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A comparison between HPGe- and NaI(Tl)-systems in finding lost point sources and optimisation of collecting parameters

Ekman, Jörgen (1999)
Medical Physics Programme
Abstract (Swedish)
Up to recently mobile gamma spectrometry has mostly been performed with NaI(Tl)-based detector systems. However lately the interest of using HPGe(High Purity Germanium)-based systems have increased and one has realised that the excellent energy resolution of HPGe-detectors, in combination with the possibility to manufacture larger crystals than before, is an advantage not only when performing in situ measurements but also when dealing with mobile spectrometry. The aim of this study is to compare a ~20% HPGe-detector with a 3"x3" NaI(Tl)-detector in the scenario of a lost 137-Cs point-source. Furthermore the dependence of various collecting parameters is examined in order to optimise a detector system for mobile measurements. The... (More)
Up to recently mobile gamma spectrometry has mostly been performed with NaI(Tl)-based detector systems. However lately the interest of using HPGe(High Purity Germanium)-based systems have increased and one has realised that the excellent energy resolution of HPGe-detectors, in combination with the possibility to manufacture larger crystals than before, is an advantage not only when performing in situ measurements but also when dealing with mobile spectrometry. The aim of this study is to compare a ~20% HPGe-detector with a 3"x3" NaI(Tl)-detector in the scenario of a lost 137-Cs point-source. Furthermore the dependence of various collecting parameters is examined in order to optimise a detector system for mobile measurements. The possibility to collect consecutive spectra with two MCA(Multi Channel Analyzer)-softwares is also studied. After interpolation and sampling of data from stationary measurements on a 137-Cs point-source the opportunity is given to simulate that a detector mounted in vehicle is passing a radiation source. This approach allows the study of parameters such as collecting time and collecting velocity. A statistical test and a detection limit are introduced to quantify whether the point source is found or not. The detectors in this study can then be compared underthe same circumstances and the experimentally results is compared with theoretical predictions. Both the 3"x 3" NaI(Tl)-detector and the ~20% HPGe detector are able to find a 54 MBq 137-Cs point-source when passing the source at a smallest distance of approximately 50m. Furthermore it is seen that a lower collecting velocity (i.e. the velocity of the vehicle) often i preferable and for a given collcting velocity there exists an optimum collecting time. The two detectors in this study have similar capability to find lost point sources with an activity of approximately 50 MBq. (Less)
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author
Ekman, Jörgen
supervisor
organization
year
type
H2 - Master's Degree (Two Years)
subject
keywords
Radioekologi
language
English
id
2156908
date added to LUP
2011-09-13 14:01:44
date last changed
2011-09-13 14:01:44
@misc{2156908,
  abstract     = {Up to recently mobile gamma spectrometry has mostly been performed with NaI(Tl)-based detector systems. However lately the interest of using HPGe(High Purity Germanium)-based systems have increased and one has realised that the excellent energy resolution of HPGe-detectors, in combination with the possibility to manufacture larger crystals than before, is an advantage not only when performing in situ measurements but also when dealing with mobile spectrometry. The aim of this study is to compare a ~20% HPGe-detector with a 3"x3" NaI(Tl)-detector in the scenario of a lost 137-Cs point-source. Furthermore the dependence of various collecting parameters is examined in order to optimise a detector system for mobile measurements. The possibility to collect consecutive spectra with two MCA(Multi Channel Analyzer)-softwares is also studied. After interpolation and sampling of data from stationary measurements on a 137-Cs point-source the opportunity is given to simulate that a detector mounted in vehicle is passing a radiation source. This approach allows the study of parameters such as collecting time and collecting velocity. A statistical test and a detection limit are introduced to quantify whether the point source is found or not. The detectors in this study can then be compared underthe same circumstances and the experimentally results is compared with theoretical predictions. Both the 3"x 3" NaI(Tl)-detector and the ~20% HPGe detector are able to find a 54 MBq 137-Cs point-source when passing the source at a smallest distance of approximately 50m. Furthermore it is seen that a lower collecting velocity (i.e. the velocity of the vehicle) often i preferable and for a given collcting velocity there exists an optimum collecting time. The two detectors in this study have similar capability to find lost point sources with an activity of approximately 50 MBq.},
  author       = {Ekman, Jörgen},
  keyword      = {Radioekologi},
  language     = {eng},
  note         = {Student Paper},
  title        = {A comparison between HPGe- and NaI(Tl)-systems in finding lost point sources and optimisation of collecting parameters},
  year         = {1999},
}