Use In X-ray Astronomy Research Articles

Characteristics and performance of thin LaBr 3(Ce) crystal for hard X-ray astronomy

We have developed a new detector using thin lanthanum bromide crystal (32 × 3 mm) for use in X-ray astronomy. The instrument was launched in high altitude balloon flight on two different occasions, December 21, 2007, which reached a ceiling altitude of 4.3 mbs and April 25, 2008 reaching a ceiling altitude 2.8 mbs. The observed background counting rate at the ceiling altitude of 4 mbs was ∼4 × 10 −3 ct cm −2 s −1 keV −1 sr −1. This paper describes the details of the experiment, the detector characteristics, and the background behaviour at the ceiling altitude.

Measurements of the linearity of an STJ and position resolution of series-connected STJs

Superconducting tunnel junctions (STJ) have been developed mainly at high-resolution spectrometers for use in X-ray astronomy. A FWHM energy resolution of 112 eV at 5.9 keV is obtained using an STJ developed at Nippon Steel Corporation connected with a cooled FET (∼100 K). The pulse height of the signal is represented by a logarithmic function of energy based on consideration of the recombination of the quasi-particles in the junction. Experiments using series-connected STJs for an imaging radiation detector are performed. Both the pulse height and the rise time of signals from 241Am α-particles indicate good position sensitivity with resolution less than 0.5 mm.

An inexpensive, hard x-ray imaging spectrometer for use in x-ray astronomy and atomic physics

We have evaluated a simple X-ray imaging spectrometer (XRIS) useful in the 20–400 keV region. The XRIS consists of an alkali halide scintillator crystal optically coupled to a commercial imaging, photomultiplier tube. The standard performance criteria (spatial sensitivity, pulse height uniformity, spatial and energy resolution) have been studied as a function of X-ray energy and crystal thickness. In particular, spatial resolutions of better than 2 mm (FWHM) have been obtained at 88 keV with standard scintillator crystal energy resolution and near 100% detection efficiency. The XRIS represents an inexpensive, easy to use alternative to more sophisticated imaging systems. We are currently planning to use it in both atomic physics and x-ray astronomy applications.

The Performance of a Multistep Proportional Counter for Use in X-Ray Astronomy

The addition of a parallel field preamplification region has been shown to dramatically improve the performance of a standard multiwire proportional counter, permitting high overall gas gains to be achieved, a prerequisite for good spatial resolution, without in any way compromising energy resolution. The resulting device, known as a multistep detector, has been tested over a wide range of operating conditions and fill gas mixtures. Results are presented here detailing the performance available with argon and xenon as the principle gases, these being of particular relevance to x-ray astronomy.

On searches for periodic pulsed emission - The Rayleigh test compared to epoch folding

The Rayleigh test has been recently invoked as a method of searching a time series for periodic pulsations. In this paper, this technique is discussed and compared to epoch folding, a technique which has had widespread use in X-ray astronomy. It is found that the Rayleigh test provides a more sensitive approach to the search for periodic pulsations when the pulses are sinusoidal or of broad duty cycle, such as those typical of the pulsing X-ray sources. Epoch folding, on the other hand, is more sensitive to the narrow pulses typical of radio pulsars.

An imaging gas scintillation proportional counter for use in X-ray astronomy

An imaging gas scintillation proportional counter (GSPC) has been constructed for use in X-ray astronomy. The IGSPC consists of a gas scintillation proportional counter (GSPC) with a 1 μm polypropylene window coupled to a multiwire proportional counter (MWPC) via a calcium fluoride window. The MWPC, filled with a mixture of argon, methane, and tetrakis (dimethylamino) ethylene, detects the UV photons emitted by the xenon gas in the GSPC. The measured energy resolution is 17.0% (fwhm) and 8.0% (fwhm) at 1.5 keV and 5.9 keV, respectively. The measured position resolution is 1.9 mm (fwhm) and 0.9 mm (fwhm) at 1.5 and 5.9 keV, respectively. We also discuss possible astrophysical observations which can be performed with an IGSPC at the focal plane of a grazing incidence telescope.

An Imaging Gas Scintillation Proportional Counter for the Detection of Subkiloelectron-Volt X-Rays

A large area imaging gas scintillation proportional counter (IGSPC) has been constructed for use in X-ray astronomy. The IGSPC consists of a gas scintillation proportional counter (GSPC) with a 1 ?m polypropylene window coupled to a multiwire proportional counter (MWPC) via a calcium fluoride window. The MWPC, filled with a mixture of argon, methane, and tetrakis (dimethylamino) ethylene, detects the UV photons emitted by the xenon gas in the GSPC. Over a sensitive area of 21 cm2 the instrument has a measured energy resolution of 17.5% (FWHM) and 1.9 mm (FWHM) spatial resolution at 1.5 keV.

Spectroscopy in X-Ray Astronomy Using Gas Scintillation Cameras

Experimental results obtained from a new, position sensitive, gas scintillation proportional counter are presented. The counter, for use in X-ray astronomy as a focal plane instrument in conjunction with a grazing incidence imaging telescope, features a useful aperture of ~ 7 cm, a two-stage scintillation region and a seven photomultiplier tube Anger camera read-out system. An energy resolution of μ 20% FWHM at 1.25 keV (< 10% at 6 keV) and a position resolution of 900 μm at 6 keV at the centre of the useful aperture are achieved.

Neutron holography using Fresnel zone plate encoding

Zone plate shadow casting is a complementary technique to the Leith–Upatnieks modification of Gabor's interferometric method for producing holograms1,2. Suggested originally by Mertz3 in 1961 for use in X-ray astronomy, the technique has received considerable attention in nuclear medicine4 for imaging radioactive organs via emitted X-rays and γ-rays and, more recently, for examining in a tomographic sense the microscopic spatial source distributions of X rays and charged particles in laser-produced plasmas5. A series of simple experiments are described here which demonstrate that zone plate encoded neutron holography can be used to image objects. An object placed in a cold neutron beam from a research reactor scatters neutrons through a Fresnel zone plate, with alternate zones of gadolinium and aluminium, which produces a hologram of the object on an X-ray film. The image is constructed by placing the hologram, linearly reduced in size, in a converging laser beam which produces a real image of the original object. Results are presented for two objects, a pair of 0.01 m diameter rubber spheres and a 0.04 m square Maltese cross made from poly-tetrafluoroethylene (PTFE).

Preliminary Studies CF Gas Fillings in Gas Scintillation Proportional Counters

Results are presented on improvements in the performance of medium energy large area gas scintillation proportional counters for use in X-ray astronomy. By a suitable choice of gas mixture the electron transit time through the drift region can be significantly lowered with a consequent reduction in the detector dead time. In addition the electron diffusion is also reduced and this should result in an increase in the background rejection efficiency.

The Lixiscope: a pocket-size X-ray imaging system

A low-intensity X-ray imaging device with the acronym Lixiscope is described. This device was originally conceived for use in X-ray astronomy where single-photon visualisation is required; however, the extension of its capabilities to medical and dental radiography soon became evident. The high sensitivity and large gain of the Lixiscope make it possible to reduce the patient dose by approximately 103 in certain diagnostic procedures, compared with conventional practice. Such extensive dose reduction not only allows safe fluoroscopic examinations, but also enables the use of radioactive sources in lieu of X-ray machines. Furthermore, because the Lixiscope produces a visible-light output image, it can be easily recorded on fast instant-processing films or used in conjunction with any other image recording and processing devices.

A Large-Area Gas Scintillation Proportional Counter for X-Ray Astronomy

An improved large-area gas scintillation proportional counter has been built, suitable for use in X-ray astronomy. This counter employs electron focusing in a drift region to achieve uniform response. We show that we can obtain a spectral resolution of 9.1% FWHM at 5.9 keV over a useful area of 100 cm2. We demonstrate that signal rise-time discrimination can be used to reject non-X-ray background as efficiently as in ordinary proportional counters.

A burst length discrimination system for a gas scintillation proportional counter

A burst length discrimination system has been developed for the rejection of background events in a gas scintillation proportional counter intended for use in X-ray astronomy. The system utilised a dual constant fraction trigger (CFT) which could determine risetimes from 0.5 to 12 μs. The principle of the dual constant fraction trigger is discussed.

A focusing gas scintillation proportional counter

An improved large-area gas scintillation proportional counter has been built, suitable for use in X-ray astronomy. This counter employs electron focusing in a drift region to achieve uniform response. We show that we can obtain a window area of 60 cm 2 and a spectral resolution of 10% fwhm or better at 5.9 keV.

A proposed X-ray focusing device with wide field of view for use in X-ray astronomy

A device is described that consists of a set of flat reflecting surfaces. At glancing incidence of X-rays of wavelength several Å and longer, this device can be used for the focusing of a sizable portion of an intercepted beam of X-rays incident in parallel. Focusing is not perfect and the image size is finite. But a one-dimensional focusing device offers a wide field of view, up to a maximum of 2 π. It appears practically possible to achieve an angular resolution of the order of one tenth of a degree. Two such systems in sequence, so as to form a double-focusing device, should offer a field of view of up to 100 square degrees at moderate angular resolution. It is proposed to use such devices in X-ray astronomy survey or monitor experiments.

Negative Affinity X-Ray Photocathodes

True image-forming telescopes for use in X-ray astronomy are available now with arc-second resolution for A ≥3A. Such telescopes have been very successfully applied on rockets and on the recent Skylab mission for solar observations. However, their application to observations of extra-solar X-ray sources has been severely limited due to a lack of sensitive X-ray imaging detectors. We describe here a new type of detector using a GaAs photocathode with quantum efficiency approaching 100%. This detector allows us to detect sources 10 to 20 times fainter than previously possible, while preserving spatial resolution on the several micron scale. We present data on the X-ray photoelectron yield for GaAs (Cs-O2) negative affinity cathodes both in reflection mode using a thick cathode and in the transmission mode using a 3.7 micron wafer. A theoretical model is developed and compared with the data to determine the electron diffusion length, the front surface electron reflection coefficient and the back surface electron escape probability for the transmission cathode. There is good agreement between the crystal parameters obtained from X-ray data and from optical data. Application to X-ray telescope imaging in a practical device is discussed.

A survey of instruments and experiments for X-ray astronomy: (Invited discourse)

A diversity of instruments have been utilized or proposed for use in X-ray astronomy. This in part reflects the fact that the field is very new, that many competing techniques have been devised for any given type of observation and that there has been a progression to increasingly sophisticated instruments. But most of this diversity is real and simply reflects the very broad range of observations that can be performed and the different kinds of observational opportunities that are presented to the several experimental groups. Useful measurements are being performed over three decades of energy extending from 0.25 keV to 500 keV, positional measurements extend from degrees to arc seconds precision, attempts have been made to measure the polarization of the X-ray sources, time variations are being studied and spectra are being measured to resolutions of the order of ∼20%. The required instruments are being flown on sounding rockets, balloons and satellites. In addition, observation of the diffuse X-ray backgrounds requires even different instruments.