R. Kurjata

Characterization and Simulation of the Response of Multi Pixel Photon Counters to Low Light Levels

The calorimeter, range detector and active target elements of the T2K near detectors rely on the Hamamatsu Photonics Multi-Pixel Photon Counters (MPPCs) to detect scintillation light produced by charged particles. Detailed measurements of the MPPC gain, afterpulsing, crosstalk, dark noise, and photon detection efficiency for low light levels are reported. In order to account for the impact of the MPPC behavior on T2K physics observables, a simulation program has been developed based on these measurements. The simulation is used to predict the energy resolution of the detector.

The T2K Side Muon Range Detector (SMRD)

The T2K experiment is a long baseline neutrino oscillation experiment aiming to observe the appearance ofe in a �µ beam. The �µ beam is produced at the Japan Proton Accelerator Research Complex (J-PARC), observed with the 295 km distant Super- Kamiokande Detector and monitored by a suite of near detectors at 280m from the proton target. The near detectors include a magnetized off-axis detector (ND280) which measures the un-oscillated neutrino flux and neutrino cross sections. The present paper describes the outermost component of ND280 which is a side muon range detector (SMRD) composed of scintillation counters with embedded wavelength shifting fibers and Multi-Pixel Photon Counter read-out. The components, performance and response of the SMRD are presented.

Scintillator counters with WLS fiber/MPPC readout for the side muon range detector (SMRD)of the T2K experiment

The T2K neutrino experiment at J-PARC uses a set of near detectors to measure the properties of an unoscillated neutrino beam and neutrino interaction cross-sections. One of the sub-detectors of the near-detector complex, the side muon range detector (SMRD), is described in the paper. The detector is designed to help measure the neutrino energy spectrum, to identify background and to calibrate the other detectors. The active elements of the SMRD consist of 0.7 cm thick extruded scintillator slabs inserted into air gaps of the UA1 magnet yokes. The readout of each scintillator slab is provided through a single WLS fiber embedded into a serpentine-shaped groove. Two Hamamatsu multi–pixel avalanche photodiodes (MPPCs) are coupled to both ends of the WLS fiber. This design allows us to achieve a high MIP detection efficiency of greater than 99%. A light yield of 25–50 p.e./MIP, a time resolution of about 1 ns and a spatial resolution along the slab better than 10 cm were obtained for the SMRD counters.

Functional imaging with MR T1 contrast: a feasibility study with blood-pool contrast agent.

The aim of this study was to prove the concept of using a long intravenous half-life blood-pool T1 contrast agent as a new functional imaging method. For each of ten healthy subjects, two dynamic magnetic resonance (MR) protocols were carried out: (1) a reference run with a typical T2* echo-planar imaging (EPI) sequence based on the blood oxygenation level-dependent (BOLD) effect and (2) a run with a T1-sensitive three-dimensional (3D) gradient-echo (GRE) sequence using cerebral blood volume (CBV) contrast after intravenous administration of a contrast agent containing a chelate of gadolinium diethylene-triamine-pentaacetate with a phosphono-oxymethyl substituent. All sequences were performed during the execution of a block-type finger-tapping paradigm. SPM5 software was used for statistical analysis. For both runs maximum activations (peak Z-score = 5.5, cluster size 3,449 voxels) were localized in the left postcentral gyrus. Visual inspection of respective signal amplitudes suggests the T1 contrast to be substantially smaller than EPI (0.5% vs 1%). A new functional imaging method with potentially smaller image artefacts due to the nature of CBV contrast and characteristics of the T1 sequence was proposed and verified.

Coronary blood flow measurement from x-ray images: experiment performed on the artery model

The paper presents the experimental validation of the coronary blood flow measured from coronarographic images. The method of flow measurement earlier presented is based on elements of the indicator-dilution theory and on the idea of using two sequences of images obtained during standard coronarographic examination. Measurements of the image intensity along the cross-section lines of the artery were performed on the sequence with the standard injection of contrast and with the small quantity of slowly injected contrast. These two sequences enable the construction of the contrast relative concentration curve in the defined earlier cross-section vs. time. The global volumetric blood flow can be calculated as a ratio of the quantity of the indicator injected during the indicator-dilution sequence by the value of the area under concentration curve. Experimental validation was performed using a simple artery model. Results of the flow calculation for five cross-section lines positioned in different intensity levels regions of the image show that the error is below 20%.

A Simple Method of Determining the Effective Attenuation Coefficient

A Simple Method of Determining the Effective Attenuation Coefficient This paper presents a simple method of determining the effective attenuation coefficient from steady-state diffuse reflectance measurements.

Single Photon Counting System for Biomedical Applications

Single photon counting system for biomedical applications was designed and tested. Examination of changes of an optical signal on a patients head during stimulation tests (finger taping) was made by the elaborated system.

DEAD TIME MEASUREMENT BY TWO-SOURCE METHOD – OPTIMIZATION OF MEASUREMENT TIME DIVISION

The article presents the analysis of the dead time measurement using two sources for a non-paralyzable detector. It determined the optimum division of count rate measurement time between both source measurement and a single source one. Results of the work can be used to optimize dead time measurement for systems which count photons or particles.

GAIN PREDICTION THEORY OF SINGLE FOIL GAS ELECTRON MULTIPLIER DETECTOR

Gain prediction theory of single foil Gas Electron Multiplier detector was developed. Gas electron multiplier (GEM) detector with single foil was developed. Soft X-ray spectra with an energy of 5.9 keV emitted by the isotope Fe-55 were measured. On this basis, the dependence of gain and energy resolution from the detector voltage was determined. The simple theory of gain dependence on various detector parameters was developed. Preliminary results of the study confirmed the potential usefulness of the GEM detector as a substitute for the multiwire proportional chamber.

Fully Automated Machine for Scanning SIMP detectors

A fully automated measurement system has been built to measure uniformmity of the parameters of SiPM detectors with very high pixel densities. It has a light source with a microfocus spot (FWHM = 3 μm at the detector surface) and a precise positioning system (1 μm accuracy). A temperature control system with water cooling has been used to set the temperature of the measured detector. Finally, a low noise, custom made front-end amplifier has been designed to receive SiPM signals. This paper presents the MAPD-3N detector measurement results uniformity of gain and relative photon detection efficiency (PDE).