The performance of multi pixel photon counters (MPPC) of 3 mm x 3 mm size, with 14400 and 3600 pixels, were studied by means of the signal from a laser light pulser and using the 3 mm x 3 mm x 20 mm LSO pixel scintillator. Special attention was paid to measure number of fired pixels, generated by the light of pulser and that of the LSO crystal, using a direct method of a comparison of the light peak position in the pulse height spectrum with that of the single photoelectron. The tests of the LSO crystal showed 1550 +/- 80 fired pixels per MeV in the MPPC with 14400 pixels assuring a good linearity of the response up to about 1 MeV energy of gamma rays absorbed in the LSO crystal. Energy resolution of 14.8% for 662 keV gamma rays from Cs-137 source and a time resolution of about 850 ps for 511 keV annihilation quanta were limited by a rather low number of the fired pixels compared to the number of photoelectrons in photomultipliers.

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 × 20 × 20 mm3 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 × 10 × 5 mm3 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.

Scintillation properties of praseodymium doped LuAG have been investigated. The crystal is a dense (6.7 g/cm3) 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 137Cs.

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 (23-25 degrees C) with a LaBr3: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 Cs-137 source.

Presently, a majority of Positron Emission Tomography (PET) systems is based on block-detectors consisting of many scintillating pixels read by photomultipliers (PMTs). An improvement of time resolution, due to a common light readout by a cluster of PMTs, proposed by Kuhn et al, and tested by us for an LSO crystal triggered an idea of the new PET detector optimized for the Time of Flight (TOF) systems, based on a continuous crystal. In the present work, optimization of timing for a 20×20×20 mm 3 LYSO crystal coupled to the 16-channel photomultiplier H8711-200MOD from Hamamatsu is presented. First, the measurements of transit time jitter, number of photoelectrons and time resolution with a small 10×10×5 mm 3 LSO crystal coupled to the H8711-200MOD PMT were performed. Results were compared with data collected for 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 with the continuous LYSO crystal were made. Also simple tests with positioning of gamma interaction inside the scintillator are reported. The final results are discussed in terms of the measured photoelectron number and requirements for the TOF-PET scanners.

Properties of praseodymium and cerium doped Lutetium Aluminum Garnet (LuAG) were compared with cerium doped Lutetium Oxyorthosilicate (LSO) and Lanthanum Bromide (LaBr3). 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 mu s and 9 mu s.

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 x 10 x 5 mm(3) LSO crystal in coincidence experiments with 511 keV annihilation quanta from Na-22 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.

Growing interest in the development of multi pixel photon counters (MPPC), a solid state photodetector known as the silicon photomultiplier (SiPM), prompts the researchers to characterize their performance. The MPPC is a new type of photon-counting device made up of multiple avalanche photodiode (APD) pixels operating in Geiger mode. The aim of this work was to characterize the MPPC detectors, using a laser diode pulser and next the MPPC coupled to a 3×3×20 mm3 LSO pixel crystal, in positron emission tomography (PET) combined with magnetic resonance (MRI) systems applications. The light yield, number of excited pixels and pulse height resolution has been determined. In scintillation tests the measurements covered a determination of the energy resolution, non-proportionality of the light yield and the time resolution for 511 keV annihilation quanta for both types of 3×3 mm2 S10362-33-025C / 050C Hamamatsu MPPC detector, with 14400 and 3600 pixels respectively.

Co-doping Lu2SiO5:Ce (LSO:Ce) with Ca divalent cations changes the scintillation properties of the crystal. In the present work an influence of Ca2+ co-doping on energy resolution, light output and non-proportionality was investigated for samples with 0, 0.1, 0.2, 0.3, 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±0.15% was measured for LSO with 0.2% Ca. Contrary to our expectations, the change in the measured energy resolution of Ca2+ 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 Ca2+. 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.

Homeland security applications demand compact, high resolution detectors for gamma and X rays identification. Most commercial instruments use scintillating crystals or CdZnTe detectors. The identification performance is therefore intrinsically linked with the progress in developing crystals with a very high light output (LaBr3Ce or SrI2) and with the manufacturing of the CdZnTe detectors. A new detector concept is proposed, which essentially improves on the existing resolution limits. It combines two distinct detection mechanisms in a compact, state-of-the-art solid-state detector, providing complementary information in different but overlapping energy ranges. The dual-range detector consists of a LaBr3(Ce3+) scintillator coupled to a silicon drift detector (SDD). The SDD serves as a high-resolution X-ray on its own, and in parallel as a light readout device for the LaBr3(Ce3+) scintillator ensuring best possible resolution at higher energies.

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 LaBr3(Ce3+) 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 LaBr3 (Ce3+) scintillator read out by an SDD. The concept was successfully demonstrated with two experimental SDD-LaBr3(Ce3+) 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.

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 137Cs 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.

A detailed study of the scintillation light pulse shape in CsI(Tl) at room temperature as a function of incoming photon energy in 6 divided by 662 keV energy range is presented. Three samples of CsI(Tl) of different amount of Tl dopant (0.01, 0.06 and 0.25 mol%) were used in measurements. A delayed coincidence single photon counting method was applied to measure the decay times in the microsecond range. Three-exponential function was fitted to the time spectra to describe the light pulse shape, which resulted in three components of tau(1) = 730 +/- 30 ns (fast), tau(2) = 3.2 +/- 0.3 mu s (slow) and tau(3) = 16 +/- 2 mu s (tail). The intensity of the second component was found to be sensibly independent of photon energy, whereas the intensities of the first and third ones varied with the energy of absorbed photon in low energy region. For a given crystal the most intense fast component was measured for 6-keV X-rays from Fe-55 at the cost of decreasing intensity of the slowest one. Furthermore, the intensity of the fast component depends on Tl concentration and reaches its maximum value for the 0.06 mol% doping, close to the well-know optimal concentration of 0.1 mol%.

The performance of several BrilLanCetrade LaBr3 crystals with the size of O6 times 6 mm2 up to O38 times 38 mm2 were studied coupled to the XP5212 and R6231MOD photomultipliers and in case of the small crystals, coupled also to large area avalanche photodiodes of Advanced Photonix, Inc. First, several photomultipliers of Photonis and Hamamatsu were compared in the work with LaBr3 to select the best one, not affecting energy resolution, besides the photoelectron statistics. The light output and energy resolution for 662 keV gamma rays from 137Cs source were measured for all crystals. Moreover, for some of them, the non-proportionality of the light yield and energy resolution versus gamma rays energy were measured and the intrinsic resolution of the crystals was calculated. For the smallest crystals of O6 times 6 mm2 further comparative tests with LAAPD were carried out.

A BC523A liquid scintillator loaded with boron-10 was tested as a detector for both fast and thermal neutrons. 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 keVee. The applied PSD method proved to be useful for n/y 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.

According to the present knowledge the non-proportionality of the light yield of scintillators appears to be the fundamental limitation of energy resolution. Thus, the understanding of its origin is of the great importance for a development of new scintillators with enhanced energy resolution. In this respect, the non-proportional response of the typical organic scintillators was studied in comparison to that of a BGO crystal. The studies covered tests of BC408 plastic, BC501A liquid scintillator and anthracene organic crystal. The measurements showed a much larger range of energies presenting non-proportional response compared to that known for inorganic scintillators. In the case of anthracene the non-proportionality covers energy range up to about 500 keV, while for the BC408 plastic and BC501A liquid scintillators, it is above 4 MeV energy lost by gamma quanta. The observed effect can be related to a strong quenching of the light for charged particles in organic scintillators, which is much larger than that observed in inorganic scintillators.

The light output, energy resolution, and nonproportionality characteristics were measured for undoped CsI and several samples of CsI with different doping by CsBr. A correlation between nonproportionality of the light yield and the intrinsic energy resolution was confirmed. Contrary to previously published results the light yield of the tested samples was found to be degraded with increasing bromine concentration. The inspection of light pulse shapes was done by the single photon coincidence method. Decay times of the scintillation pulse were measured for undoped and bromine doped crystals, showing the main scintillation in tens of nanoseconds range.

Boron-10 loaded liquid scintillators were studied in order to improve n/γ separation. Pulse shape discrimination (PSD) was done by means of a zero-crossing (ZC) method to distinguish between γ-rays and fast/slow neutrons. A significant progress was achieved for BC523A2 and EJ339A2 loaded with reduced amount of 10B (2% and 2.5%, respectively), as compared to the results obtained earlier with BC523A loaded with 5% of 10B. The improvement was probably caused by the reduction of 10B content, as indicated in the latter study. A 10B loaded scintillator EJ309B5 based on a non-flammable liquid was also studied, showing the best separation of thermal neutron capture events from fast neutrons, γ-rays and noise.

A growing interest in the development of dual modality PET/CT scanners prompts the comparative study of numerous scintillators to select the best one, which could be used simultaneously in PET detectors working in the pulsing mode and in the CT detectors working in the current mode. In the comparative measurements, done in the same experimental conditions, various samples of BGO, GSO, GSO:Ce,Zr, LGSO, LSO, LYSO, MLS, LaCl3, LaBr3 and CWO scintillators were tested. The measurements covered a determination of the light output, energy resolution, non-proportionality of the light yield, decay times of the light pulses and for the selected crystals their time resolution for 511 keV annihilation quanta. Moreover, a comparative study of afterglow, induced by 60 keV gamma-rays from a strong 241Am source (13.9 GBq), was done in the second range

Presently, a major of detectors for PET systems are based on scintillator crystals read by photomultipliers. In our previous work, a very good time resolution recorded with a 10x10x5 mm3 LSO crystal coupled to a Photonis XP20D0 and Hamamatsu R5320 photomultipliers was shown. Results for both detectors were almost identical and close to 170 ps but their properties such us quantum efficiency of the photocathode and time jitter were significantly different. The XP20D0 possessed high QE and the measured photoelectron number was 40% larger than that of R5320. The R5320 had a time jitter of 140 plusmn 7 ps at FWHM, three times better than that of XP20D0. The fact, that despite of large differences in parameters of the used PMTs a 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 towards to optimize TOF PET systems. Thanks to a close cooperation with Photonis, during last few years we gathered a 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.