Environmental influences on gamma ray spectrometry

Tyler, Andrew Nicholas (1994) Environmental influences on gamma ray spectrometry. PhD thesis, University of Glasgow.

Abstract

Spatially representative sampling of both natural and anthropogenic deposits in the
environment is limited by their inherent heterogenic distribution. This problem is
compounded when trying to relate ground measurements which are spatially restricted
to remote sensing observations which are not. This work examined these widely
experienced problems in the context of the measurement of natural (K, U and Th) and
anthropogenic ( 137Cs and ' 34Cs) radioactivity through the three techniques of soil
sampling with laboratory based gamma ray spectrometry, in-situ gamma ray
spectrometry, and airborne gamma ray spectrometry.
These three methods were applied systematically to estimate the radioactivity across
a tight geometry valley in Renfrewshire. Activity estimates from field based and
airborne gamma spectrometry were compared with each other and with the results of
high resolution gamma spectrometry of soil samples to examine the relationship
between each method under variable topographic conditions. These results
demonstrated that the distribution, and post depositional migration, of activity had
important influences on all measurement techniques, and affected the ability to make
comparisons between them.
Further detailed studies were then conducted to examine these influences. The effects
of variations in soil composition and characteristics on environmental gamma ray
spectrometry were evaluated by calculation and experimental determination.
Corrections to standard laboratory gamma spectrometric procedures were developed
to improve systematic precisio:i. These investigations also reviewed soil sampling
depth for direct effective comparison with in-situ gamma spectrometry.
The effects of small scale sampling errors on activity estimates were demonstrated to
have a quantifiable influence on the precision of activity estimation. Lateral variability
of activity distribution of natural radioactivity and anthropogenic radioactivity
deposited both from the atmosphere and from marine sources has been studied in
detail at a number of sites. The extent of variability depends on the nature of activity, its deposition mode and local environmental characteristics. Spatial variability
represents an important constraint on the interpretation of activity estimates derived
from all methods examined, and on comparisons between them. Statistically
representative sampling plans were developed and applied to enable spatial
comparisons to be made between soil sample derived activity estimates and in-situ and
remotely sensed observations.
The influence of the vertical activity distribution on in-situ and airborne measurements
has been recognised as an important variable affecting calibration. The use of the
information from the scattered gamma ray spectrum to quantify and correct for source
burial effects was examined in a series of modelling experiments. A relationship
between 'Cs source burial and forward scattering was determined and subsequently
applied to a salt marsh environment which showed pronounced subsurface maxima.
A spectrally derived calibration correction coefficient was shown to account for
variations in source burial across a single site. This provides a potential means for
surmounting one of the principal limitations of in-situ gamma spectrometry.
As a result of this work it has been possible to account for important environmental
factors which affect gamma ray spectrometry in the laboratory, in the field and from
aircraft. This has led to the development of sound methodology for comparison
between sampling, field based and remote sensing techniques.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Subjects: Q Science > QC Physics
• Colleges/Schools: College of Science and Engineering
• Supervisor's Name: Sanderson, Dr. David and Scott, Dr. Marian
• Date of Award: 1994
• Depositing User: Ms Mary Anne Meyering
• Unique ID: glathesis:1994-4893
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 27 Jan 2014 15:28
• Last Modified: 27 Jan 2014 15:37
• URI: https://theses.gla.ac.uk/id/eprint/4893