Cryptopodzols are black soils that occur under forests dominated by chestnut trees (
Castanea sativa) in Southern Switzerland. Their soil organic carbon (SOC) stocks reach an average of 150
t C
ha
−
...1 and are thus among the highest of European forest soils.
We investigated the processes leading to the accumulation and stabilisation of SOC in these soils by analysing three Cryptopodzols and one Cambisol for charred organic matter content (macrocharcoal and BPCA), the amounts of Fe and Al, and the colour and SOC content in bulk soil and density fractions. The results showed that charred organic matter produced by frequent fires in the area for more than 10,000
years is highly abundant in Cryptopodzols: the stocks of macrocharcoal and BPCA-C amount to up to 31
t ha
−
1 and 17
t ha
−
1, respectively. These high amounts of charred organic matter are responsible for the dark soil colour and high SOC concentrations that are, however, also closely related to Fe
p and Al
p concentrations. We concluded that the occurrence of charcoal across the whole profiles of Cryptopodzols seems to be the dominating factor, although both the formation of organo-metallic or organo-mineral complexes in the subsoil and the high abundance and stability of charred organic matter are responsible for the high SOC stocks in Cryptopodzols.
Our study on SOM stabilisation Cryptopodzols of Southern Switzerland suggested that organo-mineral, or organo-metallic complexation and the recalcitrance of charcoal particles are responsible for stabilising SOM. The presence of free particulate charcoal and its significant correlation to SOC is an evidence that not only sorption to mineral surfaces but also molecular recalcitrance is an important factor. BPCA-C, however, strongly interacts with metals that are organically bound, and contributes through this mechanism to the stabilisation of SOM. We conclude that fire-derived C contributes significantly to the black colour and to the high C stocks in southern Switzerland. In addition, statistical evidence suggests that sorption processes stabilise plant and, also very likely, fire-derived SOC, mainly in the subsoil. The conclusions are based on the following results: ►charcoal, which has been present in the soils for 13,000
years, and BPCA-C can be detected in much higher concentrations and stocks in the Cryptopodzols than in the Cambisol; ►charred organic matter, measured as BPCA, intensifies the dark soil colour; ►the amount of SOC and BPCA-C correlated well with the concentrations of pyrophosphate-extractable, organically bound Al and Fe fractions in the soils; ►SOC was mainly present in the light fraction of topsoils, but also in the medium and heavy fractions in the subsoil horizons.
Design characteristics and first experience concerning the new high-resolution powder diffractometer for thermal neutrons at the Swiss spallation neutron source SINQ are summarized. It is based on a ...linear position-sensitive
3
He
detector with 1600 wires and angular separation of 0.1°, permitting also real-time experiments.
A fast modulator for a dynamic supply linear RF amplifier has been integrated in a 0.35-/spl mu/m CMOS technology. The use of this modulator with an external linear power amplifier (PA) allows to ...maintain its efficiency at a higher level than it would with the same PA supplied at constant voltage. The modulator is designed to follow rapid envelope variations at high efficiency without compromising the RF PA linearity.
A new data acquisition system (DAQ) for bulk
μ
SR and low-energy
μ
SR (LE-
μ
SR) has been developed at PSI. It is based on commercial and in-house VME modules, and on the MIDAS DAQ software library. ...The system is able to cope with the different needs of the various PSI
μ
SR spectrometers, which was not possible with the existing CAMAC and ORTEC's pTA-clock based DAQ systems. The VME clock is a 64-channel CAEN V1190 TDC, using the CERN HPTDC chip, with programmable time resolution of 25, 100, 200 or 800
ps. The TDC onboard memory is continuously read through the VME bus by standard PC's or dedicated servers, using a 1-Gbit/s SIS3100/1100 VME–PCI interface. Detector rates are independently monitored using a 32-channel SIS3820 scaler module. In-house developed modules comprise an 8-channel constant fraction discriminator CFD950, a CD950 clock divider, an 8-channel linear fan-out SP950, a 16-channel NIM-ECL level converter LC950, and a programmable coincidence module FC950. All modules feature a superior performance compared to commercially available devices which allows their use also in the planned high-field
μ
SR spectrometer where a time resolution of about 100
ps is envisaged. A special external hardware logic is no longer required, since the system can deal with a rate total of 5
MHz which is sufficient for
μ
SR spectrometers with high event rate in their active veto systems.
The main characteristics of the European Space Agency (ESA) Standard Radiation Environment Monitor (SREM) are outlined. First SREM results from the Project for On-Board Autonomy-I (PROBA-I) and ...INTEGRAL spacecraft are presented.
A scalable 16-ch thermal neutron detection system has been developed in the framework of the upgrade of a neutron diffractometer. The detector is based on a ZnS:6LiF scintillator with embedded WLS ...fibers which are read out with SiPMs. In this paper, we present the 16-ch module, the dedicated readout electronics, a direct comparison between the performance of the diffractometer obtained with the current 3He detector and with the 16-ch detection module, and the channel-to-channel uniformity.
We present a digital signal processing system based on a photon counting approach which we developed for a thermal neutron detector consisting of ZnS(Ag):6LiF scintillating layers read out with WLS ...fibers and SiPMs. Three digital filters have been evaluated: a moving sum, a moving sum after differentiation and a digital CR-RC4 filter. The performances of the detector with these filters are presented. A full analog signal processing using a CR-RC4 filter has been emulated digitally. The detector performance obtained with this analog approach is compared with the one obtained with the best performing digital approach.
•Application of digital signal processing for a SiPM-based ZnS:6LiF neutron detector.•Optimisation of detector performances with 3 different digital filters.•Comparison with detector performances with a full analog signal processing.
In this paper we present the development of a one-dimensional multi-channel thermal neutron detection system for the application in neutron scattering instrumentation, e.g. strain-scanning ...diffractometers. The detection system is based on ZnS(Ag):6LiF neutron scintillator with embedded WLS fibers which are read out with a SiPM. A dedicated signal processing system allows us to suppress the SiPM dark counts and to extract the signals from the neutron absorption events.
For a single-channel detection unit which represents the elementary building block of this detection system we achieved a neutron detection efficiency of ~65% at 1.2Å, a background count rate <10−3Hz and a gamma-sensitivity <10−6 (measured with a 60Co source), while the dead time is ~20μs and the multi-count ratio is <1%. This performance was achieved even for SiPM dark count rates of up to ~2MHz.
In this paper we present the development of a one-dimensional multi-channel thermal neutron detection system for the application in neutron scattering instrumentation, e.g. strain-scanning ...diffractometers. The detection system is based on ZnS(Ag): super(6)LiF neutron scintillator with embedded WLS fibers which are read out with a SiPM. A dedicated signal processing system allows us to suppress the SiPM dark counts and to extract the signals from the neutron absorption events. For a single-channel detection unit which represents the elementary building block of this detection system we achieved a neutron detection efficiency of ~65% at 1.2 Aa, a background count rate View the MathML source <10-3Hz and a gamma-sensitivity <10 super(-6)<10-6 (measured with a super(60)Co source), while the dead time is ~20 mu s and the multi-count ratio is <1%<1%. This performance was achieved even for SiPM dark count rates of up to ~2 MHz.
The single-crystal diffractometer TriCS at the Swiss Continuous Spallation Source (SINQ) is presently in the commissioning phase. A two-dimensional wire detector produced by EMBL was delivered in ...March 1999. The instrument is presently tested with a single detector. First measurements on magnetic structures have been performed. The instrument is remotely controlled using JAVA-based software and a UNIX DEC-α host computer.
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