Andor manufactures a comprehensive range of CCD detection systems for a wide variety of x-ray applications, both imaging and spectroscopy. These detection systems can be used at varying energy levels and are custom configured to operate either directly in a vacuum chamber, attached to a chamber via a Conflat flange or "stand-alone". In addition, if your application requires indirect detection of x-ray, Andor offers a range of fibre-coupled cameras.
Applications that benefit from Andor's high-end X-ray detection solutions include:
The X-ray spectrum can be approximately divided into several regions. These regions are not separated by a well defined boundary, however for the purposes of this overview they are defined as:
Electromagnetic Spectrum
10Å = 1nm
λ(Å) = 12.4 ∕ E(keV)
Absorbtion of X-ray photon in silicon
With direct detection cameras, the CCD sensor itself is exposed to the incoming illumination. This enables photons to be absorbed directly in the sensitive depletion region of the CCD sensor, often creating several electron hole pairs. Compared to indirect detection and traditional X-ray film detection, this method boasts:
QE is the probability of a photon being detected by a CCD sensor. Remember however that in direct detection of X-ray illumination, several photoelectrons of signal are created from a single impinging photon, often yielding single photon sensitivity. The number of photoelectrons formed is related to the energy of the photon, as given by Equation 2. The figure below shows QE curves for a number of direct detection sensor options.
QE curves for a number of direct detection sensor options
No of photoelectrons generated in a direct detection pixel =
X-ray photon energy (eV) ∕ 3.65
FI is a front illuminated device and FI-DD indicates availability of a deep depletion option, offering improved hard X-ray response over FI. BN is a back illuminated option that has no anti-reflection coating (as opposed to BV codings as shown elsewhere on this site), providing the best QE available for soft to medium X-ray detection. Apart from the higher QE of back illuminated sensors, they have another important advantage over front illuminated systems: they provide significantly better protection against possible degradation of the sensor by over-exposure to energetic X-rays. Back illuminated sensors are the recommended device for your direct detection requirements.
Indirect detection is used for hard X-ray detection and when you need:
Indirect detection with phosphor-coated removable magnifying taper
With indirect detection CCDs, a phosphor coating on a fibre optic converts X-ray photons to visible photons. Characteristics of an indirect detection device, such as QE and spatial resolution, will depend on the parameters of the phosphor selected, such as thickness of the layer, chemical composition and particle size.
A novel method of phosphor deposition, developed with our suppliers, can be used on the fiber-optic of Andor's indirect detection cameras, providing excellent spatial resolution, up to four times better than traditional bulk deposition methods. The phosphor coating may be tailored to meet your requirements.
Example of a fiber optic spectroscopy sensor overcoated with GdO phosphor
Use of a phosphor coated fibre optic is the best option for protecting the CCD sensor against X-ray degradation. By solving the problem of poor phosphor spatial resolution, and enhanced sensitivity using EMCCD, much more effective indirect detection capabilities can now be achieved for energies lower than 5keV.
Overall gain of a typical phosphor coated fibre optic camera
The figure on the right illustrates how the overall gain of a typical phosphor coated fibre optic camera varies with incident photon energy. The system gain is defined as the number of detected electrons per incident X-ray photon. The gain of the system will vary depending on the type, thickness and grain size of the phosphor. It also depends on the QE of the CCD sensor and the fibre optic used.
This particular example is for a phosphor coated 1:1 fibre optic. The phosphor has been optimized to operate over an energy range of 5 to 25 keV, peaking at ~ 15 keV. For large area demagnifying fibre tapers, the overall gain becomes substantially less and EMCCD technology can be used to amplify the weak signal above the readout noise floor of the detector, even at rapid multi-MHz readout speeds – ideal for fast tomographic applications for example.
Andor supplies a wide range of dedicated CCD and EMCCD cameras for direct and indirect detection of X-ray, in both spectroscopic or imagng sensor formats. Camera platforms are available to accommodate and optimize a range of sensor sizes and types, from 128 x 128 EMCCD through to 2048 x 2048 CCD. Andor's X-ray camera range has been developed to adapt to a range of experimental configurations, and systems are available that are stand-alone, coupled to outside of vacuum chamber, or can be incorporated inside the vacuum chamber.
Researchers from the Plasma and Laser Interaction Physics research division at The Queen’s University, Belfast (QUB), are carrying out investigations that require X-ray CCD cameras. The areas of study include:
QUB researcher attaching DO camera to a vacuum chamber
A number of Andor X-ray CCD cameras are employed by the research group. One area of research that is being undertaken by the group using the Vulcan laser facility at the Rutherford Appleton Laboratory, is the development of X-ray lasers.
A special 1024 x 2048 sensor with 13μm and with the BN quantum efficiency option is the main camera of choice for these investigations. The camera has high QE, excellent resolution and a large sensitive area. The camera is a DO open front end system, designed to be attached to the outside of the vacuum chamber.A flat field spectrometer and CCD camera are used to analyze the X-ray laser beam. The camera is also used in combination with X-ray mirrors to image the X-ray laser exit point to look at the beam profile.
X-ray laser beam profile
Another area of study where this camera is used involves X-ray spectroscopy of an ionized gas jet.On site at QUB, a low temperature plasma (0.03 to 0.08keV) is employed to test the reflectivity of X-ray mirrors used in the imaging set up. Using an Andor DO420 camera coupled to a flat field spectrometer, a broadband spectrum is obtained from the plasma and a reflected spectrum from the X-ray mirror. The variation of reflectivity with wavelength can then be determined by dividing the reflected spectrum by the source spectrum.
Thanks to Prof.C.Lewis and group, Plasma and Laser Interaction Physics Research Division, The Queen's University, Belfast.
A wide range of CCD based detectors are used on High Power Laser Interaction experiments on the Vulcan and Astra central laser facilities at the Rutherford Appleton Laboratory. These range from:
Andor DX camera attached to a space resolving crystal spectrometer for emission in the 0.8 to 3kev region
CCD detectors with high dynamic range (12-16 bit) and large numbers of pixels (0.3-2.0 million) are essential to maximize the data collection and range of measurements undertaken on each experiment. Not only must the detectors have a high dynamic range but high sensitivity and low noise characteristics are essential in many experiments where signal to noise issues push detectors and experiments to their physical limits.
In recent years the introduction of thermoelectric cooling of the CCD sensors, reduced dark current devices and improved analogue to digital converters have greatly aided in achieving exceptional performance.
Currently, five Andor X-ray CCD cameras are almost continually in use on Vulcan and Astra and the preferred sensor format is 1024 x 256 pixels. Many new and novel techniques which take advantage of the unique properties of current CCD technology can be used to study the interaction of ultra short pulse laser plasma interactions.
The Rutherford Vulcan LASER facility with several Andor x-ray cameras attached
With the introduction of ever larger CCD arrays and cheaper processing power, digital data acquisition will take an ever more prominent role in experimental investigations of the future.
Thanks to Dr. D. Neely, Central Laser Facility, Rutherford Appleton Laboratory, Oxfordshire.
Reconstructed mouse thyroid image
There have been substantial efforts in trying to do microscopic imaging in small animals. Small animal imaging using I-125 labeled radiotracers is gaining popularity.
Dr Ling Meng from the Department of Nuclear Engineering and Radiological Sciences, University of Michegan in conjuction with researchers from the V. A. Medical Center in Ann Arbor and in Van Andel Research Institute in Grand Rapid, Michigan have been using I-125 labeled antibodies, peptides and other compounds as screening agents in development of diagnostic and therapeutic radiopharmaceuticals for various type of cancers.
I-125 decays via electron capture. The three highest photon emission probabilities for I-125 decay are:76% at 27.5 keV 13% at 31 keV 7% at 35 keV I-125 has a half-life of 60.14 days. The combination the low energy and long a half-life offers advantages for Single Photon Imaging Computed Tomography (SPECT) imaging:
High-resolution gamma EMCCD head
Recently they have begun to produce next-generation SPECT technology based on use of Andor's fiber-optic EMCCD (DF-897-FB) technology for rapid, highly sensitive detection of these energetic photons.
High–resolution SPECT System using fiber-optic EMCCD
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