[Show abstract][Hide abstract] ABSTRACT: In spite of the excellent performance of SiPMs in
application to the time-of-flight PET detectors, a development of
better photomultipliers for PET detectors is of importance. A
fast timing with detectors based on the PMT light readout
depends mainly on time jitter and quantum efficiency of the
PMTs. But several studies in the past showed that a screening
grid at the anode improves significantly time resolution
measured with scintillation detectors. ADIT Co. has started a
development of a 1” diameter fast PMT with the screening grid
at the anode to be applied in the block detectors in TOF PET
scanners. In the present studies, we report of the first
comparative study of the L25, classical PMT, with that equipped
further with the screening grid. It showed a large improvement
of time resolution up to 1.2 factor.
[Show abstract][Hide abstract] ABSTRACT: The purpose of this work is to present a measurement method for determining the neutron responses of various liquid organic scintillators using a time-of-flight technique in conjunction with a D–T neutron generator. The method is based on fast-neutron scattering on protons in a liquid-scintillator medium and on the acquisition of the neutron response of the medium as a function of the proton-recoil energy. This method can be applied to all scintillators that utilize fast-neutron elastic scattering.
Full-text · Article · May 2015 · Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment
[Show abstract][Hide abstract] ABSTRACT: A micro photomultiplier (microPMT or μPMT) works like a classic photomultiplier but the whole device is made directly in a silicon wafer sandwiched between two glass layers. A microPMT has dimensions of only 13x10x2 mm and its photocathode has a size of 3x1 mm. The aim of the work is to check usefulness of a microPMT in gamma spectrometry with scintillators and fast timing. In the first part of the study analysis of the energy resolution obtained with 3x3x1 mm LSO, BGO and CsI(Tl) scintillators is made. The recorded values for 662 keV are equal to 22.9% and 13.5% for CsI and LSO, respectively. The light pulse shapes of a single photoelectron and scintillation signal of LSO are also shown. The important part of the study is measurement of the number of photoelectrons and estimation of the excess noise factor. Only 2200 phe/MeV were obtained for LSO coupled with the tested microPMT. The calculated excess noise factor is equal to 1.4. In the second part, measurements of the time jitter and timing resolution with LSO crystal for 511 keV annihilation quanta are reported. The timing characteristics of the tested device is poor. Its time jitter equals to 1.5 ns, whereas timing resolution for 22Na is 620 ps. All the results are compared with data obtained with classic PMTs.
Full-text · Article · Oct 2014 · IEEE Transactions on Nuclear Science
[Show abstract][Hide abstract] ABSTRACT: In the paper we reported on the scintillation properties and pulse shape discrimination (PSD) performance of new plastic scintillators. The samples with dimension of 2 inches × 2 inches were tested: EJ299-34, EJ299-34G, EJ299-33 and EJ299-33G. They are the first commercially available plastics with neutron/gamma discrimination properties. The paper covers the measurements of emission spectra, photoelectron yield, analysis of the light pulse shapes originating from events related to gamma-rays and fast neutrons as well as neutron/gamma discrimination. The tested plastics are characterized by a photoelectron yield on a level of approximately 1600-2500 phe/MeV, depending on the sample. The highest value, measured for EJ299-34, is similar to the number of photoelectrons measured for EJ309 (2600 phe/MeV). The figure of merit (FOM) calculated for narrow energy cuts — indicating the PSD performance — showed that the PSD capabilities of the plastics are significantly lower than of EJ309. These scintillators are still under development in order to optimize the composition and manufacturing procedures. At this time the results obtained with the new plastics suggest their possible use as an alternative for liquid scintillators, especially if we consider their inflammability and non-toxicity.
Full-text · Article · Jun 2014 · Journal of Instrumentation
[Show abstract][Hide abstract] ABSTRACT: This study presents a simple experimental setup for precise inspection of scintillation decay characteristics as a function of the energy deposited in scintillators. The results are discussed for NaI:Tl, LSO:Ce and CeBr3 crystals. The tested samples were coupled to a fast response R5320 photomultiplier from Hamamatsu. The decay time constants were measured by fitting the anode pulses of the PMT registered directly with a TDS5054B digital oscilloscope from Tektronix. Simple analog electronics composed of timing single channel analyzers, gate generators and coincidence/logic unit was used for selection of the deposited energy converted into light within the scintillator, and for triggering the scope to register relevant scintillation pulses. High precision of the experimental setup allowed for registration of non-proportionality curves for all samples. Moreover, non-proportionality was measured for fast and slow decay mode of NaI:Tl separately. The measurement was also used for inspection of possible differences in the pulse shapes originating from Compton scattering events and photoabsorption.
Full-text · Article · Jun 2014 · Nuclear Instruments and Methods in Physics Research
[Show abstract][Hide abstract] ABSTRACT: The scintillation characteristics of Lu1.95Y0.05SiO5:Ce (LYSO:Ce) and Lu0.7Y0.3AlO3:Ce (LuYAP:Ce) single crystals were compared for γ-ray detection. The values of scintillation decay time and coincidence time resolution were evaluated. The scintillation decay of LYSO:Ce exhibits approximately a single-exponential component with decay time of 39 ns, whereas for LuYAP:Ce an intensity of the fast component with decay time of 21 ns is reduced (∼42%) and followed by a high intensity of slower components. The coincidence time resolution for 511 keV annihilation quanta of 234 and 894 ps was obtained, respectively, for LYSO:Ce and LuYAP:Ce detectors in coincidence experiment using a BaF2-based detector. The time resolution was also discussed in terms of a number of photoelectrons and decay time of the scintillation pulse.
Full-text · Article · May 2014 · Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms
[Show abstract][Hide abstract] ABSTRACT: The absorption, luminescence and scintillation characteristics of Y2SiO5:Ce (YSO:Ce) scintillator were investigated and compared to those of Lu1.95Y0.05SiO5:Ce,Ca (LYSO:Ce,Ca) scintillator. Due to the Ca2+ co-doping in LYSO:Ce quantified by GDMS analysis, the Ce4+ center is evidenced in the absorption spectra. For 662 keV gamma-rays (Cs-137 source), YSO:Ce shows a light yield of 15,300 ph/MeV, which is much lower than that of 32,000 ph/MeV obtained for LYSO:Ce,Ca. The coincidence timing resolution for 511 keV annihilation quanta of 234 and 478 ps was obtained, respectively, for LYSO:Ce,Ca and YSO:Ce detectors in coincidence experiment using a BaF2-based detector. Time resolution was also discussed in terms of a number of photoelectrons and decay time of the scintillation pulse.
No preview · Article · Jul 2013 · Optical Materials
[Show abstract][Hide abstract] ABSTRACT: Performance of cerium-doped Gd3Al2Ga3O12 (GAGG:Ce) scintillator in gamma-ray spectrometry has been investigated. The measurements of two samples of GAGG:Ce cover the tests of emission spectra (maximum of emission at about 530 nm), light output, non-proportionality, energy resolution, time resolution and decay time of light pulses. We compare the results with commonly known scintillators, such as NaI(Tl), LSO, LuAG etc. The results show that GAGG:Ce has a high light yield of about 33000 ph/MeV as measured with Hamamatsu S3590–18 Si PiN photodiode . The total energy resolution for 662 keV gamma-rays from 137Cs source is equal to about 6%, whereas intrinsic resolution is equal to 5.2%. Additionally, we made basic measurements of photoelectron yield, non-proportionality and total energy resolution of small sample (5×5×5 mm3) of GAGG:Ce crystal coupled to Hamamatsu MPPC array (6×6 mm2). The results show that the performance of GAGG:Ce measured with the MPPC array are similar to those measured with the PMT.
Full-text · Article · Jun 2013 · Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment
[Show abstract][Hide abstract] ABSTRACT: Presently, a majority of studies concerning application of silicon photomultipliers (SiPMs) in positron emission tomography detectors are focused on scintillators containing lanthanum (LaBr3) or lutetium (LSO, LYSO, LFS). However, the modules with the well known BGO in combination with SiPM light readout are also interesting due to unique features of SiPMs. In this work the two types of detectors, based on BGO and LSO scintillators are compared in terms of requirements for positron emission tomography scanners. The presented studies are performed with two Hamamatsu Multi Pixel Photon Counter (MPPC) arrays of 2×2 channels, with total area of 6×6 mm2 and micro-pixel size of 25 µm (S10985-025C) and 50 µm (S10985-050C). The measurements of a number of photoelectrons, energy resolution at 511 keV and 22Na time resolution are reported for various sizes of scintillators, including 3×3 mm2 pixels and single crystals covering the whole MPPC active area. The paper is more focused on optimization of the system with BGO since its performance in combination with SiPM light readout is less known. The aim of this work is to show advantages of a SiPM based detector, especially in combination with BGO, in respect to the block detectors where classic photomultipliers are used.
Full-text · Article · Jun 2013 · IEEE Transactions on Nuclear Science
[Show abstract][Hide abstract] ABSTRACT: The absorption, luminescence, and scintillation characteristics
of cerium-doped lutetium-yttrium perovskite (LuxY1�x AlO3:
Ce; x ¼ 0, 0.3, 0.7) single crystals were investigated.
The values of light yield, scintillation decay time, and
coincidence time resolution were evaluated. At 662 keV
g-rays (137Cs source), the light yield of 30 700 ph MeV�1
obtained for YAlO3:Ce is much higher than that of 16 200
and 10 600 ph MeV�1 obtained for Lu0.3Y0.7AlO3:Ce and
Lu0.7Y0.3AlO3:Ce, respectively. Scintillation decays are dominated
by a fast component with decay time value of 16–20 ns,
which nearly coincides with the photoluminescence decay time
value of 17.5 ns. In scintillation decays the intensity of the fast
component becomes reduced and the content of slower
components considerably increased with increasing lutetium
content in the crystals. The coincidence time spectra for
511 keV annihilation quanta were measured in coincidence
experiment using a BaF2-based detector and time resolution
was also discussed in terms of a number of photoelectrons and
decay time of the scintillation pulse. The photofraction for all
the crystals under 662 keV g-ray excitation was also evaluated
Full-text · Article · Jun 2013 · physica status solidi (a)
[Show abstract][Hide abstract] ABSTRACT: Relative light yield and intrinsic energy resolution of NaI:Tl, CsI:Na and CsI:Tl crystals were investigated by means of the wide angle Compton coincidence technique in wide energy range from several keV up to 1 MeV. The experimental setup consisted of a high purity germanium (HPGe) detector and the tested scintillators were put at a close separation from the HPGe detector. The tested samples were cylinders of 25 mm diameter and height coupled to a photomultiplier. Compton electron responses were compared to the results obtained with γ-ray absorption peaks. A correlation between intrinsic resolution of the tested scintillation materials and their nonproportionality was observed. Substantial differences in intrinsic resolution measured for γ-ray absorption peaks and Compton electrons were registered in the energy range between 50 keV and 200 keV. The results were discussed in terms of electron scattering, pointing to δ-ray production as an important contribution for determination of scintillator intrinsic resolution.
Full-text · Article · Mar 2013 · Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment
[Show abstract][Hide abstract] ABSTRACT: A development of silicon photomultipliers (SiPM), with a large number of micro-pixels and improved linearity of the pulse height response, allow discussing their possible application to gamma spectrometry with scintillators. Most of the measurements were done with Hamamatsu MPPCs sensors equipped with 3600 and 14400 pixels because of their well pronounced single photoelectron spectra. It allowed precisely measure the photoelectron (phe) numbers/fired pixels and then to discuss in a quantitative manner an obtainable energy resolution. The studied detectors were characterized first by means of a laser light pulser and then by 3×3×3 mm3 LFS and CsI(Tl) crystals coupled to 3×3 mm2 Hamamatsu MPPC. In the study with the light pulser, the linearity of the MPPC response, expressed in the photoelectron number measured in relation to the first photoelectron, versus a light pulse intensity observed with PMT was checked and then the pulse height resolution was measured. Through analysis of the energy resolution the lower limit of the phe number was derived, assuming Poisson statistic. Further on, based on a directly measured phe number, the discussion of an excess noise factor of MPPC was done. In scintillation tests the measurements of the energy resolution and non-proportionality of the light yield were done with LFS and CsI(Tl) and discussed in a quantitative way, based on the measured PHE number, for both types of 3×3 mm2 MPPC detectors.
Full-text · Article · Feb 2013 · Journal of Instrumentation
[Show abstract][Hide abstract] ABSTRACT: The aim of this work is to provide the characteristics of MPPC arrays with an active area of 6 x 6 mm(2) in gamma-ray spectrometry with CsI:Tl, LSO:Ce:Ca, LaBr3:Ce and BGO scintillators. The chosen scintillators have significantly different decay times of the scintillation pulses and different wavelengths of emission peaks. This allowed an investigation into the dependence of MPPC readout features on the MPPC and scintillator characteristics. The study of influence of effective dead time and the number of MPPC pixels on a readout response in relation to the brightness and speed of the scintillator were performed. The measurements covered a selection of MPPC optimum operating voltage, verification of the linearity range for a given decay time of the crystals, verification of the excess noise factor for the optimal voltage and evaluation of the Photon Detection Efficiency (PDE). The results of energy resolution and non-proportionality obtained with the MPPC array readout of CsI: Tl and BGO were compared to those obtained for the same crystals with the XP2020Q PMT readout. The results show that an MPPC can be used as effectively as a PMT for gamma spectrometry measurements in the whole tested energy ranges (up to 1.3 MeV) and for many types of scintillation crystals (BGO, CsI:Tl).
Full-text · Article · Dec 2012 · IEEE Transactions on Nuclear Science
[Show abstract][Hide abstract] ABSTRACT: Light yield nonproportionality and the intrinsic resolution of some low atomic number scintillators were studied by means of the Wide Angle Compton Coincidence (WACC) technique. The plastic and liquid scintillator response to Compton electrons was measured in the energy range of 10 keV up to 4 MeV, whereas a CaF2:Eu sample was scanned from 3 keV up to 1 MeV. The nonproportionality of the CaF2:Eu light yield has characteristics typical for inorganic scintillators of the multivalent halides group, whereas tested organic scintillators show steeply increasing nonproportionality without saturation point. This is in contrast to the behavior of all known inorganic scintillators having their nonproportionality curves at saturation above energies between tens and several hundred keV.
Full-text · Article · Jun 2012 · Journal of Instrumentation
[Show abstract][Hide abstract] ABSTRACT: Two samples of 10 mm diameter and 10 mm height CdWO4 and ZnWO4 scintillators were studied at room and liquid nitrogen temperatures. At room temperature the crystals were coupled to a Photonis XP3212 photomultiplier. During experiments at low temperatures a Large Area Avalanche Photodiode was used as a photodetector. Measurements of light output, non-proportionality of the light yield and intrinsic resolution as a function of gamma-ray energies were performed at both temperatures. The non-proportionality for the two crystals reveals temperature dependence, showing a more proportional behavior at liquid nitrogen temperature. Intrinsic energy resolution values for both crystals also show temperature dependence.
No preview · Article · Mar 2012 · Journal of Instrumentation