M. M. Madsen

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.

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.

AURORAL ZONE ELECTRIC FIELD MEASUREMENTS WITH BALLOONS

ABSTRACT Through nearly one solar rotation period (June 20 to July 13, 1975) the horizontal component of the electric field of the polar ionosphere, between 65 and 82 degrees corrected magnetic latitude, has been monitored continuously by balloon borne sensors. 1200 hours of data were obtained by ten balloons uniformly distributed over the period. The measurement reported here refers to relations between the electric field, the ionospheric current systems and the interplanetary magnetic field.

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).

The parallel plate avalanche counter: a simple, rugged, imaging X-ray counter

Abstract A two-dimensional parallel gap proportional counter has been developed at the Danish Space Research Institute. Imaging over the 120 mm diameter active area is obtained using the positive ion component of the avalanche signals as recorded by a system of wedge- and strip-electrodes. An electronically simple, but very effective background rejection is obtained by using the fast electron component of the avalanche signal. Gas gains up to 8 × 105 have been achieved. An energy-resolution of 16% and a sub-millimeter spatial resolution have been measured at 5.9 keV for an operating gas gain of 105. In principle, the position coordinates are linear functions of electronic readouts. The present model, however, exhibits non-linearities, caused by imperfections in the wedge and strip-electrode pattern. These non-linearities are corrected by using a bilinear correction algorithm. We conclude that the rugged construction, the simple electronics, the effectiveness of the background rejection and the actual imaging performance makes this a very attractive laboratory detector for low and intermediate count rate imaging applications.

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.

High-Energy/Low-Energy Proportional Counter (HEPC/LEPC) detector systems on the SRG

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 micro strip gas counter (MSGC) where the strip electrodes are deposited by photolithography onto a rigid substrate. The MSGC offers many advantages: A uniform gas gain, an excellent energy (approximately 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 X 82 mm) and HEPC ((sigma) equals 160 mm) will be discussed.