V. Rykalin

Water-equivalent path length calibration of a prototype proton CT scanner

PURPOSE The authors present a calibration method for a prototype proton computed tomography (pCT) scanner. The accuracy of these measurements depends upon careful calibration of the energy detector used to measure the residual energy of the protons that passed through the object. METHODS A prototype pCT scanner with a cesium iodide (CsI(Tl)) crystal calorimeter was calibrated by measuring the calorimeter response for protons of 200 and 100 MeV initial energies undergoing degradation in polystyrene plates of known thickness and relative stopping power (RSP) with respect to water. Calibration curves for the two proton energies were obtained by fitting a second-degree polynomial to the water-equivalent path length versus calorimeter response data. Using the 100 MeV calibration curve, the RSP values for a variety of tissue-equivalent materials were measured and compared to values obtained from a standard depth-dose range shift measurement using a water-tank. A cylindrical water phantom was scanned with 200 MeV protons and its RSP distribution was reconstructed using the 200 MeV calibration. RESULTS It is shown that this calibration method produces measured RSP values of various tissue-equivalent materials that agree to within 0.5% of values obtained using an established water-tank method. The mean RSP value of the water phantom reconstruction was found to be 0.995 ± 0.006. CONCLUSIONS The method presented provides a simple and reliable procedure for calibration of a pCT scanner.

Extruding plastic scintillator at Fermilab

An understanding of the costs involved in the production of plastic scintillators and the development of a less expensive material have become necessary with the prospects of building very large plastic scintillation detectors. Several factors contribute to the high cost of plastic scintillating sheets, but the principal reason is the labor-intensive nature of the manufacturing process. In order to significantly lower the costs, the current casting procedures had to be abandoned. Since polystyrene is widely used in the consumer industry, the logical path was to investigate the extrusion of commercial-grade polystyrene pellets with dopants to yield high quality plastic scintillator. This concept was tested and high quality extruded plastic scintillator was produced. The DO and MINOS experiments are already using extruded scintillator strips in their detectors. An extrusion line has recently been installed at Fermilab in collaboration with NICADD (Northern Illinois Center for Accelerator and Detector Development). This new facility will serve to further develop and improve extruded plastic scintillator. This paper will discuss the characteristics of extruded plastic scintillator and its raw materials, the different manufacturing techniques and the current R&D program at Fermilab.

Detector development for Proton Computed Tomography (pCT)

Proton Computed Tomography (pCT) is being developed in support of proton therapy and treatment planning. The aim of pCT, to reconstruct an accurate map of the stopping power (S.P.) in a phantom and, in the future, in patients, is being pursued with a diverse list of detector systems, using the entire arsenal of tracking and energy detectors developed for High Energy Physics (HEP). The first radiographs and 3D images are being reconstructed with prototype detectors, which will be described. Most of the existing systems are being upgraded to higher proton fluxes to reduce the scanning time.

Small scintillating cells as the active elements in a digital hadron calorimeter for the e + e − linear collider detector

The ability to distinguish between hadronic W and Z decays is one of the most challenging requirements for the future linear collider detector. Such sensitivity requires unprecedented jet energy resolution, which may be possible with energy-flow algorithms. A calorimeter that is optimized for energy-flow must have fine lateral and longitudinal segmentation. Small scintillating cells with wavelength shifting fibre readout represent an attractive basis for a digital hadron calorimeter that trades dynamic range for superior granularity, at an affordable price. We present the expected jet resolution for such a device, based on Monte Carlo simulations. Then we describe the initial prototyping studies. In particular, detailed studies are presented on cell performance under different combinations of manufacture and assembly.

Extruded plastic scintillator for MINERvA

An extrusion line has recently been installed at Fermilab in collaboration with NICADD (Northern Illinois Center for Accelerator and Detector Development). This new facility will serve to further develop and improve extruded plastic scintillator. Since polystyrene is widely used in the consumer industry, the logical path was to investigate the extrusion of commercial-grade polystyrene pellets with dopants to yield high quality plastic scintillator. The D0 and MINOS experiments are already using extruded scintillator strips in their detectors. A new experiment at Fermilab is pursuing the use of extruded plastic scintillator. A new plastic scintillator strip is being tested and its properties characterized. The initial results are presented here.

Characterization of Silicon Photomultipliers for PET Imaging

The Silicon Photomultiplier (SiPM) is a novel photodetector being developed for high energy physics applications. SiPM is attractive for PET imaging because it is compact; provides high gain at low voltage; is insensitive to magnetic fields; has a fast timing response; and is potentially inexpensive and CMOS-technology compatible. Researchers have characterized SiPM performance mostly in areas relevant to high-energy physics and astrophysics applications, with some findings demonstrating the potential usefulness of SiPM in positron emission tomography (PET) imaging. Using our photodetector characterization test-stand equipped with a 20 GSps sample rate and 6 GHz bandwidth oscilloscope, we have measured the gains in the range of 1-3 times 105 room temperature for SiPM samples obtained from different producers. We have measured the rising times and their standard deviations. Based on the measured dark-count rates at room temperature, we have also estimated the achievable energy resolution of SiPM in PET imaging when used with LSO and BGO scintillators.

Beam test results of a CsI calorimeter matrix element

This paper presents the test results of a single element of a Cesium Iodide CsI(TI) crystal calorimeter matrix using proton beam energies of 35 MeV, 100 MeV and 200 MeV. The detector element was designed to comply with the demands of high energy resolution of a few percent and with a dynamic range of two orders of magnitude under a counting rate of 10 kHz per channel. The energy range investigated in the current work was an order of magnitude less than the design capability. The readout was provided by a 28 ? 28 mm2 Hamamatsu S3584-08 photodiode coupled with the crystal through a silicone optical interface. A charge-sensitive preamplifier with low noise at high photodiode capacitance was chosen. We also report on the data acquired during crystal calibration with cosmic rays, and give a description of our data acquisition (DAQ) system.

Quality Control Studies of Wavelength Shifting Fibers for a Scintillator-Based Tail Catcher Muon Tracker for Linear Collider Prototype Detector

Detailed measurements of the wavelength shifting fiber response to a stable and reliable light source are presented. Particulars about materials, a double reference method, and measurement technique are included. The fibers studied were several hundred Kuraray, Y-11, multiclad, 1.2-mm outer diameter wavelength shifting fibers, each cut from a reel to about one meter length. The fibers were polished, mirrored, and the mirrors were UV epoxy protected. Each fiber passed quality control requirements before installation. About 94% of the fibers tested have a response within 1% of the overall mean

Design and construction of the 1st proton CT scanner

This paper discusses the design and operation of the 1st proton CT scanner for 3D imaging. Reduction of proton range uncertainties and improved dose accuracy in the patient for treatment planning are central goals. A central CT slice acquired by reconstruction of 134 million proton tracks through a 14 cm spherical polystyrene phantom with high and low density inserts is presented.

Extruded scintillator for the Calorimetry applications

An extrusion line has been installed and successfully operated at FNAL (Fermi National Accelerator Laboratory) in collaboration with NICADD (Northern Illinois Center for Accelerator and Detector Development). This new Facility will serve to further develop and improve extruded plastic scintillator. Recently progress has been made in producing co‐extruded plastic scintillator, thus increasing the potential HEP applications of this Facility. The current R&D work with extruded and co‐extruded plastic scintillator for a potential ALICE upgrade, the ILC calorimetry program and the MINERvA experiment show the attractiveness of the chosen strategy for future experiments and calorimetry. We extensively discuss extruded and co‐extruded plastic scintillator in calorimetry in synergy with new Solid State Photomultipliers. The characteristics of extruded and co‐extruded plastic scintillator will be presented here as well as results with non‐traditional photo read‐out.