PbI2 for high-resolution digital x-ray imaging

Abstract

In this paper, we discuss recent progress that has been made in the development of high resolution X-ray imaging detectors using photoconducting films oflead iodide (Pb12). Pb12 is a wide bandgap semiconductor with high X-ray stopping efficiency. We have been investigating thick films of lead iodide which can be prepared in large areas in a cost effective manner. These fihns can be coupled to readout technologies such as amorphous silicon flat panel arrays and vidicon tubes to produce X-ray imaging detectors for applications such as mammography, fluoroscopy, X-ray diffraction and non-destructive evaluation. Recent results obtained when these Pb12 films are coupled to 512 x 512 flat panel a-Si:H array are reported. This includes dark current, signal and resolution measurements. Properties of lead iodide films which are relevant to imager performance are also discussed.

Correlation between growth orientation and growth temperature for bismuth tri‐iodide films

“…The obtained bismuth tri-iodide films have thicknesses in the range 20 to 33 µm, smaller than the suitable values for 99% stopping of X-rays used for medical radiography. Thicknesses are also smaller than previous reported ones for lead iodide [8,9,11,12] and for mercuric iodide [4,5] films. Thinking on the final application, thicker films should be better, but were not yet intended.…”

“…The grain sizes achieved are in the order of the previous ones for PbI 2 films (20 -80 µm [13]), (1 -5 µm [8]) and for mercuric iodide films (50-100 µm [5], up to 50 µm [4] and 11-160 µm [7]). This grain size is well suited to TFT pixellation and should provide a spatial resolution commensurate with the needs of digital radiography.…”

“…On the other hand, if attention is paid to the final application, the selected method should permit an easy scale up to large and uniform areas. For this purpose, PVD is suitable as well, and it has been the main method employed for growing mercuric iodide [4][5][6][7] and lead iodide [8][9][10][11][12][13] films. The current success with films of these two last iodides led us to consider bismuth tri-iodide as possible compound semiconductor for X-ray imaging.…”

“…Several materials, such as Se [1], CdTe [2][3], HgI 2 [4][5][6][7], PbI 2 [8][9][10][11][12][13] and BiI 3 [14,15] have been used for growing films intended for direct and digital ionizing radiation imaging, Among them, the heavy metal iodides have resulted to have especial properties. They have high densities and atomic absorption coefficients (which determine that thicknesses of 70-80 µm are enough for 99% of absorption of 20 keV radiation), wide energy band gaps (1.7 -2.5 eV at RT), therefore they give a lower dark current through the detector without any cooling, and a relative low energy necessary for the creation of an electron-hole pair (4 -5 eV), then, they may give a higher signal to noise response [16].…”

Exciton spectra of layered PbI2 and PbI2:Zr crystals

“…This is especially associated with the possibility of using lead diiodide in various areas of electronics, in particular in sensor technology. The considerable interest in PbI 2 is due to the prospects for using it to create structures designed for detecting ionizing radiation, in particular x-radiation and γ radiation [11,12]; to convert x-radiation to a visible image [13]; and to create energy materials designed to convert radiant energy to electrical energy [14]. We should emphasize that PbI 2 crystals can be used both as scintillators [11,12] and for direct conversion of ionizing radiation to electric current or electric charge [13].…”