X-ray Charge-coupled Device Research Articles

A statistical technique for characterizing X-ray position-sensitive detectors

We present a technique for characterizing X-ray sensitive photodiode arrays and charge-coupled device (CCD) arrays. The technique uses simple statistical estimators (means, variances and correlation functions) to determine the response, noise, resolution and detective quantum efficiency of a position-sensitive detector. We apply this technique by characterizing a linear diode array and a CCD array exposed to direct illumination by X-rays. Correlations between neighboring pixels were important, and they are included in the calculation of the detective quantum efficiency and noise of the detector.

Laboratory characterization of Wölter x-ray optics

We have conducted characterization measurements of a Wölter grazing incidence x-ray microscope. The measurements were carried out on 5% sectors of a Wölter x-ray optic in a laboratory utilizing a new, very versatile, high brightness x-ray source. Absolute reflectance measurements as a function of x-ray energy were made with Si(Li) detectors to acquire continuum spectra prior to and after reflecting off the Wölter optic. Spatial resolution characteristics of the Wölter were mapped out using backilluminated pinholes or grids imaged onto film or an x-ray charge-coupled device camera. The implications of the asymmetric point spread function are considered.

High precision Wölter optic calibration facility

We have developed an off-line facility for very precise characterization of the reflectance and spatial resolution of the grazing incidence Wölter type I x-ray optics used at Nova. The primary component of the facility is a new, very versatile, high brightness x-ray source consisting of a focused DC electron beam incident onto a precision manipulated target-pinhole array. The data are recorded with a selection of detectors. For imaging measurements we use direct exposure x-ray film modules or an x-ray charge-coupled device camera. For energy-resolved reflectance measurements, we use lithium drifted silicon detectors and a proportional counter. An in situ laser alignment system allows precise location and rapid periodic alignment verification of the x-ray point source, the statically mounted Wölter optic, and the chosen detector.

A VXI-based high speed X-ray CCD detector

For time-resolved X-ray scattering, one ideally wants a high speed detector that also is capable of giving position sensitive information. Charge Coupled Devices (CCDs) have been used successfully as X-ray detectors. Unfortunately, they are inherently slow because of the serial readout. EEV has developed a CCD that has eight channels of parallel readout, thus increasing the speed eightfold. Using state-of-the-art VXI electronics, we have developed a readout system that could read the entire array in 2.5 ms using a 20-MHz readout clock. For testing and characterization, the device was clocked at a significantly slower speed of 30 kHz. The data are preamplified, and all eight channels of output are simultaneously digitized to 12 bits and stored in buffer memory. The system is controlled by a 486-based PC through an MXI bus and VXI controller using commercially available software. The system is also capable of real-time image display and manipulation.

CCD X-ray detectors: Opportunities and challenges

Charge coupled device (CCD) arrays are showing considerable promise for a variety of X-ray imaging applications. Performance characteristics such as high dynamic range, versatile readout and data-storage modes, and time-resolved capabilities, present interesting opportunities for new kinds of experiments on high-brilliance sources. We illustrate some of these possibilities with results of our recent synchrotron radiation studies using CCDs as high-resolution position-sensitive detectors. While important hurdles have already been overcome, several challenges remain for the effective exploitation of CCDs in X-ray applications. Among these are requirements for further increases in spatial resolution, radiation hardening, and very-high-speed data acquisition. Ongoing developments and future directions are discussed in this context.

Optical filter for X-ray astronomy CCDs

Charge coupled device (CCD) detectors are sensitive from the X-ray to the NIR (near infrared) region. For X-ray and soft X-ray observations in astronomy, an optical filter has to be placed in front of the CCD to suppress the UV (ultraviolet) and VIS (visible) radiation of stars by more than 6 orders of magnitude. However, this filter must remain highly transparent at photon energies above 100 eV. A prototype filter was developed for a satellite borne CCD X-ray imaging detector. This unsupported filter has an effective size of 30 mm × 10 mm and is composed of multilayered thin films of parylene N, aluminum and carbon with mass densities of 25, 30 and 25 μg/cm 2, respectively. The fabrication technique used for the filter and measurements of its optical and mechanical properties are presented.

Developments in X-ray detectors

Abstract Two types of integrating X-ray detectors, imaging plates and charge-coupled devices, represent the forefront of design in position-sensitive X-ray detectors. Their high dynamic range, spatial resolution, large active area, low noise, and ability to count at high rates make them excellent detectors for X-ray crystallography, fiber diffraction and low-angle scattering data collection.

Energy and time response of CCD X-ray detectors

An analysis of X-ray signal charge collection in charge coupled device (CCD) detectors used for X-ray imaging spectroscopy is described. The physics of X-ray signal charge collection are briefly described, and models are compared with experimental data. The implications for event recognition techniques are addressed. It was demonstrated that for the photon counting modes, the serial readout nature of the CCD pixels places a constraint on time resolution and/or count rate capability. However the methods of clocking CCDs are shown to be very flexible, and can offer a range of operating modes that enhance these performance aspects. It is shown that splitting of charge between pixels can be recognized, and a tradeoff between energy resolution and detection efficiency can be performed for some applications. However, this charge splitting places a constraint on the count rate limits attainable. These limits are discussed for a number of readout modes, including integrating count applications. >

Developments in X-ray detectors

Two types of integrating X-ray detectors, imaging plates and charge-coupled devices, represent the forefront of design in position-sensitive X-ray detectors. Their high dynamic range, spatial resolution, large active area, low noise, and ability to count at high rates make them excellent detectors for X-ray crystallography, fiber diffraction and low-angle scattering data collection.

CCDs as low-energy X-ray detectors: I. General description

The command and readout system, performances and use of commercially available X-ray charge-coupled devices (CCDs) is described. The CCDs are used as soft X-ray detectors, either directly near an X-ray source or in the focal plane of a curved Si-crystal spectrometer.

CCDs as low-energy X-ray detectors: II. Technical aspects

The technical aspects of a command and readout system for commercially available X-ray charge-coupled devices (CCDs) is described in detail, including handling of noise problems, interfacing (CAMAC) and X-ray identification by software. Some of the problems encountered and their solution have been emphasized.

The direct X-ray detection with a charge coupled device.

X-ray detection below 10 keV has made great progress with a Charge Coupled Device (CCD). The greatest advantage to use CCD is that it has a good energy resolution as well as a high spatial resolution. Several efforts are done on the development of the X-ray CCD in Europe and in U. S. A. We present the results obtained with the CCD developed in MIT/Lincoln which is scheduled to be boarded on the next Japnese astronomy satellite Astro-D. Astro-D will be the first space observatory using the X-ray CCD. We also show the results obtained with CCD available in Japan. The requirements for the future X-ray CCD are discussed.

Event recognition techniques in CCD X-ray detectors for astronomy

Charge coupled device (CCD) image sensors are rapidly gaining in importance as candidate focal plane detectors for X-ray astronomy. Methods of event selection and recognition are described, which allow excellent X-ray energy resolution (e.g. 133 eV FWHM at 4.95 keV) to be attained. The recognition and discrimination of charged particle background events is also shown to be efficient (up to 99.9%). Changes in CCD design to allow optimisation for X-ray imaging spectroscopy are discussed, and it is demonstrated that CCDs may offer, simultaneously, high spatial resolution, good energy resolution, high detection efficiency and good background rejection.