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Applications of Pulse Shape Analysis Techniques for Segmented Planar Germanium Detectors
KTH, School of Engineering Sciences (SCI), Physics.
2007 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

The application of pulse shape analysis (PSA) and γ-ray tracking techniques has attracted a great deal of interest in the recent years in fields ranging from nuclear structure studies to medical imaging. These new data analysis methods add position sensitivity as well as directional information for the detected γ-rays to the excellent energy resolution of germanium detectors. This thesis focuses on the application of PSA on planar segmented germanium detectors, divided into three separate studies. The pulse shape analysis technique known as the matrix method was chosen due to its ability to treat events with arbitrary number and combinations of interactions within a single detector. It has been applied in two experiments with the 25-fold segmented planar pixel detector -- imaging and polarization measurements -- as well as in a simulation of upcoming detectors for DESPEC at NuSTAR/FAIR.

In the first experiment, a point source of 137Cs was imaged. Events where the 662 keV γ-rays scattered once and were then absorbed in a different segment were treated by the PSA algorithm in order to find the locations of these interactions. The Compton scattering formula was then used to determine the direction to the source. The experiment has provided a robust test of the performance of the PSA algorithm on multiple interaction events, in particular those with interactions in adjacent segments, as well as allowed to estimate the realistically attainable position resolution. In the second experiment, the response of the detector to polarized photons of 288 keV was studied. The polarization of photons can be measured through the observation of the angular distribution of Compton-scattered photons, Hence the ability to resolve the interaction locations had once again proven useful.

The third study is focused on the performance of the proposed planar germanium detectors for the DESPEC array. As these detectors have not yet been manufactured at the time of this writing, a set of data simulated in GEANT4 was used. The detector response was calculated for two of the possible segmentation patterns -- that with a single pixelated contact and one where both contacts are segmented into mutually orthogonal strips. In both cases, PSA was applied in order to reconstruct the interaction locations from this response. It was found that the double-sided strip detector can achieve an over-all better position resolution with a given number of readout channels. However, this comes at the expense of a small number of complex events where the reconstruction fails. These results have also been compared to the performance of the 25-fold pixelated detector.

Place, publisher, year, edition, pages
Stockholm: KTH , 2007. , vi, 54 p.
Series
Trita-FYS, ISSN 0280-316X ; 2007:80
Keyword [en]
Position sensitive detectors; pulse shape analysis; germanium detectors; DESPEC;
National Category
Subatomic Physics
Identifiers
URN: urn:nbn:se:kth:diva-4592ISBN: 978-91-7178-837-5 (print)OAI: oai:DiVA.org:kth-4592DiVA: diva2:13014
Presentation
2007-12-13, FB53, AlbaNova, 14:00
Opponent
Supervisors
Note
QC 20101110Available from: 2007-12-19 Created: 2007-12-19 Last updated: 2010-11-10Bibliographically approved
List of papers
1. Compton imager based on a single planar segmented HPGe detector
Open this publication in new window or tab >>Compton imager based on a single planar segmented HPGe detector
2007 (English)In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 580, 1075-1078 p.Article in journal (Refereed) Published
Abstract [en]

A collimator-free Compton imaging system has been developed based on a single high-purity germanium detector and used to generate images of radioactive sources emitting gamma rays. The detector has a planar crystal with one pixellated contact with a total of 25 segments. Pulse shape analysis has been applied to achieve a 3D-position sensitivity of the detector. The first imaging results from this detector are presented, based on the reconstruction of events where a gamma ray is fully absorbed after scattering between adjacent segments.

Keyword
Compton imaging, gamma-ray imaging, segmented planar germanium detector, pulse shape analysis
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-7861 (URN)10.1016/j.nima.2007.06.065 (DOI)000250128000051 ()2-s2.0-34548487328 (Scopus ID)
Note

QC 20101110

Available from: 2007-12-19 Created: 2007-12-19 Last updated: 2017-12-14Bibliographically approved
2. A gamma-ray polarimeter based on a single segmented planar HPGe detector
Open this publication in new window or tab >>A gamma-ray polarimeter based on a single segmented planar HPGe detector
2008 (English)In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 593, no 3, 459-465 p.Article in journal (Refereed) Published
Abstract [en]

The polarization sensitivity of a segmented planar HPGe detector has been measured. For this purpose 662 keV photons from a Cs-137 source which were Compton scattered at approximate to 90 degrees in a coaxial germanium detector were utilized as a source of partially linearly polarized gamma radiation of the energy; approximate to 288 keV. The detector has a 50 x 50 x 21 mm sensitive volume and 5 x 5 electrical segmentation of the cathode contact. The degree of linear polarization is determined through the analysis of the directions of Compton scatterings inside the detector. The locations of the Compton scattering interactions and of the subsequent photo-absorption interactions have been determined with the help of pulse shape analysis (PSA), provided that these interactions are in two different segments of the planar detector. A comparison with a polarization analysis using the position resolution defined by the physical segmentation (without the use of PSA) was also performed. It is demonstrated that the use of PSA enables a much higher polarization sensitivity for events where the 288 keV photons scatter between adjacent pixels. Such events constitute 90% of the data for the 288 keV photons and are even more important for gamma-rays of lower energies.

Keyword
polarization, segmented planar germanium detector, pulse shape analysis, matrix method
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-7862 (URN)10.1016/j.nima.2008.05.063 (DOI)000259120700030 ()2-s2.0-47849098320 (Scopus ID)
Note
QC 20101110Available from: 2007-12-19 Created: 2007-12-19 Last updated: 2017-12-14Bibliographically approved
3. Position sensitivity of segmented planar HPGe detectors for the DESPEC project at FAIR
Open this publication in new window or tab >>Position sensitivity of segmented planar HPGe detectors for the DESPEC project at FAIR
2008 (English)In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 592, 325-333 p.Article in journal (Refereed) Published
Abstract [en]

One of the proposed germanium detector systems for the upcoming DESPEC array at the FAIR facility consists of triple modules of electrically segmented planar high-purity germanium detectors. In this work, the position sensitivity obtained by means of pulse shape analysis (PSA) for simulated gamma-ray interactions has been studied for the possible segmentation patterns for such detectors-the double-sided strip detector (DSSD) and the one-sided pixelated geometry. An over-all similar number of readout channels has been considered for each case, resulting in 8 + 8 strips and 16 pixels. It has been found that the higher physical granularity of the DSSD results in a significantly higher position resolution, as well as in a somewhat lower probability of merging multiple interaction points. A drawback of the DSSD geometry is the inability to assign the interactions to the correct voxels for certain complex multiple interaction patterns. This effect has been studied in detail. Finally, a comparison has been made with the existing 25-pixel planar detector at KTH [A. Khaplanov, et al., Nucl. Instr. and Meth. A 580 (2007) 1075; L. Milechina, B. Cederwall, Nucl. Instr. and Meth. A 550 (2005) 278)].

Keyword
DESPEC, segmented planar germanium detector, pulse shape analysis, matrix method
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-7863 (URN)10.1016/j.nima.2008.03.111 (DOI)000258252500021 ()2-s2.0-46649092130 (Scopus ID)
Note
QC 20101110Available from: 2007-12-19 Created: 2007-12-19 Last updated: 2017-12-14Bibliographically approved

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