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Russian Physics Journal, Vol. 50, No. 10, 2007

AUTOMATED METHOD OF PROCESSING VIDEO DATA FROM TRACK DETECTORS

A. B. Aleksandrov,1 L. A. Goncharova,1 D. A. Davydov,2 UDC 539.1.08 P. A. Publichenko,2 T. M. Roganova,2 N. G. Polukhina,1 and E. L. Feinberg1

New automated methods simplify significantly and accelerate processing of data from emulsion detectors. In addition to acceleration, automation of measurements allows large files of experimental data to be processed and their statistics to be made sufficient. It also gives impetus to the development of projects of new experiments with large-volume targets and emulsions and large-area solid-state track detectors. In this regard, the problem of increase in the number of scientists with required level of training capable of operation with automated technical equipment of this class becomes urgent. Every year, ten Moscow students master new methods working at the P. N. Lebedev Institute of Physics of the Russian Academy of Sciences with the PAVIKOM fully-automated measuring complex [1-3]. Most students now engaged in high-energy physics gain a notion of only outdated manual methods of processing data from track detectors. In 2005, a new practical work on determination of energy of neutrons transmitted through a nuclear emulsion was prepared on the basis of the PAVIKOM complex and physical experimental work of the Physical Department of Moscow State University. This practical work makes it possible to acquaint the students with initial skills used in automated processing of data from track detectors and can be included into educational process for students of physical departments.

CURRENT STATE OF EXPERIMENTAL WORKS USING THE TRACK METHOD AND ADVANTAGES OF EMULSION DETECTORS AS MEANS FOR DEMONSTRATING PARTICLE PHYSICS PHENOMENA TO STUDENTS

Nuclear emulsion has been used in experiments on particle physics for many decades. Such a long life of the method is certainly caused by the unique spatial resolution and the possibility of discrimination of particle tracks. The special place among the works with emulsion is occupied by the OPERA largest international experiment (the detector on which a neutrino beam from CERN is incident after passage of a distance of 730 km is located in the Gran Sasso Underground Laboratory in Italy). The OPERA experiment is aimed at observation of νµ and ντ oscillations by means of direct registration of τ-leptons in a nuclear photoemulsion and accumulation of reliable quantitative results on neutrino oscillations. The OPERA experiment is also sensitive to conversion of muon neutrino oscillations into electronic ones, which makes it possible to investigate mixing matrix components based on an analysis of three aromas. In this experiment, emulsions are used as a precision track detector. Extremely high spatial resolution of emulsions is best suited for solving the problem of detecting short-living τ-leptons produced in ντ interactions. The main component of the OPERA facility is a lead photoemulsion detector of modular design with a useful mass of about 1.8 kton, including a photoemulsion with a mass of about 100 ton. It has no analogs in experimental physics. The unit (from which the detecting system of the facility is constructed; the number of units is approximately 200,000) comprises layers of nuclear photoemulsion 50 μm thick poured on two sides of a 200-μm plastic base alternating with 1-mm lead plates. The coordinates of charged particle trajectories at emulsion edges are determined with high accuracy (0.1–0.2 μm), thereby providing the accuracy of measuring angles no worse that 5–8 mrad. The number of events caused by interactions of muon neutrinos from the CERN beam in the OPERA

1 P. N. Lebedev Institute of Physics of the Russian Academy of Sciences; 2 Scientific-Research Nuclear Physics Institute at M. V. Lomonosov Moscow State University, e-mail: ddavydov@list.ru. Translated from Izvestiya VysshikhUchebnykh Zavedenii, Fizika, No. 10, pp. 61–65, October, 2007. Original article submitted April 23, 2007.

1064-8887/07/5010-1026 ©2007 Springer Science+Business Media, Inc.

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detector must be as great as 50,000 for five years of exposition. This huge data array can be processed only due to recent achievements in the development of automated scanning systems with computer-controlled microscopes.

The indisputable leaders in automation of nuclear emulsion data processing are Japanese physicists who started full automation in the mid-90s. This was a true revolution in the emulsion technology that can hardly compete with explosively developing electronic methods of research without automatic data processing. About two tens of fully-automated microscopes operate nowadays at Japanese universities. The CERN and some other European scientific centers where such automatic devices are used are also actively engaged in automation of measurements in emulsions. At present, more than four tens of fully-automated facilities for nuclear emulsion data processing operate all over the world. The possibility of processing of huge data array necessary for realization of the OPERA experiment is provided by great progress in the field of creation of computer-controlled microscopes and CCD-chambers as well as by progress in the development of methods of automatic image recognition and track reconstruction. Automatic systems of the third generation, which allow scanning of emulsions approximately 1000 times faster than with the help of semi-automatic systems, have already been developed. This progress testifies to the true revolution in the field of nuclear emulsion detectors. Nowadays they can be considered as track rather than video detectors. Data can be analyzed in the automatic regime without operator. The European and Japanese participants of the OPERA experiment have these systems at their disposal. The unique system of this class in Russia is the PAVIKOM complex developed at the Institute of Physics of the Russian Academy of Sciences (IPRAS).

Training of experts-physicists skilled in object-oriented programming and methods of image recognition is also urgent now. These skills are widely used in many electronic nuclear-physics experiments, applied works, and commercial production of modern equipment thereby demonstrating the need for such specialists.

In the course of physical practical work, one of the laboratory works for students of the Physical Department of Moscow State University (MSU) was devoted to a study of nuclear emulsion irradiated by neutrons. Because of simplicity and vivid presentation, the emulsion detectors have great advantages over other detection systems in demonstration of particle physics phenomena to senior students of physical educational institutions. The emulsion had a thickness of about 40 μm and was irradiated by a collimated beam of neutrons from a polonium–beryllium source. The laboratory work was aimed at determining the energy of primary neutrons; to this end, students should measure the track lengths and angles of departure of recoil protons.

These measurements have already been carried out manually using optical microscopes, and students visually found and fixed particle tracks. However, on the modern level of technology development, full automation of nuclear emulsion data processing and creation of microprocessor-controlled systems for recognition of particle tracks and restoration of their spatial configuration are controlled by a computer using special programs. Every year, 10 Moscow students from different institutes (Moscow Physical-Technical Institute (MPTI), Moscow Engineering Physics Institute (MEPI), MSU, Moscow Institute of Steels and Alloys (MISA), and Institute of Natural Sciences (INS)) master new methods while working with the PAVIKOM complex at the IPRAS. Most students trained in high-energy physics gain a notion of only outdated technology of manual nuclear emulsion data processing with the use of optical microscopes. As one of the first steps for extending the capabilities of training specialists in modern methods of experimental nuclear physics, the laboratory work of the Physical Department of MSU aimed at investigation of neutron propagation through nuclear emulsions was fully automated. A new variant of the laboratory work was based on the PAVIKOM complex developed at the IPRAS [1, 2] and being the unique complex in Russia satisfying modern world standards.

PAVIKOM COMPLEX

In the fully automated regime, the PAVIKOM complex can: – search and digitize charged particle tracks in the detector material, – perform computer-controlled recognition and tracking, – systematize and primary process the data obtained. The operation principle is the following: an image on a CCD-matrix creates an objective of the microscope.

An analog video signal formed by a video camera is applied at the input of a digitizing and image-capturing card. The card digitizes the video signal, transfers these data to a computer memory, and also displays a digitized video signal in the window of the monitor screen.

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The complex comprises two facilities that differ by several parameters [3, 4]. In the practical work of the Physical Department, the emulsion was scanned using the PAVIKOM-2 facility [5].

The automated microscope of the PAVIKOM-2 facility (Fig. 1) is built around an MPÉ-11 microscope produced by the Leningrad Optical-Mechanical Association (LOMA). The main units of the PAVIKOM-2 facility are:

– precision table produced by the German Carl Zeiss Firm with a control unit, – digital CCD-chamber, – personal computer. The little table can be displaced at distances of 0–100 mm in the horizontal plane and at about 1 cm in the vertical

plane. The optical little table is moved along these directions by a stepped engine controlled by a controller put into operation by computer instructions. The accuracy of measuring X and Y coordinates was 0.25 μm in the horizontal plane and 3.96⋅10–3 μm along the Z axis. After modernization of the PAVIKOM-2 complex in 2006, an МС1310 high-speed image registration system (comprising an МС1310 CMOS video camera produced by the Mikrotron Firm with a matrix of 1280 × 1024 pixels, scanning and processing rate of 500 frames per second, and a 10-bit level of image digitization) was mounted and put into operation in the test regime. A Matrox Odyssey XPro board providing the possibility of effective online scanning was also mounted. The board can simultaneously independently capture an image and process it in a processor with the help of protection functions and in a Pixel accelerator. The modernization of the PAVIKOM complex allowed Russian physicists to participate in automated processing of emulsion data obtained in the largest international OPERA experiment and to train experts-physicists on the advanced experimental equipment.

In the process of modernization in 2006, the software package libACQ developed at Bern University specially for processing of the OPERA emulsion data was installed and adapted. This package involves a set of classes used to control the scanning process and simultaneously to process recorded images and to view tracks. The package has no graphic interface; it can be used only by calling the corresponding functions of control over the facility and data processing from the ROOT programming environment. Because of this, the software package is simple enough and easy for mastering; therefore, it obviates the necessity of great experience of working with this software. At the same time, the most advanced methods of data processing are used in this package. Therefore, the package can be used to realize additional opportunities of image capture and processing provided by modern boards and by controllers executing mechanical control (Fig. 2).

Fig. 1. External view of the PAVIKOM-2 automated microscope.

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SCANNING OF NUCLEAR EMULSIONS

Scanning of nuclear emulsions irradiated by neutrons in the course of the MSU educational laboratory work was performed with the following parameters: magnification of the optical system objective was 60× (with a field of view of 80 × 60 μm2), scanning step was 75 μm along the X axis, 55 μm along the Y axis, and 2 μm along the depth (scanning in one field of view was performed at 18 depths). Ten fields of view were scanned along the X axis and thirty along the Y axis. The software used for scanning created image files in JPEG format and a text file with coordinates of these images.

SOFTWARE FOR IMAGE VIEWING AND PROCESSING

For viewing and processing of scanned files in JPEG format, a special program Emulsion Viewer was written. It fulfills the following functions:

– image construction from a large number of JPEG files,

Fig. 2. Image constructed on the computer monitor by the software package libACQ and one field of view at ×60 magnification in the OPERA nuclear emulsion in the test pion region.

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– viewing of this image on different scales, – indication of image points, determination of their coordinates, and filing of these coordinates. These properties allow the program application for practical work and scientific purposes. The program was written in the Borland C++ Builder environment. It comprised standard procedures [6]. To work

with JPEG files, the object TJPEGImage from the standard file Jpeg. HPP was used. A large image constructed from JPEG-files was viewed as follows: the object of the standard class TImage including the object Canvas was imposed on the main program form. This object was a BMP image imposed on TImage. Canvas has the StretchDraw function. This function allows image transformation from TJPEGImage objects into the BMP format and draws them on Canvas one after another. Each time scanning the image, the program determines which of JPEG images fall within the screen on the given scale and displays them on Canvas.

To display the image from the file on the screen, the file should be loaded into a memory. To save the memory, only files that fall within the screen on the current scale are loaded into the program. The possibility of mirror image inversion is also envisaged in the viewing program. The program interface (Fig. 3) allows image scanning and change of the viewing scale to determine the coordinates and to change options of image loading.

CONCLUSIONS

Hi-tech methods of processing of experimental data from track detectors provide the basis for organization of some modern physical experiments. Realization of these methodically new experiments, in its turn, calls for training of experts capable of working with automated complexes. The PAVIKOM experimental complex for automated processing of data from track detectors, unique in Russia, satisfies the most advanced modern world standards. It was developed by physicists from the IPRAS and SRNPI at MSU. It is successfully used for hi-tech processing of experimental data obtained with the use of emulsion and solid-state detectors in the fields of nuclear physics, physics of cosmic rays, and high-energy physics. It

Fig. 3. Image on the computer monitor drawn during execution of the data processing program. Parts of tracks of recoil protons can be seen in the examined image.

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satisfies the needs of not only experimenters carried out in the IPRAS but also in other Russian laboratories and institutes (including the Nuclear Research Institute of the Russian Academy of Sciences (NRIRAS), SRNPI at MSU, Joint Institute for Nuclear Research (JINR), and Institute of Theoretical and Experimental Physics (ITEP)). In this respect, the PAVIKOM complex has no analogs in the world. The possibility of preparation of practical works for senior students of physical departments is a new additional field of application of the PAVIKOM complex. It is suggested to perform automated scanning of data from track detectors of the most advanced facilities of the Russian Academy of Sciences chosen by a concrete university for demonstration of particle physics phenomena. Mastering new methods of data processing using the suggested work as an example will allow not only to train physicists who have mastered automated processing of data from track detectors, but also to improve the skills of graduates from physical departments in mathematical methods of image recognition and to use this knowledge in different fields of science and engineering.

The work was supported in part by the Russian Foundation for Basic Research (grant No. 06-02-16864).

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