O. P. Ivanov

High-energy radiation visualizer (HERV): a new system for imaging in X-ray and gamma-ray emission regions

We present a description and results of the operation for /spl gamma/-ray and X-ray objects for the compact visualization system high-energy radiation visualizer (HERV). The imaging in this system is based on use of a conical collimator, scintillator plate, and image intensifier as a detector and CCD matrix as a readout device. The use of HERV as a two-dimensional X-ray image visualizer for the Compton scatter inspection system was considered and first results are discussed. The possibility of using different hexagonal-coded apertures imaging for HERV is discussed and results of Monte Carlo simulation and experiments with optical analog of coded aperture are presented.

The design and performance of a large-volume spherical CsI(Tl) scintillation counter for gamma-ray spectroscopy

This paper presents details of the design and performance of a prototype large-volume scintillation detector used for gamma-ray spectroscopy. In this detector, a spherical CsI(Tl) scintillation crystal having a diameter of 5.7 cm was polished and packed in dry MgO powder. The scintillation light from the crystal was viewed using a single 1 � 1c m 2 silicon PIN diode. A low-noise preamplifier was also integrated within the detector housing. The measured noise level was equivalent to B800 electrons (FWHM). Such a configuration provided a very good light collection efficiency, which resulted in an average of 20 electrons being generated per keV of energy deposited in the crystal. One of the key features of the detector design is that it minimises spatial variations in the light collection efficiency throughout the detector. Compared with a standard 3 in. NaI scintillation counter, this feature leads to a much-improved energy resolution, particularly for photon energies above 1 MeV. The results presented in this paper clearly demonstrate that a spherical CsI-photodiode detector could be used as an ideal replacement for the standard 3 in. NaI detectors in many applications, but especially when the incident gamma-ray spectra extend up to B10 MeV as in neutron-activated gamma-ray analysis. r 2001 Elsevier Science B.V. All rights reserved.

The improvement of image processing and noise reduction scheme of HERV and results of gamma-imaging

HERV is system for visualization in X- and gamma-ray regions developed by RECOM during last years. Its last version is real industrial prototype that was tested in conditions of complex gamma-field in strongly contaminated nuclear facilities in Russia and Germany. New special processing procedures of CCD camera frames, which operates in slow repetition mode, allow to carry out imaging without using of heavy shielding during long exposure time. Image processing procedures which allow to take into account background radiation and noise and drift of electronics are described. The results of imaging of contaminated pipelines and vessels by HERV are presented. Background dose rate in premises with contaminated equipment was up to 1 R/hour and at detector head place was from ImR/hour up to 50 mR/hour. Main contaminating nuclides were Co-60 and Cs-137. Imaging time was 0.2-1 hour. Data acquisition and processing procedures were good enough to exclude the influence of high background dose rate at place of measurement head of a device. Superposition of gamma images over optical images shows that the contaminated parts of pipelines are bends of pipes, places of their connection, valves.

HERV-high energy radiation visualizer, a new system for imaging in X-ray and gamma regions

We present description and results of operation for gamma- and X-ray objects compact visualization system-HERV. The imaging in this system is based on using of conical collimator, scintillator plate and image intensifier as detector and CCD matrix as readout device. The using of HERV as 2D X-ray image visualizer for Compton Scatter inspection system was considered and first results are discussed. The possibility of using different hexagonal coded apertures imaging for HERV is discussed and results of Monte-Carlo simulation and experiments with optical analog of coded aperture are presented.<<ETX>>

Development of method for detection of alpha contamination with using UV-camera “DayCor” by OFIL

Remote monitoring of alpha-ray contamination is very important problem for activities connected with decommission of installation of nuclear fuel processing. Large problem in this approach is solar (or other sources) UV background. New UV cameras are suitable for imaging of α-contamination by fluorescence of atmospheric air the as they are so called solar blind (SB)- they are sensitive to UV this wavelength less 290 nm only and are no sensitive to solar UV. At measurements with accumulation of a signal, for exposure of 600 sec it is possible to expect, that for a point source of alpha radiation (Ea = 5MeV) located on distance 3 m the activity, at which it can be found out, is equal 104 Bq. Homogeneous superficial pollution, which can be revealed in this case makes 100 Bq/cm2. We present results of practical application of DayCor SuperB camera for imaging of alpha sources. Our approach is based on processing of single images, processing of initial frames, summing of processed images and special filtration of final image. Instruments sensitivity for alpha contamination registration in terms of minimum measurable activities (MMA) have been estimated as, 40 – 100 Bq/cm2 (measurement time is 3600 – 600 sec correspondently).

New portable gamma-camera for nuclear environment and its application at rehabilitation works

Industrial prototype of portable gamma camera for nuclear environment was developed. Camera has new 2D position sensitive detector (PSD), which is based on generally used components as image intensifier with MCP and digital video camera with an industrial CCD. The gamma image is formatted on PSD by two-cone collimator or coded mask. The dimensions of detecting head are ~ L=50 cm and D=12 cm. Scintillating plate has useful diameter 38 mm and thickness from 1 up to 4 mm, depending on aperture used. Two co-ordinate scanning unit is assigned for distant choice of device field of view. A special portable computer is used for control of all gamma camera subsystems by operator, for processing of gamma images, storage and displaying and for operation with images. Standard distance between detecting head and computer is 50 meters. The results of application of gamma-imaging during rehabilitation activity at territory of temporal storage of radioactive wastes of RRC Kurchatov Institute are presented and discussed.

Technique for in situ measurement of Cs-137 deposit in soil under clean protected layer

A method to determine a Cs-137 soil deposit in situ, in case of a contamination protected by a clean soil layer is described. The method is based on measurements and processing of count rates in three energy ranges by a Collimated Spectrum Sensitive Detector. The thickness of an analyzed soil layer is up to 40 g/cm/sup 2/. This value corresponds to three mean free paths (mfp, 1 mfp/spl equiv//spl lambda/) of Cs-137 radiation in the soil. The thickness of the uncontaminated soil layer, covering the contaminated one, may achieve 2/spl lambda/. A minimum detectable soil deposit is about 20 kBq/m/sup 2/. An accuracy of a determination of the deposit is 20%. An estimation of the contaminated soil layer thickness slightly depends on a distribution of the contamination depth. Measurement results are presented and compared with data of a soil sampling. The developed technique is highly effective for mapping of contaminated territories. Cs-137 contamination maps of areas in Belarus and Chelyabinsk region of Russia are presented. The measurements of the Techa river bank contamination detected presence of a secondary contamination transference. This method allows to forecast a change of a dose rate after a decontamination of the territory and to determine rates of necessary rehabilitation and its efficiency.

A dip detector for in situ measuring of /sup 137/Cs specific soil activity profiles

A field method for measurement of Cs-137 contamination depth profiles is described. The method is based on the use of a collimated dip detector created as a gamma-ray probe: CsI(Tl) scintillating crystal + PIN photodiode + front-end electronics. The presented method allows determination of specific activity distribution with vertical spatial resolution of 5 cm. Exposure time for one point in the distribution profile is less than 180 s if the level of specific activity is more than 50 Bq/kg. This method may be applied for efficient and quick inspection of a contaminated rivers flood planes in areas with leakage of radioactive wastes. Application of the method for such a task gives an effective solution to obtain qualitative and quantitative characteristics of contamination.

Different methods of image reconstruction for portable X-ray and gamma-ray imager with coded aperture

The coded aperture imaging increases device sensitivity for the same detector and angular resolution. The hexagonal URA masks of ranks 6 and 9 have been used for portable gamma-ray imager instead of pinhole collimator. The combined detector: scintillator+image intensifier+CCD matrix and hexagonal URA masks with step of pattern 1.5-2.5 mm were used. The images of point objects and complex circular objects of different diameters were obtained. With tantalum mask of thickness 12 mm (total FOV-23/spl times/22 degrees, resolution-1.5 degree) system is able to detect 1 MBq Cs-137 point source at distance 1 m in time 10 min. With SNR>5. The aperture of the device is not limited by angle of fully coded aperture and sources out of this region may input into coded shadow picture. For correct image reconstruction in this case the authors consider possibility of extension of decoded image size out of fully coded aperture. The approaches to image decoding in this extended area based on a least squares fitting of estimated image to experimental data were studied.

Experience of Application of New Remote Controlled Instruments for Scanning of Distribution of Radioactive Contamination in Rooms With High Dose Rate

When carrying out the decommissioning of nuclear facilities is necessary to measure the distribution of radioactive contamination in the rooms and the equipment at high levels of background radiation. In the decommissioning of the reactor in the MR NRC “Kurchatov Institute” for such problems is developed and applied a few special systems with remote control. For a survey of high-level objects used mounted on the robot radiometric system. To determine the composition of pollutants and use a portable collimated spectrometric system. To obtain a detailed distribution of contamination of used remote-controlled gamma camera.Copyright