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ABSTRACT: A composite scintillator is a solid solution, which contains the grains of organic molecular single crystal introduced into a polymer matrix and placed inside the housing. Hereunder, we present n/γ discrimination properties of four composite scintillators; two of the them are based on p-terphenyl and two others-on stilbene. The results obtained with a stilbene single crystal and a liquid scintillator BC501A are shown as a comparison. Initial conclusion, which is drawn from the paper, is that composite scintillators could be an alternative substitution for commonly used liquid scintillators.
Journal of Instrumentation 07/2011; 6(07):P07007. · 1.87 Impact Factor
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C. Plettner,
G. Pausch,
F. Scherwinski,
C. Herbach,
R. Lentering,
Yong Kong,
K. Romer,
J. Stein,
T. Szczesniak,
M. Grodzicka,
J. Iwanowska, M. Moszynski
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ABSTRACT: Homeland security applications demand high performance Compton-camera systems, with high detector efficiency, good nuclide identification and able to operate in-field conditions. A low-Z scintillator has been proposed and studied as a promising candidate for use in the scattering plane of a scintillator-based Compton camera: CaF<sub>2</sub>(Eu). All the relevant properties for the application of this scintillator in a mobile Compton camera system have been addressed: the energy resolution and the non-linearity at room temperature and in the temperature range of -20°C to +55°C, the photoelectron yield and the relative light yield in the relevant temperature range. A new method of inferring the relative light output of scintillators as a function of temperature has been proposed.
Nuclear Science Symposium Conference Record (NSS/MIC), 2010 IEEE; 12/2010
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K. Roemer,
G. Pausch,
C.-M. Herbach,
M. Kapusta,
Yong Kong,
R. Lentering,
C. Plettner,
J. Stein, M. Moszynski,
L. Swiderski,
T. Szczesnik
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ABSTRACT: Compton cameras are of general interest in various fields of operation. Because of the ability to locate and identify remote sources, homeland security supports the development of such devices in a rugged and reliable form. The decisions upon appropriate materials for the scatter- and absorber plane depend on performance and economical trade-offs. In order to estimate the expected performance of the Compton camera, simulations are necessary. Certain experimentally determined parameters have to be fed into simulations, such as the energy resolution of the detector. Two materials with low effective atomic number (Z<sub>eff</sub>), CaF<sub>2</sub> and plastic, promise to be good candidates for the scattering plane. Those scintillators are known for quite some time, but not very well characterized with respect of energy resolution and nonlinearity. A modified Compton coincidence technique using a high purity Germanium (HPGe) detector in coincidence with the investigated is discussed in this paper: The wide-angle Compton-coincidence (WACC) setup provides a fast and reliable means for characterization of low-Z scintillators. For quality control purposes, the actual scatter detector can be monitored in-house using the WACC technique. This work presents results of different scintillator materials and sizes for validation and exploration of this method.
Nuclear Science Symposium Conference Record (NSS/MIC), 2010 IEEE; 12/2010
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L. Swiderski, M. Moszynski,
D. Wolski,
J. Iwanowska,
T. Szczesniak,
G. Pausch,
C. Plettner,
J. Stein,
P. Schotanus,
C. Hurlbut,
J. Szabelski
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ABSTRACT: Performance of a He-3 counter and a B-10 loaded liquid scintillator EJ309B5 has been studied in terms of neutron detection efficiency. The measurements were carried out in a mixed field of neutron and gamma radiation from an intense ( ~ 10<sup>6</sup> neutrons/s/4π)<sup>252</sup>Cf source. The response of both detectors to background and high intensity gamma radiation ( ~ 100 μSv/h at a detector) from a <sup>60</sup>Co source has been measured to establish background count rate and gamma rays cut-off point, respectively. The analysis showed that the properties of a He-3 counter are significantly better than that of EJ309B5. However, it has been pointed out how to improve the performance of a liquid scintillator in order to reduce gamma radiation sensitivity.
IEEE Transactions on Nuclear Science 11/2010; · 1.45 Impact Factor
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ABSTRACT: A method based on the Compton coincidence technique was applied to study the energy resolution of Compton electrons in wide energy range. The experimental setup was comprised of a High Purity Germanium (HPGe) detector and a LaBr<sub>3</sub>:Ce scintillator coupled to a photomultiplier. The detectors were set in a face-to-face geometry and the source was placed between them. Thus gating on events backscattered in the scintillator and detected in HPGe allowed one to measure the energy resolution of Compton scattered electrons at an energy corresponding to the Compton edge for a given source. This study confirms the importance of the electron scattering (6-rays) as the main component of the intrinsic resolution in scintillators. The results are particularly important for discussion of the light yield non-proportionality contribution to the energy resolution of scintillators.
IEEE Transactions on Nuclear Science 07/2010; · 1.45 Impact Factor
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ABSTRACT: The majority of current Positron Emission Tomography (PET) systems are based on block-detectors consisting of many scintillating pixels read by a smaller number of photomultipliers (PMTs). An improvement of the time resolution, using a common light readout from a cluster of PMTs, was proposed by Kuhn et al., and tested by us earlier with LSO crystals. This, triggered an idea to design a new PET detector optimized for Time of Flight (TOF) systems, based on continuous crystals. In the present u work, we report on optimization of timing with a 20 à 20 à 20 mm<sup>3</sup> LYSO crystal coupled to a 16-channel photomultiplier -a H8711-200MOD from Hamamatsu. First, measurements were =¿ performed of the transit time jitter, the number of photoelectrons and the time resolution using a small 10 à 10 à 5 mm<sup>3</sup> LSO crystal coupled to a H8711-200MOD PMT. Results were compared with data collected from fast timing photomultipliers like Photonis XP1020, XP3060, XP20D0 or Hamamatsu R9800. In the second part of the study, the time resolution measurements and the optimization of the system were made with a continuous LYSO crystal. The final results are discussed in terms of the measured photoelectron number and the requirements for the TOF-PET scanners.
IEEE Transactions on Nuclear Science 03/2010; · 1.45 Impact Factor
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L. Swiderski, M. Moszynski,
D. Wolski,
T. Batsch,
J. Iwanowska,
A. Nassalski,
A. Syntfeld-Kazuch,
T. Szczesniak,
F. Kniest,
M.R. Kusner,
G. Pausch,
J. Stein,
W. Klamra,
P. Schotanus,
C. Hurlbut
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ABSTRACT: Boron-10 loaded liquid scintillators were studied in order to improve n/¿ separation. Pulse shape discrimination (PSD) was implemented by means of a zero-crossing (ZC) method to distinguish between ¿-rays and fast/slow neutrons. Significant progress was done for BC523A2 and EJ339A2 scintillators loaded with reduced amount of <sup>10</sup>B (2% and 2.5%, respectively), as compared to the results obtained earlier with BC523A loaded with 4.4% of <sup>10</sup>B. The improvement was probably caused by the reduction of <sup>10</sup>B content, as indicated in the reported study. A <sup>10</sup>B loaded scintillator EJ309B5 based on non-flammable liquid was also studied, showing the best separation of thermal neutron capture events from fast neutrons, ¿-rays and noise.
IEEE Transactions on Nuclear Science 03/2010; · 1.45 Impact Factor
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ABSTRACT: The scintillation properties of LuAG:Ce and YAG:Ce crystals were compared with LYSO:Ce crystal under ¿ -ray excitation. Light yield non-proportionality and energy resolution were measured with a Photonis XP5500B PMT. The energy resolution, obtained in this work for 662 keV ¿ -rays, was 6.7, 7.0 and 8.7%, respectively, for LuAG:Ce, YAG:Ce and LYSO:Ce detectors. The values reflect the influence of the light yield non-proportionality on the measured energy resolution. A fast component in the scintillation decay of LuAG:Ce crystal is faster than that of the YAG:Ce crystal, whereas the relative intensity of a fast component for YAG:Ce crystal is higher than that of LuAG:Ce crystal. The coincidence time resolution, obtained in this work for 511 keV annihilation quanta, was 660, 583 and 222 ps, respectively, for YAG:Ce, LuAG:Ce and LYSO:Ce detectors in coincidence experiment together with a BaF<sub>2</sub> detector. Time resolution was also discussed in terms of a number of photoelectrons and decay time of the light pulse.
IEEE Transactions on Nuclear Science 01/2010; · 1.45 Impact Factor
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ABSTRACT: Scintillator-based Compton cameras for remote localization and identification of radio nuclides require scatter detectors made of low-Z materials. The energy resolution of such detectors in a range dominated by Compton scattering is a crucial parameter. It has to be known for performance estimates, and it must be quantified and optimized for detector designs to be used in real systems, but it is hard to measure. The Compton Coincidence Technique (CCT) appears to be the best method for reliable and direct measurements, but appropriate facilities are expensive. This paper suggests and investigates a modified CCT which provides less expensive means for qualifying of scatter detectors in a reasonable time frame. The assembly consists of a single HPGe detector, the scatter detector to be investigated, and one or more common gamma sources in close geometry. Pulse height and timing information from both detectors is gathered by multi-parameter data acquisition. Coincidences of both detectors are due to a plurality of Compton scattering angles and corresponding energy transfers. A thorough data analysis then allows extracting the detector resolution as well as the non-linearity as a function of energy from data sets measured within hours. Results obtained for NaI and plastic scatter detectors will be presented and discussed.
Nuclear Science Symposium Conference Record (NSS/MIC), 2009 IEEE; 12/2009
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ABSTRACT: A composite scintillator is non-toxic and nonflammable solid solution, which contains the grains of organic molecular single crystal introduced into a polymer matrix. Composite scintillators were designed as detectors of fast neutrons and gamma radiation. We present ¿/¿ discrimination properties of four composite scintillators: two of them are based on p-terphenyl and two other-on stilbene. The results obtained with a stilbene single crystal and a liquid scintillator (BC 501A) are shown as a comparison. First conclusion of this work is that composite scintillators can be an attractive offer for the border monitoring.
Nuclear Science Symposium Conference Record (NSS/MIC), 2009 IEEE; 12/2009
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ABSTRACT: Co-doping Lu<sub>2</sub>SiO<sub>5</sub>:Ce (LSO:Ce) with Ca divalent cations changes the scintillation properties of the crystal. In the present work an influence of Ca<sup>2+</sup> co-doping on energy resolution, light output and non-proportionality was investigated for samples with 0, 0.1, 0.2, 0.3, and 0.4 atomic percent Ca with respect to Lu. A substantial improvement of energy resolution in the co-doped crystals was found and higher light output by about 10% was observed. The best energy resolution of 7.35 plusmn 0.15% was measured for LSO with 0.2% Ca. Contrary to our expectations, the change in the measured energy resolution of Ca<sup>2+</sup> co-doped LSO samples is not reflected in the non-proportional characteristic of the studied crystals as the non-proportionality curves are independent of Ca concentration. Possible explanations of the underlying mechanism of improving the energy resolution include afterglow suppression via Ca co-doping. Earlier studies showed that calcium co-doping significantly reduces the trap population, hence the decay time of LSO is shortened and the afterglow is substantially quenched. In the current work, the integrated afterglow intensities as well as the afterglow effective decay times correlate with the concentration of Ca<sup>2+</sup>. Since the afterglow was measured about 30 ms after the crystal was irradiated by a strong X-ray source, the integral intensity does not include the faster components of afterglow. Hence, the correlation between afterglow intensity and energy resolution treated in this work is very preliminary.
IEEE Transactions on Nuclear Science 11/2009; · 1.45 Impact Factor
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L. Swiderski, M. Moszynski,
A. Nassalski,
A. Syntfeld-Kazuch,
T. Szczesniak,
K. Kamada,
K. Tsutsumi,
Y. Usuki,
T. Yanagida,
A. Yoshikawa,
W. Chewpraditkul,
M. Pomorski
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ABSTRACT: Properties of praseodymium and cerium doped Lutetium Aluminum Garnet (LuAG) were compared with cerium doped Lutetium Oxyorthosilicate (LSO) and Lanthanum Bromide (LaBr<sub>3</sub>). Light yield, its non-proportionality relative to 662 keV gamma -rays and the dependence of the energy resolution on energy of the detected gamma -rays were measured. LuAG:Pr turned out to have good proportionality, with deviation from unity around 10% at 16.6 keV and 3% at 59.5 keV. This, together with relatively high light yield of 5600 phe/MeV results in a very good energy resolution of LuAG:Pr of 5.1% measured with 662 keV gamma-rays. The measured time resolution of 308 ps is significantly larger than that of 166 ps obtained for LSO:Ce. This can be explained by smaller light yield of LuAG:Pr and the fact that only about 25% of its scintillation is emitted in short decay time modes of 17.6 ns and 52 ns, while the rest is decaying with long time modes of 1.4 mus and 9 mus.
IEEE Transactions on Nuclear Science 09/2009; · 1.45 Impact Factor
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M. Moszynski,
C. Plettner,
A. Nassalski,
T. Szczesniak,
L. Swiderski,
A. Syntfeld-Kazuch,
W. Czarnacki,
G. Pausch,
J. Stein,
A. Niculae,
H. Soltau
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ABSTRACT: The performance of a silicon drift detector (SDD) with an integrated FET, delivered by the company PNSensor, Munich, Germany, was studied in gamma spectrometry at room temperature (23-25degC) with a LaBr<sub>3</sub>:Ce crystal of 6 mm diameter and 6 mm height. The SDD characteristics were compared with those measured with a Photonis XP5212 photomultiplier, a Large Area Avalanche Photodiode (LAAPD) of Advanced Photonix, Inc., and a Hamamatsu S3590-18 Photodiode (PD). Energy resolution versus gamma ray energies and its components related to the photoelectron/electron-hole pair statistics and dark noise were measured and compared. At low energies, below 100 keV, the light readout by the photomultiplier gives the best results, while for high energies, above 300 keV, the light readout by the SDD delivers superior energy resolution. In particular, the best energy resolution of 2.7% was determined for 662 keV gamma rays from a <sup>137</sup>Cs source.
IEEE Transactions on Nuclear Science 07/2009; · 1.45 Impact Factor
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ABSTRACT: The new 1 inch and 1.5 inch in diameter photomultipliers for timing applications from Photonis and Hamamatsu have been tested. Time resolution of XP1020, XP3060, R9800 and R9420 was measured with a 10 times 10 times 5 mm<sup>3</sup> LSO crystal in coincidence experiments with 511 keV annihilation quanta from <sup>22</sup>Na gamma source. Results were discussed in terms of measured photoelectron number and time jitter. Single photoelectron spectra were recorded and excess noise factor for each tube was also calculated. The final comparison of the tested tubes and their timing properties were presented in relation to large amount of experimental data of various types of PMTs collected during last few years. Especially, observed linear dependency between the time resolution normalized to the number of photoelectrons and time jitter was pointed out. Inconsistency of the data collected with the Hamamatsu R9420 PMT resulting from the overestimated photoelectron number was reported and further studied. Additional experiments with LED light source and different experimental set-ups were discussed and comparison of the two methods of the photoelectron number measurements was performed.
IEEE Transactions on Nuclear Science 07/2009; · 1.45 Impact Factor
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ABSTRACT: Scintillation properties of praseodymium doped LuAG have been investigated. The crystal is a dense (6.7 g/cm<sup>3</sup>) scintillator with a short decay time around 20 ns and wavelength emission spectrum peaked at 310 nm. The tested sample was 10 mm times 10 mm times 5 mm cuboid, polished on all surfaces. The dopant concentration amounts to 0.23 mo1%. A light yield of 16000plusmn1600 ph/MeV was measured using high sensitivity (13.7 muA/1mF) Photonis photomultiplier (PMT) XP5500B. High quantum efficiency of this PMT (35%) allowed us to register 5600plusmn400 phe/MeV using 12 mus shaping time in the spectroscopy amplifier. The measured energy resolution was equal to 5.0plusmn0.1%. Response of LuAG:Pr to gamma-rays was found to be proportional over wide energy range. Deviation from proportionality does not exceed 10% at 16.6 keV. This results in good intrinsic energy resolution of LuAG:Pr amounting to 3.0plusmn0.3%, measured with 662 keV gamma-rays from <sup>137</sup>Cs.
IEEE Transactions on Nuclear Science 07/2009; · 1.45 Impact Factor
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ABSTRACT: A novel concept for improving gamma ray spectroscopy in compact instruments is presented. The dual-range photon detector (DRPD) consists of a silicon drift detector (SDD) which is optically coupled with a LaBr<sub>3</sub>(Ce<sup>3+</sup>) crystal. In contrast to similar configurations investigated so far the SDD points to the radiation source. Pulse shape discrimination allows separating the distinct detection mechanisms which correspond to gamma absorption in the SDD or in the scintillator, respectively. This arrangement combines for the first time the excellent performance of an SDD as X-ray detector on its own with the striking energy resolution of a LaBr<sub>3</sub>(Ce<sup>3+</sup>) scintillator read out by an SDD. The concept was successfully demonstrated with two experimental SDD-LaBr<sub>3</sub>(Ce<sup>3+</sup>) systems. An energy resolution (FWHM) of 2.7% and 2.9% at 662 keV was measured with the two distinct systems operated in scintillator mode whereas scintillator-photomultiplier combinations with the same crystals yielded only 3.3% and 3.1%, respectively. The SDD mode provided an energy resolution surpassing the scintillator resolution by about one order of magnitude in the limited energy range up to 100 keV. Measurements with various radioactive sources demonstrated that this mode uncovers line structures which could never be resolved with scintillators or CZT detectors. Homeland security programs could profit from the proposed detector concept.
IEEE Transactions on Nuclear Science 07/2009; · 1.45 Impact Factor
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ABSTRACT: The performance of undoped NaI crystal of a high purity of 7 N grade, developed by Saint-Gobain Crystals for a dark matter search, was studied at liquid nitrogen temperature using an avalanche photodiode. The measured quantities covered light output expressed in the electron-hole (e-h) pair number, non-proportionality characteristics, energy resolution and finally intrinsic resolution of the studied crystals. In contrast to the previous study, the new crystals showed comparable non-proportionality curves to that known for NaI(Tl) at room temperature and a poor energy resolution of about 8% for 662 keV gamma rays from a <sup>137</sup>Cs source. The performed study highlights a role of undoped NaI crystals in a better understanding of limitations of energy resolution in scintillation detectors. A high sensitivity to traces of doping may help to find the way of a modification of non-proportionality of other scintillators by a selective doping or co-doping. A further study of slow components of NaI light pulses and their influence on the energy resolution may clear up its possible deterioration caused by defects in the crystal structures.
IEEE Transactions on Nuclear Science 07/2009; · 1.45 Impact Factor
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ABSTRACT: Presently, a majority of detectors for PET systems is based on scintillator crystals read by photomultipliers. In our previous work, very good time resolution recorded with a 10times10times5 mm<sup>3</sup> LSO crystal coupled to Photonis XP20D0 and Hamamatsu R5320 photomultipliers was shown. Results were almost identical for both detectors and close to 170 ps but the properties such us quantum efficiency of the photocathode and transit time jitter were significantly different. The XP20D0 possessed high QE and the measured photoelectron number was 40% higher than that of the R5320. The R5320 had the time jitter of 140plusmn7 ps at FWHM, three times better than that of the XP20D0. The fact, that despite of the large differences in the parameters of the used PMTs comparable time resolution was achieved, triggered our further study of the most important properties of the photomultipliers and their influence on timing and energy resolution, with a goal of optimizing time-of-flight (TOF) PET systems. Thanks to a close cooperation with Photonis, during last few years we gathered large amount of information and experimental data of various types of PMTs. The aim of this paper is to present general conclusions and dependencies that were derived from these multiple experiments. This should help to develop an ultimate, PMT based detector, for TOF PET systems.
IEEE Transactions on Nuclear Science 03/2009; · 1.45 Impact Factor
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L. Swiderski, M. Moszynski,
D. Wolski,
T. Batsch,
A. Nassalski,
A. Syntfeld-Kazuch,
T. Szczesniak,
F. Kniest,
M.R. Kusner,
G. Pausch,
J. Stein,
W. Klamra
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ABSTRACT: A BC523A liquid scintillator loaded with boron-10 was tested as a detector for both fast and thermal neutrons. A pulse shape discrimination (PSD) method based on a zero-crossing principle was applied to distinguish between neutron and gamma radiation. High quantum efficiency Photonis XP5500B photomultiplier was used to enhance light detection from the scintillator. This allowed a good registration of the energy spectrum of neutron capture events on boron-10, corresponding to about 60 keV gamma-rays. The applied PSD method proved to be useful for n/gamma discrimination. A good resolving power of the method was achieved even without gating on neutron capture events. A comparison with a standard BC501A liquid scintillator was done to evaluate thermal neutrons detection efficiency in BC523A.
IEEE Transactions on Nuclear Science 01/2009; · 1.45 Impact Factor
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ABSTRACT: The performance of undoped NaI crystal of a high purity of 7 N grade, developed by Saint-Gobain Crystals for a dark matter search, was studied at liquid nitrogen temperature using avalanche photodiode. The measured quantities covered the light output expressed in the electron-hole (e–h) pair number, non-proportionality characteristics, energy resolution and finally the intrinsic resolution of the studied crystals. In contrast to the previous study, the new crystals showed comparable non-proportionality curves to that known for NaI(Tl) at room temperature and a poor energy resolution of about 8% for 662 keV gamma rays from <sup>137</sup>Cs source. The performed study highlights a role of undoped NaI crystals in a better understanding of limitations of energy resolution in scintillation detectors. A high sensitivity to traces of doping may help to find the way of a modification of non-proportionality of other scintillators by a selective doping or co-doping. A further study of slow components of the NaI light pulses and their influence on energy resolution may clear up its possible deterioration by defects in the crystal structures.
Nuclear Science Symposium Conference Record, 2008. NSS '08. IEEE; 11/2008
