Physics

The potential of photon detectors to achieve precise timing information is of increasing importance in many domains, PET and CT scanners in medical imaging and particle physics detectors, amongst others. The goal to increase by an order of magnitude the sensitivity of PET scanners and to deliver, via time-of-flight (TOF), true space points for each event, as well as the constraints set by future particle accelerators require a further leap in time resolution of scintillator-based ionizing radiation detectors, reaching eventually a few picoseconds resolution for sub MeV energy deposits. In spite of the impressive progress made in the last decade by several manufacturers, the Single Photon Time Resolution (SPTR) of SiPMs is still in the range of 70-120ps FWHM, whereas a value of 10ps or even less would be desirable. Such a step requires a break with traditional methods and the development of novel technologies. The possibility of combining the extraordinary potential of nanophotonics with new approaches offered by modern microelectronics and 3D electronic integration opens novel perspectives for the development of a new generation of metamaterial-based SiPMs with unprecedented photodetection efficiency and timing resolution.

A new instrument is required to accommodate the need for increased portability and accuracy in laser power measurement above 100 W. Reflection and absorption of laser light provide a measurable force from photon momentum exchange that is directly proportional to laser power, which can be measured with an electrostatic balance traceable to the SI. We aim for a relative uncertainty of 10 ?? with coverage factor k=2 . For this purpose, we have designed a monolithic parallelogram 4-bar linkage incorporating elastic circular notch flexure hinges. The design is optimized to address the main factors driving force measurement uncertainty from the balance mechanism: corner loading errors, balance stiffness, stress in the flexure hinges, sensitivity to vibration, and sensitivity to thermal gradients. Parasitic rotations in the free end of the 4-bar linkage during arcuate motion are constrained by machining tolerances. An analytical model shows this affects the force measurement less than 0.01 percent. Incorporating an inverted pendulum reduces the stiffness of the system without unduly increasing tilt sensitivity. Finite element modeling of the flexures is used to determine the hinge orientation that minimizes stress which is therefore expected to minimize hysteresis. Thermal effects are mitigated using an external enclosure to minimize temperature gradients, although a quantitative analysis of this effect is not carried out. These analyses show the optimized mechanism is expected to contribute less than 10 ?? relative uncertainty in the final laser power measurement.

We designed the Mixer operating at 2.4 GHz for WIFI-band using ADS software and fabricated using Rogers 4350B substrate. We designed the single-balanced mixer using the diode (HSMS-281x model). We measured the isolation across all ports of the mixer. We measured the conversion loss of the mixer. We performed the non-linear measurements, which include IM3 vs frequency. The performance metrics are compared with the data-sheet values and explained if any discrepancy exists.

We describe the concept of a new gamma ray scintronic detector targeting a time resolution of the order of 25 ps FWHM, with millimetric volume reconstruction and high detection efficiency. Its design consists of a monolithic large PbWO4 scintillating crystal with an efficient photocathode directly deposited on it. With an index of refraction higher for the photocathode than for the crystal, this design negates the total reflection effect of optical photons at the crystal/photo-detector optical interface, and thus largely improves optical coupling between the crystal and the photodetector. This allows to detect efficiently the Cherenkov light produced by 511 keV photoelectric conversions in PbWO4, and to optimize the detector time resolution. Furthermore, the low-yield, fast scintillation light produced additionally by PbWO4 increases the detected photon statistics by a factor 10, thus fostering accurate (3 dimensional) localization of the gamma ray interaction within the crystal and providing a fair measurement of the deposited energy. This paper lists the technological challenges that have to be overcome in order to build this scintronic detector. We show that all the key technologies have now been demonstrated and present results of a preliminary Monte Carlo simulation, which include an innovative event reconstruction algorithm to support the claimed performances of the detector.

Bioimpedance measurements are a non-invasive method to determine the composition of organic tissue. For measuring the complex bioimpedance between two electrodes, an alternating current with a constant amplitude is injected into the tissue. The developed voltage drop is used to calculate the real and imaginary part of the impedance under test. Measurements in the past indicated that it could be possible that the beating of the heart has an effect on the measured phase shift of the impedance under test. In this work a hardware system is developed, capable of measuring changes of the bioimpedance phase shift with high resolution. Two different measurement methods are used. The first method is an analog circuit, which has been developed in a previous project. The other method uses the integrated circuit AFE4300 (Texas Instruments) [1]. The results of both methods are transmitted with a microcontroller (Xmega256A3BU from Atmel Corp.) via the USB interface to a host PC. On the host PC the visualization of the measurements and the control of the embedded system is achieved with a developed LabView program. The work includes the development of the hardware and software, as well as a comparison of the accuracy of the two measurement methods. The result of a verification of the systems is that both measurement methods have an effective resolution of about 0.3°.

A large-scale neutrino observatory based on Water-based Liquid Scintillator (WbLS) will be excellently suited for a measurement of the Diffuse Supernova Neutrino Background (DSNB). The WbLS technique offers high signal efficiency and effective suppression of the otherwise overwhelming background from neutral-current interactions of atmospheric neutrinos. To illustrate this, we investigate the DSNB sensitivity for two configurations of the future Theia detector by developing the expected signal and background rejection efficiencies along a full analysis chain. Based on a statistical analysis of the remaining signal and background rates, we find that a rather moderate exposure of 190kt ⋅ yrs will be sufficient to claim a ( 5σ ) discovery of the faint DSNB signal for standard model assumptions. We conclude that, in comparison with other experimental techniques, WbLS offers the highest signal efficiency of more than 80\% and best signal significance over background.

Results obtained with a new very compact detector for imaging with a matrix of Leak Microstructures (LM)are reported. Spatial linearity and spatial resolution obtained by scanning as well as the detection of alpha particles with 100% efficiency, when compared with a silicon detector, are stressed. Preliminary results recently obtained in detecting single electrons emitted by heated filament (Ec < 1 eV) at 1-3 mbar of propane are reported.

Migdal effect is attracting interests because of the potential to enhance the sensitivities of direct dark matter searches to the low mass region. In spite of its great importance, the Migdal effect has not been experimentally observed yet. A realistic experimental approach towards the first observation of the Migdal effect in the neutron scattering was studied with Monte Carlo simulations. In this study, potential background rate was studied together with the event rate of the Migdal effect by a neutron source. It was found that a table-top sized ∼(30cm ) 3 position-sensitive gaseous detector filled with argon or xenon target gas can detect characteristic signatures of the Migdal effect with sufficient rates (O( 10 2 ∼ 10 3 ) events/day). A simulation result of a simple experimental set-up showed two significant background sources, namely the intrinsic neutrons and the neutron induced gamma-rays. These background rates were found to be much higher than those of the Migdal effect in the neutron scattering. As a consequence of this study, it is concluded that the experimental observation of the Migdal effect in the neutron scattering can be realized with a good understanding and reduction of the background.

This paper addresses three-dimensional signal distortion and image reconstruction issues in x-ray Bragg coherent diffraction imaging (BCDI) in the event of a general non-orthogonal orientation of the area detector with respect to the diffracted beam. Growing interest in novel BCDI adaptations at fourth-generation synchrotron light sources has necessitated improvisations in the experimental configuration and the subsequent data analysis. One such possibly unavoidable improvisation that is envisioned in this paper is a photon-counting area detector whose face is tilted away from the perpendicular to the Bragg-diffracted beam during acquisition of the coherent diffraction signal. We describe a likely circumstance in which one would require such a detector configuration, along with experimental precedent at third generation synchrotrons. Using physically accurate diffraction simulations from synthetic scatterers in the presence of such tilted detectors, we analyze the general nature of the observed signal distortion qualitatively and quantitatively, and provide a prescription to correct for it during image reconstruction. Our simulations and reconstructions are based on an adaptation of the known theory of BCDI sampling geometry as well as recently developed projection-based methods of wavefield propagation. Such configurational modifications and their numerical remedies are potentially valuable in realizing unconventional coherent diffraction measurement geometries and eventually paving the way for the integration of BCDI into new materials characterization experiments at next-generation light sources.

A novel fusion product separator, based on a gas-filled 8 T superconducting solenoid has been developed at the Australian National University. Though the transmission efficiency of the solenoid is very high, precision cross section measurements require knowledge of the angular distribution of the evaporation residues. A method has been developed to deduce the angular distribution of the evaporation residues from the laboratory-frame velocity distribution of the evaporation residues measured at the exit of the separator. The features of this method are presented, focusing on the example of 34 S+ 89 Y which is compared to an independent measurement of the angular distribution. The establishment of this method now allows the novel solenoidal separator to be used to obtain reliable, precision fusion cross-sections.