ALBERT

Notes: The pH buffering and aluminium solubility characteristics of acid soil are important in determining the soil's response to changes in precipitation acidity. The chemistry of soil organic matter (humic substances) plays a key role in both processes, yet is complex and still poorly understood. Nevertheless, models of humic substance chemistry have been developed, one of which is WHAM–S, which contains a model (Model V) of proton and metal binding at discrete sites on humic substances and considers electrostatic effects on the binding strength. Here we have tested the ability of WHAM–S to model solution pH and Al using batch titration studies on organic and mineral soil horizons from forested sites in Norway, Germany and Spain, with ambient pH values from 3.73 to 5.73. We optimized the model predictions by adjusting the amounts of soil aluminium and humic substances within defined limits, taking the contents of copper chloride-extractable Al and the base-extractable organic matter as starting values. The model simulated both pH and dissolved Al well with optimized amounts of aluminium and humic substances within the defined limits (root mean squared error for pH from 0.01 to 0.22, for p[Al]aq (total dissolved Al) from 0.03 to 0.49, five data points). Control of dissolved Al by dissolved organic matter was important particularly at above-ambient pH. In two mineral horizons we improved the fits by assuming that Al could precipitate as Al(OH)3. The optimized model also gave reasonable predictions of pH and dissolved Al in supernatants obtained by repeated leaching of the soil horizons. The results show that humic substances dominate the control of pH and dissolved Al in most of the horizons studied. Control by Al(OH)3 occurs but is the exception.

Notes: Organically-bound Al in acidic, base-poor sandy soils seems to be a major contributor to dissolved Al. This hypothesis has been tested under field conditions at two intensely acidified sites. The research was conducted at the agricultural trial fields at Lyczyn, Poland, which have been fertilized continuously for 30 yr with 130 kg ha−1 a−1 N (as NH4NO3 or urea). The effect of depletion of Al on its solubility was also studied.Field data confirmed that mobilized Al originates largely in the organically bound fraction of soil Al. Depletion of this fraction resulted in a considerable decrease in the mobility of Al such that, at pH = 3.0 and reaction times of a few weeks, small amounts of Al were mobilized. Apparently, the rate at which Al is dissolved from structural silicates, which are abundant in the soil investigated, is small. This suggests that at sites in Poland most exposed to acid deposition, where the rates of soil acidification and depletion of organically-bound Al are greatest, both the concentration of Al and the soil solution pH are expected to decline with time.

Notes: At the KVI there are presently four ion sources available: POLIS, for polarized protons and deuterons, to be injected in the new superconducting cyclotron AGOR ECRIS3, to produce highly charged ions for AGOR, ECRIS4, to produce highly charged ions for the Atomic and Surface Physics research facility (essentially a copy of ECRIS3), and CUSP, for high intensity AGOR beams of protons, deuteron, or alpha particles. We will report here on the performance and status of POLIS and ECRIS3. POLIS is an atomic beam type polarized ion source, according to the well known scheme with a cryo cooled dissociator, watercooled hexapole magnets, "strong field" and "weak field" radio frequency (rf) transitions for hydrogen and deuterium, and a 2.45 GHz electron cyclotron resonance (ECR) type ionizer. The source was constructed in a joint effort with the Forschungszentrum Karlsruhe, Cyclotron department. The ionizer section was modified and can be operated up to 40 kV. Following successful tests and deuteron polarization measurements at low energies, POLIS was connected to AGOR in November 1996. Most parts are now adapted to the AGOR-KVI control system. The first experiments with proton beams (190 MeV) from AGOR were done with polarized beams. As a consequence, the first measurement of proton polarization could be done only during these experiments, and all efforts to improve the polarization had to take place also during experiments. Efforts to get the weak field transition in operation have given a present best value of polarization of 70%±0.5% of the theoretical value. This value is deduced from an assumed analyzing power of the applied reaction. The strong field unit is not perfect; the best value which has been observed is 56%±0.5%. However, the difference between the given polarizations could be the result of a systematic error in the measurement of polarization "zero." The output of POLIS is in the order of 50 μÅ. The running time is usually 1–2 weeks (with nozzle at 53 K) until the dissociator and nozzle become contaminated; with a nitrogen layer (nozzle at 35 K) the polarization degree tends to be higher, but the running time is reduced to 3–5 days. POLIS has been in operation during more than 70% of the 33 weeks scheduled for experiments with AGOR since November 1996. Present activities concentrate on the improvement of the strong field unit, increasing the ionizer efficiency and the running time. ECRIS3 is a room temperature ECR ion source, with rf and gas feed according to the CAPRICE scheme. Its performance has been reported earlier (RIKEN 95). Gas mixing is important for the production of highly charged ions. Like in other sources, the anomaly for oxygen isotopes has also been measured. One new observation concerning gas mixing, in particular for the production of argon beams, is the following: For medium charge states, e.g., Ar8+, there is a slight preference for helium as a mixing gas, as compared to pure argon. In fact, oxygen is not good here. On the contrary, for high charge states like Ar14+, oxygen is a very good mixing gas, helium has only a small effect, but the best results have been obtained with isotopic 18O as a mixing gas. Recently, the same has been observed with CAPRICE 10 GHz at CEN-Grenoble, and to some extent with ECRIS4.© 1998 American Institute of Physics.