Diploma thesis in Physics submitted by Florian Freundt born in ...

More documents

Recommendations

Info

4.2. On site measurement of O2, CO2, CH4 and Radon 4 Measuring methods Mass Spectrometer noble gas [ peak heights ] Mass Spectrometer calibration gas [ peak heights ] Sample total gas amount [ mol ] 4.1.4 Resulting data WuCEM data evaluation software Sample noble gas amount [ ccSTP ] Sample noble gas mixing ratios [ Vol% ] Sample deviation from atm. air [ % atm. air ] Figure 4.1: Schematic diagram showing how the raw data was processed. Volume of 1 mol of gas at STP [ ccSTP/mol ] Atmospheric air noble gas mixing ratios [ Vol% ] The detected signals are converted to gas amounts in units ccSTP 1 by comparing peak heights of the calibration gas measurements with those of the measured sample gas using a specialized evaluation software called WuCEM. The resulting gas amounts are therefore limited in accuracy by statistical fluctuations, variations of the spectrometer’s sensitivity and the accuracy of the calibration gas composition. Data characterizing the accuracy of the individual isotope readings resulting from these measurements can be found in Table B.7. Gas concentrations were calculated by dividing the gas amounts by the molar volume at STP and by the measured total gas amount of the sample to deliver standardized and comparable gas concentrations. Since the interest of this study is to show whether the soil air composition deviates from atmospheric air composition, the noble gas concentrations were divided by the mixing ratio literature data of the respective noble gas isotopes [Porcelli et al., 2002], resulting in a relative indication of deviation, expressed in percent relative to atmospheric air. A schematic representation of the processing can be found in Figure 4.1. 4.2 On site measurement of O2, CO2, CH4 and Radon 4.2.1 Geotech BM2000 Biogas Monitor The Geotech BM2000 Biogas Monitor is a portable device capable of measuring O2, CO2, CH4 and CO, see Datasheet D.1. The O2 concentration is measured electrochemically, providing a measuring range of 0 to 25 Vol% O2 with an error of ±1 Vol%. CO2 and CH4 are measured by 1 cm 3 gas at standard conditions for temperature and pressure, i.e. T = 273.15 K, p0 = 101.325 kPa. 46
4 Measuring methods 4.2. On site measurement of O2, CO2, CH4 and Radon infrared spectroscopy. The range of the CO2 and of the CH4 sensor is 0 – 100 Vol% with an accuracy of ±0.5 Vol% at 0 – 5, ±1.0 Vol% at 5 – 15 and ±3.0 Vol% above 15 Vol%. Calibration of the device was verified by using a certified test gas, confirming the provided accuracies but showing a slight overestimation of O2, well within the given error range though (see Table B.2). Atmospheric air was regularly sampled before and after soil air samplings (see Figure C.7), the mean O2 value of (20.89±0.04) Vol% is in good agreement with the literature value of 20.9 Vol% [Porcelli et al., 2002]. 4.2.2 Durridge RAD7 Radon Detector The Durridge RAD7 Radon Detector detects α-particles of characteristic energies created within the decay chains of 222 Rn and 220 Rn, using a solid state detector. Solid state detectors consist of semiconductor material, a PN junction diode in reverse bias. An α-particle hitting the depletion layer creates electron-hole pairs that get separated by the electrical field spanning the junction, leading to a measurable current. The energy resolution depends on the semiconductor’s bandgap, allowing to differentiate between the different decaying Radon isotopes: The RAD7 detects the 6.00 MeV α-decay of 218 Po, which itself is the product of 222 Rn decay, and the 6.78 MeV α-decay of 216 Po, belonging to the 220 Rn decay chain. This allows for the parallel monitoring of 222 Rn and 220 Rn, leading to a more detailed source of information: while the readings of the long-lived 222 Rn (t 1/2 = 3.82 days) will usually increase in every one of the three 10 minute cycles due to its long lifetime, readings of the short-lived 220 Rn (t 1/2 = 55.6 sec) should be constant in all three cycles. A change in 220 Rn readings in one of the three cycles therefore indicates an inflow of differently composed air causing dilution or enrichment depending on its 220 Rn content. 47
Page 1: Faculty of Physics and Astronomy He
Page 5: Measuring annual variation of soil
Page 8 and 9: CONTENTS CONTENTS 3.1 Setup of the
Page 11 and 12: Chapter 1 Introduction Understandin
Page 13: 1 Introduction Molins and Mayer [20
Page 16 and 17: 2.1. Noble gas temperatures 2 Theor
Page 24 and 25: 2.2. Physical processes and propert
Page 26 and 27: 2.2. Physical processes and propert
Page 28 and 29: 2.3. Soil atmosphere composition 2
Page 35 and 36: Chapter 3 Sampling sites and method
Page 37 and 38: 3 Sampling sites and methods 3.1. S
Page 43 and 44: Chapter 4 Measuring methods 4.1 Mas
Page 45: 4 Measuring methods 4.1. Mass spect
Page 50 and 51: 5.2. Temperature profiles 5 Results
Page 52 and 53: 5.3. O2 and CO2 profiles 5 Results
Page 54 and 55: 5.4. Borehole sealing 5 Results 5.4
Page 56 and 57: 5.4. Borehole sealing 5 Results Fig
Page 58 and 59: 5.5. Noble gases 5 Results 8 days,
Page 60 and 61: 5.5. Noble gases 5 Results 5.5.3 So
Page 62 and 63: 5.5. Noble gases 5 Results 5.5.4 So
Page 64 and 65: 6 Discussion This rather extreme am
Page 66 and 67: )! )! *+,-./-01234*-56-20301.7*38*9
Page 68 and 69: 6 Discussion Table 6.1: Synthetic d
Page 71: Chapter 7 Summary The results of th
Page 74 and 75: 8 Outlook Considering the manifold
Page 76 and 77: A.1. Gas sample size A Calculations
Page 78 and 79: A.3. Fractionation-Values A Calcula
Page 80 and 81: Table B.3: Noble gas volume mixing
Page 82 and 83: Table B.5: Calculated values of rel
Page 84 and 85: Table B.8: Precipitation record of
Page 86 and 87: Table B.10: Complete dataset of nob
Page 89 and 90: Appendix C Additional plots and fig
Page 91 and 92: C Additional plots and figures Figu
Page 93 and 94: C Additional plots and figures �
Page 95 and 96: C Additional plots and figures Figu
Page 97 and 98:
C Additional plots and figures O 2
Page 99 and 100:
C Additional plots and figures 4 He
Page 101 and 102:
C Additional plots and figures 20 N
Page 103 and 104:
C Additional plots and figures Figu
Page 105 and 106:
C Additional plots and figures 10 1
Page 107 and 108:
Appendix D Datasheets 107
Page 109 and 110:
D Datasheets LogTag TREX-8 Technica
Page 111 and 112:
Bibliography [Aeschbach-Hertig 1994
Page 113 and 114:
BIBLIOGRAPHY BIBLIOGRAPHY [Friedric
Page 115 and 116:
BIBLIOGRAPHY BIBLIOGRAPHY [Riveros-
Page 117:
Acknowledegment At the end of this
show all

Diploma thesis in Physics submitted by Florian Freundt born in ...

Create successful ePaper yourself

Delete template?

Save as template?