Radiation detection, using materials to convert high-energy photons to low-energy photons (X-ray imaging) or electrical charges (X-ray detector), has become essential for a wide range of applicatio

Metal Halide Perovskites for X-ray Imaging Scintillators and Detectors

High energy X-ray radiation sensitive scintillating materials for medical imaging, cancer diagnosis and therapy

Fabrication and imaging characterization of high sensitive CsI(Tl) and Gd2O2S(Tb) scintillator screens for X-ray imaging detectors

Within detector output data resolving individual signals by determining a signal form for signals present in the data, estimating parameters for the signals including signal temporal position, and determining the energy of the signals from the signal form and the estimated parameters.

Method and apparatus for resolving individual signals in detector output data

The afterglow problem has been preventing CsI:Tl single crystal scintillators from being used for applications in the field of computer tomography and high-speed imaging. We show that Yb2+ codoping in CsI:Tl can reduce it at least by one order of magnitude after 50 ms from X-ray cut-off compared to ordinary CsI:Tl. After optimization of the Yb2+ and Tl+ concentrations, the doubly doped CsI:Tl,Yb crystal exhibits an ultra-high light yield of 90000 ± 6000 photons MeV−1, energy resolution 7.9%@511 keV and low afterglow level of about 0.035% at 80 ms. Simultaneous improvement in afterglow, light yield and energy resolution in CsI:Tl-based scintillators paves the way to its application in computer tomography and high-speed imaging. The physical mechanism and role of ytterbium ions in afterglow suppression are proposed.

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CsI:Tl+,Yb2+: ultra-high light yield scintillator with reduced afterglow

We have manufactured thallium-doped cesium iodide (CsI:Tl) scintillator thin films by the thermal deposition method. The scintillation characteristics of the CsI:Tl thin films were studied by X-ray-induced luminescence for different Tl doping concentrations between 0.05 and 1.0 mol%. The wavelength of the main emission peak was about 550 nm and the light intensity was increased and the emission peak shifted toward the long wavelength for higher Tl concentration in the X-ray luminescence case. X-ray diffraction (XRD) and scanning electron microscopy (SEM) for observation of structural properties was used to investigate the relationship between the microstructure affected by the evaporation condition and post-heat treatment, and the scintillation properties of samples. The imaging performance of the various CsI:Tl films fabricated will also be evaluated by an X-ray radiographic test after coupling to a CCD sensor.

Scintillation characteristics and imaging performance of CsI:Tl thin films for X-ray imaging applications

Thallium doped cesium iodide (CsI:Tl) scintillator films for the use as a converter for X-ray imaging detectors were fabricated by the thermal deposition method. The microstructures of these scintillating layers were affected by various deposition conditions such as vapor pressure, substrate temperature and post-heat treatment or rapid thermal annealing (RTA). CsI(Tl) scintillator films with various polycrystalline structures were manufactured under different process conditions and prepared for experiments. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to investigate the crystal structure and morphology properties. Light output and spatial resolution of the samples were strongly affected by the microstructures, which are determined by the deposition conditions and post-heat treatment. Imaging characteristics of the various CsI:Tl films were also measured under X-ray exposure conditions by coupling them to a CCD image sensor.

The sensitivity and spatial resolution dependence on the microstructures of CsI:Tl scintillation layer for X-ray imaging detectors

X-ray imaging detectors in combination with scintillator screens have been widely used in digital X-ray imaging applications. Gd 2 O 2 S:Tb was used as scintillation material for pixelated scintillator screens based on silicon substrates (wafer) with a micropore array of various dimensions fabricated using the photolithography and deep reactive ion etching (DRIE) process. The relative light output and the modulation transfer function (MTF) of each fabricated scintillator screen were measured by a cooled CCD and compared with those of Lanex screens. The spatial resolution of our scintillator screens was higher but their light outputs were lower than those of Lanex screen probably due to the loss of light at the wall surfaces. Therefore further treatment of the wall surface, such as reflective coating, seems necessary to compensate the light loss.

Fabrication and characterization of pixelated Gd2O2S:Tb scintillator screens for digital X-ray imaging applications

Pixelated-scintillator films used for X-ray image sensors were developed and tested. The air gap between scintillator pixels reduces the transport of visible light photons generated by X-rays into the neighboring pixels so it will maximize the overall spatial resolution as well as the light collection efficiency of an X-ray imager. For further improvement, the inter-pixel gaps and surface are filled and coated with a reflective or a lower refractive material than an CsI(Tl) scintillator. The scintillator films of 30–40 μm thickness were made with thallium-doped CsI by the conventional physical vapour deposition process on glass substrates with a photo resist layer patterned by UV lithography. In this work, the effects on light collection efficiency and spatial resolution of the pixelated-scintillator films before and after reflective coating were evaluated using a CCD sensor and X-rays within the medical diagnostic energy range.

Improvement of the sensitivity and spatial resolution of pixelated CsI:Tl scintillator with reflective coating

During the last decade, digital X-ray imaging systems have been replacing analog X-ray imaging systems of conventional X-ray film-screen combination for radiography applications Indirect detection methods consisted of an X-ray converter (or a scintillator film) and photodiode arrays are more widely used in medical diagnoses and industrial fields Two major scintillation materials such as terbium doped gadolinium oxysulfide (Gd 2 O 2 S:Tb, GOS) and thallium doped cesium iodide (CsI:Tl) are commonly used In this work, GOS scintillator films were manufactured by mixing and thermal hardening of Gd 2 O 2 S:Tb powder, dispersion agent, hardening agent, and other organic additives And CsI:Tl scintillator films with columnar structure were also fabricated by the thermal evaporation method The scintillation properties, such as emission spectrum and light yield etc, of the GOS and CsI:Tl films were measured by X-ray luminescence and photo-luminescence (PL) methods The maximum luminescent intensity of both scintillators was observed at 540–560nm wavelength In order to investigate the imaging performances of both GOS and CsI:Tl films as converters of X-ray imaging detectors, both scintillator films were coupled with an CCD sensor The light response to X-ray dose, signal-to-noise ratio (SNR), spatial resolution were measured and analyzed under the same X-ray conditions As X-ray dose increases, the SNR curves showed linear relationship And the spatial resolution of two scintillator films was resolved at 7∼8lp/mm

Sungho Chang

Papers

Scintillation characteristics and imaging performance of CsI:Tl thin films for X-ray imaging applications

The sensitivity and spatial resolution dependence on the microstructures of CsI:Tl scintillation layer for X-ray imaging detectors

Fabrication and characterization of pixelated Gd2O2S:Tb scintillator screens for digital X-ray imaging applications

Improvement of the sensitivity and spatial resolution of pixelated CsI:Tl scintillator with reflective coating

Fabrication and comparison Gd 2 O 2 S(Tb) and CsI(Tl) films for X-ray imaging detector application