Summer student project presentations 2019

Due to mysterious low energy, alpha like events reconstructing in the bulk of the DEAP-3600 dark matter detector, we look into the possibility of small amounts of dust particles being present in the liquid argon of the detector. Monte Carlo simulations of alpha decays inside spherical norite dust particles are produced and compared to data with hopes to explain these events. With some discrepancies between the reconstructed position of these simulated dust events and the data of interest, different position distributions of dust particles in the detector are tested to converge upon a realistic description of potential dust in the detector.

The assay of lead 210 was attempted using a novel method for Accelerated Mass Spectrometry. Using this technique we propose a method for Pb210 assay to which can be applied to most materials for impurity determination for many pressing radiation background investigations. Our method can uniquely eliminate molecular background drastically improving sensitivities while requiring far less than a gram of sample to be assayed making it advantageous over other assay techniques. Chemical procedure and AMS techniques were combined to observe Pb210 concentration never before seen in Kapton and the technique was compared and proved by the assay of Pb210 concentration in Sn-free solder.

I performed a number of studies relating to position reconstruction for DEAP-3600 with the purpose of investigating some open questions. The studies performed include looking into failure populations for one of the position reconstruction algorithms (TimeFit2) as well as code review for that processor. I also investigated evidence of potential liquid argon flow which may be present within the detector. Finally I investigated a known issue with another position reconstruction algorithm (mblikelihood) where some events are incorrectly placed on the surface of the detector.

Multiphoton microscopy uses nonlinear light-matter interactions to achieve non-destructive, label-free imaging, and is a rapidly emerging optical imaging technique for investigating biological samples. Nonlinear light is only produced by molecules with specific properties, such as fluorescent or non-centrosymmetric structures, allowing for chemically-selective images to be generated. Typically, the nonlinear light produced is very small and must be detected by a photodetector such as a photomultiplier tube or avalanche photodiode. Silicon photomultipliers (SiPM) are an attractive alternative for low-light detection due to their high gain, low cost, and small size. This talk explores an initial application of SiPMs in a multimodal, multiphoton microscope to image various biological and nonbiological samples, and identifies key benefits and challenges involved in their use.

The Enriched Xenon Observatory is looking to observe the Standard Model forbidden neutrinoless double beta decay through the decay of 136-Xe. If observed, this would imply that the neutrino is a Majorana particle. One method currently being developed at Carleton University for use by nEXO is barium tagging which once completed, will be able to detect the decay of 136-Xe to 136-Ba++. This would remove any non-ββ backgrounds, which would lead to a significant increase in sensitivity. My work this summer was to restart the operation of Barium tagging which involves using two frequency locked lasers to excite trapped 136-Ba+ ions, and to measure the emitted fluorescence to calculate the population of 136-Ba+ ions that are present within the trap.

DEAP-3600 is a liquid argon (LAr) dark matter detector. Its chief advantage lies in the success of pulse-shape discrimination (PSD) at suppressing electromagnetic backgrounds from scintillation events in the LAr. The pulse-shapes of LAr Scintillation serve as a basis for PSD and are modeled as a convolution of detector effects and LAr scintillation physics, the latter of which consists of the singlet and triplet lifetimes of the beta decay of the isotope Ar39. There is evidence in the data that alongside the singlet and triplet lifetimes there is a third, intermediate, component currently unaccounted for. The subject of this presentation is the addition of an intermediate component which could potentially see the improvement of the fidelity of simulations of important PSD variables.

I will talk about the work on the process of the commissioning the EXO-100 cryostat for future experiments. It will describe the many issues faced when getting the cryostat to full functionality and how these problems were solved.

In preparation for the High-Luminosity upgrade to the LHC, here at Carleton University we are building small-strip Thin Gap Chamber (sTGC) detectors as part of the New Small Wheel (NSW) to be installed within ATLAS. Currently around 90% of the Level-1 Muon triggers from ATLAS are false, which is obviously a huge issue, and these sTGC detectors will act as an additional trigger to drastically reduce the amount of false triggers while also improving the response time and position tracking of the detector. My work this summer has been to create a python script to be used as a tool to analyse measurements made during the assembly process in order to infer how the construction variations will affect the physics involved once the detector is installed within ATLAS.

Silicon photomultiplier (SiPM) modules appear to be an interesting and inexpensive replacement for conventional photomultipliers, presenting a variety of applications as detectors. One of the difficulties using these units as detectors is having a proper readout system to acquire and process the correct information for the experiment. Thus my task over the last 4 months was to learn, develop, and design the parts of an adequate readout system using a particular SiPM. These parts include platforms to properly bias and amplify the SiPM and its signals, and a platform that will digitize and process the signals into meaningful data using an FPGA. This detector and readout system will then be used to measure the efficiency of a probe that will need to extract the product of a particular decay in the LXe TPC in the nEXO project. The topics discussed during this presentation involve the development and design process of the different platforms that will make the SiPM work, as well as the application of the knowledge gained in designing each platform.

The future generation of water Cerenkov detectors gives the possibility to look into new models for the individual photodetectors used in these large-scale systems. For this,
Canada has proposed a model for the upcoming Hyper-Kamiokande which constitutes of a matrix of PMTs (called a multi-PMT). Some of the improvements of this proposed model with reference to others are shown in this presentation, giving an analysis of effective area, quantum efficiency and collection efficiency for photon wavelengths in the Cerenkov spectrum. Details on how to further upgrade such model are also mentioned.

Brachytherapy is a type of radiation therapy where radioactive sources are placed near or within a tumor. Patient treatment plans are developed and assessed by calculating the dose; the amount of energy deposited from radiation per unit mass of tissue. The Carleton Laboratory for Radiotherapy Physics (CLRP) group has developed a dose calculation algorithm, called egs_brachy, which is used for brachytherapy treatments. My role has been to create an application, called egs_brachy GUI (Guided User Interface) to extend egs_brachy for use in clinical applications. I will give an overview of egs_brachy GUI and discuss its process.