as on plant material (tree leaves and wheat) from the vicinity of two German boiling water reactors (Philippsburg and Isar/Ohu) are reported. Atmospheric C02 samples taken routinely with an integration time of one or two weeks 1.75 km downwind of the Philippsburg reactor (900 MW electrical power) show a maximum 14C excess concentration of AI4C (excess) = 300 -C 7%0, corresponding to 12.7 mBq m-3 (STP air). The long-term average excess amounts to AI4C (excess) = 47 & 3%0, corresponding to 2.0 mBq m-3 (STP air). The concentrations observed with plant material at the same sampling site range between AI4C (excess) = 0% and 120%0, corresponding to 0 and 27 mBq (g carbon)-’. With the meteorological dispersion parameters actually measured at the nuclear power plants, the dispersion factors for the various sampling sites and for the individual periods of sampling were calculated on the basis of a one-dimensional Gaussian plume model. With the observ...

Research paper thumbnail of Aufbau und Weiterentwicklung von optischen Verfahren zur Messung von Gasblasen in Wasser; Messungen von Blasendichtespektren in Wind/Wasser-Kanälen in Marseille und Heidelberg

Ein optisches Blasengrößenmeßgerät (nach Th. Wais, 1983), das die von Luftblasen in Wasser reflek... more Ein optisches Blasengrößenmeßgerät (nach Th. Wais, 1983), das die von Luftblasen in Wasser reflektierten Anteile eines Laserstrahls registriert (Reflexionsprinzip), wurde am linearen Wind/Wasser-Kanal in Marseille (I.M.S.T.) eingesetzt. Für Messungen am zirkularen Windkanal in Heidelberg wurde ein anderes optisches Blasengrößenmeßgerät aufgebaut, das die Minderung der Lichtintensität eines Laserstrahls durch Luftblasen registriert (Lichtstreutechnik). Für beide Techniken wurde eine elektronische Schaltung entwickelt, die die von den Luftblasen erzeugten Impulse erkennen und in digitalisierter Form im Rechner abspeichern kann. Bei verschiedenen Windgeschwindigkeiten (10-13.1 m/sec) und in verschiedenen Tiefen wurden Blasendichte als Funktion des Radius gemessen. Die Ergebnisse wurden mit anderen Kanalmessungen und mit einer theoretischen Ableitung der Blasendichte verglichen.

Research paper thumbnail of The Age of the Holstein Interglaciation: A Reply

Quaternary Research, 1988

Research paper thumbnail of General properties of the paramagnetic centre at< i> g</i>= 2.0006 in carbonates

Research paper thumbnail of Influence of the Mg-content on ESR-signals in synthetic calcium carbonate

International Journal of Radiation Applications and Instrumentation. Part A. Applied Radiation and Isotopes, 1989

Carbonate crystals doped with various concentrations of Mg2+-ions have been grown by a gel-diffus... more Carbonate crystals doped with various concentrations of Mg2+-ions have been grown by a gel-diffusion method. An increase of the Mg/Ca-ratio to more than about 1 caused a phase change in the crystal lattice from calcite to aragonite. The properties of the ESR-signals of the synthetic carbonates were studied and compared with natural marine carbonates. The following results were derived: (a) In the presence of Mg2+-ions the synthetic carbonates display the same ESR-signals as natural calcites of marine origin with similar properties (thermal stability, radiation sensitivity). (b) The saturation value of the signal at g = 2.0006 in synthetic calcites was found to be strongly related with the Mg-content in the crystals. (c) The signal at g = 2.0036 (axial symmetry) which is present in calcite was not influenced by the Mg-concentration. Its saturation value decreases when the crystal phase changed from calcite to aragonite and in complement the signal at g = 2.0031 appeared. (d) The signals at g = 2.0057 and g = 2.0031 are most probably not of organic origin.

Research paper thumbnail of General properties of the paramagnetic centre at< i> g</i>= 2.0006 in carbonates

Research paper thumbnail of Basic ESR studies on recent corals

... Electron spin resonance (ESR) dating of stalagmites of the Caune de l'Arago at Tautavel.... more ... Electron spin resonance (ESR) dating of stalagmites of the Caune de l'Arago at Tautavel. ... 135–138. Y. Yokoyama, JP Quaegebeur, R. Bibron, C. Leger, HV Nguyen and G. Poupeau, Electron spin resonance (ESR) dating of stalagmites of the Caune de l'Arago at Tautavel. ...

Research paper thumbnail of Dose-response and thermal behaviour of the esr signal at g = 2.0006 in carbonates

Quaternary Science Reviews, 1992

Growth curves of the ESR dating signal at g = 2.0006 on irradiation have been carefully examined.... more Growth curves of the ESR dating signal at g = 2.0006 on irradiation have been carefully examined. They revealed that a description by a single exponential saturation function is only a good approximation in the dose range smaller than 1 kGy. In this dose range the saturation dose, Do, for carbonates was found to be between 400 and 800 Gy. The systematic deviations from this function and statistical uncertainties limit the reliable AD range to about 250 Gy. Expanded functions and models that explain the observed deviations are given.