Initial PET Performance Evaluation of a Preclinical Insert for PET/MRI with Digital SiPM Technology

Hyperion-IID is a positron emission tomography (PET) insert which allows simultaneous operation in a clinical magnetic resonance imaging (MRI) scanner. To read out the scintillation light of the employed LYSO crystal arrays with a pitch of 1 mm pitch and 12 mm in height, digital silicon photomultipliers (DPC 3200-22, Philips Digital Photon Counting) (DPC) are used. The basic PET performance in terms of energy resolution, coincidence resolution time (CRT) and sensitivity as a function of operating parameters, such as the operating temperature, the applied overvoltage, activity and configuration parameters of the DPCs, were evaluated on system level. The measured energy resolution did not show a large dependency on the selected parameters and is in the range of 12.4-12.9% for low activities and degrades to ~13.6% at activities of ~100 MBq. The CRT strongly depends on the selected trigger scheme (trig) of the DPCs. We measured approximately 260 ps, 440 ps, 540 ps and 1300 ps for trig 1-4, respectively. The trues sensitivity for a NEMA NU 4 mouse-sized scatter phantom with a 70-mm-long tube of activity was dependent on the operating parameters and was determined to be 0.4-1.4% at low activities. The random fraction stayed below 5% at activities up to 100 MBq and the scatter fraction was evaluated as ~6% for an energy window of 411-561 keV and ~16% for 250-625 keV. Furthermore, we performed imaging experiments using a mouse-sized hot-rod phantom and a large rabbit-sized phantom. In 2D slices of the reconstructed mouse-sized hot-rod phantom ({\O} = 28 mm), the rods were distinguishable from each other down to a rod size of 0.8 mm. There was no benefit of the better CRT of trig 1 over trig 3, where in the larger rabbit-sized phantom ({\O} = 114 mm), we could show a clear improvement of image quality using the time-of-flight information.Comment: Final journal version including the supplemntal data. The images in the supplement were compressed to meet the arXiv file size limi

Observation of High-Energy Astrophysical Neutrinos in Three Years of IceCube Data

A search for high-energy neutrinos interacting within the IceCube detector between 2010 and 2012 provided the first evidence for a high-energy neutrino flux of extraterrestrial origin. Results from an analysis using the same methods with a third year (2012-2013) of data from the complete IceCube detector are consistent with the previously reported astrophysical flux in the 100 TeV - PeV range at the level of $10^{-8}\, \mathrm{GeV}\, \mathrm{cm}^{-2}\, \mathrm{s}^{-1}\, \mathrm{sr}^{-1}$ per flavor and reject a purely atmospheric explanation for the combined 3-year data at $5.7 \sigma$. The data are consistent with expectations for equal fluxes of all three neutrino flavors and with isotropic arrival directions, suggesting either numerous or spatially extended sources. The three-year dataset, with a livetime of 988 days, contains a total of 37 neutrino candidate events with deposited energies ranging from 30 to 2000 TeV. The 2000 TeV event is the highest-energy neutrino interaction ever observed.Comment: 8 pages, 5 figures. Accepted by PRL. The event catalog, event displays, and other data tables are included after the final page of the article. Changed from the initial submission to reflect referee comments, expanding the section on atmospheric backgrounds, and fixes offsets of up to 0.9 seconds in reported event times. Address correspondence to: J. Feintzeig, C. Kopper, N. Whitehor

Measurement of the cosmic ray energy spectrum with IceTop-73

We report on the measurement of the all-particle cosmic ray energy spectrum with the IceTop air shower array in the energy range from 1.58 PeV to 1.26 EeV. The IceTop air shower array is the surface component of the IceCube Neutrino Observatory at the geographical South Pole. The analysis was performed using only information from IceTop. The data used in this work were taken from June 1, 2010 to May 13, 2011. During that period the IceTop array consisted of 73 stations, compared to 81 in its final configuration. The measured spectrum exhibits a clear deviation from a single power law above the knee around 4 PeV and below 1 EeV. We observe spectral hardening around 18 PeV and steepening around 130 PeV.M. G. Aartsen ... G. C. Hill ... et al. (IceCube Collaboration

Measurement of atmospheric neutrino oscillations with IceCube

We present the first statistically significant detection of neutrino oscillations in the high-energy regime (>20 GeV) from an analysis of IceCube Neutrino Observatory data collected in 2010 and 2011. This measurement is made possible by the low-energy threshold of the DeepCore detector (~20 GeV) and benefits from the use of the IceCube detector as a veto against cosmic-ray-induced muon background. The oscillation signal was detected within a low-energy muon neutrino sample (20-100 GeV) extracted from data collected by DeepCore. A high-energy muon neutrino sample (100 GeV-10 TeV) was extracted from IceCube data to constrain systematic uncertainties. The disappearance of low-energy upward-going muon neutrinos was observed, and the nonoscillation hypothesis is rejected with more than 5σ significance. In a two-neutrino flavor formalism, our data are best described by the atmospheric neutrino oscillation parameters |Δm(32)(2)|=(2.3(-0.5)(+0.6))×10(-3) eV(2) and sin(2)(2θ(23))>0.93, and maximum mixing is favored.M. G. Aartsen ... G. C. Hill ... et al. (IceCube Collaboration

Determination of the Recovery Time of Silicon Photomultipliers

This thesis describes the determination of the recovery time of dierent silicon photo- multipliers. The experimental setup uses two LEDs to rst re all the pixels of the SiPM and then probe the recovery process with a second identical light pulse. The SiPM re- covers with an exponential process with two time constants. The recharge of the pixels attributes to the dominating fast time constant and the recharge of the bulk attributes to the slow time constant, which dominates the tail of the recovery. The pixel recovery time is approximately between 7 ns and 50 ns and is smaller for small pixel sizes. The bulk recovery time is between approximately 100 ns and 200 ns and is more dominant for a large pixel size. An increase of the recovery time as a function of the overvoltage has been observed

A Public Resource for West Croydon

The work was an invitation to make a wall painting on flank wall of a high street revealed during East Architects’ masterplanning of West Croydon transport hub. Our proposal was: This wall in the public realm has the potential to sign local resources and knowledge, ideally free things that are available in the borough, or point to unexpected destinations. We will find local organisations, resources and spaces that could benefit from some unsolicited attention and produce adverts for them. Each sign would be designed specifically in one or two colours and produced as vitreous enamel signs with an etched panel of captions giving further information. The signs are all unsolicited, imposed is the wrong word, but we were keen to not seek approval or be interpreted as a ‘service’. The limitations of the project were the borough itself and the budget for producing the enamel tiles. The research method was to meet local interest groups, go to annual meetings, council offices, bat walks, fungus farms, apple pressing days, etc. and to visit the enamel factory to better understand the process of printing on metal. The outcome is a permanent installation of fourteen enamel signs and an etched steel key to those signs. The audience are visitors to Croydon as well as residents and the recipients of signs