No description available.

A two-scintillator paddle muon telescope with variable angular acceptance at the earth's surface was used to study correlations between flux distribution and barometric pressure. The detector was placed in 2 different locations around Georgia State University with varying paddle separations of 0, 7, and 14 inches. Correlation and anti-correlation analyses were conducted by using the muon count from the detector along with the barometric pressure, surface temperature, stratospheric temperature and solar activity. It was observed that there was a short and long-term variation relationship between cosmic ray counts and barometric pressure and also cosmic ray counts and temperature. No significant relationship was found between cosmic ray flux and solar activity. A new two-scintillator paddle telescope with larger detecting area was constructed in order to observe a stronger correlation between cosmic ray flux and pressure.

The purpose of this study was to determine how well the Monte Carlo transport code FLUKA can simulate a tissue-equivalent proportional counter (TEPC) and produce the expected delta ray events when exposed to high energy heavy ions (HZE) like in the galactic cosmic ray (GCR) environment. Accurate transport codes are desirable because of the high cost of beam time, the inability to measure the mixed field GCR on the ground and the flexibility they offer in the engineering and design process. A spherical TEPC simulating a 1 um site size was constructed in FLUKA and its response was compared to experimental data for an 56Fe beam at 360 MeV/nucleon. The response of several narrow beams at different impact parameters were used to explain the features of the response of the same detector exposed to a uniform field of radiation. Additionally, an investigation was made into the effect of the wall thickness on the response of the TEPC and the range of delta rays in the tissue-equivalent (TE) wall material. A full impact parameter test (from IP = 0 to IP = detector radius) was performed to show that FLUKA produces the expected wall effect. That is, energy deposition in the gas volume can occur even when the primary beam does not pass through the gas volume. A final comparison to experimental data was made for the simulated TEPC exposed to various broad beams in the energy range of 200 - 1000 MeV/nucleon. FLUKA overestimated energy deposition in the gas volume in all cases. The FLUKA results differed from the experimental data by an average of 25.2 % for yF and 12.4 % for yD. It is suggested that this difference can be reduced by adjusting the FLUKA default ionization potential and density correction factors.

No description available.

The Daya Bay reactor neutrino experiment aims to determine sin2 2θ13 with a sensitivity of 0.01 or better at 90% confidence level. One of the major backgrounds to neutrino measurements is the muon-induced neutrons. An ex- periment had been set up inside the Aberdeen Tunnel laboratory, Hong Kong, to study spallation neutrons induced by cosmic-ray muons in an underground environment similar to the Daya Bay experiment. The Aberdeen Tunnel laboratory is 22 m above sea level at 22:23?N and 114:6?E. The amount of overburden is approximately 235 m of rocks, which is equivalent to 611 m.w.e. Rock compositions in the Aberdeen Tunnel area is similar to that in Daya Bay. MUSIC simulation results showed that in the laboratory the mean energy of muons 〈Eμ〉= 122 GeV and the integrated muon intensity I = 9:64 X10??6 cm??2 s??1. A Bonner Spheres Neutron Spectrometer (BSS) was developed to measure the ambient neutron energy spectrum. The BSS consists of a thermal neutron detector and a set of eight polyethylene spherical shells. The overall detection efficiency of the BSS was (96:7 +3:3 ??13:1)% with a detector background rate of (1:96_0:03)_10??3 s??1. The total neutron fluence rate measured at the Surface Assembly Building (SAB) of the Daya Bay experiment was (5:20 +0:81 ??0:44) _ 10??3 cm??2 s??1, which agreed with the neutron fluence rate measured in the air/ground interface in Taiwan. The unfolded SAB neutron energy spectrum showed a clear thermal-neutron peak around 20 meV and a cascade peak around 100 MeV. Detectable number of neutrons could be seen at 1 GeV. The neutron fluence rate measured at the Aberdeen Tunnel (ABT) laboratory was significantly higher then some other underground laboratories. The unfolded ABT neutron energy spectrum showed a pronounced evaporation peak around 1 MeV, and a sup- pression in the cascade peak. Detections of muon-induced neutrons inside the Aberdeen Tunnel laboratory is achieved by a Muon Tracker and a Neutron Detector. The Muon Tracker consists of three main layers of crossed plastic scintillator hodoscopes capable of determining the incoming direction of muons. The average efficiency for most of the hodoscopes was above 95%. The Neutron Detector consists of about 760 L of gadolinium-doped liquid scintillator and sixteen photomultiplier tubes. The liquid scintillator target is shield by about 1900 L of mineral oil from external radiations. The overall average detection efficiency of muon-induced neutrons was about 16%. The measurement of muon-induced neutrons in the Aberdeen Tunnel lab- oratory started from June 2011, with a total live time of about 30 days. The average rate of the accepted muon events was 0.013 Hz. The muon-induced neutron yield was determined to be Nn = (8:5 _ 0:4(syst.) _ 1:8(stat.)) _ 10??5 neutron/(μg cm??2). This value agreed with the parametrization of FLUKA-1999 simulation results if the muon energy dependence of muon-induced neutron yields was considered. / published_or_final_version / Physics / Doctoral / Doctor of Philosophy

The muon-induced radioactive isotopes, especially neutrons, are dangerous background component for rare-event detection in underground experiments, like neutrino-less double-beta decay and dark matter search. Understanding these cosmogenic backgrounds is crucial for these experiments. An underground experiment aiming at measuring the cosmic-ray muons' flux and their neutron production yield in liquid scintillator through spallation process is being carried out in the Aberdeen Tunnel laboratory located in Hong Kong with a total vertical overburden of 235 m of rocks (611 m.w.e.). The Aberdeen Tunnel detection system is constituted of a Muon Tracker (MT) for muon tagging and a Neutron Detector (ND) for neutron detection. The MT consists of 60 plastic scintillator hodoscopes to determine the incoming muon direction and the ND is a two-zone detector containing 760 L of gadolinium-doped liquid scintillator as target volume and 1900 L of mineral oil as shields. The experiment has been taking data stably since 2012. To obtain reliable results, the detector performance and the stability of the experiment have been studied in this work. Muon-induced fast neutrons can be captured in Gd-LS with characteristic energies released and the capture time follows a characteristic exponential distribution. By using the capture time and energy information, we can select the neutron candidates and thus calculate the neutron production yield. The energy of a neutron capture event is reconstructed from the calibrated photo-multiplier tube signals, while the directions of cosmic-ray muons can be reconstructed from the MT. The mean energy of the incoming muons that pass the selection criteria was estimated by a simulation code MUSIC that transported atmospheric muon spectrum through the mountains to the laboratory, and is found to be 92 GeV. The neutron production yield is calculated to be Yn = (3:28 ±0:12(sta:) ±0:24(sys:)) X 〖10〗^(-4) (n/μ〖gcm〗^(-2)) for both the showering muon and single muon events. This result is about two times higher than the expectation value from previous simulations and experiments. The neutron production yield of the single muons is calculated to be Yn = (1:04 ± 0:08(sta:) ± 0:07(sys:)) X 〖10〗^(-4) (n/μ〖gcm〗^(-2)). This reveals a enhancement of the neutron production from the muons accompanied by showers. / published_or_final_version / Physics / Master / Master of Philosophy

Galaxy clusters are the most massive bound systems known in the Universe and are believed to have formed through large scale structure formation. They host relativistic cosmic-ray (CR) populations and are gravitationally bound by large amounts of Dark Matter (DM), both providing conditions in which high-energy gamma rays may be produced either via CR interactions with the intracluster medium or through the annihilation or decay of DM particles. Prior to the launch of the Fermi satellite, predictions were optimistic that these sources would be established as γ-ray-bright objects by observations through its prime instrument, the Large Area Telescope (LAT). Yet, despite numerous efforts, even a single firm cluster detection is still pending. This thesis presents a number of studies based on data taken by the LAT over its now seven year mission aiming to discover these γ rays. Using a joint likelihood technique, we study the γ-ray spectra of a sample of nearby clusters searching for a CR-induced signal due to hadronic interactions in the intracluster medium. While we find excesses in some individual targets, we attribute none to the cluster. Hence, we constrain the maximum injection efficiency of hadrons being accelerated in structure formation shocks and the fraction of CR-to-thermal pressure. We also perform a refined search targeting the Coma cluster specifically due to its large variety of existing observations in other wavebands. In the latter case we find weak indications of an excess which however falls below the detection threshold. Because the cluster emission we consider is inherently extended, we need to take into account the imperfect modeling of the foreground emission, which may be particularly difficult such as is the case with the Virgo cluster. Here, we assess the systematics associated with the foreground uncertainties and derive limits based on an improved background model of the region. For the first time we derive limits on the γ-ray flux from CR and DM-interactions in which we take into account the dynamical state of the system. For DM we also include the contribution from substructure. The DM domain is further explored by searching for line-like features as they arise from the annihilation of DM into two photons in a large sample of clusters, including Virgo and Coma. Finding no evidence for γ-ray lines, we derive limits on the DM annihilation cross section that are roughly a factor 10 (100) above that derived from observations of the galactic center assuming an optimistic (conservative) scenario regarding the boost due to DM substructure. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Submitted. Paper 4: Submitted.</p>

Inflation, which posits an exponential expansion in the early universe, is well motivated since it resolves questions that are left unexplained by standard LCDM cosmology, such as the flatness and homogeneity of the universe. The exponential expansion of universe during inflation explains the structure in the universe by freezing out the quantum fluctuations of space. These quantum fluctuations are also expected to generate a background of gravitational waves which would then imprint a B-mode polarization signal on the Cosmic Microwave Background. The Bicep2 and Keck Array experiments search for B-mode polarization from inflationary gravitational waves in the Cosmic Microwave Background. Bicep2 and the Keck Array use small aperture, cold, on-axis refracting optics optimized to target the degree angular scales at which the inflationary B-mode polarization is expected to peak. In this thesis we describe the optical design of Bicep2 and the Keck Array. The small aperture design allows us to fully characterize the far-field performance of the instrument on site at the South Pole using thermal and amplified sources on the ground. We describe the efforts taken to characterize the main beam shapes of each polarization sensitive bolometer, as well as the differential beam paramters of each co-located orthogonally polarized detector pair. We study the residual temperature to polarization leakage induced by the beam mismatches after the principle modes have been mitigated in the analysis. / Physics

published_or_final_version / Physics / Doctoral / Doctor of Philosophy

Existing techniques measure soil moisture either at a point or over a large area many kilometers across. To bridge these two scales, we used the mobile cosmic-ray probe, or cosmic-ray rover, an instrument similar to the recently developed COSMOS probe, but bigger and mobile. This study explores the challenges and opportunities for making maps of soil moisture over large areas using the cosmic-ray rover. In 2012, soil moisture was mapped 22 times in a 25 km x 40 km survey area of the Tucson Basin at 1 km² resolution, i.e., at a scale comparable to that of a pixel for the Soil Moisture and Ocean Salinity (SMOS) satellite mission. The soil moisture distribution is influenced mainly by climatic variations, notably by the North American monsoon, which resulted in a systematic change in the regional variance as a function of the mean soil moisture.