A possible method for WIMPs detection using liquid xenon scintillation is discussed. Background from cosmic and radioactive gamma rays at energies down to the keV region can be easily rejected by requiring the presence of proportional scintillation. The results from a basic test are presented and a prototype detector design is proposed.
We describe the current status of the development of imaging electron drift Liquid Argon Detectors (ICARUS) and the development of the Visible Light Photon Counter (VLPC) for scintillating fiber tracking for (SPC) SSC/LHC detectors. We then propose a detector that combines these two techniques to detect massive WIMPs through the possible identified Xe recoil in a liquid Xenon detector.
This paper describes a type of cosmic ray detector for isotopic and energy detection of energetic nuclei which derives both dimensions of position information from one side of the detector. This simplifies the required readout electronics, since only one precision amplifier connected to the other side is required for an accurate detection of the energy loss. Two dimensional readout is enabled by the use of pixels consisting of closely spaced interdigitated electrodes alternately connected to row and column lines. Spreading of the charge produced by the cosmic ray results in the charge being collected by more than one electrode producing both a row and column signal on one side of the detector. The design, fabrication, and characterization of the interdigitated-pixel detector is discussed.
A new design for a broad-band imaging telescope intended for operation within the energy range from about 15 keV to more than 1 MeV is described. The detection plane of this coded aperture telescope consists of an array of position-sensitive scintillation counters that are designed to provide a constant spatial resolution of 1 cm over the full energy range. The detection elements are intimately shielded by the combination of a phoswich veto system and an active shield. The predicted background rates indicate that the telescope could provide a good imaging capability and a competitive sensitivity within a modest payload mass.
The imaging properties of a gamma-ray telescope which employs a coded aperture in conjunction with a modular detection plane have been investigated. Gaps in the detection plane, which arise as a consequence of the design of the position sensitive detector used, produce artifacts in the deconvolved images. The effect is generally to reduce the signal to noise ratio for the detection of point sources. The application of an iterative image processing algorithm is shown to restore the image quality to that expected from an ideal detector.
A new position-sensitive gamma-ray detector to cover the energy band from 15 keV to 1 MeV has been investigated. The detector concept is based on the use of an array of discrete 1 X 1 X 5 cm phoswich scintillation bars viewed by position-sensitive photomultiplier tube (PSPMT). The test results show that the energy resolution, about 40% FWHM at 60 keV and 12% FWHM at 511 keV, can be easily obtained when using CsI(Na) crystals. The point- spread function for the location of each event is smaller than the cross section of a single bar over the entire energy range. This means that there is virtually no ambiguity in locating signals from different bars. The outputs from the CsI(Na) and GSO veto crystals can be distinguished by a pulse-shape discriminator designed especially for this system. Those multi- site events which deposit energy only in the CsI(Na) array can be recognized using the position sensing capability of the tube.
CsI scintillation crystals are widely used as detection in (gamma) -ray astronomy observations. In the MeV energy region, one of the most important background sources in CsI is the (beta) decays induced in the crystal by cosmic ray protons and their secondaries. One recent idea for reducing this background is to use discrete detector arrays to reject the large amount of localized (beta) decay events. Two experiments were carried out with 1 cm3 CsI crystals bombarded with energetic proton beams and fast/thermal neutrons, with the aim of evaluating the effectiveness of this method in pixelated (1 cm3) CsI detectors. The ratio of the number of decays resulting in single site and multiple site events was found to be less than 1 in the energy band above 400 keV for the proton induced spallation background, while it is above 8 for the neutron induced background. The combined result indicates that more than 80% of the induced radioactive decays in the energy band between 200 keV and 2 MeV are single site events, and thus their rejection by the use of discrete CsI arrays will significantly improve the sensitivity of the detector.
The AXAF program has undergone major changes since the Announcement of Opportunity was extended by NASA Headquarters in 1983. The science instruments (SI's) for AXAF have also experienced several design changes since they are competitively selected in 1985. Moreover, two separate complementary missions are now being baselined for AXAF; one is designated AXAF-I for imaging and will include the high precision Wolter type I optics, and the other is called AXAF-S for spectroscopy. Furthermore, on-orbit servicing has been eliminated from the program, and mission lifetime has been reduced. The resulting less-costly AXAF will still be superior to any previous x-ray observatories. Both missions continue to be managed for NASA through the Observatory Projects Office (OPO) at the Marshall Space Flight Center (MSFC). AXAF-I contains two focal plane SI's, the high resolution camera (HRC), and the AXAF charge-coupled device (CCD) imaging spectrometer (ACIS), as well as the high-energy transmission grating spectrometer (HETGS) and the low-energy transmission grating spectrometer (LETGS). AXAF-I launch is scheduled for September 1998.
Soft (gamma) -ray imaging instruments onboard currently operating astrophysical observatories attain angular resolutions on the order of 10 arc minutes using coded apertures with uniformly redundant arrays. In crowded regions, e.g. the galactic plane and center regions, unambiguous association with candidates at other wavelengths will often require improved localizations. We discuss a (gamma) -ray telescope design using 'chirp-Z' function codes and coarse position-sensitive image plane detectors. Image plane detector systems consisting of CsI scintillators and avalanche photodiodes are evaluated. Position sensitivity is achieved by either using a matrix of individual CsI/APD detectors or CsI scintillator rods. The aim is to design a narrow field-of-view telescope with sub-arcminute resolution to be flown on a small spacecraft.
The proposed Hard X-ray Imager (HXI) telescope consists of a single 10 X 10 cm microchannel plate (MCP) detector combined with a URA coded aperture. The telescope is nominally configured for a 2.3 degree field of view and an angular resolution of 10 arcsec. Thus providing an order of magnitude or greater spatial resolution improvement over existing hard X-ray telescope. Depending on the final telescope design, the resolution may approach the 1 arcsec domain. The HXI detector has a spatial resolution of 50 micrometers ((sigma) ) and a single photon timing resolution of 1 microsecond(s) ec. The currently operating prototype detector has sensitivity from 10 to 120 keV with a quantum efficiency (QE) varying from 20% at 20 keV to of 8% at 100 keV.
In order to continue the achievements in high energy (10 MeV - 100 GeV) gamma-ray astronomy made with the Energetic Gamma-Ray Experiment Telescope (EGRET) instrument on the Compton Gamma Ray Observatory (CGRO), a 'next generation' high energy gamma- ray telescope with a large increase in sensitivity coupled with improved angular resolution will be required. This 'next generation' telescope is envisioned as a 2 m X 2 m active area telescope using drift chambers for the imaging detector. The four major components of the instrument are the anticoincidence shield, the track imaging system, the coincidence/time-of- flight system and the energy measurement system. In this paper we discuss the design goals and challenges for the four subsystems and the techniques we are utilizing to achieve them as well as the design and performance of high speed electronics that we have developed specifically for this application.
MART-LIME is a coded mask imaging telescope to be flown onboard the international observatory SPECTRUM X-(Gamma) in 1995. This high-energy instrument, the center of which is a high-pressure proportional counter sensitive to the 5 - 150 keV energy range, will be characterized by a limiting sensitivity of about 1 milliCrab for a 105 s observation period. The imaging capability of the instrument is provided by a coded-mask aperture system, used in conjunction with a position sensitive detector. The basic pattern of the coded aperture is a 71 X 73 URA mask (twin prime). With the addition of an outer frame comprising 18 pixels on each side, a fully coded field-of-view of 2.6 degree(s) X 2.6 degree(s) is obtained, while a partially coded field-of-view is achieved up to 6 degree(s). Test procedures used to determine the performance of the MART-LIME detector are discussed. Results showing the spectroscopic capabilities of a Laboratory-Prototype detector are presented.
Recent results obtained by balloon and satellite borne coded-mask instruments have been used to simulate the imaging performance of MART-LIME, a coded mask telescope to be flown on board the international observatory SPECTRUM-X-GAMMA on 1995. In particular, we discuss a 6x6 square degree field-of-view centered on the hard X-Ray source responsible for the high energy emission from Galactic Center, at energies above 30 keV. The contributions of GX1+4, GRS1758-25, Terzan 2, Tr 1741-322 and GX354-0 to this field-of-view are also considered. Deconvolved images obtained via the cross-correlation technique are presented. From these images, the limiting sensitivity of the telescope in a crowded sky field is correctly determined.
Most high energy Cosmic Rays are charged but a few are gamma rays generated by extremely energetic processes which are not understood. Precise directions for the gamma rays will indicate their sources. The most energetic gamma rays produce Extensive Air Showers (EAS) in the atmosphere. From the earliest days of radar there have been attempts to use radio techniques to measure the energy of Cosmic Ray air showers. None have used radio techniques to measure the direction of Cosmic Ray induced Extensive Air Showers. This paper examines the different mechanisms by which radio waves of a wide range of frequencies are reflected from both the relativistic shower front of the EAS and the temporary column of ionization left behind. It is shown that under certain conditions there is a relatively strong reflected signal. It is estimated that a few percent of the high energy (PeV 1015 eV) cosmic ray flux reaching the earth are gamma rays. The current angular resolution of Cosmic Ray detectors is little better than one degree. This paper considers the possibility of scattering radio waves from the ionization produced by an EAS to provide, in conjunction with a ground based EAS gamma ray telescope, a new form of high energy gamma ray telescope. It will provide precise direction coordinates for the primary cosmic ray particle significantly better than the best current methods for single events. Precision direction coordinates should reveal gamma sources against the general background of charged cosmic ray events. A design is proposed for a novel high resolution, high energy gamma ray telescope.