Pulse Shape Analysis and Identification of Multipoint Events in a Large-Volume Proportional Counter in an Experimental Search for 2K Capture Kr-78

A pulse shape analysis algorithm and a method for suppressing the noise component of signals from a large copper proportional counter in the experiment aimed at searching for 2K capture of Kr-78 are described. These signals correspond to a compound event with different numbers of charge clusters due to from primary ionization is formed by these signals. A technique for separating single- and multipoint events and determining the charge in individual clusters is presented. Using the Daubechies wavelets in multiresolutional signal analysis, it is possible to increase the sensitivity and the resolution in extraction of multipoint events in the detector by a factor of 3-4.Comment: 10 pages, 8 figures. submitted to Instruments and Experimental Techniques; ISSN 0020/441

A dating method with 39Ar

The principles of a dating method based on the cosmic-ray-produced radioisotope 39Ar are given. Technical requirements such as background and standard gas samples and gas proportional counting systems are described. With samples extracted from Greenland ice it can be demonstrated that39Ar ages agree with ages obtained by other methods. First results on ocean water samples show that with this isotope valuable information on ocean mixing and circulation can be expected.39Ar results on groundwater samples disagree for some aquifers with conventional14C ages; possible explanations are discussed, especially underground production of 39Ar

Underground production of radionuclides in the Milk River aquifer, Alberta, Canada

Most cosmogenic radionuclides that may be used to estimate groundwater ages in excess of 100 ka are also produced underground byin situ nuclear reactions. Radioactive equilibrium betweenin situ production and decay would be approached within such long residence times. Radionuclide production byin situ nuclear reactions within the groundwater and within its host rock has been calculated theoretically and compared with some measured radionuclide contents of the groundwater. The fractional transfer ofin situ produced37Ar,39Ar and222Rn from rock to groundwater necessary to account for the total measured groundwater contents were found to be similar, although site specific. The implications for radionuclide release mechanisms and for groundwater dating by the use of cosmogenic radionuclides, including those which are applicable for very old groundwaters (36Cl,81Kr,129I), are discussed

Dissolved gases in the milk river aquifer, Alberta, Canada

Geochemical relations between the noble gases,40Ar/36Ar ratio, N2 and CH4 contents of groundwaters from the Milk River aquifer, Albert, Canada, have been investigated. The CH4 contents for many of the groundwaters are several times their N2 contents and cause degassing to occur as the hydrostatic pressure decreases during their ascent in the wells. Recharge temperatures, derived for those groundwaters that were not degassed, indicate that the youngest groundwaters were recharged under cooler climatic conditions than prevailed during earlier recharge. This conclusion is supported by the stable isotope compositions of the groundwater. The4He concentration in the groundwater varies with depth according to the theoretical concentration/depth profile for accumulated radiogenic4He in the aquifer and its adjacent shales. The corresponding flux of4He to the atmosphere is <2% of the total crustal4He production rate. Excess radiogenic40Ar is associated with CH4 and both gases originated within the adjacent shales. The CH4 is biogenic and was produced in an aqueous environment which ranged from marine to freshwater as the connate fluids in these marine shales were replaced. The degassing process has been modelled to explain the residual dissolved gas contents of the groundwater and to show that the CH4/N2 ratio in situ was ∼12

Ten years low-level counting in the underground laboratory in Bern, Switzerland

Although new techniques of direct atom counting have been developed, which are also discussed at this conference, the good old low-level counting technique is still important. Looking back to the first decade of measurements in our underground laboratory, we realize that many interesting results have been obtained. The following examples are discussed: 39Ar is up to now only measured in Bern. This isotope has been used for ice and groundwater dating and for studying ocean water circulation, mixing and equilibrating with the atmosphere. 37Ar results have already been presented at the two preceding High Tatras LLC conferences. Now the full 15 years' series of measurements is given and shortly discussed. 3H measurements are possible without enrichment by direct liquid scintillation counting down to the present low environmental levels of 20–80 pCi/l in precipitation. Series of results of two selected areas are presented. 14C is measured routinely in several gas proportional counters. With each counter about 60 samples and 40 standard, background or blank samples are measured per year. As an example, the 14C results measured in tree leaves at reference stations in Switzerland, unaffected by man-made contributions, are presented

81Kr and 85Kr in groundwater, milk river aquifer, Alberta, Canada

The85Kr activity of well No. 9 is (2.1 ± 0.3) mBq/cm3 STP ofKr or ≈0.3% of the modern atmospheric activity indicating that no young water component is present in this groundwater and that no contamination occurred in extracting a Kr gas sample for81Kr analysis. The81Kr concentration was measured by laser resonance ionization spectroscopy to be 82 ± 18% of the modern atmospheric concentration. Only 5000 atoms of81Kr were used in the final analytical step which represent ≈7% of the initial number present in a water sample of 50 1. An upper limit of 140 ka is calculated for the age of the water from a simple81Kr decay model. Of key importance for the future use of a81Kr dating technique is the conclusion that subsurface production of81Kr appears to be unimportant

Exploring an aquifer system by integrating hydraulic, hydrogeologic and environmental tracer data in a threedimensional hydrodynamic transport model

This article presents a numerical model of a part of an aquifer that is recharged by infiltration from the Swiss pre-Alpine river Töss in the Linsental (north-eastern Switzerland). The nearby city of Winterthur makes use of this aquifer as a resource of drinking water. The presented model is part of a larger interdisciplinary research program undertaken with the goal to evaluate the possible impacts of a planned revitalization of the severely canalized river Töss. Above all it should show the extent of decrease of the groundwater residence time if the river bed is allowed to move towards the drinking water wells. The flow model was constrained and calibrated by transport modelling of tritiogenic 3He. This tracer reflects both the aging of the water (by accumulation of 3He resulting from tritium-decay) as well as the two different components of the mixture (river water free of tritiogenic 3He due to degassing, and groundwater enriched in 3He due to accumulation). By simulating a Dirac-pulse-shaped input of a conservative tracer at different sources (river cells or upstream flux boundary cells) it is possible to determine the age distributions as well as the mixing ratios of the two types of water at the two pumping stations within the model area. The same calculations for a hypothetical river course passing directly beside the pumping stations indicate a decrease of the mean residence time of the pumped water together with an increase of the amount of the younger river water component