Sin ttulo de diapositiva

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Optimisation of Environmental Gamma Spectrometry
using Monte Carlo Methods
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Francisco Javier Hernandez Suarez Radioactivity
in the Environment and studies of Environmental
systems group, Department of Physics Uppsala
University
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Contents
Environmental Gamma Spectrometry
Gamma Spectrometry Laboratory
Efficiency Calibration of HPGe Detectors
Self-absorption Corrections
Measurement of Radiotracers in Env. Samples
Conclusions
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Environmental Gamma Spectrometry
Use of Radionuclides as tracers of Environmental
processes
Simultaneous and Absolute Measurement of Gamma
Emmitting Radionuclides in Diversous
Environmental Systems
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Environmental Gamma Spectrometry
Use environmental systems as indicators of global
change
Examples of radionuclides measurable by gamma
Spectrometry
U-235, U-238(Th-234), Th-232(Ac-228), K-40, Be-7
Ra-226, Pb-214, Bi-214, Tl-210, Pb-210
Th-231, Th-227, Ra-223, Bi-211
Th-228, Ra-224, Pb-212, Tl-208
Cs-137, Cs-134, Am-241
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Environmental Gamma Spectrometry Laboratory
Dynamic range of measuring possibilities 0.1 -
250 g
Ultra low-level background
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Environmental Gamma Spectrometry Laboratory
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Environmental Gamma Spectrometry Laboratory
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Efficiency Calibration of HPGe Detectors
Absolute measurement of activities
Homogeneous Sources with Minimised absorption
Impractical for the calibration of many
sample-to-detector geometries
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Efficiency Calibration of HPGe Detectors using
Monte Carlo Methods
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Efficiency Calibration of HPGe Detectors using
Monte Carlo Methods
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Self-absorption corrections using Monte Carlo
Methods
Semi-empirical method
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Self-absorption corrections using Monte Carlo
Methods
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Measurement of Radiotracers in Environmental
Samples
Spectrometry of Th-234 (U-238)
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Conclusions
Monte Carlo simulations cannot yet completely
replace the experimental determination of the
efficiency of Ge-detectors.
However, Monte Carlo simulations do provide
valuable data to facilitate the calibration of
the efficiency of Ge-detectors without the need
of extensive experimental work.
The main limitation in the simulation of the
performance of Ge-detectors is the inaccurate
knowledge of all the input parameters related to
the sample-to-detector geometry.
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Conclusions
Simulating the performance of Well type
Ge-detectors requires the modelling of the charge
collection process in the crystal.
Monte Carlo methods provide flexible means to
perform self-absorption corrections in
environmental gamma spectrometry
The 63 keV peak (self-absorption corrected) is
the most suitable peak for the calculation of the
Th-234 (U-238) activity
Gamma spectrometry can be used quantitatively for
the simultaneous measurement of multitracers in
sediment fractions