Final Scientific/Technical Report Development of Large-Area Photo-Detectors

This proposal requested ADR funds for two years to make measurements and detector proto-types in the context of planning a program in conjunction with Argonne National Laboratory to develop very large-area planar photodetectors. The proposed detectors have integrated transmission-line readout and sampling electronics able to achieve timing and position resolutions in the range of 1-50 psec and 1-10 mm, respectively. The capability for very precise time measurements is inherent in the design, and provides a �third� coordinate, orthogonal to the two in the plane, for the point of origin of photons or charged particles, allowing �tomographic� reconstruction in 3-dimensions inside a volume

Low-Dose TOF-PET Based on Surface Electron Production in Dielectric Laminar MCPs

We present simulations of whole-body low-dose time-of-flight positron emission tomography (TOF-PET) based on the direct surface production [1] by 511 keV gamma rays of energetic electrons via the Photo-electric and Compton Effects, eliminating the scintillator and photodetector sub-systems in PET scanners. In Ref. [1] we described Microchannel Plates (MCP) constructed from thin dielectric laminae containing heavy nuclei such as lead or tungsten (LMCP$^{\rm{TM}}$). The laminae surfaces are micro-patterned to form channels, which can then be functionalized to support secondary electron emission in the manner of conventional MCPs. We have simulated direct conversion using modifications to the TOPAS Geant4-based tool kit. A 20 $\times$ 20 $\times$ 2.54 cm$^3$ LMCP, composed of 150-micron thick lead-glass laminae, is predicted to have a $\ge 30$% conversion efficiency to a primary electron that penetrates an interior wall of a pore. The subsequent secondary electron shower is largely confined to one pore and can provide high space and time resolutions. In whole-body PET scanners the technique eliminates the scintillator and photodetector subsystems. The consequent absence of a photocathode allows assembly of large arrays at atmospheric pressure and less stringent vacuum requirements, including use of pumped and cycled systems. TOPAS simulations of the Derenzo and XCAT-brain phantoms are presented with dose reductions of factors of 100 and 1000 from a literature benchmark. New applications of PET at a significantly lower radiation dose include routine screening for early detection of pathologies, the use in diagnostics in previously unserved patient populations such as children, and a larger installed facility base in rural and under-served populations, where simpler gamma detectors and lower radiation doses may enable small low-cost portable PET scanners.Comment: Version 9d incorporates reviewer comments during revision process. 22 pages, 18 figure

A 96-Channel FPGA-based Time-to-Digital Converter

We describe an FPGA-based, 96-channel, time-to-digital converter (TDC) intended for use with the Central Outer Tracker (COT) in the CDF Experiment at the Fermilab Tevatron. The COT system is digitized and read out by 315 TDC cards, each serving 96 wires of the chamber. The TDC is physically configured as a 9U VME card. The functionality is almost entirely programmed in firmware in two Altera Stratix FPGA's. The special capabilities of this device are the availability of 840 MHz LVDS inputs, multiple phase-locked clock modules, and abundant memory. The TDC system operates with an input resolution of 1.2 ns. Each input can accept up to 7 hits per collision. The time-to-digital conversion is done by first sampling each of the 96 inputs in 1.2-ns bins and filling a circular memory; the memory addresses of logical transitions (edges) in the input data are then translated into the time of arrival and width of the COT pulses. Memory pipelines with a depth of 5.5 $\mu$s allow deadtime-less operation in the first-level trigger. The TDC VME interface allows a 64-bit Chain Block Transfer of multiple boards in a crate with transfer-rates up to 47 Mbytes/sec. The TDC also contains a separately-programmed data path that produces prompt trigger data every Tevatron crossing. The full TDC design and multi-card test results are described. The physical simplicity ensures low-maintenance; the functionality being in firmware allows reprogramming for other applications.Comment: 32 pages, 13 figure

The Boundary Conditions of the Heliosphere: Photoionization Models Constrained by Interstellar and In Situ Data

The boundary conditions of the heliosphere are set by the ionization, density and composition of inflowing interstellar matter. Constraining the properties of the Local Interstellar Cloud (LIC) at the heliosphere requires radiative transfer ionization models. We model the background interstellar radiation field using observed stellar FUV and EUV emission and the diffuse soft X-ray background. We also model the emission from the boundary between the LIC and the hot Local Bubble (LB) plasma, assuming that the cloud is evaporating because of thermal conduction. We create a grid of models covering a plausible range of LIC and LB properties, and use the modeled radiation field as input to radiative transfer/thermal equilibrium calculations using the Cloudy code. Data from in situ observations of He^O, pickup ions and anomalous cosmic rays in the heliosphere, and absorption line measurements towards epsilon CMa were used to constrain the input parameters. A restricted range of assumed LIC HI column densities and LB plasma temperatures produce models that match all the observational constraints. The relative weakness of the constraints on N(HI) and T_h contrast with the narrow limits predicted for the H^O and electron density in the LIC at the Sun, n(H^0) = 0.19 - 0.20 cm^-3, and n(e) = 0.07 +/- 0.01 cm^-3. Derived abundances are mostly typical for low density gas, with sub-solar Mg, Si and Fe, possibly subsolar O and N, and S about solar; however C is supersolar. The interstellar gas at the Sun is warm, low density, and partially ionized, with n(H) = 0.23 - 0.27 cm^-3, T = 6300 K, X(H^+) ~ 0.2, and X(He^+) ~ 0.4. These results appear to be robust since acceptable models are found for substantially different input radiation fields. Our results favor low values for the reference solar abundances for the LIC composition.Comment: 14 pages, 4 figures, submitted to Astronomy & Astrophysics together with papers from the International Space Sciences Institute workshop on Interstellar Hydrogen in the Heliospher

A proposal to study hard hadron - hadron collisions

We propose a novel technique to study hadron-hadron collisions in which a significant fraction of the available energy is carried off in directions transverse to the beam. The technique is independent of the details of the final state so is ideally suited to searching for the jet-like particle clusters predicted by the parton model. The detector consists of a small calorimeter and several planes of 1 meter square proportional chambers

The "Solar Model Problem" Solved by the Abundance of Neon in Stars of the Local Cosmos

The interior structure of the Sun can be studied with great accuracy using observations of its oscillations, similar to seismology of the Earth. Precise agreement between helioseismological measurements and predictions of theoretical solar models has been a triumph of modern astrophysics (Bahcall et al. 2005). However, a recent downward revision by 25-35% of the solar abundances of light elements such as C, N, O and Ne (Asplund et al. 2004) has broken this accordance: models adopting the new abundances incorrectly predict the depth of the convection zone, the depth profiles of sound speed and density, and the helium abundance (Basu Antia 2004, Bahcall et al. 2005). The discrepancies are far beyond the uncertainties in either the data or the model predictions (Bahcall et al. 2005b). Here we report on neon abundances relative to oxygen measured in a sample of nearby solar-like stars from their X-ray spectra. They are all very similar and substantially larger than the recently revised solar value. The neon abundance in the Sun is quite poorly determined. If the Ne/O abundance in these stars is adopted for the Sun the models are brought back into agreement with helioseismology measurements (Antia Basu 2005, Bahcall et al. 2005c).Comment: 13 pages, 3 Figure

A search for direct muon production in the forward direction

We propose to search for direct muon production in the forward direction from 300 GeV protons incident on a heavy nuclear target. By using the first stage of the Ml beam as a source of a diffracted proton beam and the second and third stages of Ml as a spectrometer, one can make a measurement of the direct muon to pion ratio at values of x between 0.3 and 0.75. If this ratio is on the order of 10{sup -4}, the event rates are on the order of 800 direct muons/hr. at an x of .5. The modifications to the Ml beam are minor