|Year : 2020 | Volume
| Issue : 2 | Page : 94-99
Environmental radiation mapping methodology and applications
Shashank Saindane1, RN Pujari1, S Murali1, M V R. Narsaiah1, Sanjay D Dhole2, NR Karmalkar2
1 Radiation Safety Systems Division, Bhabha Atomic Research Centre, Mumbai, Maharashtra, India
2 Savitribai Phule Pune University, Pune, Maharashtra, India
|Date of Submission||06-Jul-2020|
|Date of Acceptance||07-Jul-2020|
|Date of Web Publication||27-Aug-2020|
Mr. Shashank Saindane
Radiation Safety Systems Division, Bhabha Atomic Research Centre, Trombay, Mumbai . 400 085, Maharashtra
Source of Support: None, Conflict of Interest: None
World over there have been isolated cases of reported radiation emergencies, occurring at a very small probability. Environmental radiation mapping of vast area using mobile platforms is one of the methodologies used for quick radiological assessment. The utilization of several portable radiation monitoring instruments for mapping an area and the techniques developed are described. Design aspects of mobile monitoring vehicle for appropriate positioning of detectors and the speed of vehicle are optimized. The mobile radiological monitoring of cities help in quickly generating baseline data and data of a city is given in this paper. The utility of gamma spectrometer in a mobile monitoring vehicle are dealt in detail. The paper discusses various aspects of mobile monitoring, methodology, its application and representation on geographical information system under different situations.
Keywords: Baseline gamma radiation, geographical information system, mobile monitoring, nationwide radiation mapping
|How to cite this article:|
Saindane S, Pujari R N, Murali S, Narsaiah M V, Dhole SD, Karmalkar N R. Environmental radiation mapping methodology and applications. Radiat Prot Environ 2020;43:94-9
|How to cite this URL:|
Saindane S, Pujari R N, Murali S, Narsaiah M V, Dhole SD, Karmalkar N R. Environmental radiation mapping methodology and applications. Radiat Prot Environ [serial online] 2020 [cited 2020 Sep 26];43:94-9. Available from: http://www.rpe.org.in/text.asp?2020/43/2/94/293639
| Introduction|| |
Background radiation is a measure of the level of ionizing radiation present in the environment at a particular location which is not due to deliberate introduction of radiation sources. Background radiation originates from a variety of sources, both natural and artificial. These include both cosmic radiation and environmental radioactivity from naturally occurring radioactive materials (such as radon and radium), as well as man-made fallout from nuclear weapons testing and nuclear accidents.
The natural background radiation level in the environment varies from place to place due to the change in concentration of radionuclides such as40 K and decay products of naturally occurring radioactive series of238 U and232 Th in the earth crust and cosmic radiation. The intensity of cosmic radiation, which varies with altitude, also changes the background radiation.
The main objectives of the environmental radiation monitoring-based mapping are as follows:
- In case of dispersion of activity due to nuclear/radiological emergency-to check the effectiveness of mobile monitoring and methodology
- To locate the presence of any unusual radiation levels or orphan sources
- To ascertain the gamma background dose rate along important locations such as different routes, airport, railway stations, and crowded areas.
The mobile environmental monitoring based mapping techniques (Saindanceet al 2005) are used in preoperational studies while setting up a nuclear power plant (NPP), during the operation of an NPP to confirm and give confidence to public that the NPPs operation is safe and finally during an emergency, if any. For emergency preparedness program, mobile environment radiationmapping for radiological aspects is absolutely necessary to identify the areas under potential response for radiological consequences management. This mobile mapping technique also helps the decision makers to take appropriate decision during any radiation emergency. A new threat perception due to radiation has arisen due to malicious use of radiation source to create panic in public (2009), there is a need for radiological sanitation of the event where crowd is expected in large number. Detailed mobile radiation mapping during the operation of NPP, during an emergency or during a big public event (Saindane et al. 2012) ensures the protection of public against the potential release/malicious usage of radioactive material for spreading fear.
| Monitoring Methodology|| |
The environment monitoring can be done by various methodologies. One of the methodologies discussed in the paper is by deploying set of optimized instruments on any mobile platform or specially designed mobile platform (vehicle) equipped with all the state of art instruments/systems (Saindane et al 2018). The different radiation monitoring instruments/systems typically installed inside the vehicle to cover both the side of the route is illustrated in [Figure 1]. To get position coordinates, global positioning system (GPS) antennas are either mounted at the front or backside of the vehicle for the reliable satellite coverage. The vehicle speed for this type of monitoring is generally optimized at 20 km/h. Data acquisition time is set at 2 s and data averaging of 5 readings is kept for compilation and interpretation of monitoring data. The dose rate is recorded along with the longitude and latitude which is stored in the personal computer (PC) during the mobile monitoring based mapping. During the continuous radiological monitoring, whenever the dose rate is found to be on the higher side (than observed average prevalent), the vehicle is stopped and detailed radiological monitoring is carried out with portable field spec to find the reason of variation in the radiation background. Soil, grass, rock, and granite samples showing abnormal dose rates are collected from the different places during the monitoring route to verify the dose rates along with online recorded dose rates. The samples collected are then analyzed using NaI(Tl) Gamma Spectrometry system in the laboratory. This type of monitoring has to be performed regularly to ascertain the dose rates in the area during different seasons. The main advantage of this type of monitoring with respect to other monitoring technique is that the dose rates and spectrum are recorded along with positional coordinates and a vast area is covered to generate the baseline data. Moreover, these data are stored in a database and successive monitoring in the same area during different seasons helps to generate a figure for finalizing the background of the area.
Systems used on the mobile platform
The space in the vehicle is segregated into three different areas: Driver cabin, operation area, and equipment/storage area, as shown in [Figure 1]. The installed systems in the mobile monitoring vehicle are classified on the basis of distinct operational systems.
| Mobile Gamma Spectrometry Systems|| |
Mobile gamma spectrometry systems (MGSS) is a Mobile Gamma Spectrometric Scanner based on NaI(Tl) detectors with size 3” x 3” are installed in such a way that it covers both the sides of the road. Energy measurable range is from 20 to 3000 KeV with an intrinsic relative error of ±20%. Ambient gamma radiation dose rate measurement range is from 10 nSv/h to 150 μSv/h. Gamma radiation sensitivity for241 Am is 12,700 cps/μSv/h, for137 Cs is 1960 cps/μSv/h and for60 Co is 1030 cps/μSv/h. Minimal detectable level of gamma radiation dose rate from a source, moving at 1.8 km/h is 50 nSv/h.
GPS is integrated into PC with positioning accuracy of 3 m. All detecting units with smart probes transmit measured data over Bluetooth wireless link into the PC. Scanner operates in continuous radiation environment scan mode (integral count rate measurement mode). When radioactive source is detected the scanner measures radiation level and identifies radionuclide composition. The different identified radionuclides are displayed on screen and also operator hears a corresponding voice message in a wireless headset. The measured results are continuously transmitted for subsequent processing by PC and can be plotted onto a map using application software tools.
| Plastic Scintillator Based Monitoring System|| |
Four cylindrical plastic scintillator detectors (size - 5 cm Ø × 50 cm length) are installed at four corners of the vehicle with each having sensitivity of 1.2 cps/nGy/h (for60 Co isotope) and is used to detect any incremental low level activity in the presence of background. It is an online system and interfaced with PC. All the four-unit gives individual readings and can be combined together to give an average figure of survey location along with positional coordinates.
| In Built Radiation Monitoring System|| |
An indigenously built radiation monitoring system developed in Bhabha Atomic Research Centre is fitted on a lower rack, containing alpha, beta, and gamma counting system interfaced to a specially designed Universal Counting Unit. The measurements are based on ZP1220 energy compensated GM detectors mounted on either side of the mobile platform which constantly measures the dose rates. The Universal Counting Unit is based on 89 LV52 microcontroller and serial pheripheral interface memories used for data storage. Each of the acquired data set contains real time, position coordinates, and dose rate data from detectors and GPS is connected on serial RS232 communication port for real time processing and is displayed and stored in nonvolatile memory for later analysis. About 50,000 data points can be stored for use. The system is rugged and can be deployed for any mobile platform. The system consumes about 150 mA current at 12 V DC including the GPS, enabling continuous operation of about 12 h with the 2 KVA UPS/inverter installed in the vehicle. Using PC software support, the system provides on-line radiological status onto the map of the area being surveyed which helps in on the spot decision-making. GM detectors used in the system have good sensitivity of 15.6 cps/μGy/h. These detectors are energy compensated to get energy independent response within ±30% from energies 100 KeV–1.2 MeV. The detector operates on 450 V DC bias.
| Gamma Register|| |
Gamma Register is a battery operated OFFLINE Gamma dose logging system. During the radiological monitoring these registers are installed at both the side of the mobile monitoring vehicle. It has two G. M detectors for covering the range of 20 nGy/h–10 mGy/h. The system can operate with its internal battery for 3 to 4 years and is capable of storing 12,800 data points in its built-in memory along with the time information. The stored data are downloaded to a PC using an infrared-based remote reader connected to a PC through a standard RS-232 interface using proprietary software.
| Field Spectrometer|| |
Field Spectrometer (Field Spec 1K channel spectrometry system) is a commercially available portable Gamma dose rate meter with built-in 1.4” x 2” NaI(Tl) scintillation detector and GM detector. It performs gamma spectrometry and nuclide identification which allow distinguishing man-made and natural radioisotopes. The spectrum is acquired whenever there is an observed increase in background radiation level. Data analysis can be done using TMCA gamma analysis software after transfer of data to a PC. Up to 250 spectra of 1024 channels can be stored in the unit and directly transferred to a desktop PC for further and advanced analysis.
| Alpha/beta Continuous Air Monitor|| |
It is a portable, lightweight, battery-powered, continuous air monitor that can be used for assessing air activity level at incident area, emergency-response, fixed location, and for any other application requiring air activity level. The solid-state, ion-implanted, silicon detector, and multichannel analyzer provide the input for an embedded processor board serve as beta detection and the alpha spectral analysis is used for radon background compensation.
| Response and Calibration|| |
The validity and accuracy of measured data depends on the instrument's calibration and response. Hence, all the systems/instruments are calibrated with a standard source at the calibration facility for various radiation levels of 0.5 μGy/h, 1.0 μGy/h and 1.5 μGy/h.
The calibration factors were generated to optimize the data for different instruments used for mobile mapping for different speed for data analysis. The factors were arrived for detection by driving the vehicle at different speed and different sources (137 Cs and60 Co) which were kept at 1 m distance from the road.
The response of detector to detect the radioactive source changes when it is in motion with respect to the source. This was done experimentally and theoretically by simulating the condition. Theoretically, it was assumed that source of137 Cs and60 Co of 37 MBq is kept at the same height of the vehicle's detector for dose rate evaluation. These evaluations were then validated experimentally with the known137 Cs source of activity 3.2 MBq. During experiment the detector acquisition time was selected for 1 s. The continuous response data acquired at different speed by system inside the vehicle is shown in [Figure 2].
The results represented in [Table 1] shows the radiation dose rate evaluated by theoretical method for different speeds of the vehicle for 37 MBq of137 Cs and60 Co as a separate case. The correlation factors were obtained by calculating the ratio of radiation dose rate at stationary position with respect to the dose rate at different speeds of vehicle, respectively. These correlation factors can be used to calculate dose rate at the stationary with respect to dose rate at different speeds. [Table 2] shows the experimental values, i.e., dose rates measured by vehicle at different speeds for known activity and the theoretical generated dose rates.
|Table 1: Theoretically generated figures mobile platform at different speed|
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|Table 2: Validation of the results of mobile laboratory (experimental and theoretical)|
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Dose rate at stationary (μGy/h) = Dose rate at the specified speed × Correlation factor of the speed (A)
Activity of the orphan source (MBq) = (3.7 ×. R2 K)/(0.5.Σ Ei. Yi) (B)
Where X - Dose rate at specified speed (μGy/h); R - Distance in meter (m) from the source; K - Correlation factor; Ei- Energy in MeV; Yi- Yield of the energy.
The correction factor of the different speeds is multiplied by the radiation dose rate detected by mobile platform to obtain the dose rate at rest. Furthermore, the activity of the orphan source can be estimated by taking the distance and energy of the radionuclide. [Figure 3] shows the comparison of experimental value and value obtained theoretically. The differences in the theoretical and experimental dose rates was due to the environmental background dose rate which has been added up in experimental value not taken into consideration in theoretical method. It is observed and concluded that as speed of mobile platform increases its response reduces.
|Figure 3: Experimental response of the mobile platform with different speeds for a known activity|
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| Applications of Mobile Environmental Mapping|| |
Depending on the type of application, the mobile mapping methodology and technique is selected for different situation and the selection of the systems are carried out on the basis of requirement of sensitivity, adjustable acquisition time, portability, power supply, data storage facility (inbuilt memory), speed of vehicle, and data tagging of positional coordinates with dose rates. The data are then interpreted in terms of dose rate or a map containing color variations.
Radiological monitoring of metro city
The radiological monitoring of metro cities is carried out regularly to generate base line dose rate data. This base line dose rate in turn would help to assess the radiological impact assessment due to nuclear/radiological event leading to increase in radiological status of the city. Apart from the generating base line – data the other objectives of this radiation mapping is to locate the presence of any orphan sources which may lead to radiological emergency. [Figure 4] shows the radiological data displayed for the Mumbai metro city. Radiological monitoring was carried out on city's main roads, police stations, railway stations, and crowded place. The radiological data is then projected on the GIS datasets consisting of layers such as settlements, roads, hospitals, police stations, shelters, railway stations etc. of Mumbai city. The datasets are standardized and the stored dose rates can be effectively used during the emergency. [Figure 5] shows the readings (nGy/h) of different instruments at some places in Mumbai city.
|Figure 4: Radiological monitoring data of Mumbai city projected on GIS platform|
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Mapping at major public events
As identified by International Atomic Energy Agency (IAEA), the potential usage of radioactive material for malicious purpose major public events (MPE) cannot be ruled out. Detailed mobile radiation mapping before and during any MPE can ensure the protection of public against such threats. MPE mapping is distributed in three different phases such as pre- and post-event. In these three during event phases, radiation monitoring techniques were largely distributed as mobile radiation monitoring of city, detail scanning of all venues with hand held detectors and monitoring of the stadium entry and exit point. The mobile radiation mapping of the city holding MPE is generally carried out with an objective to detect the presence of orphan sources, if any. The mobile radiation monitoring was mainly focused on main road networks and areas surrounding MPE during the Commonwealth Games (CWG) as shown in [Figure 6].
|Figure 6: Mobile monitoring mapping carried out at a major public events in Delhi|
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Mapping during emergency scenarios
The emergency scenarios consists of range of accidents and events that covers lost, hidden or misplaced radioactive sources, transport accidents, and explosions/malevolent use of any radiological dispersal devices. Each case has special characteristic concerning the amounts and type of radionuclides potentially being released and time behavior of release. All of these are strongly reflected on the radiation monitoring activities and measurements needed to manage the situation at hand. The assessment of any spread of radioactive contamination and early detection of orphan radiation sources in public domain by using this technique is very useful and helpful.
| Results and Discussions|| |
The response to radiological emergencies require quick assessment of radiological status for which appropriate systems and monitoring strategy is to be developed and tested for detection of orphan sources, hotspots or any spread of radioactive contamination in the environment. Since there are large number of radiological threat/emergency situations affecting the environment, systems, and methodology are developed for conducting radiation measurements in the environment and are optimized for various nuclear and radiological emergency scenario. The application of mobile monitoring technique during any major public event is for the prevention of any malicious use of radioactive material whereas during Mayapuri radiological emergency, it helped in quick detection and identification of contaminated areas and its decontamination. The early detection and decontamination has prevented the further spread of radioactive contamination and any possible internal exposure to the public. The data are recorded inside the mobile laboratory which can be transferred through mobile technique to control room. During emergency conditions, the data transferred to control room gives an added advantage as the control measures for response can be initiated at the earliest.
| Conclusions|| |
The environmental mapping by mobile monitoring laboratory/vehicle plays an important role in radiological surveillance. The application mentioned in the paper discusses the usage and relative parameters. The response to any radiological emergency requires quick analysis of the radiological status and the impact assessment for which, appropriate monitoring methodology and strategy is developed and tested for detection of orphan sources, hotspots, or any spread of radioactive contamination in the environment. Since there are large number of radiological threat/emergency situations affecting the environment, systems, and methodology are developed for conducting radiation measurements in the environment and are optimized for various nuclear and radiological emergency scenario. The application of mobile monitoring technique during a MPE is for the prevention of any malicious use of radioactive material whereas during radiological emergency, for example, Mayapuri, it helped in quick detection and identification of contaminated areas and its decontamination. The early detection and decontamination has prevented the further spread of radioactive contamination and any possible internal exposure to the public. Experience acquired during mobile monitoring for emergency planning zone of NPP sites will help in planning of environmental impact assessment required for various emergency scenarios.
The authors express their sincere gratitude to Shri. Suresh Babu RM, Associate Director, Health Safety and Environment Group, BARC for his constant inspiration, guidance, and support for the development of the mobile laboratory and other staff members for their support during the development of this system.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]
[Table 1], [Table 2]