title: GEANT4 simulation of the effects of Doppler energy broadening in Compton imaging

authors: Uche, Chibueze Zimuzo

subjects: Doppler broadening

abstract: A Monte Carlo approach was used to study the effects of Doppler energy broadening on Compton camera performance. The GEANT4 simulation toolkit was used to model the radiation transport and interactions with matter in a simulated Compton camera. The low energy electromagnetic physics model of GEANT4 incorporating Doppler broadening developed by Longo et al. was used in the simulations. The camera had a 9 × 9 cm scatterer and a 10 × 10 cm absorber with a scatterer to-absorber separation of 5 cm. Modelling was done such that only the effects of Doppler broadening were taken into consideration and effects of scatterer and absorber thickness and pixelation were not taken into account, thus a ‘perfect’ Compton camera was assumed. Scatterer materials were either silicon or germanium and the absorber material was cadmium zinc telluride. Simulations were done for point sources 10 cm in front of the scatterer. The results of the simulations validated the use of the low energy model of GEANT4. As expected, Doppler broadening was found to degrade the Compton camera imaging resolution. For a 140.5 keV source the resulting full-width-at-half-maximum (FWHM) of the point source image without accounting for Doppler broadening and using a silicon scatterer was 0.58 mm. This degraded to 7.1 mm when Doppler broadening was introduced and degraded further to 12.3 mm when a germanium scatterer was used instead of silicon. But for a 511 keV source, the FWHM was better than for a 140 keV source. The FWHM improved to 2.4 mm for a silicon scatterer and 4.6 mm for a germanium scatterer. Our result for silicon at 140.5 keV is in very good agreement with that published by An et al.

text: GEANT4 simulation of the effects of Doppler energy broadening in Compton imaging A Monte Carlo approach was used to study the effects of Doppler energy broadening on Compton camera performance. The GEANT4 simulation toolkit was used to model the radiation transport and interactions with matter in a simulated Compton camera. The low energy electromagnetic physics model of GEANT4 incorporating Doppler broadening developed by Longo et al. was used in the simulations. The camera had a 9 × 9 cm scatterer and a 10 × 10 cm absorber with a scatterer to-absorber separation of 5 cm. Modelling was done such that only the effects of Doppler broadening were taken into consideration and effects of scatterer and absorber thickness and pixelation were not taken into account, thus a ‘perfect’ Compton camera was assumed. Scatterer materials were either silicon or germanium and the absorber material was cadmium zinc telluride. Simulations were done for point sources 10 cm in front of the scatterer. The results of the simulations validated the use of the low energy model of GEANT4. As expected, Doppler broadening was found to degrade the Compton camera imaging resolution. For a 140.5 keV source the resulting full-width-at-half-maximum (FWHM) of the point source image without accounting for Doppler broadening and using a silicon scatterer was 0.58 mm. This degraded to 7.1 mm when Doppler broadening was introduced and degraded further to 12.3 mm when a germanium scatterer was used instead of silicon. But for a 511 keV source, the FWHM was better than for a 140 keV source. The FWHM improved to 2.4 mm for a silicon scatterer and 4.6 mm for a germanium scatterer. Our result for silicon at 140.5 keV is in very good agreement with that published by An et al.

year: 2011

title: Noosphere rising: Internet-based collective intelligence, creative labour, and social production

authors: Peters, Michael A.

abstract: Our article relocates the debate about creative labour to the terrain of peer-to-peer interneting as the paradigmatic form of nonmarket - social - production. From Yann Moulier Boutang we take the point that creative labour is immaterial; it is expressed through people connected by the internet. Drawing on two social systems thinkers, Francis Heylighen and Wolfgang Hofkirchner, we transpose this connectedness up to a conception of creative labour as a supra-individual collective intelligence. This intelligence, we argue, is one of the internets emergent properties. We then present a model of internet development that flags the potential of digitally-evoked collective intelligence to facilitate what the Marxist philosopher George Caffentzis calls postcapitalist commoning. Yoking together systems theorizing about the internet and socialist envisioning of social transformation, we identify two sets of internet tools for coordination that can assist with the convivial reconstruction of society along the lines of peer-based production.

text: Noosphere rising: Internet-based collective intelligence, creative labour, and social production Our article relocates the debate about creative labour to the terrain of peer-to-peer interneting as the paradigmatic form of nonmarket - social - production. From Yann Moulier Boutang we take the point that creative labour is immaterial; it is expressed through people connected by the internet. Drawing on two social systems thinkers, Francis Heylighen and Wolfgang Hofkirchner, we transpose this connectedness up to a conception of creative labour as a supra-individual collective intelligence. This intelligence, we argue, is one of the internets emergent properties. We then present a model of internet development that flags the potential of digitally-evoked collective intelligence to facilitate what the Marxist philosopher George Caffentzis calls postcapitalist commoning. Yoking together systems theorizing about the internet and socialist envisioning of social transformation, we identify two sets of internet tools for coordination that can assist with the convivial reconstruction of society along the lines of peer-based production.

year: 2015

title: Iwi interests and the RMA: An evaluation of the quality of first generation council plans

authors: Jefferies, Richard

subjects: New Zealand

abstract: This working paper analyses the processes adopted by councils for involving hapū
/iwi in plan implementation, including the resource consents process. Three topic issues were investigated to assess plan implementation — urban amenity,
storm water, and issues of importance to iwi. Questions were asked about the capacity of hapū/iwi to engage in the resource consent
process, which resource issues were of concern to them, their relationship with
council and consent applicants, and their perception of the consent process. Most resources listed in the questionnaire were of concern to hapū/iwi, with water
quality, wāhi tapu and heritage the most commonly cited. In conclusion, we found a general dissatisfaction on the part of hapū/iwi with
councils’ performance with respect to both Treaty relationships and consent
processing under the RMA. A further contributing factor to the poor relationships
found between hapū/iwi and councils, was the lack of clarity over the role of hapū and
iwi in resource management. In several districts, diverging responses from hapū/iwi
and councils to questions about level of understanding and commitment suggests there
is a need for more effective communication. These problems are compounded by the
generally low capacity of hapū/iwi to participate in resource consent processes. These findings suggest that there is much to be done to improve relationships and
behaviour of these key stakeholder groups in the plan implementation process if key
provisions in the RMA related to hapū/iwi interests are to be fulfilled. The differences
shown in reciprocal perceptions have serious implications for establishing a sound
working partnership between councils and hapū/iwi in their areas. Making clear these
discrepancies is a first step towards taking the measures needed for building a better
partnership. Further, the capacity of hapū/iwi to participate could be better utilised if
there was greater integration between regional and district councils on issues of
significance and processes for iwi involvement.

text: Iwi interests and the RMA: An evaluation of the quality of first generation council plans This working paper analyses the processes adopted by councils for involving hapū
/iwi in plan implementation, including the resource consents process. Three topic issues were investigated to assess plan implementation — urban amenity,
storm water, and issues of importance to iwi. Questions were asked about the capacity of hapū/iwi to engage in the resource consent
process, which resource issues were of concern to them, their relationship with
council and consent applicants, and their perception of the consent process. Most resources listed in the questionnaire were of concern to hapū/iwi, with water
quality, wāhi tapu and heritage the most commonly cited. In conclusion, we found a general dissatisfaction on the part of hapū/iwi with
councils’ performance with respect to both Treaty relationships and consent
processing under the RMA. A further contributing factor to the poor relationships
found between hapū/iwi and councils, was the lack of clarity over the role of hapū and
iwi in resource management. In several districts, diverging responses from hapū/iwi
and councils to questions about level of understanding and commitment suggests there
is a need for more effective communication. These problems are compounded by the
generally low capacity of hapū/iwi to participate in resource consent processes. These findings suggest that there is much to be done to improve relationships and
behaviour of these key stakeholder groups in the plan implementation process if key
provisions in the RMA related to hapū/iwi interests are to be fulfilled. The differences
shown in reciprocal perceptions have serious implications for establishing a sound
working partnership between councils and hapū/iwi in their areas. Making clear these
discrepancies is a first step towards taking the measures needed for building a better
partnership. Further, the capacity of hapū/iwi to participate could be better utilised if
there was greater integration between regional and district councils on issues of
significance and processes for iwi involvement.

year: 2002-10-31