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ABSTRACT: New fast, ultra low-noise UV-enhanced avalanche photodiodes (APD) were recently developed by Excelitas Technologies (formerly PerkinElmer Optoelectronics, Vaudreuil, QC, Canada). for use with scintillation crystals. The novel epitaxial type “buried junction” APD structure was designed for detecting photons with wavelengths shorter than ~600 nm at high gain with very low dark current. It typically exhibits extremely low noise level (<;0.1 pA/√Hz per mm<sup>2</sup>) up to multiplication gains of 200-300. The photodetecting performance of the UV-enhanced APDs with scintillators of potential interest in the fields of high-energy physics and medical imaging is presented. Energy resolution under 8% at 662 keV and subnanosecond timing resolution for annihilation radiation can be reached with LGSO 90% Lu (45 ns).
Nuclear Science Symposium Conference Record (NSS/MIC), 2010 IEEE; 12/2010
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M. Bergeron,
C.M. Pepin,
J. Cadorette,
J. Beaudoin,
M. Tetrault,
M. Davies, H. Dautet,
P. Deschamps,
H. Ishibashi,
Y. Kurata,
R. Lecomte
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ABSTRACT: The scintillator is one of the key building blocks that critically determine the physical performance of PET detectors. The quest for scintillation crystals with improved characteristics has been crucial in designing scanners with superior imaging performance. Recently, it was shown that the decay time constant of high lutetium content Lu<sub>1.8</sub>Gd<sub>0.2</sub>SiO<sub>5</sub>:Ce (LGSO) scintillators can be adjusted between 30 ns and 48 ns by varying the cerium concentration from 0.025 mol% to 0.75 mol%, thus providing interesting characteristics for phoswich detectors. The large light output (90-120% NaI), the better spectral match and the high initial photoelectron rate (~200 phe<sup>-</sup>/ns) of these scintillators with avalanche photodiode (APD) readout promise to provide superior energy and timing resolution. Moreover, their improved mechanical properties as compared to conventional LGSO (Lu<sub>0.2</sub>Gd<sub>1.8</sub>SiO<sub>5</sub>:Ce) make block array manufacturing readily feasible. To verify these assumptions, new phoswich block arrays made of LGSO-90%Lu with low and high mol% Ce concentrations were fabricated and assembled into LabPET modules. Typical crystal decay time constants were 32 ns and 48 ns, respectively. We therefore report on the initial evaluation of this modified version of the LabPET detector module. Phoswich crystal identification performed using a non-optimized digital pulse shape discrimination algorithm yielded an average 10% error. At 511 keV, energy resolution of 20 ± 2% and 15 ± 1% were obtained, while coincidence timing resolution between 4.9 ± 0.3 ns and 4.1 ± 0.1 ns were achieved. The improved characteristics of this new LGSO-based phoswich detector module are expected to enhance the LabPET scanner performance, first by improving sensitivity due to the overall higher stopping power of the detector module, and second by narrowing the coincidence time window, thus minimizing the random event -
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rate. Altogether these two improvements will significantly enhance the noise equivalent count rate performance of an all LGSO-based LabPET scanner.
Nuclear Science Symposium Conference Record (NSS/MIC), 2010 IEEE; 12/2010
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ABSTRACT: The luminescence and nuclear spectroscopic properties of the new cerium-doped rare-earth scintillator lutetium-yttrium oxyorthosilicate (Lu<sub>0.6</sub>Y<sub>1.4</sub>Si<sub>0.5</sub>:Ce, LYSO) were investigated and compared to those of both recent and older LSO crystals. UV-excited luminescent spectra outline important similarities between LYSO and LSO scintillators. The two distinct Ce1 and Ce2 luminescence mechanisms previously identified in LSO are also present in LYSO scintillators. The energy and timing resolutions were measured using avalanche photodiode (APD) and photomultiplier tube (PMT) readouts. The dependence of energy resolution on gamma-ray energy was also assessed to unveil the crystal intrinsic resolution parameters. In spite of significant progress in light output and luminescence properties, the energy resolution of these scintillators appears to still suffer from an excess variance in the number of scintillation photons. Pulse-shape discrimination between LYSO and LSO scintillators has been successfully achieved in phoswich assemblies, confirming LYSO, with a sufficient amount of yttrium to modify the decay time, to be a potential candidate for depth-of-interaction determination in multicrystal PET detectors.
IEEE Transactions on Nuclear Science 07/2004; · 1.45 Impact Factor
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ABSTRACT: The luminescence and nuclear spectroscopic properties of the new cerium-doped rare-earth scintillator lutetium-yttrium oxyorthosilicate (Lu<sub>0.6</sub>Y<sub>1.4</sub>SiO<sub>5</sub>:Ce, LYSO) were investigated and compared to those of both recent and older LSO crystals. UV-excited luminescent spectra outline important similarities between LYSO and LSO scintillators. The two distinct Ce1 and Ce2 luminescence mechanisms previously identified in LSO are also present in LYSO scintillators. The energy and timing resolutions were measured using avalanche photodiode (APD) and photomultiplier tube (PMT) readouts. The dependence of energy resolution on gamma-ray energy was also assessed to unveil the crystal intrinsic resolution parameters. In spite of significant progress in light output and luminescence properties, the energy resolution of these scintillators appears to still suffer from an excess variance in the number or scintillation photons. Pulse-shape discrimination between LYSO and LSO scintillators has been successfully achieved in phoswich assemblies, confirming LYSO to be a potential candidate for depth-of-interaction determination in multi-crystal PET detectors.
Nuclear Science Symposium Conference Record, 2002 IEEE; 12/2002
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ABSTRACT: Proton radiation damage of Si avalanche photodiodes were measured
at 53 to 189MeV proton energy. The annealing rates were monitored at
-10°C, room temperature, and 55°C. The results are compared with
the previously published data
Radiation Effects Data Workshop, 2001 IEEE; 02/2001
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ABSTRACT: An integrated, 0.8-μ CMOS charge-sensitive preamplifier previously designed for LSO/APD based PET systems has been further investigated for use with multi-crystal/APD PET detectors. In addition to low-noise, wide-band performance and power efficiency, high dynamic range and good signal-to-noise ratio over a broad range of shaping times are required to process the signals from crystals being used in phoswich detectors, which have a wide range of scintillation decay time and light output characteristics. The preamplifier equivalent noise charge (N<sub>eq</sub>) was measured as a function of input capacitance and amplifier shaping time constant. The performance of the preamplifier was also assessed using APDs coupled to a variety of scintillators. Measurements were obtained at a preamplifier input-device current of 2 and 4 mA. The higher bias lead to marginal improvements of the timing performance but had no effect on energy resolution
Nuclear Science Symposium Conference Record, 2000 IEEE; 02/2000
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ABSTRACT: The measurement of depth of interaction (DOI) within detectors is
necessary to improve resolution uniformity across the FOV of small
diameter PET scanners. DOI encoding by pulse shape discrimination (PSD)
has definite advantages as it requires only one readout per pixel and it
allows DOI measurement of photoelectric and Compton events. The PSD time
characteristics of various scintillators were studied with avalanche
photodiodes (APD) and the identification capability was tested in
multi-crystal assemblies with up to four scintillators. In the PSD time
spectrum of an APD-GSO/LSO/BGO/CsI(Tl) assembly, four distinct time
peaks at 45, 26, 88 and 150 ns relative to a fast test pulse, having
resolution of 10.6, 5.2, 20 and 27 ns, can be easily separated. Whereas
the number and position of scintillators in the multi-crystal assemblies
affect detector performance, the ability to identify crystals is not
compromised. Compton events have a significant effect on PSD accuracy,
suggesting that photopeak energy gating should be used for better
crystal identification. However, more sophisticated PSD techniques using
parametric time-energy histograms can also improve crystal
identification in cases where PSD time or energy discrimination alone is
inadequate. These results confirm the feasibility of PSD DOI encoding
with APD-based detectors for PET
IEEE Transactions on Nuclear Science 07/1999; · 1.45 Impact Factor
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ABSTRACT: The performance characteristics of GSO, LSO and YSO scintillators
coupled to new “reverse” avalanche photodiodes (ReAPD) were
investigated and compared to those of BGO. The energy and timing
resolutions were measured as a function of photodiode bias and amplifier
shaping time constant. While the performance of BGO and GSO is
critically dependent on these operating parameters because the
signal-to-noise ratio is degraded by the dark and excess noise from the
ReAPD, that of the high-luminosity LSO and YSO scintillators is not. The
energy resolution in these crystals is demonstrated to be limited by the
scintillator resolution. Further analysis indicates that excess variance
in the number of photons generated in the crystal is mostly responsible
for their disappointing energy resolution. This feature appears to be
related to the important non-linearity in scintillation response as a
function of incident gamma-ray energy observed for these high-luminosity
scintillators
IEEE Transactions on Nuclear Science 07/1998; · 1.45 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: A Block detector, consisting of a four by four array of lutetium
oxyorthosilicate (LSO) scintillator crystals coupled to a two by two
avalanche photodiode (APD) array was built and tested. The detector
block was 8.5 by 8.5 by 10 millimeters so that the crystals were on 2.13
millimeter centers. The APD array has an active area of approximately 9
by 9 millimeters divided into four diodes of 4.5 by 4.5 millimeters
each. A standard reach-through process was used to fabricate the diodes.
Each of the sixteen crystals in the block was easily identified. The
average FWHM of the peaks in ratio space was 4% of full scale. The
average energy resolution was 16.2% for 511 keV gamma rays. A single LSO
crystal coupled to an APD and put in time coincidence with a plastic
detector produced a time coincidence of 1.9 nanoseconds FWHM
Nuclear Science Symposium, 1998. Conference Record. 1998 IEEE; 02/1998
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[show abstract]
[hide abstract]
ABSTRACT: A detector module allowing individual crystal identification
without analog coding is proposed. The basic cell is made of a 2×2
array of scintillators having different decay times that can be
identified by pulse shape discrimination. A 16 pixel module consisting
of a 2×2 array of these quad scintillator cells coupled to a
2×2 avalanche photodiode (APD) array was assembled and tested. In
this design, the signal-to-noise ratio can be optimized in two ways: (a)
the electronic noise in individual APD channels is minimized by avoiding
light sharing between photodetectors; (b) light collection efficiency is
improved by eliminating light septa within cells to allow scintillation
light propagation across crystals. All four crystals in a
BGO/LSO/YSO/CsI(T1) assembly can be clearly separated and individually
gated for energy. An energy resolution better than 13% can be obtained
in all pixels for 511 keV gamma-rays
Nuclear Science Symposium, 1998. Conference Record. 1998 IEEE; 02/1998
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[show abstract]
[hide abstract]
ABSTRACT: The measurement of depth of interaction (DOI) within detectors is
necessary to improve resolution uniformity across the FOV of small
diameter PET scanners. DOI encoding by pulse shape discrimination (PSD)
has definite advantages as it requires only one readout per pixel and it
allows DOI measurement of photoelectric and Compton events. The PSD time
characteristics of various scintillators were studied with avalanche
photodiodes (APD) and the identification capability was tested in
multi-crystal assemblies with up to four scintillators. In the PSD time
spectrum of an APD-GSO/LSO/BGO/CsI(Tl) assembly, four distinct peaks at
45, 26, 88 and 150 ns relative to a fast test pulse, having resolution
of 10.6, 5.2, 20 and 27 ns, can be easily separated. Whereas the number
and position of scintillators affect detector performance, the ability
to identify crystals is not compromised. Compton events have a
significant effect on PSD accuracy, suggesting that photopeak energy
gating should be used for better crystal identification. More
sophisticated PSD techniques using parametric time-energy histograms
also improve crystal identification in cases where PSD time or energy
discrimination alone is inadequate. These results confirm the
feasibility of PSD DOI encoding with APDs for PET
Nuclear Science Symposium, 1998. Conference Record. 1998 IEEE; 02/1998
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[show abstract]
[hide abstract]
ABSTRACT: The effects of proton radiation damage on EG&G C30902S Si
avalanche photodiodes (APD's) were measured. The APD bulk leakage
current increased at 0.29 fA/rad, or about 1800 dark photoelectrons per
rad(Si) at -10°C under 16.2 MeV protons. There was little change in
the breakdown voltage with the radiation doses up to 30 krad(Si). The
increase in the total dark currents below the breakdown voltage was
insignificant until 3 krad(Si)
IEEE Transactions on Electron Devices 01/1998; · 2.32 Impact Factor
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ABSTRACT: The dark count rate of avalanche photodiodes was used to monitor
single neutron created damage and annealing. The experiments achieve a
maximum time resolution of 10 ms. Irradiations are carried out at
different temperatures between 5°C and 25°C. Monotonic forward
annealing after the neutron interaction was observed with two distinct
decay times of 75 ms and 725 ms, respectively. Stepwise forward
annealing was observed after this initial period. For some cases reverse
stepwise annealing on a time scale up to 30 minutes was detected. The
monotonic annealing is discussed in connection with the motion of
vacancies in the damage region. The stepwise annealing is suggested to
be related to single defect configuration changes
IEEE Transactions on Nuclear Science 01/1997; · 1.45 Impact Factor
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ABSTRACT: A new reach-through avalanche photodiode, designed for use with
sources of short-wavelength light such as scintillators, is described.
The device has a double junction p<sup>+</sup>-p-n-p<sup>-</sup>-n<sup>+
</sup> structure in which the central three layers, which comprise about
99% of the device thickness, are fully depleted. The p<sup>+</sup>
light-entry surface extends across the whole device and can be placed in
contact with a scintillator. The multiplying p-n junction is buried and
is located about 4 μm below the p<sup>+</sup>-layer so that only
primary photo-electrons generated by short-wavelength (i.e., strongly
absorbed) light are fully multiplied. The p<sup>-</sup>-n<sup>+</sup>
junction, or array of junctions, is located at the back of the wafer and
is surrounded by a guard-ring. Typical characteristics for a device 120
μm thick and having a 25 mm<sup>2</sup> sensitive area, are a quantum
efficiency (Q.E.) of 80% at 480 nm, a capacitance of 30 pF, operating
voltage of <500 V, a speed of response of ~3 ns, a noise current of
less than 1 pA/Hz<sup>1/2</sup> at a gain of 100, and an effective k
value of .030
IEEE Transactions on Nuclear Science 07/1996; · 1.45 Impact Factor
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ABSTRACT: The effects of individual bistable defects on the dark counting rate of avalanche photodiodes have been monitored and their temperature dependence studied. The presence of a bistable defect in the diode is indicated by the repeated random switching of the counting rate between two well‐defined rates. Four of the defects studied were produced via reaction with a single neutron from a Be–Am source, while two were found to exist without irradiation. Results were analyzed in terms of the activation energies of the electron generating capabilities of the defects, and the effective potential barriers between the two structural configurations of the bistable states. Among the six defects studied, two of them could be of the same type. © 1995 American Institute of Physics.
Applied Physics Letters 06/1995; · 3.84 Impact Factor
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ABSTRACT: The properties of avalanche photodiodes and associated electronics required for photon counting in the Geiger and the sub-Geiger modes are reviewed. When the Geiger mode is used, there are significant improvements reported in overall photon detection efficiencies (approaching 70% at 633 nm), and a timing jitter (under 200 ps) is achieved with passive quenching at high overvoltages (20-30 V). The results obtained by using an active-mode fast quench circuit capable of switching overvoltages as high as 15 V (giving photon detection efficiencies in the 50% range) with a dead time of less than 50 ns are reported. Larger diodes (up to 1 mm in diameter) that are usable in the Geiger mode and that have quantum efficiencies over 80% in the 500-800-nm range are also reported.
Applied Optics 07/1993; 32(21):3894-900. · 1.41 Impact Factor
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ABSTRACT: Summary form only given. The authors discussed the properties of two new avalanche photodiodes (APDs) suited for application with scintillating fiber tracking systems, considered optimal packaging approaches for efficient optical coupling from scintillating fibers to APDs which allow the diode area to be minimized, and predicted their performance when used in either the Geiger mode, together with a fast quench circuit, or in the sub-Geiger mode, in conjunction with a low-noise preamplifier. In either case, detection efficiencies of over 85% for a five-photon pulse were predicted and measured. The use of these devices in the linear mode, with possible application to scintillating fiber calorimeters, was also considered. It was shown both theoretically and experimentally that, for short pulses (a few nanoseconds) of greater than about 10 photons, better signal-to-noise ratios are possible using APDs than using photomultiplier tubes
Nuclear Science Symposium and Medical Imaging Conference, 1991., Conference Record of the 1991 IEEE; 12/1991
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ABSTRACT: An improved version of a recently developed “Buried Junction” avalanche photodiode (APD), designed for use with scintillators, is described and characterized. This device, also called the “Reverse APD”, is designed to have a wide depletion layer and thus low capacitance, but to have high gain only for e–h pairs generated within the first few microns of the depletion layer. Thus it has high gain for light from scintillators emitting in the 400–600 nm range, with relatively low dark current noise and it is relatively insensitive to minimum ionizing particles (MIPs). An additional feature is that the metallurgical junction is at the back of the wafer, leaving the front surface free to be coupled to a scintillator without fear of junction contamination. The modifications made in this device, as compared with the earlier diode, have resulted in a lower excess noise factor, lower dark current, and much-reduced trapping. The electrical and optical characteristics of this device are described and measurements of energy and timing resolution of this device with several scintillators (BGO, LSO and GSO) of potential interest in high-energy physics and PET imaging systems are presented.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment.
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ABSTRACT: Avalanche photodiodes in the Geiger mode have been used to monitor, in real time, the increase in dark-current generation rate caused by lattice damage induced by single fast-neutron elastic collisions. This damage has been monitored, at room temperature, for periods up to several days with a timing resolution as low as 10 ms. A variety of short-term and long-term annealing effects are observed as well as the creation of what appear to be multi-stable single-defect generation centers having switching times of several minutes. Although the observed short and long-term damage is consistent with that observed using a variety of other methods, our new technique has the sensitivity to permit the observation of the creation and evolution of individual multi-stable defects in relatively pure, very-low-defect concentration silicon which is depleted of mobile carriers so that many of the complicating effects of defect-impurity pairing and electron or hole trapping can be ignored.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms.
