The main goal of this STSM is to work on the doping effect on the timing performances of scintillator. On one hand FZU is well experienced in the physics associated to the impurities effects in the energy transfer process. On the other hand the trainee, Gael Patton is preparing a PhD on the role of defect on the memory effects in scintillating materials. Sharing experiences will be a good opportunity for the 2 research groups (ILM and FZU)

STIR is an open source image reconstruction toolkit, well validated by the scientific community.
It is feature-rich and versatile but it doesn’t include the option to reconstruct with TOF information.
The purpose of this STSM is the implementation of TOF reconstruction algorithm which will distribute free in a future version of STIR.The distribution of this feature is going to help numerous researchers in their studies and provide a common background for results sharing.

The feasibility of using colloidal nanocrystals (NCs) to provide sub-100 picosecond response to high energy excitation will be investigated. Toward this end, the photo-response of shape- and composition-controlled NCs including core/shell quantum dots (QDs) and 2-dimensional nanoplates (NPLs) under high energy excitation will be measured.

Performing precise timing measurements of the FlexToT v2 ASIC using the characterization setup at CERN based on the NINO ASIC, taking advantage of equipments which are not available at the home institution nor at national collaborators, such as co-doped LSO:Ce,Ca scintillators and HPTDCs. In particular, the coincidence time resolution (CTR) and the single photon time resolution (SPTR) will be evaluated under different conditions, aiming at precisely characterizing the best possible timing performance of the lexToTv2 ASIC for TOF-PET applications.

The activity aims to verify the influence of the strain/stress on the functional optical properties of the crystal in order to evaluate if the stress state has an effect on the light transport. If this effect is verified, the activity will determine a correlation between stress and optical performances of the crystal in order to characterize this phenomenon.

Timing become crucial feature of detecting systems to be applied in collider experiments. Particularly, it is important for experiments at LHC with high luminosity. Lead tungstate scintillation material is used at two experiments at LHC. So it is important to understand a limit of this scintillation material for fast timing. It is suggested that rise time of scintillation in a low light yield self-activated scintillator is one of the limiting factors for a very fast timing. However, no reliable data of the rise time in PWO are available for the moment. We expect that it is faster in PWO than in a doped scintillator. So, essential of the work plan is to examine different possibilities to measure rise time in the range 20-80 ps . The brainstorming with Colleagues from Vilnius University is also in the plan.

The working plan aims to test the TOF capability of new PET module developed in the frame of the Crystal clear collaboration for the next generation of PET using the TOF-­‐PET Asic developed by the Lisbon group. At CERN the module based on a 64 LYSO:Ce crystals matrix and a MPPC array (Hamamatsu) was tested using a CAEN DT5740 digitizer. The time binning of the digitizer does not allow the realization of time measurements as CTR (“Coincidence Time resolution”) but the TOF-­‐PET Asic can reach this purpose with a time binning of 50 ps. The increase of the time resolution due to the finer time binning reduce the random coincidence rate and this feature makes this kind of device more suitable in PET scanner.

Recently, we started preparation of the series of experiments to measure decay time of scintillation materials by non-linear optics methods. First results are encouraging. It was already found that rise time of PWO at photo-excitation is less than 25 ps, whereas rise time of photo-luminescence of GAGG:Ce depends on wavelength of excitation. During October – November 2015 we performed a set of modeling experiments. Thickness of samples was optimized and new samples were prepared by RINP optical shop. We plan to carry on new measurements during the week from 10th of December 2015. Scheduled activity agreed with Prof. Gintautas Tamulaitis, head of he chair and dedicated laboratory.

Intraband luminescence (IBL) is one of the candidate processes for extremely fast scintillators. This prompt (about 1 ps decay time) emission with a relatively low efficiency (10-5–10-3 eV/eV) is connected with the radiative transitions of hot electrons (e-IBL) or hot holes (h-IBL) between the levels of the conduction or valence band of a crystal, respectively. Despite a low efficiency, this process can be still considered for TOF-PET to provide a time marker for the event. Our recent studies have been aimed at finding the materials with the highest IBL yield and proposing the ways IBL could be utilized for fast timing. All our spectral data were obtained so far at a single experimental setup in Tartu utilizing a high-density electron beam excitation. These data may suffer from the influence of surface effects and needs to be verified using a different experimental technique implementing an excitation method more similar to that in PET. The proposed working plan for the STSM contains the measurement of time and spectral properties of IBL in several popular scintillating materials utilizing pulsed low-density x-ray luminescence setup available in CERN.

Theoretical estimations of the efficiency of intarband luminescence in different crystals. Dependence of intraband luminescence on electron band structure. Treating and discussion of experimental results of excitation of intraband luminescence. Discussion of other possible approaches for achievement of main goals of WG2.

In our group, we have been working on LSO background radiation for attenuation correction (AC) and our results are quite promising [1]. Until this moment, we have applied our approach to the Siemens 3T MR-BrainPET scanner available at our research center, which does not have Time-Of-Flight (TOF) capabilities. Therefore, the transmission and emission measurement cannot be performed simultaneously, but rather sequentially. This is incompatible with clinical practice and can only be done in research facilities. In this STSM, our goal is to apply the developed approach to the GE Signa scanner [2], which has TOF capabilities. For this purpose, we will perform measurements with the LSO background for two different phantoms (cylinder phantom and head phantom) without any activity, but also with activity to evaluate the AC performance. We will also acquire MR images of these phantoms. Furthermore, we will have to convert the acquired data to a format readable by our program, perform the necessary corrections and reconstruct the data. We will perform different pre-processing of the data: random correction, sinogram compression, bin calculations and reconstruction to evaluate the best processing pipeline. We will also evaluate the acquisition time necessary for obtaining a reasonable attenuation correction map.

In our group, we have been working on LSO background radiation for attenuation correction (AC) and our results are quite promising [1]. Until this moment, we have applied our approach to the Siemens 3T MR-BrainPET scanner available at our research center, which does not have Time-Of-Flight (TOF) capabilities. Therefore, the transmission and emission measurement cannot be performed simultaneously, but rather sequentially. This is incompatible with clinical practice and can only be done in research facilities. In this STSM, our goal is to apply the developed approach to the GE Signa scanner [2], which has TOF capabilities. For this purpose, we will perform measurements with the LSO background for two different phantoms (cylinder phantom and head phantom) without any activity, but also with activity to evaluate the AC performance. We will also acquire MR images of these phantoms. Furthermore, we will have to convert the acquired data to a format readable by our program, perform the necessary corrections and reconstruct the data. We will perform different pre-processing of the data: random correction, sinogram compression, bin calculations and reconstruction to evaluate the best processing pipeline. We will also evaluate the acquisition time necessary for obtaining a reasonable attenuation correction map.

The EU-project PALADIN (positron annihilation detection beyond the limits, ref. nb. 659317) aims to overcome present technological limits and pushing time resolution beyond current limits. Therefore, a new detector based on monolithic scintillation crystals combined with digital photon counter (DPC) arrays is being designed. The future detector will be incorporated in a PALS setup at the Reactor Institute at TU Delft and used for TU Delfts materials research on renewable energy. Hence, the detector performance will be investigated for application in clinical TOF-PET devices allowing to go beyond state-of-the-art spatial and temporal resolution. This short term scientific mission of approximately two weeks will mainly serve to acquire practical knowledge of the experimental set up for the researcher Florian Dachs. This will help him for his master thesis project to develop a detailed simulation using GEANT4 with the goal to investigate the characteristics of the detector system. Besides acquiring knowhow of the detector system, the problem of self triggering due to photo emission during cell recharge will be investigated experimentally and a strategy for minimizing this effect should be found during the STSM. Apart of the scientific value, the STSM will also allow to get to know the partner-team at TU Delft in person, which will strengthen the team-spirit of the collaboration.

Light production, transport, transmission and absorption in scintillating crystals are related to optical properties like the refractive indices. Refractive indices variations and distribution can be induced by defects, stress condition and orientation of the optic indicatrix. Some setups have been arranged at CERN in order to observe crystal condition and to induce stress distribution during luminescence properties measurements. Since the results from the previous STSM at CERN are encouraging, the activity aims to test more deeply the influence of quality and stress conditions to luminescence performances of the scintillating crystals by means of the arranged measurement benches.

In the framework of the CT-PPS project the LIP group is pursuing a new version of the TOFPET chip suitable for the PPS timing detectors. A necessary step in this project is the design and test of the front-end part of the chip, which includes the amplifiers and discriminators, adapted to the Ultra Fast Silicon Sensors. The objective of the present STSM proposal is precisely the development of a new version of the front-end suitable for the UFSD. The design has to take into account the different characteristics of the silicon signal, in particular the fact that the typical signal charge is about 1 fC (100 times smaller than the 1 p.e. signal provided by SiPMs) and the very fast rising time of the signal. A new preamplifier stage adapted to the TOFPET2 input could be a possible solution, but other solutions are also being exploited. The development of circuits with the capability to provide time measurements with excellent resolution is one of the main motivations of the WG4 in the FAST network.

Tahereh Niknejad is presently preparing a PhD at the Instituto Superior Técnico, Lisbon. The research work is done in close collaboration with the company Petsys Electronics. For here project she needs to reconstruct images form a technical prototype PET scanner. The challenge is to take advantage of the excellent time resolution made possible with SiPMs, and to demonstrate the corresponding improved image resolution.

The scintillating crystals are the fundamental components of high energy physics calorimeters and PET. Light production, transport, transmission and absorption are related to the different crystal species by means of the refractive indices. The optic indicatrix summarize the optic crystal behavior determining the the refractive indices by the Dielectric Impermeability tensor. Refractive indices variations and distribution can be induced by defects, stress condition and orientation. Luminescence properties measurements of crystals submitted to induced stress distribution and as a function of orientation are mandatory to test the light efficiency and decay time.

Experimental studies of the decay kinetics of Ce3+ emission in the mixed crystals of complex oxides. Evaluation of Ce3+ emission rise time modification throughout the set of mixed crystals. Treating and discussion of the obtained experimental results. Discussion of other possible approaches for achievement of main goals of WG2.

Experimental studies of the decay kinetics of Ce3+ emission in the mixed crystals of complex oxides. Evaluation of Ce3+ emission rise time modification throughout the set of mixed crystals. Treating and discussion of the obtained experimental results. Skills acquisition in carrying out of the experiments to measure the fast decay kinetics using the X-ray source with ps time resolution.

1. Measuring of photodetection and timing properties of the KETEK SiPMs with different sensitive area by using of variable connection schemes in order to select of the optimum SiPM type and readout way for TOF PET application.
2. Implementation of differentiation pulse technique for improving of SiPM+scintillator crystal timing resolution. Selection of the best fast amplifier for usage with wide bandwidth digital scope as a reference setup.
3. Development and implementation of the dedicated algorithm for digital processing with data from single detector obtained by using wide bandwidth digital scope. Data analysis with ROOT.
4. Selection of the fast scintillator and its geometry. Two possible candidates are LYSO and GAGG scintillator crystalls.
5. Development of a prototype module for TOF PET application on the basis of KETEK SiPMs and PETsys TOF ASIC evaluation kit (http://www.petsyselectronics.com/web/ ) with two identical detectors’ arrays.
6. Experimental study of the developed TOF PET module with Na-22 source.

Detailed characterization of luminescence properties, especially decay measurement in very wide time range from 100 ps to ms, were realized for ZnO:Ga‐SiO2 composites, ZnCd(Mg)O solid solutions and LPE made multicomponent garnet thin films.

Sufficient difference in Free Carriers Absorption mechanisms is recognized in YAGG and GAGG doped with Ce crystals.

The new FBK SiPMs has been tested with the ASIC “STiC, designed for “EndoToFPET-US”, performing single-photon time resolution (SPTR) measurements. We employed a pulsed laser and the ASIC has been used with particular settings to obtain each threshold crossing time. The first results are relatively promising: it is the first SPTR measurement of FBK SiPM using a full integrated ASIC. With a 1x1mm2 FBK NUV SiPM we obtained s~60 ps, which include the laser pulse width and all the noise contributions.

An 8-by-8 mm² LG-SiPM prototype has been already developed by the FBK. Miniature monolithic crystals are provided by Forschungszentrum Jülich GmbH. With the existing hardware, proof-of-concept study for LG-SiPM 8-by-8 mm² coupled to monolithic scintillators based detectors can be characterized can be performed. First feasibility measurements should demonstrate the possibility to identify the x- and y-position of the scintillator event inside a monolithic 8-by-8-by-3 mm³ crystal. If x and y positions can be determined, the scintillation detector will be characterized for its spatial, energy and timing resolution. Results from simulations that have been run at the Foprschungszentrum Jülich GmbH during the year 2015 were very promising and encourage us to proceed with measurements. The measurements should take place at FBK. In advance, the measurement will be prepared in cooperation between FBK and Forschungszentrum Jülich GmbH. The total measurement time is planned for 5 days. The first day is for preparing the final measurement setup. During the second and third days, the previous prepared position algorithms will be applied to characterize the position-encoding of this detector setup. This is a necessary step for the fourth and fifth days, where the energy and timing resolution measurements are planned. Measurements of energy resolution, spatial resolution and timing resolution are planned for 3 typical positions in the plane of the entrance window (i.e. center, corner, center of border) The results of these measurements should be published in paper providing a full characterization of the new 8-by-8 mm² LG-SiPM prototype coupled to monolithic crystal. Further work to be performed after this feasibility study include a full characterization of this type of scintillation detector, the comparison of detector performances of the 8-by-8 mm² LG-SiPM between the monolithic and a pixilated detector setup. Especially the comparison of the timing resolution is an important result for FAST. If the indented scintillation detector design is feasible, it would be a very interesting detector concept for high spatial resolution and high sensitivity small animal PET inserts for simultaneous preclinical PET/MR imaging.

My objective is to develop a comprehensive model of a spectrometric chain using a Silicon photo-multiplier (SiPM) to be integrated in the C++ digitizer module of the Monte Carlo simulation platform GATE. Once validated, this development will be released within the GATE public version. The team at CERN has a long expertise in SiPM operation and characterization. Thus, the objective of this second short-term scientific mission (STSM) of two weeks will be to assess against experimental measurements performed at CERN the simulation results from the C++ modules that would have been developed in Marseille following the first STSM spent at CERN.

I was shared experiences and knowledge about chemical technology of glass, development and preparation of new scintillation glasses and glass ceramics on the basis of inorganic glass matrix co-doped by cerium, dysprosium and europium. It was studied luminescence kinetics glasses and glassceramics.

Luminescent and kinetics properties of garnets doped Ce(III)-ions with partial introduction of bivalent and tetravalent elements in lattice were studied. The results are interesting for understanding future modification of garnets with purpose to improve their scintillations properties.

An 8-by-8 mm² LG-SiPM prototype has been already developed by the FBK. Monolithic crystals can be provided by Forschungszentrum Jülich. With the existing hardware, the LG-SiPM 8-by-8 mm² monolithic based detectors can be characterized. The measurements should take place at FBK. The measurement will be prepared in cooperation between FBK and Forschungszentrum Jülich in advance. The planned measurement time in total is planned to be 5 days. The first days are for preparing the measurement setup. During the last days, the measurements will take place. An option is to let advanced measurements run after leaving the FBK, depending on the availability of the measurement setup. The results of these measurements should be published in paper providing a characterization of the timing resolution of the new 8-by-8 mm² LG-SiPM prototype coupled to monolithic crystal.

LuAG:Ce garnets with partial substitution of Lu3+ and Al3+ ions onto Ca2+ and Ge4+ ions respectively were obtained with using co-precipitation method. Their structural and luminescent properties were studied.

It was developed scintillation glasses and glass ceramics on the basis of inorganic glass matrixes Li2O-SiO2, CaO-SiO2, SrO-SiO2, BaO-Al2O3-SiO2 and co-doped by cerium, europium, dysprosium and terbium ions in the different molar ratio. The effects of rare earth ions upon spectral and luminescent properties of the glasses and glass ceramics were established. The optimal ratio of the rare earth oxides was determined for the scintillation glasses. It was exchanged experiences on researching physico-technical properties glass and glass ceramics.

Spectral-time resolved measurement using streak camera
Testing various matrices: PS, PVA, SiO2 (lead glass substrate)
Coincidence time resolution measurement using 511 keV on ZnO:Ga-PS / LYSO sandwich samples

Major result: The energy level diagram of GAGG crystal, solely doped with Ce and codoped with Mg was developed. Future plans: To consider possibilities to increase an efficiency of the retrapping mechanism to increase light yield in complex garnet systems at simultaneous keeping the fast rise time. Publication(s) or Presentation(s) or submission(s): Draft of the article for submission to Journal of Luminescence is prepared. We expect to submit it before end of December 2016.

Scintillators are critical for the behavior of medical devices; their structural condition and quality affect the response of the entire medical system. Luminescence performances, light production, transport, energy resolution and sensitivity, could be affected by the structural, defectiveness and stress condition as well as the aging of the crystal. Cross measurements between the light response of the crystal coupled with devices like Position Sensitive Photomultipliers or Silicon Photomultipliers and non-destructive photoelastic observation, could give additional information in order to characterize deeply the crystal and the medical system. In addition an evaluation of the magnitude of the influence of the crystal structural quality condition and stress distribution on the performances of the system could be carried out. The activity is intended to be not only a measurements based STSM but also a training activity, so to give the opportunity to exchange knowledge and experience about the fields involved in the scientific mission. In fact, in parallel with the measurement campaigns, training period about the laboratory session and the simulation tools have to be provided. The outcome of this STSM could be a better understanding of the influences of the crystal condition on its response in terms of energy resolution and sensitivity and the acquisition of experiences and knowledge by both the scientific groups (Ancona and Athens).

The major task and objective for this exchange is to practice on existing 4D reconstruction algorithms in particular Patlak plots on existing simulated data on a cylindrical geometry, and to get familiarized with the STIR framework and its relevant classes. Time permitting, the second objective is to start using orthogonal temporal basis functions for the estimation of kinetic parameters instead of a B-spline basis in the current 4D reconstruction process. Since the activity distribution in the body is ruled by systems of differential equations involving compartmental models, using spline wavelets in combination with spatiotemporal regularization in dynamic PET imaging would be advantageous over conventional B-spline wavelets in modelling TACs.

To investigate the luminesce kinetics and scintillation properties of the glass and glass ceramics for fabrication of scintillation materials based on inorganic glass matrix SiO2–SrO, SiO2–SrO-Gd2O3, SiO2–SrO-Y2O3 and co-doped by cerium, terbium and europium. • Optimize compositions of inorganic glass matrix. Optimize heat treatment conditions, glass-ceramics. To share experience and knowledge about scintillation glasses and glass ceramics.

Recently, in a collaboration with Prof. G.Tamulaitis group from Vilnius University, we disclosed some processes which are in charade for the development of excitation in Gd based and multi-ion co-doped GAGG crystals. We are in progress to prepare samples of the GAGG garnet crystals with multi doping and hope to start measurements in the Vilnius University in the third decade of January 2017. Results to be obtained may have a crucial impact on the future development of GAGG technology and its implementation in medical imaging. We plan to carry on the measurements of new samples during two weeks

TOFFEE is an ASIC developed to achieve timing resolution in the order of few tents of picoseconds for signals in the order of 10fC, from sensors with capacitance up to 15pF. TOFFEE was received in October 2016, and the first tests done on the ASIC without sensors connected, confirmed the design characteristics. These tests were conducted with a dedicated board for test purpose.
New tests are foreseen in January 2016 on a board integrating both the TOFFEE and UFSDs. These detectors are silicon detectors with internal gain for proton detection. The tests will be conducted with a setup composed by a infrared LASER capable to emulate the energy deposition of a MIP in silicon.
A resolution as good as 40ps is expected for signals of 8fC, with capability to remove time walking for signals in the range from 5fC to 30fC.

The proposed working plan for the STSM contains the measurement of spectral-decay properties and yield of IBL and other emissions in the materials of APb2X5 family, as well as some other materials promising for fast timing – the oxyfluoride crystals of ABOF (A = K,Rb, B = W,Mo,Ti) family and complex fluoride crystals with radiation-modified crystalline structure.

In the frame of the STSM we will focus on the checking possibility of obtaining complex compounds with garnet structure with partial substitution of Y3+ and Al3+ ions for Sn(II) and Sn(IV) ions respectively. We are planning to use only Sn(II) salt as a reactant. Using of Sn(II) salt as a reactant has a several purposes:

• check the possibility of using coprecipitation method for obtaining Y3-xSn(II)xAl2-xSn(IV)x(AlO4)3:Ce (x value up to 1.5) garnets and study their structural properties;
• study luminescence properties of Y3-xSn(II)xAl2-xSn(IV)x(AlO4)3:Ce (x value up to 1.5) samples;

Due to of the strong reducing properties of Sn(II) ions, they must to protect the Ce3+ ions from oxidation at precursor annealing on air. Furthermore, using of Sn ions can allow to increase the red emission in garnets, that have a practical interest.

TOFFEE is an ASIC developed to achieve timing resolution in the order of few tents of picoseconds for signals in the order of 10fC, from sensors with capacitance up to 15pF. TOFFEE was received in October 2016, and the first tests done on the ASIC without sensors connected, confirmed the design characteristics. These tests were conducted with a dedicated board for test purpose.
New tests are foreseen in January 2016 on a board integrating both the TOFFEE and UFSDs. These detectors are silicon detectors with internal gain for proton detection. The tests will be conducted with a setup composed by a infrared LASER capable to emulate the energy deposition of a MIP in silicon.
A resolution as good as 40ps is expected for signals of 8fC, with capability to remove time walking for signals in the range from 5fC to 30fC.

Experimental studies of the influence of Ca, Zr and Sc co-dopants on the band structure as well as luminescent and decay characteristics of GAGG:Ce single crystals will be carried out. We expect to obtain the decrease of Ce3+ emission decay time and to prevent considerable suppression of the light output.

SiPM-devices produced with different technologies without package (chips) from KETEK shall be irradiated with different gamma doses at the National Institute for Laser, Plasma and Radiation Physics in Romania. During the STSM Andrei Stancalie will evaluate similar devices both irradiated and non-irradiated in order to compare the radiation induced effects on the operating parameters of various SiPMs.

Recently, in a collaboration with Prof. G.Tamulaitis group from Vilnius University, we developed energy level diagram for electronic excitation transfer in GAGG:Ce and GAGG:Ce, Mg crystals. We also have prepared detailed article about transfer processes in this crystal and going to submit it early in February 2017. On the other hand, we got an impression that there is a general feature of the excitation transfer at codoping of Ce doped crystals with Mg or Ca. To prove this concept we decided to carry on research of another class of the materials, namely oxyorthosilicate LSO:Ce, codoped with Ca. Also, investigation of the GAGG with different concentrations of Mg and Ce will be performed.

The STSM work will be focused on the STIR reconstruction algorithm for PET module with depth of interaction and timing capability. The first part of the study will be centered on the calculation and the method to obtain the coefficients for the component based normalization. The second part of the work will go into the details of the STIR reconstruction with particular attention to the method to store data and to find the best procedure to obtain reconstructed images starting from experimental measurements.

The purpose of this visit to Fondazione Bruno Kessler (FBK) will be the study of the timing characteristics of different scintillation crystals, such as cerium doped gadolinium gallium garnet (Gd3Al2Ga3O12:Се, GAGG:Ce) single crystals codoped by magnesium and cerium doped yttrium aluminium garnet (Y3Al5O12:Ce, YAG:Ce). Measurements will be performed using the coincidence timing technique. This technique, as performed in FBK, involves using a 22Na radioactive source to simultaneously produce two 511 keV photons in opposite directions and two identical gamma detectors, each composed of a scintillator crystal under study, a SiPM and a signal amplification circuit, to detect the emitted photons. As the photon pairs are always produced at the same time, the difference in detection times indicates the timing characteristics of the detector. The comparison of the results obtained during this STSM with those obtained in the previous STSM will allow us to describe the influence of different production techniques on the timing characteristics of the GAGG:Ce,Mg crystals. Comparison of new coincidence timing measurement results with time-resolved photoluminescence spectroscopy and nonlinear optical pump-probe femtosecond response measurements performed in Vilnius University will allow us to improve our understanding of the underlying charge transfer mechanism in garnet crystals.

The cerium-doped lutetium oxyorthosilicate Lu2SiO5:Ce (LSO:Ce) is one of the most widely used scintillators in medical imaging devices. We have recently submitted a paper revealing the mechanisms through which codoping of Ce-doped scintillation single crystals by divalent alkali-earth ions influences the luminescence band scintillation properties of these materials. The study at Giessen will be aimed at investigating the temperature dependence of the response function of LSO based detectors. Measurements will be performed at temperatures from -45 ºC to 20 ºC, at different time intervals. We will gain information about the influence of temperature on charge transfer properties of LSO crystals, the role of various defects and the importance of different growth conditions on LSO:Ce scintillator properties. The data that would be obtained in Giessen will complement our previous research and lead to a better understanding of the excitation transfer processes in orthosilicates.

Total body PET leads to a much higher image quality but also a huge increase of data when imaging at equal dose as the current PET-CT studies. Therefore it is more appropriate to apply fast and accurate rebinning methods before reconstruction. These methods will be developed using Monte Carlo simulations of the compact total body PET20.0 design proposed by UGent and VUB. The goal is to achieve close to real time reconstruction, so the aim is to do reconstructions as fast as the acquisition of a total body PET scan in PET 20.0. The current estimate is 20% sensitivity and total body images should be acquired in about 20 sec. Therefore fast methods with simple algorithms as proposed in one of the papers by the promotor of this STSM will be tested for this geometry.

Colloidal semiconductor nanocrystals with suppressed Auger recombination have proven to be a promising source of prompt photons under pulsed X-ray excitation. Previous studies have concluded in a sub-100ps effective decay time for CdSe 2D nanoplatelets (NPLs) and sub-1ns for CdSe/CdS giant shell quantum dots (GS QDs) with an estimation of around 500 and 1000 photons per 511 keV energy deposition distributed within the first 100ps, respectively. The multiexcitonic dynamic present in these systems under ionizing radiation is partially understood at the level of excitonic and biexcitonic emission. However, a red shift of 50 meV for the CdSe NPLs and a blue shift of 82 meV for CdSe/CdS GS QDs points towards higher order multiexcitonic generation with the possibility of excited-state for the quantum dots case or hot intraband luminescence (IBL). The potential presence of IBL in the emission spectrum of nanocrystals could be also a channel contributing to the fast component exhibited by these materials.
In this work the emission kinematics of CdSe NPLs and CdSe/CdS GS QDs under electron and X-ray excitation will be further studied in order to determine the IBL contribution to NPLs/QDs emission. The high dynamic range of the pulsed cathodoluminescence setup based at the Institute of Physics, University of Tartu will allow the determination of possibly longer decay components present in these materials under X-ray excitation. This is especially interesting for the GS QDs. This study is particularly important for the understanding of light emission processes in materials with high quantum confinement in one or three directions.

Summary Working Plan (250 words) The emergence of new solid-state avalanche photodetectors, e.g. SiPMs, with unprecedented timing capabilities opens new ways to profit from ultrafast and prompt photon-emission in scintillators. In time of flight positron emission tomography (TOF-PET) and high energy timing detectors based on scintillators the ultimate coincidence time resolution (CTR) achievable is proportional to the square root of the scintillation rise time, decay time and the reciprocal light yield, CTR ∝ √(τr*τd/LY). Hence, the precise study of light emission in the very first tens to hundreds of picoseconds is indispensable to understand time resolution limitations imposed by the scintillator. At CERN we found two rise time components in L(Y)SO:Ce, the first below the resolution of our setup <10ps and a second component being ~300ps. Co-doping with Ca almost completely suppresses the slow rise component leading to a very fast initial scintillation emission with a rise time of <10ps.
The pulsed cathodoluminescence setup based at the Institute of Physics, University of Tartu will allow the precise measurement of this long rise time components for various temperatures and excitation energies. This will be particularly important in understanding the exact nature of the scintillation rise time in state-of-the-art fast scintillators commonly used in TOF-PET and their possible improvement for fastest timing. The setup at Tartu will further allow estimating the hot-intraband luminescence yield, which will be compared to the prompt photon yields measured at CERN. For these studies an ID-Quantique photon detector will be brought, installed and tested in single photon counting mode at Tartu.

During our previous STSM, we demonstrated the possibility of obtaining complex oxide compounds with garnet structure and composition Y2Ca(Mg)AlGe(AlO4)3: Ce. It is important that germanium is one of the glass forming elements, and its high percentage in the garnet structure looks promising in view of forming glass ceramics based on the complex substituted garnets. Glass ceramics have a number of advantages in comparison with single crystals: easy obtaining and handling, inexpensive production, environment friendliness. In this STSM mission we propose to check the possibility of obtaining the glass ceramics based on complex substituted garnets Y2CaAlGe(AlO4)3:Ce and Y2MgAlGe(AlO4)3:Ce. We plan to use the Y2O3-Al2O3-SiO2 system as a glass matrix. Furthermore, using GeO2 should allow for decreasesing the temperature of glass formation, while Ca2+ (Mg2+) ions can used for fine tuning of the optical properties of the obtained glass ceramics. Understanding the main aspects of obtaining glass ceramics based on the compounds with garnet structure is important for future development of inexpensive and effective scintillation materials based on them.

SiPM-devices produced with different technologies with and without package (chips) from KETEK shall be irradiated with different doses of ionizing radiation at the National Institute for Laser, Plasma and Radiation Physics in Romania. The radiation type will vary between X-Ray, electron beam and protons. During the STSM, Andrei Stancalie will evaluate similar devices both irradiated and non-irradiated in order to compare the radiation induced effects on the operating parameters of various SiPMs.

1. Investigate the luminesce kinetics and scintillation properties of the glass ceramics based on MO–SiO2 (M = Sr, Ba) system doped by cerium, terbium and europium ions which fabricated at two thermal treatment cycles.
2. Compare structural and photoluminescence properties of glasses and achieved glass ceramic materials and optimization the compositions of glass matrix.
3. Establish optimal thermal treatment conditions of glasses for obtaining glass ceramics with higher emission efficiency.
4. Determinate of the optimal ions of the rare earth elements as doping atoms in glass ceramics.

Scintillators are critical for the behavior of medical devices; their structural condition and quality affect the response of the entire medical system. Luminescence performances, light production, transport, energy resolution and sensitivity, could be affected by the structural, defectiveness and stress condition as well as the aging of the crystal. Cross measurements between the light response of the crystal coupled with devices like Position Sensitive Photomultipliers or Silicon Photomultipliers and non-destructive photoelastic observation, could give additional information in order to characterize deeply the crystal and the medical system. The results from the previous STSM have highlighted, qualitatively, some differences in the samples population from the photoelastic point of view. It would be interesting to deepen the analysis of these differences and verify how they can affect the functional yield of the scintillators by means of possible measurements which define the scintillator response.

We propose to investigate the effect of Сe4+ and Mg2+ ions on the luminescence decay phenomena in glass ceramics of garnet-dased materials. It is well known that glasses and glass ceramics materials might be remelted many times. Moreover, each remelting does not lead to any change in the composition of the glass, but, in the case of luminescent glasses, leads to oxidation of rare-earth ions. By studying garnet-based glass ceramic materials we found that after remelting of the initial glasses in air they become yellowish. One of the reasons of the coloration change might be linked with an increase Ce4+ concentration in the glasses. Therefore, we propose to obtain glass ceramics from Ce4+-rich glasses and investigate the peculiarities of the photoluminescence decay in these garnet-based glass ceramic materials. It is expected that the garnet composition in glass ceramics will be close to Y2MgAlGe(AlO4)3: Ce3+, Ce4+.

The STSM work will be focused on the implementation and evaluation of a dual head PET for simultaneous nuclear imaging during hyperthermia. Aim of the host, is the development and optimisation of high resolution PET detectors capable of providing insights in the biological process that occur when NPs are heated and thus monitor the successful organ targeting, drug release and/or real time response to therapy.
During the STSM, the development and evaluation of a dual head PET system for use inside the coil of hyperthermia system will be performed. The PET detectors will be based on SiPMs which are insensitive to magnetic fields. Transfer of technology as well as collaboration in terms of software reconstruction will be will be carried out during the STSM between the host and home institute.
During the first days installation of the PET system will be held. Evaluation tests then will be performed to confirm system's capabilities. Measurements in coincidences will be carried out for initial characterisation of the system and then the detectors will be placed inside the magnetic field to verify their insensitivity. Efthymios Lamprou will learn on BGO technology but also train the team at BET for data acquisition system that Efthymios has developed. Efthymios we be trained in the evaluation process and PET focal plane algorithms.
The present STSM work will be the first step in the construction of a PET system specially designed for simultaneous nuclear imaging during hyperthermia treatment providing the possibility to monitor the successful organ/tumor targeting, drug release and real time response to therapy. We consider that this projects fits perfectly the approaches of WG5 Cost Fast Action.

Inorganic wide gap crystals doped with trivalent cerium and especially praseodymium ions are candidates for fast scintillators. The d-f luminescence of such crystals is characterized by a decay time from one to several tens of nanoseconds, in addition, the yield of d-f luminescence in the UV region can be rather high.
The proposed working plan for this STSM contains the measurements and study of spectral properties, build-up dynamics and decay kinetics of pulse cathodoluminescence and pulse photoluminescence in VUV-UV-VIS emission regions in the materials of complex crystals doped with Pr3+ and Ce3+ ions as well as some other materials promising for fast timing. The main objects of research are crystals of complex phosphates, borates and some silicates doped with Pr3+ or Ce3+ ions. Preliminary studies of stationary X-ray excited luminescence indicate in these crystals a high yield of d-f emission in the UV region at room temperature. To evaluate these materials for fast scintillation applications the decay time, rise time and relative cathodoluminescence yield will be determined.

Aim of the study is to make measurements of FCA of YAP:Ce and to correlate them with the results of the CTR measurements. Workpan includes samples preparation, adaptation of the equipment for measurements, measurements of YAP:Ce samples at different pump. Selection of the samples for CTR measurements in at BKF, Trento.

1. Electrical and optical characterization of β-Ga​2​O​3:Ce crystals, which yield a candidate for a new fast and efficient scintillator, grown at LICG, will be performed.
2. Although it is possible to observe scintillation from all three states of matter, the today’s scintillator market is dominated by inorganic solid state materials, the majority of which are wide bandgap insulators. Semiconducting scintillators have also been considered, but they have received much less attention so far. Such a situation, however, is likely to change rapidly, since it seems that a properly developed semiconductor could offer both an extremely high light output and a very short decay time. Therefore the proposed study on β-Ga2O3:Ce has a real chance to contribute to the action goals by introducing a new fast semiconductor scintillator.
3. Techniques:
   • Hall​​ effect​​ measurements​​ with​​ a​​ Lake​​ Shore​​ HMS​​ 7504
   • capacitance-voltage measurements with a C-V Boonton 7200 Capacitance Meter and a HP 4284A LCR Meter
   • deep​​ level​​ transient​​ spectroscopy​​ with​​ a​​ DLTS​​ BioRad​​ DL8000
   • optical​​ transmittance​​ in​​ the​​ range​​ of​​ 200-2500​​ nm​​ with​​ a​​ Lambda​​ 19​​ Perkin​​ Elmer​​ spectrometer
   • photoluminescence​​ measurements​​ with​​ a​​ Horiba​​ Jobin​​ Yvon​​ HR​​ 800​​ spectrometer
4. ​Electrical​ and optical​ characterization​​ of​​ β-Ga​2​O​3​:Ce​​ crystals

In the field of fast timing research, wide band gap semiconductors synthesised as colloidal nanocrystals have proven to be a promising source of prompt photoemission. Materials studied so far are CdSe based nanoplatelets and CsPbBr3 nanocrystals, both of them presenting a fast decay component of the order of 300ps under laser excitation and an even faster component of ~ 25ps when excited with ionizing radiation. Harvesting these fast decay components for the purpose of radiation detection constitutes a major challenge that our group is trying to overcome by embedding the nanoparticles in a solid host. The purpose of the host apart from providing mechanical stability is to facilitate the energy transfer between the incoming ionizing particle and the nano-phase. Previous trials embedding NPLs in polystyrene concluded in the partial degradation of the luminescent properties, which lead to a CTR result of 370ps. The first objective of this STSM would be to learn how to synthetize large amounts of CdSe nanoplatelets, either bare or core-crown and study how to properly embedded them in a suitable host. Measurement of their radioluminescent spectral-timing properties would also be done within the same group using a pulsed X-ray tube and a set of spectral filters. A feasibility study to implement some features of the mentioned readout chain into the CERN ‘s setup would be also consider in order to improve the signal-to-noise ratio of our X-ray excited data.

The purpose of this visit to Fondazione Bruno Kessler (FBK) will be the study of the timing characteristics of different scintillation crystals, such as cerium doped gadolinium gallium garnet (Gd3Al2Ga3O12:Се, GAGG:Ce) single crystals codoped by magnesium and cerium doped yttrium aluminium garnet (Y3Al5O12:Ce, YAG:Ce). Measurements will be performed using the coincidence timing technique. This technique, as performed in FBK, involves using a 22Na radioactive source to simultaneously produce two 511 keV photons in opposite directions and two identical gamma detectors, each composed of a scintillator crystal under study, a SiPM and a signal amplification circuit, to detect the emitted photons. As the photon pairs are always produced at the same time, the difference in detection times indicates the timing characteristics of the detector. The comparison of the results obtained during this STSM with those obtained in the previous STSM will allow us to describe the influence of different production techniques on the timing characteristics of the GAGG:Ce,Mg crystals. Comparison of new coincidence timing measurement results with time-resolved photoluminescence spectroscopy and nonlinear optical pump-probe femtosecond response measurements performed in Vilnius University will allow us to improve our understanding of the underlying charge transfer mechanism in garnet crystals.

We propose performing the study of luminescence properties of a set of rare earth doped arsenate crystals. Compounds based on AsO4 complexes have been earlier synthesized, however, to the best of our knowledge their luminescent properties remained practically unstudied. Lutetium and yttrium arsenates belong to the chernovite structural type (zircon type compound) while lanthanum arsenate is isostructural with monazite [1,2]. The studies of arsenates were mainly devoted to the determination of elastic constants [3], possibilities to grow single crystals [4], structural properties [5]. Raman spectroscopy and infrared reflectivity study were applied to determine the vibrational modes [6,7]. Only the luminescence properties of Eu3+ ions were studied in some of arsenates so far [8,9,10]. LuAsO4 is a relatively dense compound (6.92 g/cm3) that is favorable for its application as a scintillator. In particular, Ce3+ doped crystals may be considered as some fast scintillators if the Ce3+ emission is possible in arsenates in principle, i.e 4f and 5d Ce3+ states are located in the bandgap. To the best of our knowledge there is no literature data on the luminescence properties of Ce3+ ions in arsenates. Preliminary studies of the Ce-doped arsenates at the home institution have shown that LuAsO4:Ce and LaAsO4:Ce are characterized by an intensive emission band peaking around 410-430 nm at 300 K. The excitation bands have been found at 360, 300 and 240 nm. The luminescence is stable in a wide temperature region, and is partially quenched at 300 K. The studies of the nominally undoped LuAsO4 have shown that the emission at 410 nm is observed as well. However, its intensity is by one order of magnitude lower than in Ce doped sample that may be connected with the presence of traces of Ce3+ in the nominally undoped sample. Moreover the corresponding emission band has not been observed in YAsO4:Ce that is tentatively attributed to the lower bandgap value of YAsO4 and possibility of thermal ionization of 5d(1) Ce3+ state at 300 K.
Therefore, we suppose that we really observe the emission of Ce3+ ions in lutetium and lanthanum arsenates. It makes arsenates an interesting object of study as a fast scintillator. The studies of decay characteristics of LuAsO4:Ce are not available at home institute and motivate us to submit the current application for STS mission. Fundamental tasks such as the determination of the bandgap values and estimation of the energy transfer efficiency from the host to the Ce3+ emission centers are also in scope of the proposed work program. It requires the experimental setup with excitation in VUV spectral region that is also available in the host institute.

PETsys has developed an ASIC (TOPFET2 ASIC) and a complete readout system designed to digitize and store data originated from Silicon PhotoMultipliers (SIPMs) for time of flight PET. Over the last year, I performed extensive tests of the system reading signals generated by the interaction of gamma rays with scintillation crystals coupled to Silicon Photomultipliers (SIPM). In particular, considering PET applications, the results for coincidence time resolution and energy resolution has been measured for a series of SIPM models and various LYSO crystal configurations.
The purpose of the short term scientific mission in the CERN crystal clear group is to perform new measurements of timing performance of the TOFPET ASIC together with Dr. Stefan Gundacker, who has a large experience and extensive record of published results obtained with different SIPMs coupled to different fast scintillation crystals. CERN group uses a different electronic readout system, based on a different ASIC (NINO chips) and amplification and discrimination method. The goal of this STSM is to compare the impact of both electronic readout systems on the time coincidence resolution of scintillator detectors composed of the most recent SIPM models and fast scintillator crystals available. The experimental setup and data analysis methods used by both groups will also be compared and discussed.

1. Aim and motivation.
   The goal of the proposed research is to combine renowned luminescent properties of rare-earth compounds with exceptional properties of diamond such as chemical stability, high conductivity and radiation hardness by creating composite materials using nanoparticles of rare-earth compounds embedded into CVD or single crystalline diamond. Such composite materials can be used for monitoring radiation from free-electron lasers and in other cases, when the detection of high-flux radiation is required. Experimental studies of cathodoluminescence of prepared composite materials including time-resolved fluorescence spectra and kinetics are envisaged. For the samples with reasonable fluorescence yield excitation spectra measurements are to be performed.
2. Proposed contribution to the scientific objectives of the Action.
   Superfast timing relies on the hot intraband luminescence (HIL) and a lot of compounds have been tested within this action. Most of them were ionic crystals, while diamond is a covalent one, thus it will allow to extend the studies to the family of covalent materials.
3. Techniques
   There is a wide range of fields interested in luminescent diamonds: quantum information technologies; optical biomarkers, and scintillators (X-ray beam monitors). Intense hard x-ray pulses at high repetition rates of >100 Hz at new generation light sources such as x-ray free-electron lasers or insertion devices at 4th generation storage rings formulate new requirements to the scintillators to be used to monitor their radiation: fluorescence decay time faster than 1 ns; low Z, exceptional radiation hardness and high thermal conductivity to withstand intense hard x-ray pulses at high repetition rate. The known fluorescence properties of the impurity-vacancy centers in diamond are quite suitable for engineering single photon emitters, however the search for new and better photoluminescence sources in a diamond matrix is still an ongoing activity. Quite recently a few successful attempts to incorporate europium ions into the diamond matrix were reported. They look quite encouraging for the development of new fast low-Z scintillators to be used at new XFEL sources for "static" measurements, however for time-resolved ones it would be interesting to use cerium.
   During suggested session of measurements we plan to address the following problems:
   1. To investigate the effect of nanoparticle size on the luminescence spectra and kinetics in Eu- and Ce-doped diamond films.
   2. To investigate the origin of substantial changes in the luminescence spectra of Eu-doped diamond nanocomposites after covering the layer of EuF3 nanoparticles with a diamond layer.
   3. To study the difference of fluorescence properties of nanocomposites with CVD and single crystalline diamond.
   4. To investigate fluorescence properties of nanocomposites using several cerium compounds.
   5. To investigate temperature dependence of the luminescence of chosen nanocomposites.
   The main technique to be applied is time-resolved cathodoluminescence.
4. Planning
   
   1. To use the electron gun of the Institute of Physics, University of Tartu to study cathodoluminescence spectra and kinetics in a wide time range from picoseconds to milliseconds to address the following questions:
      1. The effect of the specific rare-earth compound used for the fabrication of a nanocomposite on the fluorescence spectra and kinetics;
      2. The effect of the size of the rare-earth compound nanoparticle used for the fabrication of a nanocomposite on the fluorescence spectra and kinetics;
      3. To study fluorescence temperature dependence of chosen nanocomposites;
      4. To compare fluorescence yield of nanocomposites with known scintillators.
   2. To use UV and VUV spectroscopy to shed light on substantial luminescence spectra changes of rare-earth nanoparticles in a powder and when embedded into diamond. Measurements of luminescence excitation spectra are suggested in the energy region 2 – 8 eV.

1. Aim and motivation.
   The goal of the proposed research is to combine renowned luminescent properties of rare-earth compounds with exceptional properties of diamond such as chemical stability, high conductivity and radiation hardness by creating composite materials using nanoparticles of rare-earth compounds embedded into CVD or single crystalline diamond. Such composite materials can be used for monitoring radiation from free-electron lasers and in other cases, when the detection of high-flux radiation is required. Experimental studies of cathodoluminescence of prepared composite materials including time-resolved fluorescence spectra and kinetics are envisaged. For the samples with reasonable fluorescence yield excitation spectra measurements are to be performed.
2. Proposed contribution to the scientific objectives of the Action.
   Superfast timing relies on the hot intraband luminescence (HIL) and a lot of compounds have been tested within this action. Most of them were ionic crystals, while diamond is a covalent one, thus it will allow to extend the studies to the family of covalent materials.
3. Techniques
   There is a wide range of fields interested in luminescent diamonds: quantum information technologies; optical biomarkers, and scintillators (X-ray beam monitors). Intense hard x-ray pulses at high repetition rates of >100 Hz at new generation light sources such as x-ray free-electron lasers or insertion devices at 4th generation storage rings formulate new requirements to the scintillators to be used to monitor their radiation: fluorescence decay time faster than 1 ns; low Z, exceptional radiation hardness and high thermal conductivity to withstand intense hard x-ray pulses at high repetition rate. The known fluorescence properties of the impurity-vacancy centers in diamond are quite suitable for engineering single photon emitters, however the search for new and better photoluminescence sources in a diamond matrix is still an ongoing activity. Quite recently a few successful attempts to incorporate europium ions into the diamond matrix were reported. They look quite encouraging for the development of new fast low-Z scintillators to be used at new XFEL sources for "static" measurements, however for time-resolved ones it would be interesting to use cerium.
   During suggested session of measurements we plan to address the following problems:
   1. To investigate the effect of nanoparticle size on the luminescence spectra and kinetics in Eu- and Ce-doped diamond films.
   2. To investigate the origin of substantial changes in the luminescence spectra of Eu-doped diamond nanocomposites after covering the layer of EuF3 nanoparticles with a diamond layer.
   3. To study the difference of fluorescence properties of nanocomposites with CVD and single crystalline diamond.
   4. To investigate fluorescence properties of nanocomposites using several cerium compounds.
   5. To investigate temperature dependence of the luminescence of chosen nanocomposites.
   The main technique to be applied is time-resolved cathodoluminescence.
4. Planning
   To use the electron gun of the Institute of Physics, University of Tartu to study cathodoluminescence spectra and kinetics in a wide time range from picoseconds to milliseconds to address the following questions:
   1. The effect of the specific rare-earth compound used for the fabrication of a nanocomposite on the fluorescence spectra and kinetics;
   2. The effect of the size of the rare-earth compound nanoparticle used for the fabrication of a nanocomposite on the fluorescence spectra and kinetics;
   3. To study fluorescence temperature dependence of chosen nanocomposites;
   4. To compare fluorescence yield of nanocomposites with known scintillators.

This STSM is part of a collaboration between Spanish and Israeli physicists, on the feasibility of TOF-PET using liquid xenon (LXe) as a scintillator with SiPM readout. The project name is PETALO: Positron Emission TOF Apparatus based on Liquid xenOn. The two Israeli collaborators travelling to Spain are Dr. Lior Arazi (Israeli PI, Ben-Gurion University, Beer-Sheva, Israel) and Dr. Michael Rappaport (Weizmann Institute of Science, Rehovot, Israel). The Spanish principal investigators are Prof. Juan José Gómez Cadenas (IFIC, Valencia, Spain) and Dr. Paola Ferrario (IFIC, Valencia, and Donostia International Physics Center, Donostia-San Sebastián, Spain). The purpose of the trip is to converge on a basic design for a prototype comprising a dedicated cryostat with two PETALO cells, each composed of a LXe volume with SiPM readout. The Spanish collaborators are leading this ERC-funded project, and have conducted a thorough Monte-Carlo study demonstrating its feasibility. The Israeli collaborators will contribute from their knowledge and experience in designing and operating LXe detectors (L. Arazi is a detector physicist, with particular expertise in LXe detectors for dark matter searches, and M. Rappaport is an expert on cryogenics, who have designed, together with L. Arazi, the LXe system at the Weizmann Institute). In addition to the setup basic design, the collaborators will prepare a detailed experimental plan for measuring the energy and spatial resolution of the system, as well as its coincidence resolving time. Two different configurations will be implemented: one using conventional SiPMs coated with TPB, and the other using VUV sensitive SiPMs.

This STSM is part of a collaboration between Spanish and Israeli physicists, on the feasibility of TOF-PET using liquid xenon (LXe) as a scintillator with SiPM readout. The project name is PETALO: Positron Emission TOF Apparatus based on Liquid xenOn. The two Israeli collaborators travelling to Spain are Dr. Lior Arazi (Israeli PI, Ben-Gurion University, Beer-Sheva, Israel) and Dr. Michael Rappaport (Weizmann Institute of Science, Rehovot, Israel). The Spanish principal investigators are Prof. Juan José Gómez Cadenas (IFIC, Valencia, Spain) and Dr. Paola Ferrario (IFIC, Valencia, and Donostia International Physics Center, Donostia-San Sebastián, Spain). The purpose of the trip is to converge on a basic design for a prototype comprising a dedicated cryostat with two PETALO cells, each composed of a LXe volume with SiPM readout. The Spanish collaborators are leading this ERC-funded project, and have conducted a thorough Monte-Carlo study demonstrating its feasibility. The Israeli collaborators will contribute from their knowledge and experience in designing and operating LXe detectors (L. Arazi is a detector physicist, with particular expertise in LXe detectors for dark matter searches, and M. Rappaport is an expert on cryogenics, who have designed, together with L. Arazi, the LXe system at the Weizmann Institute). In addition to the setup basic design, the collaborators will prepare a detailed experimental plan for measuring the energy and spatial resolution of the system, as well as its coincidence resolving time. Two different configurations will be implemented: one using conventional SiPMs coated with TPB, and the other using VUV sensitive SiPMs.

The work of Rafel Manera is devoted to work on the FastIC ASIC that is currently developed in the CLUES project in collaboration between the Institute of Cosmos Sciences of the University of Barcelona (ICC-UB) and the European Organization for Nuclear Research (CERN). The master thesis is dedicated to the study and design of different building blocks for the FastIC ASIC in 65 nm CMOS technology. The student has some experience developing analog circuits within the group and a stay at CERN could be a great opportunity to increase his experience in this field to get prepared for a PhD after the master studies. The objectives of the STSM at CERN will be to study the design challenges of the 65 nm CMOS process, explore Rail-to-Rail OTA topologies to be included in the FastIC and participate in the development, layout and the assembly of the FastIC ASIC. Additionally, Rafel Manera will be fully integrated in the microelectronics group at CERN and will learn from experienced designers.

he work of David Sanchez is devoted to study the usage of monolithic crystals with SiPM arrays and HRFlexToT [1] based readout as basic module for PET application. The first objective of this STSM is to compare the measures of different setups using HRFlexToT and NINO readouts. These comparisons will include the use of different SiPMs as wells as various scintillator crystals in order to validate a wide range of scenarios. Single Photon Time Resolution (SPTR) and Coincidence Time Resolution (CTR) are going to be the main figures of merit to be obtained. The second objective of the STSM will consist in the simulation of different SiPM and crystal configurations using the GATE [2] + Cadence tool developed at UB, as well as learning and comparing with the Monte Carlo simulation environment used at CERN.

CC-UB is focused on developing electronics for the future upgrades of different detectors in LHCb (Calorimeter electronics, the Scifi tracker and different detectors at SHIP). In the framework of these activities, the purpose of the group is to undertake the study of ultrafast read-out electronics for high energy physics with time stamp for photo sensors for the CALO, TORCH and RICH detectors in LHCb. Moreover, read-out electronics exploiting Time-of-Flight methods are becoming necessary in medical imaging applications such as Positron Emission Tomography, as improvement in time resolution directly translates into better signal-to-noise ratio of reconstructed images, allowing the eventual possibility of real-time imaging reconstruction thus important breakthroughs in medical diagnosis.

The purpose of this STSM to CERN will be the first functional characterization of a new production of Large Area Sparse Cell SiPMs (LASC SiPMs) developed for fast timing detector in HEP like the CMS timing layer. For future experiments, time resolution required is of 30 ps and these performance should remain after exposure to radiation. The new detectors will be preliminarily tested and packaged at Fondazione Bruno Kessler (FBK) in August 2018, to be evaluated in a test beam at CERN from 12th to 18th September 2018. The STSM to CERN will be in the week preceding the test beam, with the aim of studying the device performance and their compliance to the experiment specifications. The SiPM production under evaluation was developed to demonstrate uniform timing and efficient light collection across 11x11 mm2 surface area of LYSO:Ce scintillation crystals. Moreover, we explored some innovative process solutions to improve the radiation tolerance of the silicon photodetectors. The LASC SiPMs feature NUV-HD low field technology, with a large area (5x5 mm2) and small cell size (15 and 20 μm). Moreover, in order to reduce the power consumption, a sparse cell layout was developed. The functional measurements scheduled for this STSM will be focused on the baseline characterization of the detectors before irradiation. We will measure the main functional parameters of the LASC SiPMs, as dark count rate and dark noise components, microcell gain and photo-detection efficiency. We will also study the timing performance of LASC SiPMs coupled to LYSO:Ce crystals.

The STSM work will be focused on evaluating and exploring the potential capabilities of monolithic crystals, coupled to SiPM arrays to be considered as detector blocks for TOF-PET scanners. In this direction, the host institution will provide its expertise on optimizing the custom TOFPET2 ASIC-based readout for light-sharing applications and signals with low gain, aiming to achieve the best in terms of timing. The host in collaboration with the home institution, will design novel approaches and calibration methods for improving detector performance. Finally, evaluation in several detector configurations will be carried out in terms of energy, spatial and timing resolution. During the first days installation of the PET system will be held. Evaluation tests then will be performed to confirm system's capabilities. Measurements in coincidences will be carried out for initial characterization of the system and then then software processing algorithms will be developed to improve the timing resolution. Expertise from both institutes will be exchanged in terms of hardware as well as of software processing. The present STSM work will be the first step in the construction of a PET system designed for accurately decode of the gamma impacts in all three coordinates and in time. A system of this approach will be of high interest in several clinical and preclinical applications. We consider that this projects fits perfectly the approaches of WG5 Cost Fast Action.

In framework of our development of positron-emission tomography detectors’ block in National Research Nuclear University “Moscow Engineering Physics Institute” (NRNU MEPhI www.mephi.ru, Russia) we cooperated with AQUA lab of EPFL in Neuchatel in order to use their MD-SiPMs in the our prototype. Both our organizations are the FAST members.
· AQUA lab has ongoing project devoted to development of high-performance PET detectors based on CIS fully-integrated multichannel Digital Silicon Photomultipliers.
Taking aforementioned into account is quite important to evaluate parameters of developed and produced sensors by using standard techniques in order to achieve conditions for the correct comparison with existing already mass-market SiPMs .
So one of the most important task of the proposed STSM is

1. development of methods of analogue and digital SiPM parameter’s measurement those are available with the provided by AQUA lab equipment. Then we are planning to carry out
2. measuring of photodetection and timing properties of the AQUA lab SiPMs with the different sensitive areas in order to select of the optimum SiPM type and readout way for TOF PET application for room temperature. It is known that SiPM parameters are sensitive to the temperature, and cryogenic temperature region is still not so good explored and understood.
3. Measuring of main parameters for cryogenic conditions and development of an analytical approach to describe fundamental properties of SiPMs at cryogenic temperatures. Finally all measurements require
4. Analysis of the data obtained and looking for possible ways for SiPM parameters improvement in the frameworks of custom and standard CMOS technology. Finding the ways of detection efficiency and timing SiPM properties improving for the analogue and digital SiPMs in custom and CMOS technology are the key points for production of sensor for the new generation of PET systems for the future theranostics medicine.

Despite long-lasting efforts on theoretical analysis of photon detection processes in scintillator detectors since the 1960s, there is a lack of simple and reasonable closed-form expressions of a time resolution. Promising results in form of approximations of coincidence time resolution of scintillator detectors with leading edge discriminator have been obtained by S. Vinogradov (NDIP-2017) utilizing transient statistics of filtered marked point processes approach. The approximations appear to be in a good agreement with a few experimental results on multiphoton time resolution of laser and fast scintillator light pulses measured by MEPhI SiPM lab.
A goal of this project is a systematic assessment of the correctness of the analytical models and approximations in a wide range of variability of scintillator detector parameters and operating conditions.
Therefore, there are a set of light pulse detection measurements with a variety of SiPMs to be done for that:

• Short laser pulse (picosecond – nanosecond time range)
• Scintillator pulse (nanosecond – microsecond time range)
• LED pulse of variable duration (nanosecond – microsecond time range).

Some experimental data could also be retrieved for the same analysis from previous studies of SiPM and/or PMT time resolution with various light sources.
Analysis of the theoretical and experimental results will clarify correctness and applicability of the analytical models and their approximations for the most demanded practical applications.

Aim of this STSM is the study of the changes of the THz characteristics of the ionizing radiation induced defects in rare earth activated nanocrystal containing glass ceramic samples and/or halide and complex oxide single crystal samples. THz characteristics modifications (i.e. density modifications) can be conveniently located when the THz pulse propagation will be studied. Romanian group has experience to conduct similar experiments, access to ionizing radiation sources. Latvian part can provide necessary samples. 2. Proposed contribution to the scientific objectives of the Action. Fast processes can be detected rare earth or transition metal doped monocrystals, ceramics and polycrystals. This research will pay attention to radiation induced structure changes in host matrix of such materials. 3. Techniques - Please detail what techniques or equipment you may learn to use, if applicable. The TeraView TPS Spectra 3000 spectrometer will be used with the Transmittance and the Reflectance Imaging Module. Terahertz waves can penetrate through materials opaque to other parts of the EM spectrum. THz radiation does not initiate any changes in chemical structure, as opposed to UV radiation or X-rays for example. 4. Planning - Please detail the steps you will take to achieve your proposed aim. Time schedule and itinerary Activity no. 1: Rare earth activated nanocrystal containing glass ceramics, halide and complex oxide sample selection, preparation and primary characterization in the laboratory (luminescence, XRD). Cutting and polishing of the glass ceramics samples. Expected dates: Until 23/09/2018 Location: Institute of Solid State Physics, University of Latvia, Riga, Latvia Activity no. 2: Exposure of the samples to ionizing radiation. The measurements of the optical spectral transmittance and terahertz (THz) spectral response before and after exposure. Expected dates: 23/09/2017 – 29/06/2017 Location: National Institute for Laser Plasma and Radiation Physics, Magurele, Romania Activity no. 3: Analysis of results, preparation of report.

Scintillators are critical for the behavior of medical devices; their structural condition and quality affect the response of the entire medical system.
Luminescence performances, light production, transport, energy resolution and sensitivity, could be affected by the structural, defectiveness and stress condition as well as the aging of the crystal. Cross measurements between the light response of the crystal coupled with devices like Position Sensitive Photomultipliers or Silicon Photomultipliers and non-destructive photoelastic observation, could give additional information in order to characterize deeply the crystal and the medical system. The results from the previous STSM have highlighted, qualitatively, some differences in the samples population from the photoelastic point of view. The same anomalous samples have been tested and differences in terms of sensitivity, decay time and in the images carried out by the PSPMT. In order to go deeper in the analysis, by the STSM other anomalous samples will be investigated trying to have a confirmation of the strange behavior and the correlation with the photoelastic images.
If this correlation is confirmed photoelasticity could be considered as a method for the control and the selection of homogeneous crystals.
The activity period could be scheduled as follow:

• Activity 1: build up a system for photoelastic system and observe the available samples in order to quantify the differences
• Activity 2: Measurement of the optical properties (light transmission, absorption, reflectance)
• Activity 3: measure performances (Light yield, decay time, tests with the PSPMT, etc..) of the samples of the Activity 1
• Activity 4: compare and analyse the results from the cross measurements.