| 1. |
- Fröjdh, Christer, et al.
(author)
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Characterization of area sensitivity in 55 um pixellated CdTe X-ray imaging detectors
- 2007
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In: IEEE Nuclear Science Symposium Conference Record. - New York : IEEE conference proceedings. - 9781424409228 ; , s. 1234-1236
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Conference paper (peer-reviewed)abstract
- X-ray imaging detectors with energy resolution, based on a single photon processing CMOS readout circuit attached to a detector chip, are being developed by different groups. In order to achieve high quantum efficiency it is preferable to use high-Z semiconductor materials. However the fluorescent X-ray photons of such materials have high energies and are able to travel long distances thereby reducing both the spatial resolution and the energy resolution of the detector. In addition charge sharing in the detector and non-uniformities in both the detector and the readout electronics will affect the signal. In this work we have characterized a 1 mm thick CdTe detector with a pixel size of 55 um x 55 um, bump bonded to the MEDIPIX2 single photon processing readout chip. The area sensitivity of the detector is evaluated using a narrow X-ray beam of monoenergetic photons. From these measurements the effects of fluorescence and charge sharing can be evaluated.
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| 2. |
- Hidvegi, Attila, et al.
(author)
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A high-speed data acquisition system for segmented Ge-detectors
- 2007
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In: 2007 IEEE Nuclear Science Symposium Conference Record. - : IEEE. - 1424409233 - 9781424409235 - 9781424409228 ; , s. 536-537
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Conference paper (peer-reviewed)abstract
- When using segmented Ge-detectors for gamma ray tracking it is necessary to determine the segment pulse shapes with high accuracy. A high-speed data acquisition system with many channels, high precision and with high sampling rate is required. There are also many other applications for such a system. Our system uses high performance FPGAs (Xilinx Virtex-V [2]) to cope with the data rates delivered by the high speed ADC chosen (Atmel 2Gsps, 10 bits) and to make all the data processing onboard in real time. Each board contains four such ADCs, which can either handle four channels up to full speed, or achieve higher sampling rates with interleaving. The boards can communicate with each other over different types of high-speed communication links. Control and monitoring is implemented with embedded processors. The processed result will be transmitted over Ethernet to final storage. The project introduces many challenging issues: signal integrity, ADC performance, interfacing ADCs to the FPGA, synchronisation of ADCs across the entire system, implementing flexible processing algorithms, high speed interconnection between boards and managing the significant heat generation. This is an ongoing project with interesting potentials for the future.
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| 3. |
- Mizuno, T., et al.
(author)
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High sensitivity balloon-borne hard X-ray/soft Gamma-Ray Polarimeter PoGOLite
- 2007
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In: Nuclear Science Symposium Conference Record, 2007. NSS ’07. IEEE. - : IEEE. - 9781424409228 ; , s. 2538-2544
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Conference paper (peer-reviewed)abstract
- The Polarized Gamma-ray Observer - Lightweight version (PoGOLite) is a new balloon experiment capable of detecting 10% polarization from a 200 mCrab source in the 25-80 keV energy range in a single 6-hour flight for the first time. Polarization measurements of hard X-rays and soft gamma-rays are expected to provide a powerful probe into high-energy emission mechanisms as well as source geometries. PoGOLite uses Compton scattering and photo-absorption to measure polarization in an array of 217 well-type phoswich detector cells made of plastic and BGO scintillators. The adoption of a well-type phoswich counter concept and a thick polyethylene neutron shield provides a narrow field-of-view (1.25 msr), a large effective area ( gt; 250 cm2 at 40-50 keV), a high modulation factor (more than 25%) and the low background ( 100 mCrab) required to conduct high-sensitivity polarization measurements. Through tests in laboratories and accelerator facilities of a scaled-down prototype with the front-end electronics of flight design and an extensive study by Monte Carlo simulation, we have demonstrated high instrument performance. PoGOLite will be ready for a first engineering flight in 2009 and a science flight in 2010, during which polarization signals from the Crab Nebula/pulsar, Cygnus X-1 and other objects will be observed.
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| 4. |
- Pearce, Mark, et al.
(author)
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PAMELA : a payload for antimatter matter exploration and light-nuclei astrophysics - status and first results
- 2007
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In: 2007 IEEE NUCLEAR SCIENCE SYMPOSIUM CONFERENCE RECORD, VOLS 1-11. - 9781424409228 ; , s. 42-47
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Conference paper (peer-reviewed)abstract
- PAMELA is a satellite-borne experiment designed for precision studies of the charged cosmic radiation. The primary scientific goal is the study of the antimatter component of the cosmic radiation (antiprotons, 80 MeV - 190 GeV; and positrons, 50 MeV - 270 GeV) in order to search for evidence of dark matter particle annihilations. PAMELA will also search for primordial antinuclei (in particular, anti-helium), and test cosmic-ray propagation models through precise measurements of the antiparticle energy spectrum and studies of light nuclei and their isotopes. Concomitant goals include a study of solar physics and solar modulation during the 24th solar minimum by investigating low energy particles in the cosmic radiation; and a reconstruction of the cosmic ray electron energy spectrum up to several TeV thereby allowing a possible contribution from local sources to be studied. PAMELA is housed on-board the Russian Resurs-DK1 satellite, which was launched on June 15th 2006 in an elliptical (350-600 km altitude) orbit with an inclination of 70 degrees. PAMELA consists of a permanent magnet spectrometer, to provide rigidity and charge sign information; a Time-of-Flight and trigger system, for velocity and charge determination; a silicon-tungsten calorimeter, for lepton/hadron discrimination; and a neutron detector. An anticoincidence system is used offline to reject false triggers. In this article the PAMELA experiment and its status are reviewed. A preliminary discussion of data recorded in-orbit is also presented.
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| 5. |
- Sundin, Kurt, et al.
(author)
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SIMIND based pinhole imaging: Development and validation
- 2007
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In: 2007 IEEE Nuclear Science Symposium Conference Record, vols 1-11. - 1082-3654. - 9781424409228 ; , s. 3998-4005
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Conference paper (peer-reviewed)abstract
- Monte Carlo programs, like the SIMIND program, have become increasingly used to simulate imaging systems like the scintillation camera and SPECT systems. Up to now, it has not been able to simulate a pinhole-imaging device with SIMIND. The aim of this work was to develop a routine for pinhole-imaging consisting of a knife-edge collimator and a conical shielding. The routine tracks the path of each photon through the pinhole-collimator and scores if photons either i) pass geometrically through the pinhole ii) penetrate through the edges of the pinhole or iii) being scattered in the collimator. This allows for calculation of fractions of geometrical, penetrating and scattered photons that contribute to an image. Variance reduction is implementing by forcing the photon, emitted from the last interaction point (or from the initial decay location), into a direction towards the center of the pinhole. Characteristic x-ray emissions from photon interactions are included. Results from simulations were compared to results from experimental studies using a SPECT system with a physical pinhole-collimator. The parameters compared were here the sensitivity (cps/MBq) and the shape of line-spread functions as function of distance. Comparisons were also made with results from previously published Monte Carlo simulations of pinhole collimators for different radionuclides. Results from our simulations mostly showed a good agreement but for some cases we found differences especially in the values of the fraction of geometrical, penetrating and scattered photons when comparing to previously reported results. Our conclusion is, however, that the routine provides accurate pinhole collimator simulations.
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| 6. |
- Tanaka, T., et al.
(author)
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Data acquisition system for the PoGOLite astronomical hard X-ray polarimeter
- 2007
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In: Nuclear Science Symposium Conference Record, 2007. - 9781424409228 ; , s. 445-449, s. 445-449
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Conference paper (other academic/artistic)abstract
- The PoGOLite is a new balloon-borne instrument to measure the polarization of hard X-rays/soft gamma-rays in the 25-80 keV energy range for the first time. In order to detect the polarization, PoGOLite measures the azimuthal angle asymmetry of Compton scattering and the subsequent photo-absorption in an array of detectors. This array consists of 217 well-type phoswich detector cells (PDCs) surrounded by a side anti-coincidence shield (SAS) composed of 54 segments of BGO crystals. At balloon altitude, the intensity of backgrounds due to cosmic-ray charged particles, atmospheric gamma-rays and neutrons is extremely high, typically a few hundred Hz per unit. Hence the data acquisition (DAQ) system of PoGOLite is required to handle more than 270 signals simultaneously, and detect weak signals from astrophysical objects (100mCrab, 1.5 cs(-1) in 25-80 keV) under such a severe environment. We have developed a new DAQ system consisting of front-end electronics, waveform digitizer, Field Programmable Gate Array (FPGA) and a microprocessor. In this system, all output signals of PDC / SAS are fed into individual charge-sensitive amplifier and then digitized to 12 bit accuracy at 24 MSa/s by pipelined analog to digital converters. A DAQ board for the PDC records waveforms which will be examined in an off-line analysis to distinguish signals from the background events and measure the energy spectrum and polarization of targets. A board for the SAS records hit pattern to be used for background rejection. It also continuously records a pulse-height analysis (PHA) histogram to monitor incident background flux. These basic functions of the DAQ system were verified in a series of beam tests.
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| 7. |
- Valastyán, Iván, et al.
(author)
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Gated tomographic imaging in ectomography using a dynamic heart phantom
- 2007
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In: Nuclear Science Symposium Conference Record, 2007. NSS '07. IEEE. - : IEEE. - 9781424409228 ; , s. 3414-3417
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Conference paper (peer-reviewed)abstract
- A new computer controlled dynamic heart phantom and the connection of an ECG unit to a tomographic gamma camera system, developed for ectomographic imaging, is presented. The phantom is used for validation of the camera. Measurements were performed to test the phantom as well as to study the feasibility of gated imaging in ectomography. The camera is intended for early diagnosis of myocardial and cerebral infarctions.
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| 8. |
- Örbom, Anders, et al.
(author)
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Serial digital autoradiography with a silicon strip detector as a high resolution imaging modality for TRT Dosimetry
- 2007
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In: 2007 IEEE Nuclear Science Symposium Conference Record, vols 1-11. - 1082-3654. - 9781424409228 ; , s. 4054-4056
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Conference paper (peer-reviewed)abstract
- This study aims to investigate the possibility of implementing serial autoradiography using a silicon strip detector as an imaging modality in pre-clinical radionuclide therapy research, in order to study the effect of non-uniform uptake on absorbed dose distribution and biological response. Tumor tissues expressing CD20 (B-cell lymphoma) or carcinoembryonic antigen (CEA; colorectal cancer) were excised from animals injected with I-131-labelled anti-CD20 or anti-CEA antibodies and antibody fragments. The tumors were cryosectioned at 100 mu m and imaged using a real-time silicon- strip imager with a pixel-size of 50 mu m. Software was developed to correct for image artifacts and to realign the image sections into a volume by a two-step process with least square error and mutual information registration measures. The realigned volumes were convolved with beta dose point kernels to provide the dose rate distribution for I-131 and Y-90 at the time of sacrifice. Using these volumes, comparisons can be made between uptake and penetration of different antibodies and the dose rate uniformity of different radionuclides. Simulations performed using measured I-131 and I-125 energy spectra showed that energy separation with less than 5% error could be performed with 100 counts per pixel. Imaging and subsequent separation of a sample containing both I-131 and I-125 proved the possibility of simultaneous imaging of two targeting agents in the same tissue. Thinner tissue sections were also set aside and successfully used for H&E staining and immunohistochemistry to enable future comparison of uptake and dose rate in different cell-type populations in the tissue. This method successfully provides high-resolution activity and dose rate volumes and has potential for multi-labeling imaging and co-registration with histology. As a complimentary imaging modality it can aid in investigating the effect of non-uniform uptake. Optimization is still needed in both the sectioning protocol and realignment software.
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