LIQUID XENON MULTIWIRE PROPORTIONAL CHAMBERS FOR NUCLEAR MEDICINEAPPLICATIONS

The need for improved spatial resolution in nuclear medicine has long been recognized. Notable attempts to achieve this goal are the gas-filled wire chambers and solid-state detectors. (1) However, at energies above 100 keV, gas-filled chambers suffer from poor detection efficiency and a long recoil electron range in the gas. While it is advantageous to pressurize these chambers to 10 or more atmospheres, structural design of the thin window presents a formidable task. High-resolution optimal collimators do not appear to have sufficient strength to be used as a pressure support window. Solid-state detectors, while having the potential of a gamma camera with a superb energy resolution, are presently studied on a very small scale due to technological and cost limitations. Aside from the detector, the parallel-hole collimator presents a real limit to the resolution of the camera. A factor of two improvement in the resolution results in a factor of four loss in the collimator's transmission. A careful analysis of optimal collimators and the application of collimators designed for a specific depth range and resoluation are part of our overall program. Our goal has been the development of a liquid-xenon multiwire gamma camera with 2- to 3-mm spatial resolution, high counting-rate performance, high sensitivity, and the potential for scaling-up in size. Important ingredients for successful imaging in the prototype chamber discussed in this paper were the discovery of electron multiplication in liquid xenon, (2) the development of reliable purification techniques, (3) and the ability to extract electrons from the liquid into the gaseous phase. This paper is specifically addressed to the subject of detector development with liquid-xenon totally-filled chambers and recent work with dual-phase chambers in which the {gamma} rays are converted in the liquid phase and are electronically detected in the gaseous phase

ELECTRONIC PROCESSES IN LIQUID XENON

Several basic errors appeared in an article recently published by Prunier et al. entitled, 'Some Properties of Xenon Liquid-Filled Nuclear Detectors'. The article describes an experiment to measure electronic phenomena in liquid xenon using single wire cylindrical chambers. The author here describes some errors made in their interpretation of their experimental observations

LIQUID XENON FILLED WIRE CHAMBERS FOR MEDICAL IMAGINGAPPLICATIONS

In 1968, Luis Alvarez suggested that a high-resolution multiwire particle detector could be developed using a thin layer of liquified noble gas as the detection medium. After key problems in chamber construction, purification, and readout had been solved, a spatial resolution of 15 {micro} rms was demonstrated. Work is in progress to build high-resolution chambers and measure their properties for particle physics experiments at high-energy accelerators. The liquid xenon multiwire chamber also has potential in nuclear medicine for imaging isotope distributions with an unprecedented combination of gamma-ray detection efficiency and spatial resolution. A preliminary 24-wire chamber has been constructed; this chamber detects 280-keV gamma rays with 65% efficiency and 4-mm FWHM spatial resolution. Initial images of point and distributed sources are very promising, and the liquid purity can be maintained for periods exceeding several days

TEST OF A LIQUID ARGON CHAMBER WITH 20-u m RMS RESOLUTION

A measurement of the spatial resolution of a liquid-argon filled chamber was performed with minimum ionizing particles. Two multi-strip chambers with 20-{micro}m strip spacing operating in the ionization mode were used in the experiment. They perform in accordance with a simple model based on electron diffusion. An estimate of the amount of electron diffusion in liquid argon is given and the time jitter distribution has a FWHM of 200 ns. Under best conditions, the spatial resolution is better than 20 {micro}m rms with an efficiency of nearly 100%

HIGH-RESOLUTION LIQUID-FILLED MULTI-WIRE CHAMBERS FOR USE INHIGH-ENERGY BEAMS

The authors describe experiments with liquid-xenon-filled wire chambers operating in the proportional mode and the difficulty of achieving useful gain when the anode wires have a spacing < 1 mm. As a result, they have largely turned our attention to chambers with closely spaced wires operated in the ionization mode. They have previously demonstrated a spatial resolution of 15 {micro} rms in this mode, using a 5-wire chamber and a collimated alpha source. They describe the construction of two small high-resolution test chambers to be filled with liquid argon, krypton, or xenon. The chambers consist of two flat cathodes 1 to 2.5 mm apart with a wire plane between them. The wire plane is an array of 24 wires, 5 {micro} in diameter, spaced on 20-{micro} centers, and a charge amplifier is attached to each wire. The space resolution (expected rms < 20 {micro}), time resolution (expected rms < 50 ns), and efficiency will be measured in an accelerator beam. Chambers of this type with only a few hundred wires have sufficient area to cover nearly every beam at NAL

BaBrI:Eu2 + , a new bright scintillator

The scintillation properties of BaBrI:Eu2+ are reported. Crystals were produced by the vertical Bridgman technique in a sealed quartz ampoule. Excellent scintillation properties were measured. A light yield of 81,0007 +- 3000 photons per MeV (ph/MeV) of absorbed gamma-ray energy was measured. An energy resolution (FWHM over peak position) of 4.870.5percent was observed for the 662keV full absorption peak. Pulsed X-ray luminescence measurements show two exponential decay components of 297 and 482 ns with a contribution to the total light output of 23percent and 77percent, respectively. Under X-ray and UV excitation, the emission corresponds to a broadband center at 413 nm. These initial values make BaBrI:Eu2+ one of the brightest and the fastest known Eu2+ doped scintillators

GaAs as a Bright Cryogenic Scintillator for the Detection of Low-Energy Electron Recoils From MeV/c 2 Dark Matter

This article presents the measurements of the luminescence and scintillation under X-ray of undoped, Si-doped, and Si, B codoped gallium-arsenide (GaAs) samples at cryogenic temperature over a wide infrared (IR) region using Si and InGaAs photodetectors. The undoped GaAs has a narrow emission band at 838 nm (1.48 eV) and a low light output of about 2 ph/keV. The GaAs:Si has three broad luminescence bands at 830 nm (1.49 eV), 1070 nm (1.16 eV), and 1335 nm (0.93 eV) and a light output of about 67 ph/keV. GaAs:(Si, B) has four luminescence bands at 860 nm (1.44 eV), 930 nm (1.33 eV), 1070 nm (1.16 eV), and 1335 nm (0.93 eV) with a light yield of approximately 119 ph/keV. With advances in photodetection, GaAs promises to be a useful cryogenic scintillator for the detection of electron recoils from MeV/c2 dark matter

Advances in Cryogenic Avalanche Detectors

Cryogenic Avalanche Detectors (CRADs) are referred to as a new class of noble-gas detectors operated at cryogenic temperatures with electron avalanching performed directly in the detection medium, the latter being in gaseous, liquid or two-phase (liquid-gas) state. Electron avalanching is provided by Micro-Pattern Gas Detector (MPGD) multipliers, in particular GEMs and THGEMs, operated at cryogenic temperatures in dense noble gases. The final goal for this kind of detectors is the development of large-volume detectors of ultimate sensitivity for rare-event experiments and medical applications, such as coherent neutrino-nucleus scattering, direct dark matter search, astrophysical (solar and supernova) neutrino detection experiments and Positron Emission Tomography technique. This review is the first attempt to summarize the results on CRAD performances obtained by different groups. A brief overview of the available CRAD concepts is also given and the most remarkable CRAD physics effects are discussed.Comment: 60 pages, 58 figures. Invited talk at MPGD2011 Conference, Aug 29 - Sep 3, 2011, Kobe, Japan. Journal version + Fig. 1a adde