The X-ray Sensitivity of an Amorphous Lead Oxide Photoconductor

The photoconductor layer is an important component of direct conversion flat panel X-ray imagers (FPXI); thus, it should be carefully selected to meet the requirements for the X-ray imaging detector, and its properties should be clearly understood to develop the most optimal detector design. Currently, amorphous selenium (a-Se) is the only photoconductor utilized in commercial direct conversion FPXIs for low-energy mammographic imaging, but it is not practically feasible for higher-energy diagnostic imaging. Amorphous lead oxide (a-PbO) photoconductor is considered as a replacement to a-Se in radiography, fluoroscopy, and tomosynthesis applications. In this work, we investigated the X-ray sensitivity of a-PbO, one of the most important parameters for X-ray photoconductors, and examined the underlying mechanisms responsible for charge generation and recombination. The X-ray sensitivity in terms of electron–hole pair creation energy, W±, was measured in a range of electric fields, X-ray energies, and exposure levels. W± decreases with the electric field and X-ray energy, saturating at 18–31 eV/ehp, depending on the energy of X-rays, but increases with the exposure rate. The peculiar dependencies of W± on these parameters lead to a conclusion that, at electric fields relevant to detector operation (~10 V/μm), the columnar recombination and the bulk recombination mechanisms interplay in the a-PbO photoconductor.

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Bilayer lead oxide X-ray photoconductor for lag-free operation

Scientific Reports ◽

10.1038/s41598-020-77050-w ◽

2020 ◽

Vol 10 (1) ◽

Author(s):

Oleksandr Grynko ◽

Tristen Thibault ◽

Emma Pineau ◽

Gytis Juska ◽

Alla Reznik

Keyword(s):

Real Time ◽

Electric Fields ◽

Lead Oxide ◽

Thick Layer ◽

Hole Mobility ◽

Direct Conversion ◽

Complete Suppression ◽

Bilayer Structure ◽

X Ray ◽

Different Temperatures

AbstractPolycrystalline Lead Oxide (poly-PbO) was considered one of the most promising photoconductors for the direct conversion X-ray medical imaging detectors due to its previous success in optical imaging, i.e., as an optical target in so-called Plumbicon video pick-up tubes. However, a signal lag which accompanies X-ray excitation, makes poly-PbO inapplicable as an X-ray-to-charge transducer in real-time X-ray imaging. In contrast, the recently synthesized Amorphous Lead Oxide (a-PbO) photoconductor is essentially lag-free. Here, we report on our approach to a PbO detector where a thin layer of a-PbO is combined with a thick layer of poly-PbO for lag-free operation. In the presented a-PbO/poly-PbO bilayer structure, the poly-PbO layer serves as an X-ray-to-charge transducer while the a-PbO acts as a lag prevention layer. The hole mobility in the a-PbO/poly-PbO bilayer structure was measured by photo-Charge Extraction by Linearly Increasing Voltage technique at different temperatures and electric fields to investigate charge transport properties. It was found that the hole mobility is similar to that in a-Se—currently the only commercially viable photoconductor for the direct conversion X-ray detectors. Evaluation of the X-ray temporal performance demonstrated complete suppression of signal lag, allowing operation of the a-PbO/poly-PbO detector in real-time imaging.

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Flexible x-ray imaging detector based on direct conversion in amorphous selenium

Journal of Vacuum Science & Technology A Vacuum Surfaces and Films ◽

10.1116/1.4882835 ◽

2014 ◽

Vol 32 (4) ◽

pp. 041507 ◽

Cited By ~ 11

Author(s):

Tsung-Ter Kuo ◽

Chien-Ming Wu ◽

Hui-Hsin Lu ◽

Isaac Chan ◽

Kai Wang ◽

...

Keyword(s):

Direct Conversion ◽

Amorphous Selenium ◽

X Ray ◽

X Ray Imaging ◽

Imaging Detector

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Analysis of lead oxide (PbO) layers for direct conversion X-ray detection

IEEE Transactions on Nuclear Science ◽

10.1109/tns.2005.856790 ◽

2005 ◽

Vol 52 (5) ◽

pp. 2035-2040 ◽

Cited By ~ 46

Author(s):

M. Simon ◽

R.A. Ford ◽

A.R. Franklin ◽

S.P. Grabowski ◽

B. Menser ◽

...

Keyword(s):

Lead Oxide ◽

Direct Conversion ◽

X Ray

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Analysis of lead oxide (PbO) layers for direct conversion X-ray detection

IEEE Symposium Conference Record Nuclear Science 2004. ◽

10.1109/nssmic.2004.1466833 ◽

2005 ◽

Cited By ~ 5

Author(s):

M. Simon ◽

R.A. Ford ◽

A.R. Franklin ◽

S.P. Grabowski ◽

B. Menser ◽

...

Keyword(s):

Lead Oxide ◽

Direct Conversion ◽

X Ray

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X-Ray Analysis for Electron Beam Enhancement in the Plasma Focus Device*

Advances in X-ray Analysis ◽

10.1154/s0376030800006698 ◽

1974 ◽

Vol 18 ◽

pp. 184-196 ◽

Cited By ~ 6

Author(s):

R. L. Gullickson ◽

R. H. Barlett

Keyword(s):

Electric Fields ◽

Plasma Focus ◽

Average Energy ◽

High Energy ◽

Plasma Focus Device ◽

X Rays ◽

Stored Energy ◽

Power Law Distribution ◽

X Ray ◽

Thermoluminescent Dosimeters

AbstractThe plasma focus device, a form of linear pinch discharge, produces an intense x-ray and neutron (D2) burst from a magnetically heated dense plasma. Rapidly changing magnetic fields at pinch time generate large axial electric fields which accelerate electrons and ions. In the experiments reported here the x-ray production during the plasma pinch of a 96 kilojoule (at 20 kV) plasma focus device was measured.The purpose of these experiments was to evaluate the energy in accelerated electrons in the plasma focus device and to learn how to enhance these electron hursts. Well focused, megampere electron beams at a few hundred kilovolts, lasting less than 10 nanoseconds have applications in fusionable pellet heating experiments. (1) X-rays were monitored to evaluate these electron bursts using a defocusing bent crystal spectrometer, doubly diffused silicon (PIN) detectors, with Ross filters, thermoluminescent dosimeters (TLDs) with filters, and x-ray pinhole photography.Thermoluminescent dosimeters indicated maximum x-ray yields of 140 joules above 3 keV at 57.3 kilojoules stored energy (16 kV) for a conversion efficiency to x-rays of 0.2%. 40 joules are above 60 keV and 15 joules above 80 keV. The hard x-ray pulse typically rises in 3 ns and frequently has a pulse width less than 10 ns. The low energy x-ray spectrum consists almost entirely of lines from the high Z anode insert, and the high energy spectrum is characteristic of a nonthermal power law distribution with an exponent of 2.2 ± 0.8. Peak hard x-ray production is obtained at 1 torr deuterium in contrast to peak neutron production (3 x 1010) at 5 torr. The addition of argon reduces total x-ray yield and increases the relative fraction of soft x-rays.These measurements suggest that the plasma focus produces 1200 joules of electrons with an average energy of 150 keV, in 10 nanoseconds with a stored energy of 57.3 kilojoules. This is a power of 1.2 × 1011 watts and power density of 1.5 × 1013 watts cm−2.

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Silicon Detector System for X-Ray Pulse Calorimetry of Laser-Produced Plasmas*

Advances in X-ray Analysis ◽

10.1154/s0376030800006728 ◽

1974 ◽

Vol 18 ◽

pp. 213-221 ◽

Cited By ~ 1

Author(s):

J. H. McQuaid ◽

C. E. Violet ◽

J. Petruzzi

Keyword(s):

Silicon Detector ◽

Direct Conversion ◽

X Rays ◽

Electron Pairs ◽

Analog To Digital ◽

X Ray ◽

New Type ◽

A Charge ◽

Readout Scheme ◽

Charge Sensitive Preamplifier

AbstractThe instrumentation for measuring x-ray yields from laser produced plasma is described. This new type of calorimeter is composed of a silicon detector, a charge-sensitive preamplifier and an analog-to-digital readout scheme for multiplexing up to ten detector outputs.X-rays interacting with the detector produce hole-electron pairs in proportion to the total energy lost in the detector (∼1012 eV). In this application the detector can be characterized as a solid-state ionization chamber. The detector signal is coupled to a charge-sensitive preamplifier which generates a voltage pulse proportional to the x-ray energy absorbed. In this way the x-ray energy is measured by “direct conversion” rather than measuring the temperature rise due to an energy flux.

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Impact of charge carrier trapping on amorphous selenium direct conversion avalanche X-ray detectors

Journal of Applied Physics ◽

10.1063/1.5000510 ◽

2017 ◽

Vol 122 (13) ◽

pp. 134502 ◽

Cited By ~ 6

Author(s):

Salman M. Arnab ◽

M. Z. Kabir

Keyword(s):

Charge Carrier ◽

Direct Conversion ◽

Amorphous Selenium ◽

X Ray ◽

Carrier Trapping ◽

Charge Carrier Trapping

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Imaging local electric fields produced upon synchrotron X-ray exposure

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1407771112 ◽

2014 ◽

Vol 112 (3) ◽

pp. 696-701 ◽

Cited By ~ 6

Author(s):

Christopher M. Dettmar ◽

Justin A. Newman ◽

Scott J. Toth ◽

Michael Becker ◽

Robert F. Fischetti ◽

...

Keyword(s):

Electric Fields ◽

Second Harmonic ◽

Soft Materials ◽

Local Fields ◽

X Rays ◽

Electron Hole ◽

X Ray ◽

X Ray Absorption ◽

Static Electric Fields ◽

Cryogenic Conditions

Electron–hole separation following hard X-ray absorption during diffraction analysis of soft materials under cryogenic conditions produces substantial local electric fields visualizable by second harmonic generation (SHG) microscopy. Monte Carlo simulations of X-ray photoelectron trajectories suggest the formation of substantial local electric fields in the regions adjacent to those exposed to X-rays, indicating a possible electric-field–induced SHG (EFISH) mechanism for generating the observed signal. In studies of amorphous vitreous solvents, analysis of the SHG spatial profiles following X-ray microbeam exposure was consistent with an EFISH mechanism. Within protein crystals, exposure to 12-keV (1.033-Å) X-rays resulted in increased SHG in the region extending ∼3 μm beyond the borders of the X-ray beam. Moderate X-ray exposures typical of those used for crystal centering by raster scanning through an X-ray beam were sufficient to produce static electric fields easily detectable by SHG. The X-ray–induced SHG activity was observed with no measurable loss for longer than 2 wk while maintained under cryogenic conditions, but disappeared if annealed to room temperature for a few seconds. These results provide direct experimental observables capable of validating simulations of X-ray–induced damage within soft materials. In addition, X-ray–induced local fields may potentially impact diffraction resolution through localized piezoelectric distortions of the lattice.

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Time of Flight of Drifting Electrons and Holes in Stabilized a-Se Film

MRS Proceedings ◽

10.1557/proc-764-c3.53 ◽

2003 ◽

Vol 764 ◽

Author(s):

Dong-Gil Lee ◽

Ji-Koon Park ◽

Jang-Yong Choi ◽

Jae-Hyung Kim ◽

Sang-Hee Nam

Keyword(s):

Electric Field ◽

Applied Electric Field ◽

Time Of Flight ◽

Amorphous Selenium ◽

X Rays ◽

Large Area ◽

X Ray ◽

Transit Times ◽

Flat Panel Detectors ◽

Photo Response

AbstractLarge area, flat panel detectors are being investigated for digital radiogrpahy and fluoroscopy. Theses detectors employ an x-ray conversion layer of photoconductor to detect x-rays. The amorphous selenium layer that is currently being studied for its use as an x-ray photoconductor is not pure a-Se but rather a-Se doped with 0.2-0.5% As and 10-30 ppm Cl, also known as stabilized a-Se. The suitability of the stabilized a-Se is largely determined by its charge on generating, transporting and trapping properties.In this paper, a conventional time-of-flight measurement was carried out to analyze the transport properties of charge carriers. A laser beam with pulse duration of 5 ns and wavelength of 350 nm was illuminated on the surface of the stabilized a-Se with thickness of 400 μm. The photo response signals of the hole and electron were measured at the applied electric field of 10 V/μm as a function of time. The measured transit times of the hole and electron were about 229.17μs and about 8.73μs at 10 V/μm, respectively. The measured mobility indicated a slight dependence with respect to the applied electric field with a range of 4-10 V/μm. The experimental results showed that the measured mobility of the hole and electron was 0.04584 cm2V-1s-1 and 0.00174 cm2V-1s-1 at the electric field of 10 V/μm.

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