Dual Photomultiplier Tubes Research Articles

Standardisation of 231Pa by defined solid angle and liquid scintillation methods at NPL

231Pa is the longest-lived decay product in the 235U decay chain and precise standards of this radionuclide are required to enable accurate, traceable measurements in nuclear dating applications such as geochronometry and nuclear forensics. Three independent techniques were used at NPL to determine the activity per unit mass of a freshly separated 231Pa solution as part of an international CCRI(II) comparison: CCRI(II)-K2.Pa-231.The first method was defined solid angle α counting and is the first result reported in a BIPM comparison with this instrument. The second method was 4πα liquid scintillation (LS) counting combined with the CIEMAT/NIST method using commercially available LS counters. The third technique used was 4π(LS)α-γ coincidence counting on an NPL-built system comprising an LS counter with dual photomultiplier tubes (PMTs) coupled to a 70% relative efficiency HPGe γ-spectrometer. Excellent agreement between the three methods was obtained.

Pulse-shape discrimination and energy resolution of a liquid-argon scintillator with xenon doping

Liquid-argon scintillation detectors are used in fundamental physics experiments and are being considered for security applications. Previous studies have suggested that the addition of small amounts of xenon dopant improves performance in light or signal yield, energy resolution, and particle discrimination. In this study, we investigate the detector response for xenon dopant concentrations from 9 ± 5 ppm to 1100 ± 500 ppm xenon (by weight) in 6 steps. The 3.14-liter detector uses tetraphenyl butadiene (TPB) wavelength shifter with dual photomultiplier tubes and is operated in single-phase mode. Gamma-ray-interaction signal yield of 4.0 ± 0.1 photoelectrons/keV improved to 5.0 ± 0.1 photoelectrons/keV with dopant. Energy resolution at 662 keV improved from (4.4 ± 0.2)% (σ) to (3.5 ± 0.2)% (σ) with dopant. Pulse-shape discrimination performance degraded greatly at the first addition of dopant, slightly improved with additional additions, then rapidly improved near the end of our dopant range, with performance becoming slightly better than pure argon at the highest tested dopant concentration. Some evidence of reduced neutron scintillation efficiency with increasing dopant concentration was observed. Finally, the waveform shape outside the TPB region is discussed, suggesting that the contribution to the waveform from xenon-produced light is primarily in the last portion of the slow component.

Ranging through Shallow Semitransparent Media with Polarization Lidar

Abstract A new approach to shallow depth measurement (<2 m) using polarization lidar is presented. The transmitter consists of a 532-nm linearly polarized laser coupled with conditioning and polarization optics. The prototype lidar evaluates the differing polarization attributes of signals scattered from semitransparent media surfaces, simultaneously receiving signals polarized in the planes parallel and perpendicular to the transmitted laser signal via dual photomultiplier tubes. In the event the first surface nearly preserves the incident polarization and the second surface depolarizes the incident energy, signals scattered from the second surface are isolated from the first by a polarization analyzer in the receiver. This approach translates depth measurements into the conditions of single surface range measurements, giving the ability to resolve extremely shallow depths (e.g., 1 cm) independent of laser or detector pulse widths. This approach can circumvent dead time issues in photon-counting systems and can be applied to extremely shallow and deeper waters for depth determination. Furthermore, the approach provides an estimate of the first surface linear depolarization ratio, enabling differentiation between surfaces with variable scattering properties. Using this technique to acquire range-resolved observations through shallow semitransparent media to measure depth removes the dependency on sophisticated and, subsequently, costly lidar components by becoming independent of system bandwidth. The limiting factor in-depth resolution is driven only by the timing resolution of the time-to-digital converter. This approach allows for the use of common lasers, optics, and detector equipment, making it comparatively cheaper and less complex while achieving vast improvement in the accuracy and precision of shallow depth measurements.

A Large Field of View Coincidence Imaging System Based on One-Dimensional Sharing Block Detectors

For such as breast cancer imaging, dedicated coincidence imaging detector will be promising for new instrumentation of nuclear medicine. For this purpose, a large field of view (FOV) coincidence imaging system was developed and tested. The imaging system consists of four sets of one-dimensional sharing block detectors and a single gamma probe and measures coincidence between these two detectors. The one-dimensional sharing detector uses 5 GSO blocks optically coupled to 6 dual photomultiplier tubes (PMT). The size of a single GSO is 2.9 mm times 2.9 mm times 15 mm. The signals from four one-dimensional sharing detectors are fed to weighted summing circuits. They are digitized by 100 MHz free running analog to digital (A-D) converters and are used to calculate the position of gamma interaction. Coincidence was measured between this gamma imaging detector (panel detector) and a hand-held single gamma probe. Acquired data was transferred to a personal computer and displayed. Most spots corresponding to GSO crystals were resolved in the position histogram. Spatial resolution was around 4 to 6 mm FWHM when the detector is greater than 25 mm. The sensitivity was 0.1-0.2% when the single probe was 25 mm away from the imager surface. Images of phantoms were successfully obtained. We conclude developed coincidence imaging system has large FOV and easy to handle, reasonable spatial resolution and may have potential to be a new instrument for nuclear medicine.

Development of a one-dimensional sharing block detector using dual PMTs for PET

We propose and test a one-dimensional (1-D) sharing block detector using dual photo-multiplier tubes (PMT). The detector consists of scintillator blocks and dual PMTs. The dual PMTs are optically coupled on the scintillator blocks and overlap in one dimensional. With this configuration, the scintillator size of the block detector can be reduced to half that of a conventional block detector in one direction, and isotropic spatial resolution can be obtained in transaxial and axial directions using commercially available dual PMTs. First, we measure the position and energy response for minimum configuration; one GSO block and two dual PMTs. The size of a single GSO is 2.9 mm/spl times/2.9 mm/spl times/20 mm. The scintillators are arranged in an 8/spl times/8 matrix with multi-layer optical film inserted partly between scintillators to obtain the resolved position response. We obtain good position and energy responses with this configuration. Next, we fabricate a 1-D sharing block detector with five GSO blocks and six dual PMTs. With this configuration, we also obtain reasonable position and energy responses. These results indicate that the proposed 1-D sharing block detector is a promising solution for developing high-resolution and low cost PET systems.

Evaluation of granulated BGO, GSO:Ce, YAG:Ce, CaF 2:Eu and ZnS:Ag for alpha/beta pulse shape discrimination in a flow-cell radiation detector

Granulated BGO, GSO:Ce, YAG:Ce, and CaF 2:Eu; CaF 2:Eu coated with a fluorescent polymer, and combinations of coated and uncoated CaF 2:Eu with ZnS:Ag were evaluated for their ability to discriminate between alpha and beta particles in a flow-cell radiation detector. The evaluations were based on the analysis of pulse shape spectra. Various granulated scintillators were packed into flow cell detectors that were coils of 3.0 mm OD×1.5 mm ID fluorinated ethylene propylene Teflon ® tubing positioned between dual photomultiplier tubes for analysis. The best pulse shape discrimination was obtained for a combination of equal masses of uncoated CaF 2:Eu (63–90 μm) and ZnS:Ag (10 μm), which had a 9% spillover. Additional research is needed to reduce the spillover.

Performance evaluation of a large axial field-of-view PET scanner: SET-2400W.

The SET-2400W is a newly designed whole-body PET scanner with a large axial field of view (20 cm). Its physical performance was investigated and evaluated. The scanner consists of four rings of 112 BGO detector units (22.8 mm in-plane x 50 mm axial x 30 mm depth). Each detector unit has a 6 (in-plane) x 8 (axial) matrix of BGO crystals coupled to two dual photomultiplier tubes. They are arranged in 32 rings giving 63 two-dimensional image planes. Sensitivity for a 20-cm cylindrical phantom was 6.1 kcps/kBq/ml (224 kcps/microCi/ml) in the 2D clinical mode, and to 48.6 kcps/kBq/ml (1.8 Mcps/microCi/ml) in the 3D mode after scatter correction. In-plane spatial resolution was 3.9 mm FWHM at the center of the field-of-view, and 4.4 mm FWHM tangentially, and 5.4 mm FWHM radially at 100 mm from the center. Average axial resolution was 4.5 mm FWHM at the center and 5.8 mm FWHM at a radial position 100 mm from the center. Average scatter fraction was 8% for the 2D mode and 40% for the 3D mode. The maximum count rate was 230 kcps in the 2D mode and 350 kcps in the 3D mode. Clinical images demonstrate the utility of an enlarged axial field-of-view scanner in brain study and whole-body PET imaging.

Tritium monitoring system for near ambient measurements

The authors describe the current status of research on an improved tritium measurement system at the Oak Ridge National Laboratory (ORNL) for the US Navy. Present tritium-in-air monitoring systems installed by the Navy can reliably measure to less than 10 mu Ci/m/sup 3/, but medical and safety issues are pushing measurement needs to below 1 mu Ci/m/sup 3/, which is equivalent to 1-10 mu Ci/ml in liquid samples, using calcium metal converter. A significant effort has been expended over the past 10 years by the Navy RADIAC development program at ORNL on various schemes to improve the detection of tritium in both air and liquid at near ambient levels. One such scheme includes a liquid flowthrough system based on an NE 102 sponge scintillator with dual photomultiplier tubes for tube noise rejection.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Evaluation of the Karolinska new positron camera system; the Scanditronix PC2048-15B

The PC2048-15B is the brain version of the new generation of Scanditronix positron camera systems, now being installed at the Karolinska Hospital in Stockholm, Sweden. The system has eight rings with 256 BGO crystals per ring. The dimensions of the crystals are 6*12*30 mm. Data corresponding to 15 image slices are simultaneously recorded. The detector rings are based on block-detector units, each with 16 scintillation crystals mounted on two dual photomultiplier tubes. The system is described, and test results including spatial resolution, sensitivity to true and random coincidences, scatter correction, count rate linearity, spatial independence, and reproducibility are presented. Clinical results are discussed, including rCBF studies and receptor studies, to cover the two most extreme situations met in brain PET (positron emission tomography) studies, i.e. high count rate and high resolution requirements.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Detector, shielding and geometric design factors for a high-resolution PET system

The authors evaluated the resolution, efficiency, and scatter rejection of a novel high-resolution PET (positron emission tomography) system designed for animal studies which is based on a 2-D modular detector system. A digital positioning system was evaluated by testing different encoding methods. Tungsten interplane septa of different thicknesses and geometries were evaluated by Monte Carlo simulations and experiments. The detector system consists of a 6*8 array of BGO crystals coupled to two dual photomultiplier tubes (PMTs). The crystals are 3.5 mm wide with 4-mm transaxial spacing and are 6.25 mm long with 6.75-mm axial spacing. PMT outputs are digitized, and Anger-camera-type logic is used to determine the X and Y location of the scintillator event. Data are then sorted into the appropriate detector using a column lookup table and the column dependent row lookup tables.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A preliminary evaluation of the Scanditronix PC2048-15B brain scanner.

The PC2048-15B is the brain version of the new generation of Scanditronix positron camera systems. It is based on a detection unit with 16 scintillating crystals mounted on 2 dual photomultiplier tubes. A system description is given and preliminary test results including spatial resolution, sensitivity to true and random coincidences, scatter correction, and count rate linearity are presented.

A preliminary evaluation of a positron camera system using weighted decoding of individual crystals

The whole-body positron camera PC4096-15WB is based on a detection unit with 16 scintillating crystals mounted on two dual photomultiplier tubes. The design ideas are specified and a system description is given. Preliminary test results including spatial resolution, sensitivity to true and random coincidences, scatter correction, and count-rate linearity are presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Performance characteristics of Positologica III: a whole-body positron emission tomograph.

A whole-body, multislice positron emission tomograph, Positologica III, has been constructed based on a sampling method "positology." The scanner consists of four continuously rotating detector rings with 192 bismuth germanate (BGO) crystals (12 X 24 X 24 mm) arranged at irregular intervals along each ring, providing seven tomographic images at 16 mm intervals simultaneously, for a total axial coverage of 12 cm. The patient aperture is 54 cm in diameter, and the field of view is 40 cm in diameter and 12 cm in depth. Newly developed dual photomultiplier tubes are used with 12 mm wide BGO crystals to provide a packing ratio of 0.894. The spatial resolution at the center of the field is 7.6 mm full width at half maximum, and 2.5 mm hot spots were delineated in the Derenzo phantom. The sensitivity for a 20 cm diameter cylindrical phantom is 34.2 and 52.2 kcps/muCi/ml for true planes and cross planes, respectively. In clinical studies the posterior papillary muscle of the heart was visualized in the myocardial scan, and the lung behind the pulmonary artery was also visualized in the pulmonary ventilation scan. These results suggest that our machine has sufficient resolution for most of the clinical studies of the body.

Detector Identification with Four BGO Crystals on a Dual PMT

The current trend towards higher resolution positron emission tomography (PET) requires the development of small but efficient detectors. This paper presents the initial characterization of a detector composed of four equally spaced, 4.5mm wide bismuth germanate (BGO) crystals coupled to the face of a Hamamatsu R1548 dual photomultiplier tube (PMT). The intrinsic optical cross talk between the two segments of the dual PMT exhibits a spatial dependence that has been exploited for crystal identification. Misidentification of crystals due to the combined effects of compton scattering of gamma rays between crystals, crystal penetration of gamma rays, and the imperfection of the optical cross talk identification scheme has been studied under various conditions. The detector pair spatial resolution on axis was measured to be 2.9mm full width at half maximum (FWHM), and the intrinsic peak efficiency was found to be higher than that of the larger detectors currently in use in the Montreal Neurological Institute's (MNI) Positome III camera.