Development of a Software for the speditive mapping of Radiological Diffusion in order to improve the rescue operations.

Abstract This paper deals with the analysis of orphan sources, analyzing the radiological protection problems in case of finding and securing of these sources with particular attention to the following aspects: • Operators safety and security; • Exposed population safety and security; • The identification of dangerous areas to the managing and timing of rescue operations. These points are also the main problems to be met by the persons in charge to decide on securing of the radiological source. In this paper, after defining the characteristics that the radiological sources must have to be defined orphan, the authors examine the fundamental radiometric parameters. The aim of this work is to develop a software that needs as boundary conditions the dose rate measured at a certain distance from the source and a hardware access to the web and allows to perform a geo-referencing of radiological risks on maps available in the network. A particular attention has been dedicated to the theoretical model and support tools for decision chosen for the operators responsible for the securing of the radiological source. This research has: • define the conceptual model of a Spatial Decision Support System (SDSS) oriented to the problem of radiation hazard identifying the requirements of both the component "mobile" than to support a Control Room; • developed the prototype of the software for terminal operators in the field that allows access via the web to make geo-referencing expeditious source location and dose rate measured at a certain distance from the source of maps available online; • developed the prototype of the Operating Room components according to the paradigm SOA (Service Oriented Architecture), which allows usability through OGC web services within the platform of processing of SDSS Intergraph I2RMS. In this paper the fundamental radiometric parameters and the main protective measures are presented and then the architecture of the software system is described with a detailed analysis of the first results obtained with the software prototype developed in order to demonstrate that this tool allows the management of the radiological emergency by operators and in particular by decision makers simplifying the management of the safety and security operations. 2 1. Introduction Radioactive sources are used throughout the world for many applications; particularly in industry, medicine and research. The risks associated with such uses is strictly connected to their physical characteristics: activity, types of radionuclides, methods of manufacture, etc.. In case of conventional application the risks associated are usually well known and their activities are generally normed. In the European Union provisions on the protection of population and workers against the risks of ionizing radiation are given with EURATOM directives, assimilated by the EU States. In Italy the main guidelines are contained in Legislative Decree no. March 17, 1995, n. 230, as amended. The problems related to sources, so-called "orphan", (which, for various reasons, are not under control) are different. These sources may be found by people (workers or citizens) unaware of their nature and possible risks, which may also be involved in serious radiation injuries with fatal outcome. The sealed orphan sources are regulated by Decree 6 February 2007, n. 52, implementing the EURATOM Directive 2003/122/EC, which provides, among other things, the preparation by the Prefect of a provincial action plan, in accordance with the National Plan of emergency, to guarantee the safety in case of discovery or suspected presence of orphan sources in the territory. The sealed sources may also present special risks due to the small dimensions, often lower than those of a pen, which does not allow an easy identification. Rather frequently is the case of sources which, contained in metal casing, have been gathered by scrappers and flow rates in steel plants where, at times, have been fused with consequent problems of contamination. To protect against such events, melting plants have to equip themselves of radiometric instrumentation for control the metal scrap in input, so as to reduce the risk of accidental introduction of radioactive sources in the processing cycle. Such monitoring is provided in Article 157 of Legislative Decree no. 230/95 and subsequent amendments. However, even these control systems cannot avoid the presence of radioactive materials. As part of the Community Action in the field of radioactive waste (Council Resolution of 15 June 1992 on the renewal of the Community Action Plan in the field of radioactive waste, OJ C 158, 25.6.1992), the European Commission published a study on the management and disposal of disused sealed radioactive sources in the European Union (Angus et al., management and disposal of disused sealed radioactive sources in the European Union, EUR 1886, 2000.). Sometimes the competent national authorities are faced with situations where the sources are not managed properly or are left without any control, with the possibility that can result in serious health consequences for workers or the population. The chances of these kind of risks increase when the sources are no longer used and are simply stored or left unattended for long periods. In fact, we see a loosening of controls between the time when the sources are withdrawn from use and the time they are returned to the farmers for the purpose of reuse or treated as waste and subject to the system of management of radioactive waste. The health and economic consequences of accidents which result in inadequate control of sources can be particularly severe. 2. Radiological characteristics to measure radiological risks The main radiological characteristics, and particularly those useful for the present work, are commonly divided into: 1. Source: • Activities • Constant range 2. Field Values: • Exposure • Kerma (the kerma is actually a size of dose, but its measurement in air is also used as the field value) 3. Values of the dose • Absorbed dose; • Dose Equivalent; • Effective Dose. Among these variables there is a direct relationship: Source FieldDose The suitable instrumentation for detecting the presence of radiation and to perform 3 measurements of field, the dose and to detect the type of radionuclide is available. 3. In field operations with unknown radiological source In the case of operation with the presence of orphan source, the operators (in most of the cases) are working with a source with unknown characteristics. External exposure of an operator may be limited by observing the following rules: 1) reducing the irradiation time: the value of the dose in fact increases linearly with the intensity of the radiation and with time (Figure 1). Figure 1: Dose vs time trend The operation must therefore be planned carefully in order to minimize, as far as possible, the intervention times. In any case, however, should not be exceeded dose values established by law. Three quantities are defined dose: the absorbed dose (D), the equivalent dose (H) and the effective dose (E). The equivalent and effective doses relate the amount of radiation received by a person with the resulting biological damage, and for this reason are called radio-protection quantities. In order to plan operation with sealed source (in absence of contamination risk) the most important value is the effective dose (E). 2) increasing the distance. Taking into account a generic distance d from the source, the value of the field, in terms of intensity of exposure, is inversely proportional to the square of the distance and directly proportional to the activity, and is expressed by the equation (1): 2 d A I X    (1) where: Ix = Exposition Intensity [C/(Kg*h)], Г = Gamma specific constant (it is a characteristics of each radionuclides), [(C*m2) / (Kg*h*Bq)], A = Source activity [Bq], d = Source distance [m]. The trend of intensity versus the distance is shown in Figure 2. Figure 2 : Intensity vs distance trend It is evident how is important to organize rescue operations keeping the greatest possible distance from the source. From the knowledge of the field, in the case of exposure to the whole body with the radiation  (our case study) it is possible calculate the values of the doses that can be assumed. 3) Using a screen/shield to reduce the intensity of radiation. The radiation, propagating in space, interact with matter in their passage causing an ionization that can be direct (for the alpha and beta radiation) or indirectly (for the gamma radiation and neutron). The interaction between radiation and matter and the different penetration capacity are function of:  the type of radiation;  its energy;  the characteristics of the crossed material. 4 Alpha radiation rapidly convert their kinetic energy in material ionization, with a modest path. The freed electrons, in turn, cause a secondary ionization. Following a possible excitation of the atom, an emission of electromagnetic radiation of low energy (non-ionizing) it is also possible. Alpha radiation are arrested by less than 10 cm of air or by a simple sheet of paper. In the case of irradiation of people, such radiation stop on the very first layer of the skin and only in case of high energy (about 7 MeV) can reach the "germinative layer" of the skin, at a depth of 70 micrometers. These radiations are therefore not dangerous in case of external irradiation. The scenario changes in case of internal contamination of the human body (with internal irradiation), where the damage would be led directly to organs and tissues. Beta radiation and electrons have modest capacity of penetration of matter but still higher than those of alpha particles. These radiation can move in air for about 4 m or 4 mm in water (for energies with order of magnitude of 1 MeV). The germinative layer of the skin is achieved by particles with energies above 70 keV. PPE (Personal Protective Equipment) used by firefighters provide good shielding. In the air are produced dozens of ionizations per centimeter path. As a result of excitation of the atoms of the material crossed by beta radiation there is the re-emission of energy in the form of electromagnetic waves. The strong deceleration of the beta particles can cause an emission of X-ray-called "bremsstrahlung." The emission has an increases intensity proportional with the atomic number of the irradiated material. The phenomenon constitutes a risk greater than the one of the beta radiation from which it derives, being X-rays more difficult to shield. It is useful do not use materials with a high atomic number to shield beta radiation. A good shielding of the beta radiation is also given by a first layer of material of low density, which reduces the production of X-rays, and by a later high density, to shield the X-rays produced. Indirectly ionizing radiation (X and gamma rays and neutrons) have an high penetration capability. Gamma radiation is absorbed by huge length of matter. The interaction mechanism between matter and radiation are three (and it depends by energy and matter characteristics). At low energies the photoelectric effect prevails, at medium energies the Compton effect prevails and at great energies the pairs creation prevails. While for the charged particles the beam of radiation is slowed down in an almost uniform mode and is stopped almost simultaneously, for photons the beam is reduced as it progresses within the material, and the photons that continue on their path maintain the same initial energy. For such radiation it is important to refer to the so called half-value layer (HVL), or half-value thickness through which the initial intensity of the incident radiation is halved. These thicknesses are a function both of the type of the crossed material that the energy of the radiation. The X and gamma radiation are effectively attenuated by materials with a high atomic number, such as lead. Neutrons do not interact with the electrons of the atoms of the materials crossed, but only with the nucleus, causing various reactions as a function of energy, including the emission of charged particles and gamma rays. During an operation with the presence of radioactive source sealed, there is an immediate need to delimit an area beyond which must be kept the population. This area should have dimensions not less than those of the so-called "area of concern", so as to ensure that outside it does not exceed the legal limit of 1 mSv effective dose. The limits of the of the attention area can be determined analytically with the data of the source(if known) or following in field measures of intensity and dose. In first instance is necessary to determine the area of attention for the population. This is possible by making measurements of field intensity or dose, depending on the instruments available. After that, with the knowledge of the value of the intensity of dose and the relative distance is uniquely identifies the intensity-distance curve, so you can plan the intervention (Figure 3). Multiple measurements are necessary to reduce the errors Figure 3: Operation with an unknown source Assuming that the operators is working with a tool that gives us the intensity value of the effective dose. At a distance d1 the operator measures an intensity value of effective dose IE1. The value of IE1 compared to the values (unknown) of activity A and the constant Г is (2): 5 2 1 1 d A I E   (2) Taking into account a generic distance d2,the value of intesity can be espressed as in equation (3): 2 2 2 d A I E   (3) obtaining the value ГxA by (2) and (3) it is possible write the equation (4) 2 2 2 1 1 2 I xd I xd E E  (4) and calculate the effective intensity IE2 at a generic distance d2 (5): 2 2 2 1 2 1 d d I I x E E  (5) By the equation (5) (setting the intensity values of effective project for the operation) is possible to calculate the relative distances and in particular the width of the attention area. 4. Proposal for a geo-referenced program to improve the rescue operations From this analysis it is clear that the primary task for responders is to protect the population from the risks arising from exposure to ionizing radiation and then promptly define the so-called “attention area” (working in safety and security condition of course). It is possible identify, in an analytical way, the size of this “attention area” in few seconds and to carry out calculations of the dose assumed by those who remain in the irradiated area. One of the problems that can be put in the immediate is that related to the possible evacuation of buildings or the closure of roads that are dealing with irradiation phenomena. The principal needs are two: o - locate the area actually affected by the radiation problem; - evaluate the possibility to move the source by a distance sufficient to avoid at least the evacuation of particular buildings, such as hospitals or allow the reopening of communication routes important. The authors thought that the achievement of this task can be facilitated by geo-referencing the results of radiological calculations. For this reason the authors have developed a software (interfaced with GEOMEDIA) for this case ,an unknown source, by applying the equation outlined above, taking as a simplifying assumption that the source is punctual. In the first screen of the software developed, called "CALCOLI", can be typed the intensity values measured in Sv/h, the distance to which the measurement was taken and the estimated time of operation. By setting these boundary conditions the software developed can calculate the values attention are, the operating distance and the in-field distance for special rescues teams, as well as the distance of attention for the population in case of non-removal of the source, conventionally identified for a residence time of 365 days (Figure 4-See end of document – devo impostarle nel documento). Figure 4: Mask Calculations After that the software user can pass to the second screen, where there is a road map of the world. On the left there is a zoom slider and darts to move the vision of the map, an operation which can also be performed with the mouse in order to frame the area concerned (See Figure 5 See end of document – devo impostarle nel documento). Figure 5: Mask map The display of the various areas of attention is possible by clicking on the "draw" (after signing on the map the source point). The identification of the source point can be done manually by clicking with the mouse on the point identified or by entering the coordinates of latitude and longitude values. In Figure 6 (See end of document – devo impostarle nel documento) was simulated the presence of a source with the interesting area of focus Policlinico Tor Vergata University. The software immediately gives a map of the area to evacuate. See four areas identified by four circles. The largest is the attention area for the population. Figure 6: Area of radiological risk The code developed is a web application built with Silverlight. Silverlight is a Microsoft technology that allows to deploy RIAs (Rich Internet Application). The programming language used is C # (C sharp). Regarding the map, has 6 been used for the control Silverlight Bing Map, component developed by Microsoft. Bing Map control provides functions that allow, in giving input coordinates, to draw the map. This software has been interfaced with the software GEOMEDIA (QUI ENTRI TU ANDREA)……… 5. Conclusion Orphan sources are a potential danger to the population. In case of their occurrence is important to take the necessary radiation protection measures, such as evacuation or closure of areas adjacent to quickly identify the areas affected by the radiation hazard. The use of a geo-referenced software makes more simple to achieve good safety and security standards. It is clear how such tool, providing an overview of the scenario and in particular the areas involved, can facilitate the operations of operators equipped with a handheld computer with web access. The detection of a different area in which place safely, temporarily, the source is relatively simple and can be readily verified using the software. The program can also be a useful aid for companies that deal with transport of radioactive sources, with the possibility to check, for the intended path, the areas potentially affected as a result of an accident with the exposure source. The program, finally, may be potentiated with a mask for the case of known source, for which it is known in addition to the type of radionuclide activity value, as well as with the inclusion of other fields for the evaluation of additional elements such as values of doses taken by those who is the field of radiation. Bibliography