R. Becker

Beam test results for a tungsten-cerium fluoride sampling calorimeter with wavelength-shifting fiber readout

A sampling calorimeter using cerium fluoride scintillating crystals as active material, interleaved with heavy absorber plates, and read out by wavelength-shifting (WLS) fibers is being studied as a calorimeter option for detectors at the upgraded High-Luminosity LHC (HL-LHC) collider at CERN. A prototype has been exposed to electron beams of different energies at the INFN Frascati (Italy) Beam Test Facility. This paper presents results from the studies performed on the prototype, such as signal amplitudes, light yield and energy resolution.

Studies of wavelength-shifting liquid filled quartz capillaries for use in a proposed CMS calorimeter

Studies have been done and continue on the design and construction of a Shashlik detector using Radiation hard quartz capillaries filled with wavelength shifting liquid to collect the scintillation light from LYSO crystals for use as a calorimeter in the Phase II CMS upgrade at CERN. The work presented here focuses on the studies of the capillaries and liquids that would best suit the purpose of the detector. Comparisons are made of various liquids, concentrations, and capillary construction techniques will be discussed.

The SAFIR project: an innovative high rate preclinical PET/MR detector towards dynamic multimodal imaging

SAFIR (Small Animal Fast Insert for mRi) is an innovative, high rate, PET detector insert for MRI, to be used for quantitative dynamic pre-clinical imaging, with very high activities injected in the animals, up to 500 MBq. The PET detector will be designed to allow for ultra short acquisition periods (of the order of a few seconds) simultaneously with the MRI, permitting unprecedented temporal resolutions in preclinical dynamic multimodal imaging. High sensitivity (~ 6%), high spatial resolution (~1.5 mm FWHM), excellent coincidence timing resolution (CTR ~ 300 ps FWHM) and a fast DAQ system able to cope with the huge data throughput are required. Parallel with the hardware efforts, dedicated 4D algorithms for image reconstruction must be developed. The overall state of the project will be presented, including ongoing activities towards the choice and characterization of the detector components (crystals, SiPMs and readout chips), MonteCarlo simulations, and first reconstruction of various simulated sources. Special emphasis will be given to the results of a recent high rate test, where the TOFPET ASIC has been tested with Hamamatsu S12642-0404PB-50 SiPM arrays coupled to matrices of LYSO:Ce crystals (3.1x3.1x12 mm3 each), exposed to a 500 MBq activity of FDG radiotracer in a volume of about 0.5 cm3.

Monte-Carlo simulation based estimation of NECR, sensitivity, and spatial resolution of a novel preclinical PET insert for MR

The Small Animal Fast Insert for mRi (SAFIR) will be a PET insert for the Bruker BioSpin 70/30. It aims at applications where fast processes such as blood perfusion in the rodent brain are to be monitored comprehensively and non-invasively. Employing electronics originally designed for time-of-flight applications, coincidence resolving times of less than a nanosecond can be achieved allowing for short coincidence time windows. Consequently, random contributions to the coincidence events are suppressed, making short acquisition frames with very high tracer concentrations possible. This will allow collecting sufficient count statistics in a few seconds. Geant4-based Monte Carlo simulations were used to characterize the performance of the reference design consisting of polished LSO-like crystals, one-to-one coupled to Silicon Photomultipliers. The crystals are grouped into 8×8 matrices, which are arranged into 24 modules and 10 rings. Similar methods as described in the NEMA NU 4-2008 standard were employed. The simulation results on NECR, sensitivity, and spatial resolution will be presented. Most notably, the NECR at 500 MBq is almost nine times higher than at 50 MBq for the given scanner. Combined with a very high sensitivity, this allows for short acquisition times using these very high injected doses. In addition, essentially random-free measurements at standard activities below 50 MBq are possible.

Studies of the high rate coincidence timing response of the STiC and TOFPET ASICs for the SAFIR PET scanner

The proposed SAFIR PET detector will measure positron electron annihilations at injected activities up to 500 MBq in a mouse or rat. The system is required to have the best possible timing resolution in order to remove accidental coincidences (randoms) and maximise the image quality for short time frames allowing the possibility of 4-D kinetic modelling of simultaneous PET and MRI for the first time. Two different ASICs, TOFPET and STiC, have been investigated with LYSO crystal scintillators coupled to SiPM detectors and using ^(18)F sources up to 480 MBq. Timing responses are very encouraging with a coincidence time resolution of ~100 ps measured at low activities, degrading to 130 ps at the foreseen scanner maximum event rate. Sensitivities for single event rates and coincidences are measured and compared with Geant4 Monte Carlo simulations.