P. Jonasson

A new position sensitive proportional counter with microstrip anode for neutron detection

Abstract In an ionization chamber the anode is made of a glass plate on the surface of which very small conductor strips are fixed. The applied electric potential alternates between each strip. This microstrip anode replaces the wires generally used for electron multiplication in position sensitive gas detectors. The measured energy resolution, the position resolution and the value of the limiting counting rate are reported.

Microstrip proportional counters for X-ray astronomy

Abstract Four position sensitive proportional counters will be delivered by the Danish Space Research Institute as focal plane instruments for the Soviet Danish Rontgen Telescope (SODART). These detectors will incorporate the novel microstrip electrode design. This design has been tested with xenon gas and an 55Fe X-ray source. The energy resolution is better than 14% FWHM up to gas gains of 104, the rise time of pulses from X-ray events is fast, 100 ns, allowing for efficient background rejection by rise time analysis. A position resolution of 1 mm FWHM is easily obtained by resistive charge division of the signals from the cathodes and from a wire grid placed in front of the microstrip plate. The detector performs without significant degradation of gain or energy resolution at fluxes exceeding 106/s cm2 and a total dose of 1011 photons.

X-ray calibration of the SODART flight telescopes

The on- and off-axis imaging properties and effective area of the two SODART flight telescopes have been measured using the expanded beam x-ray facility at the Daresbury synchrotron. From on-axis measurements the encircled power distribution and the point spread function at three energies 6.627 keV, 8.837 keV and 11.046 keV have been measured using a one-dimensional position sensitive detector. We found that the point spread function can be presented well by a function which is a sum of a Gaussian divided by the radius and two exponential terms where the first has a 1/e value close to 2 arcmin and the other a 1/e value of ca. 15 arcmin. The data have been used to calculate the half power diameter (HPD) for three different SODART focal plane detectors, the high energy proportional counter (HEPC) with a field of view (FOV) of 65 arcmin, the low energy proportional counter (LEPC) with a FOV of 33 arcmin and the 19 element solid state detector array (SIXA) with a FOV of 18 arcmin. We found that the HPD decreases with increasing energy due to poorer figure of the outermost mirrors. The HPD falls in the range from 2.4 to 3.8 arcmin depending on energy and FOV. Data have also been obtained on the on- and off-axis effective area at all three energies and compared to that obtained from a raytracing of an ideal telescope configuration. We found that the measured on-axis effective area integrated over a FOV of 105 arcmin is ca. 65% of the area predicted from an ideal geometry. Finally the one- dimensional detector data has been used to obtain the radial dependence of the on-axis HPD and the on-axis effective area and the data from the two-dimensional position sensitive detector has been used to obtain the azimuthal dependence of the on-axis HPD and the on-axis effective area.

Studies of multilayers and thin-foil X-ray mirrors using a soft X-ray diffractometer

A versatile x-ray diffractometer is described in detail. Two applications to the study of x-ray optical elements are presented. The first is a Bragg reflection study of state-of-the-art multilayers deposited both on conventional Si-wafer substrates and on superpolished substrates such as fused quartz and electroless nickel. These data are compared to data previously obtained at FeKα. The second study is a reflectivity and scattering study of various thin-foil x-ray reflectors proposed for up-coming x-ray satellite missions. All the data have been obtained at MgKα = 1.2536 keV.

A versatile three/four crystal X-ray diffractometer for X-ray optical elements: Performance and applications

Abstract A versatile X-ray diffractometer for the study of X-ray optical elements such as grazing incidence mirrors, crystals and X-ray gratings has been built and put into operation at the Danish Space Research Institute. The diffractrometer is built on a 1.5 m long granite bench with the X-ray source located at one end of the bench where it can be rotated around a fixed vertical axis. The beam defining elements are perfect crystals of Si, Ge or quartz. With these it is possible to define a highly collimated beam of a few arcsec fwhm in the scattering plane. Examples of measurements on various X-ray optical elements are presented. The deconvolution of the experimental data is discussed in general terms and as an example the results of a calculation of the diffractometer resolution function for a four crystal setup are presented.

The X-ray imager on AXO

DSRI has initiated a development program of CZT X-ray and gamma-ray detectors employing strip readout techniques. A dramatic improvement of the energy response was found operating the detectors as the so-called drift detectors. For the electronic readout, modern ASIC chips were investigated. Modular design and the low-power electronics will make large area detectors using the drift strip method feasible. The performance of a prototype CZT system will be presented and discussed. One such detector system has been proposed for future space missions: the X-Ray Imager (XRI) on the Atmospheric X-ray Observatory (AXO), which is a mission proposed to the Danish Small Satellite Program and is dedicated to observations of X-ray generating processes in the Earth’s atmosphere. Of special interest will be simultaneous optical and X-ray observations of sprites that are #ashes appearing directly above an active thunderstorm system. Additional objective is a detailed mapping of the auroral X-ray and optical emission. XRI comprises a coded mask and a 20]40 cm2 CZT detector array covering an energy range from 5 to 200 keV. ( 2001 Elsevier Science B.V. All rights reserved.

Development of large-area CZT detector systems

DSRI has initiated a development program of CZT x-ray and gamma ray detectors employing strip readout techniques. A dramatic improvement of the energy response was found operating the detectors as so-called drift detectors. For the electronic readout, modern ASIC chips were investigated. Modular design and the low power electronics will make large area detectors using the drift strip method feasible. The performance of a prototype CZT system will be presented and discussed.

Application of microstrip proportional counters at the Danish Space Research Institute

Abstract The low energy proportional counter LEPC (0.2–8 keV) and the high energy proportional counter HEPC (2–25 keV) for the Danish-Russian X-ray telescopes XSPECT/SODART are presently being tested at DSRI. The sensor principle of these detectors is based on the novel microstrip proportional counter (MSPC) where the strip electrodes are deposited by photolithography onto a rigid substrate. The MSPC offers many advantages: a uniform gas gain, excellent energy (∼ 13% at 6 keV) and position-resolutions (⪡ 1 mm), a fast charge collection and a low operating voltage. The energy response, imaging and background rejection performance of LEPC (82 × 82 mm) and HEPC ( O = 160 mm ) will be discussed. The presentation will also include first results obtained with a high energy (∼ 150 keV) MSPC which is planned as a candidate for the X-ray monitor for the International Gamma-Ray Astrophysical Laboratory (INTEGRAL).

Two Wireless Imaging Proportional Counters

Two types of wireless position sensitive X-ray proportional counters are under development at the Danish Space Research Institute. One detector - the microstrip proportional counter - employs very narrowly spaced conducting strips deposited on an isolating substrate instead of wires. The gas gain is uniform over the entire detector area and the achievable energy resolution is close to or better than the best achievable for single wire proportional counters. The position readout is made using a wedge and strip electrode mounted on the back-side of the insulating glass substrate. The second detector employs a uniform electric field between two parallel electrodes in order to achieve amplification. Parallel electrodes have better energy resolution, better timing resolution and are easier to construct and more durable than multiwire chambers. The parallel gap is formed between an etched Ni mesh and a segmented anode in the form of a wedge and strip electrode. The X-ray photon energy is derived from the mesh electrode, whereas the position information is taken from the anode. Submilimeter position resolutions have been achieved. In both detectors the energy signal has a very fast risetime and background rejection based on pulse shape analysis is, therefore, very efficient. The background rejection efficiencies achieved and the optimum rejection method for spaceborne detectors will be discussed.

A Multiwire Proportional Counter For Low Energy X-Ray Imaging

Development of a detector for a Bragg spectrometer experiment is described, including the test setup and the read out electronics. A few examples of the position resolution are presented.We have built and put into operation a computer controlled test-stand with: A collimated x-ray beam in the energy range of 0.5 to 6 kev and the width of 50 to 200 microns, an x-y translation table for positioning the detector,a gas system for recirculating and filtering of different gas mixtures and pressures and an electronics system using the charge division method for event position determination. Charge pulses from the detector are digitized and analysed in a micro-processor where the position and energy spectra are stored. Background rejection is determined by energy, position and rise time windows in the micro-processor software.