Session E12: Instrumentation and Applications

Small, Fast, Gas Detector for High-Energy Electrons

A Parallel Plate Avalanche Counter (PPAC) measured electromagnetic showers from $\pi^0$s made by 120 GeV protons on 29 mm (7 X$_0$) of Ta. The largest signals resulted from $\pi^0 $s made by protons that interacted near the surface, so that most of the 29 mm was available for development of showers. Isobutane at 120 torr filled the 0.6 mm gap between 1.0 cm$^2$ plates. With 950 V between the plates the PPAC put -40 mV signals into 50 $\Omega$ coax (no electronic amplification). The 120 GeV protons were from the Meson Test Beam Facility at Fermilab. Tests of the detector in our Iowa laboratory were made by placing a 7 mCi $^{137}$Cs source to the side of the detector. Signals from Compton scattered electrons traveling along the gap between the plates were as large as -20 mV. With most PPACs the shape of the signal from the electrons in the avalanche is dominated by the RC time constant, C is the capacity of the detector and R = 50 $\Omega$. With our small PPAC the shape of the signal is governed by the motion of the charges between the plates. The electron signal has a width, FWHM, of about 1.4 ns.   

Qweak Detector Update

The Qweak experiment at Jefferson Laboratory will make the first measurement of the weak charge of the proton to constrain new electron-quark interactions at the TeV-scale. The experimental observable of interest is the small, parity-violating asymmetry in the elastic scattering of electrons from protons. Cerenkov light emitted by the scattered electrons in quartz bars will be converted to current by phototubes. The desired signal resides in the small ( $<$ 1 ppm) change in average anode current when the longitudinal beam polarization is reversed. Results from a prototype test will be presented as well as our latest design for the full-size detector. The anticipated performance in terms of linearity and total noise (relative to counting statistics) will also be discussed.   

Critical Need for Radiation Damage Tools for Space Missions

NASA has a new vision for space exploration in the 21st Century encompassing a broad range of human and robotic missions including missions to Moon, Mars and beyond. As a result, there is a focus on long duration space missions. NASA, as much as ever, is committed to the safety of the missions and the crew. Exposure from the hazards of severe space radiation in deep space long duration missions is `the show stopper.' Thus, protection from the hazards of severe space radiation is of paramount importance for the new vision. There is an overwhelming emphasis on the reliability issues for the mission and the habitat. Accurate risk assessments critically depend on the accuracy of the input information about the interaction of ions with materials, electronics and tissues. A huge amount of essential experimental information for all the ions in space, across the periodic table, for a wide range of energies of several (up to a Trillion) orders of magnitude are needed for the radiation protection engineering for space missions that is simply not available (due to the high costs) and probably never will be. Therefore, there is a compelling need to develop reliable accurate models of nuclear reactions and structures that form the basic input ingredients. State-of-the-art nuclear cross sections models have been developed at the NASA Langley Research Center, however a considerable number of tools need to be developed to alleviate the situation. The vital role and importance of nuclear physics for space missions will be discussed.   

Nuclear imaging of iodine uptake in mouse tissues

We have designed and employed a compact gamma camera based on pixellated scintillators and position-sensitive photomultipliers to obtain in vivo images in mice of biological substances tagged with 125-I. Biomedical imaging studies make use of radioactive isotopes of iodine. In these applications, protection of the thyroid from the effects of the radioactive material can be important. We have studied \textit{in vivo} the effectiveness in mice of pre-administration of KI in various concentrations to evaluate both the biologically effective doses for thyroid protection and the potential for use in general sodium iodide symporter studies. These findings have important implications for both intentional and accidental exposure to radioiodine.   

Neutron-Induced Partial Gamma-Ray Cross-Section Measurements on 238U Using a Monoenergetic and Pulsed Beam at TUNL

An experimental program is being developed at TUNL to study (n,2n) excitation functions on actinide nuclei using monoenergetic neutrons in the 5 to 18 MeV energy range with the goal of improving the partial cross-section data for the NNSA Stockpile Stewardship Program. Measurements have been performed on a $^{238}$U target in the TUNL shielded neutron source area using a pulsed neutron beam with incident neutron energies of 6, 8, 10, and 14 MeV. The emitted gamma rays were measured using different types of HPGe detectors. The pulsed beam permitted the use of time-of-flight techniques to distinguish (n,2n) events from background events. Experimental techniques and analysis of the measurements will be presented.   

Thermal neutron probe of trace elements in synthetic sapphire for LIGO optics

In pursuing the direct detection of gravity waves the Laser Interferometer Gravitational-wave Observatory (LIGO) experiment continues to push the limits of technology. In advanced versions of the interferometer more than 800 kW of laser power is expected to be stored in the Fabry-Perot cavities that make up LIGO's 4-km long arms. As part of an effort to assess the suitability of synthetic sapphire as a test mass material we have implemented a program of trace element measurements with the goal of identifying correlations between optical absorption at 1064 nm and trace element content of high purity sapphire. Small commercially-produced synthetic sapphire samples ($\sim $50 -- 200 mg) have been exposed to thermal neutrons in the NIST 20 MW reactor at fluxes of $\sim $8 x 10$^{13}$ neutrons /cm$^{2}$s and subsequently counted on calibrated high resolution gamma-ray spectrometers. Initial measurements show a broad range of elements present, most of which occur at concentrations at or below the parts-per-billion level. Details of the experiments will be presented with results.