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A method is presented for measuring the energy density of X-ray pulses with a duration of approximately 200 ns from a source with an energy of 2–3 J in its discharge circuit. A bismuth germanate (BGO) scintillator crystal is used for measurements. The absolute calibration of the energy scale has been carried out by measuring the amplitude spectrum of cosmic muons. The energy flux of an X-ray pulse, measured at a distance of 1 m from the anode of the source, is 20 GeV/cm2.

X-ray detectors operating in the energy integrating mode are successfully used in many different applications. Nevertheless the direct photon counting detectors, having the superior parameters in comparison with the integrating ones, are rarely used yet. One of the reasons for this is the low value of the electrical signal generated by a detected photon. Silicon photomultiplier (SiPM) based scintillation counters have a high detection efficiency, high electronic gain and compact dimensions. This makes them a very attractive candidate to replace routinely used detectors in many fields. More than 10 years ago the digital scanning radiography system based on multistrip ionization chamber (MIC) was suggested at Budker Institute of Nuclear Physics. The detector demonstrates excellent radiation resistance and parameter stability after 5 year operations and an imaging of up to 1000 persons per day. Currently, the installations operate at several Russian airports and at subway stations in some cities. At the present time we design a new detector operating in the photon counting mode, having superior parameters than the gas one, based on scintillator – SiPM assemblies. This detector has close to zero noise, higher quantum efficiency and a count rate capability of more than 5 MHz per channel (20% losses), which leads to better image quality and improved detection capability. The suggested detector technology could be expanded to medical applications.

Problems related to X-ray imaging with minimum radiation doses are described, a method for constructing systems for X-ray imaging of people at these doses is proposed, the main components of these systems are briefly described, and their optimal applications in medicine and security systems are characterized.

The scintillation crystal bismuth germanate Bi 4 Ge 3 O 12 (BGO) is widely used in many applications. The developed in the Nikolaev Institute of Inorganic Chemistry, Novosibirsk, Russia, unique technique allows routine production of top quality large sized BGO crystals. One of the important properties of the scintillation crystal is its radiation hardness. The intensive study of the radiation hardness of BGO crystals has been carried out by the collaboration of the institutes of Siberian Branch of the Russian Academy of Science, Novosibirsk. The influence on radiation hardness of the raw material purity and growth procedure has been studied. The final tests of the crystal radiation hardness were done by irradiation with gamma rays from 137Cs radioactive source. The degradation of a light output of the best crystals is less than 10% after irradiation with expected at astrophysics experiment at satellite doses of 10–100 krad. Based on results of this research, the radiation hard BGO crystals for “INTEGRAL” and “ASTRO-H” satellite missions have been made. The self-recovering of the crystal light output is clearly seen. The time scale of the self-recovery strongly depends on a dose of the irradiation. It is days for 1 krad irradiation, weeks - for 10 krad irradiation and much more time is required for 100 krad irradiation. The all irradiated with 100 krad dose completely recover after annealing. It reveals that will be no essential degradation if this dose will be integrated over years of operation.

High-resolution X-ray computed tomography (HRXCT) is a technology ideally applicable to a wide range of geological investigations. It is an express non-destructive method to produce images corresponding to series of slice projections through a sample. In the present study, HRXCT was applied to rock samples with the use of synchrotron radiation from the VEPP-3 storage ring, at the “X-ray microscopy and tomography” station. The method was calibrated and preliminary measurements were carried out on the Low-Dose Digital Radiographic Device “Siberia”. The data obtained have determined the internal structure of rock samples with a spatial resolution of 100 μm. HRXCT has been applied to the xenoliths of diamondiferous eclogites from the Udachnaya kimberlitic pipe located in Yakutia, Russia. It has allowed determination of the distribution of rock-forming (garnet and clinopyroxene) and accessory (diamond, rutile, and sulfide) minerals of different X-ray absorption. This is important to find out the genetic relationship of diamonds with associated minerals and the sequence of crystallization.

The security system of personal radiographic inspection for detection of explosive materials and plastic weapons was developed in BINP recently. Basic system parameters are: maximum scanning height— 2000 mm , image width— 800 mm , number of detector channels—768, channel size— 1.05×1 mm , charge collecting time for one line—2, 5 ms , scanning speed— 40 cm/s , maximum scanning time— 5 s , radiation dose per one inspection μSv . The detector is a multichannel ionization Xe chamber. The image of inspected person will appear on the display just after scanning. The pilot sample of this system was put into operation in March, 2003.b

Low-dose digital radiographic device “Siberia” based on a multistrip ionization chamber was developed in Budker Institute of Nuclear Physics. Originally, the detector was filled with Xe gas under 10 bar pressure, however, the latest study showed that Kr filled detector at 20 bar has higher signal-to-noise ratio (SNR) than Xe one. The main factor affecting SNR is amplitude fluctuation of detected signal. Kr has lower value of K-shell binding energy and less K-shell fluorescence yield than Xe gas. It leads to less distortion of registered X-ray spectra and better energy localization. As a result the detector has better channel shape and higher DQE value.

The new effective one-dimensional detector for digital scanning radiography is presented. The progress in the design of low-noise electronics allowed the Multistrip Ionization Chamber to be used as the X-ray detector. The detector has been designed for use in the Low-dose Digital Radiographic Device “Siberia” instead of a multiwire proportional chamber. The working gas is Xe under 12 atm pressure. The main detector parameters are as follows: total number of channels, −1024; channel size, −0.4×0.4 mm2; space resolution, −1.25 lp/mm; contrast sensitivity, −1%; dynamic range, −480; surface dose for chest image, −3 to 5 mR.

X-ray detectors for use with a scanning radiographic device have been developed based on the technique of compensated semi-insulating GaAs. The main detector feature is a linear current–voltage characteristic due to the use of Ohmic contacts. The detector consists of two identical detectors connected to power supplies with different polarities in order to minimize the detector leakage current. Testing of the detectors has been carried out at the Budker Institute of Nuclear Physics. The detector was used with the digital X-ray apparatus “LDRD SIBERIA–N”. The detector parameters have been studied, looking at the dependence with radiation dose, with the applied bias voltage and with the gamma photon energy, using photons in the range of 60–120 keV. Images of a test-object were obtained with a resolution of 1.4 line pairs per mm for a detector with 400 μm pitch and 2.8 line pairs per mm for a detector with 200 μm pitch.

Two types of one-dimensional X-ray detectors for scanning radiography are presented. One of them is a fast Multi Wire Proportional Chamber (MWPC) operating in direct photon-counting mode. The MWPC parameters: efficiency – 30%, width of channel – 0.6 mm, total number of channels – 640, maximum counting rate per chamber – 3×10 8 counts/s. Patient irradiation effective dose from lung radiography is 7μSv. Since 1997, the radiographic device based on MWPC went into mass production and 60 devices were in operation in Russian hospitals to the end of 1999. However, progress in design of the low noise electronics allowed to use the Multistrip Ionisation Chamber (MIC) instead of MWPC. The MIC parameters: efficiency close to 80%, width of channel – 0.4 mm, total number of channels – 1024. Application of MIC has some advantages over MWPC. MIC has higher counting rate, higher spatial resolution, low sensitivity to gas impurity and lower cost. The electronics noise is equivalent to signal from 4 photons.

In this paper we consider two types of gaseous detectors for radiography. The first one, the Multiwire Proportional Chamber, is used at present as a part of the digital radiographic system. It works in counting mode, has a quantum efficiency of 30% and a spatial resolution of 0.6 mm. Our new detector, the Multistrip Ionisation Chamber, is filled with Xe at 10 atm., has a quantum efficiency up to 70% and a spatial resolution of 0.4 mm. This method with integration of collected charge allows to avoid the problems of counting rate and gas ageing and considerably reduces the cost of electronics.

The multiwire proportional chamber (MWPC), operating in a direct photon-counting mode, is used as the basis of 1D and 2D X-ray detectors. The 1D detector used in our scanning radiographic systems is serially produced. Its counting rate is about 200 MHz, its spatial resolution 0.6 mm, the number of channels is 640. The 2D detector, designed for diffraction structural researches on synchrotron radiation at the storage ring VEPP-3, is being commissioned now. Its characteristics are: 5 MHz, 1.5 mm, 65536 channels. The second 1D detector (10 MHz, 75 μm, 3300 channels, σ = 150 μm) is made for the same purposes. A third 1D detector with a registration angle of 60° (500 MHz, 0.6 mm, 1900 channels) is under development. All the detectors operate in a frame-by-frame mode and are free (except 2D) of parallax error.

Application of MultiWire Proportional Chambers (MWPC) and MicroStrip Gas Chambers (MSGC) in medical radiography is discussed. These detectors are capable of detecting X-rays in counting mode with high efficiency, thus giving essential dose reduction compared to film/screen techniques. This was demonstrated on several Digital Radiographic Devices (DRD) with one-dimensional MWPC and scanning in the orthogonal direction. Effective pixel sizes of 1 mm and 0.5 mm for different devices with highly parallel readout systems has been achieved. The counting rate capability of DRDs is ∼ 500 kHz/pixel, which is enough to get high statistics of X-rays with a short exposure. Dose saving factors from 1 to 2 orders of magnitude for several common examinations were demonstrated. Further development of this approach can be made with MSGC which reproduce operation of MWPC in a much smaller scale. First tests of prototype chambers with 200 μm pitch of strips at high pressure have shown the possibility to reach a gain of ∼ 104 in a 6 bar Xe mixture. A proper choice of substrate material permits one to avoid charging problems at high fluxes. These features allow, one to build a counting device with 0.2 mm pixels for the detection of X-rays of 20–60 keV.

A digital radiographic device for medical diagnostics is described, with the spatial resolution improved by about a factor of 2 as compared to the previous modifications of this system operating in the hospitals of Moscow and Novosibirsk. The distribution of radiation intensity in the horizontal direction is measured with the help of MWPC, while in the vertical direction it is measured by a mechanical scanning. To avoid parallax, the chamber anode wires are not parallel, but “looking” at the source of X-rays. Each anode wire is connected to a separate electronic channel, which registers the X-ray quanta absorbed in the working volume of the chamber, with an energy exceeding 1–2 keV. To improve the spatial resolution of the chamber by a factor of 2 compared to the pitch of anode wires, the readout system registers separately the events with a hit at one anode wire and the events which contains two coincident hits at neighboring wires. The main characteristics of the device are the following: the number of channels of the MWPC is 640; the geometrical size of the channels is 0.6 mm; differential nonlinearity after performing corrections is not more than 1.5%. The dimensions of the digital image are 640 × 512.

A digital radiographic installation for medical diagnosticsics described. Distribution of X-ray intensity in horizontal direction is measured by a one-coordinate MWPC with a 1.2 mm channel. A two-dimensional image is produced by mechanical scanning with 1 mm channel width in vertical direction. The number of pixels in the image is 320×256. The MWPC works in count mode with quantum efficiency 25% (50 keV) and count rate capability 600 kHz/channel. Results of testing a prototype with 64 channels 0.6 mm width are also presented.

In the present report, we summarize the results of our efforts to create a x-ray counting detector for digital scanning radiography based on the silicon photomultipliers (SiPM) at Budker Institute of Nuclear Physics for the last year. We have performed a comparative study of the possible candidates for scintillator—YAP, LFS-3, LGSO, LYSO and two types of SiPMs—HAMAMATSU MPPC with 25 μ m pixel (S10362-33-025C) and KETEK SiPM with 15 μ m pixel (MP15V9 type) o 2.5 mm. To measure real detector parameters we have built a detector prototype based on a 32-channel Omega EASIROC front-end chip. The results obtained in this study demonstrate that such detector could reach quantum efficiency >95%, counting rate —5 MHz, energy resolution ~ 34% (at 59.5 keV) and spatial resolution that is determined by scintillator and SiPM size.

1D imaging arrays of GaAs x-ray detectors are designed, fabricated, and tested. Each array consists of 64 detectors arranged with a pitch of 0.4 mm. In x-ray testing, an almost linear relationship is found between the detector response and the tube current. Zero detector cross coupling is observed in scanning an x-ray beam along any array.