Radiation Field Mapping Research Articles

Field Test of the MiniRadMeter Gamma and Neutron Detector for the EU Project CLEANDEM.

In the framework of the H2020 CLEANDEM project, a small robotic vehicle was equipped with a series of different sensors that were developed for the preliminary inspection of areas possibly contaminated by radiation. Such unmanned inspection allows to identify dangerous locations prior to the possible start of human operations. One of the developed devices, named the MiniRadMeter, is a compact low-cost sensor that performs gamma and neutron radiation field mapping in the environment. The MiniRadMeter was successfully tested in a simulated field mission with four "hidden" radioactive sources and a neutron generator. In this work, we describe the test procedure and the results, which were supported by the outcome of dedicated Monte Carlo simulations.

The Gamma and Neutron Sensor System for Rapid Dose Rate Mapping in the CLEANDEM Project.

The decommissioning of nuclear installations, as well as the possible necessary accident remediations, requires the physical presence of human operators in potentially radiologically hostile environments. The number of active nuclear reactors worldwide is greater than 400, and most of them are 40 to 50 years old, thus implying that soon they will have to be dismantled. In the framework of the H2020 CLEANDEM project, a small robotic vehicle is being developed that is equipped with a series of different sensors for areas that are significantly contaminated by radiation. In this work, we describe the MiniRadMeter system, a compact low-cost sensor capable of being used to perform quick gamma and neutron radiation field mapping of environments prior to the possible start of human operations. The miniature gamma sensor is a 1 cm3 scintillator counter with moderate spectroscopic features read out by means of a 6 × 6 mm2 SiPM, whereas neutrons are detected by means of a silicon diode coupled to a layer of 6LiF and placed inside a 6 × 6 × 6 cm3 polyethylene box. The front-end and data acquisition electronics were developed based on a Raspberry Pi4 microcomputer. In this paper, the system performance and the preliminary test results are described.

Abstract

Dosimetry methods for use in dose assessment for individuals following acute exposure to radiation are described. Primary methods include biodosimetry and physical dosimetry techniques, while additional supplementary methods are bioassays, neutron activation, and radiation field mapping. Biodosimetry methods include the established techniques of dicentric chromosome assay, cytokinesis-block micronucleus assay, translocation analysis by fluorescent in-situ hybridization, premature chromosome condensation, and the γ-H2AX assay. Emerging techniques include RNA expression-based, protein-based, and metabolomic-based assays. Physical dosimetry methods include electron paramagnetic resonance and the luminescence-based techniques of thermoluminescence and optically stimulated luminescence. Electron paramagnetic resonance methods are used to assess absorbed dose in biologically derived materials, such as bone, teeth, and keratinous tissue, as well as non-biologically derived materials such as sugars, glasses, and polymeric materials used in fabrics and other personal items. Thermoluminescence and optically stimulated luminescence techniques are used to assess absorbed dose in the components of personal electronics, along with other items such as plastic cards, fabrics, and clothing. There have also been similar efforts for teeth and dental repair ceramics. Since the above-listed techniques cannot distinguish between exposure to internal and external sources, bioassays may be used to assess exposure from internal contamination, including thyroid counting, chest counting, and excretion analysis methods. When a neutron exposure is expected, neutron activation analysis in blood, hair, or other non-biological items is useful. Radiation field mapping can be a useful method for determining locations where doses to individuals may be expected to be high and may complement radiation transport calculations performed for that purpose. Since immediate medical assessment is concerned with tissue reactions (deterministic effects), the quantity of interest for the above dosimetry methods is absorbed dose (expressed in gray). This Report concludes with a summary of the various methods and a brief discussion of the uses of such information in the aftermath of acute radiation exposure.

7 External Dose Assessment Methods Based on Radiation Field Mapping

7 External Dose Assessment Methods Based on Radiation Field Mapping

A Multiparametric Model for Mapping Cellularity in Glioblastoma Using Radiographically Localized Biopsies.

The complex MR imaging appearance of glioblastoma is a function of underlying histopathologic heterogeneity. A better understanding of these correlations, particularly the influence of infiltrating glioma cells and vasogenic edema on T2 and diffusivity signal in nonenhancing areas, has important implications in the management of these patients. With localized biopsies, the objective of this study was to generate a model capable of predicting cellularity at each voxel within an entire tumor volume as a function of signal intensity, thus providing a means of quantifying tumor infiltration into surrounding brain tissue. Ninety-one localized biopsies were obtained from 36 patients with glioblastoma. Signal intensities corresponding to these samples were derived from T1-postcontrast subtraction, T2-FLAIR, and ADC sequences by using an automated coregistration algorithm. Cell density was calculated for each specimen by using an automated cell-counting algorithm. Signal intensity was plotted against cell density for each MR image. T2-FLAIR (r = -0.61) and ADC (r = -0.63) sequences were inversely correlated with cell density. T1-postcontrast (r = 0.69) subtraction was directly correlated with cell density. Combining these relationships yielded a multiparametric model with improved correlation (r = 0.74), suggesting that each sequence offers different and complementary information. Using localized biopsies, we have generated a model that illustrates a quantitative and significant relationship between MR signal and cell density. Projecting this relationship over the entire tumor volume allows mapping of the intratumoral heterogeneity in both the contrast-enhancing tumor core and nonenhancing margins of glioblastoma and may be used to guide extended surgical resection, localized biopsies, and radiation field mapping.

Radiation mapping inside the Bunkers of medium energy accelerators using a robotic carrier

The knowledge of ambient and peak radiation levels prevailing inside the bunkers of the accelerator facilities is essential in assessing the accidental human exposure inside the bunkers and in protecting sensitive electronic equipments by minimizing the exposure to high intensity mixed radiation fields. Radiation field mapping dynamically, inside bunkers are rare, though generally dose-rate data are available in every particle accelerator facilities at specific locations. Taking into account of the fact that the existing neutron fields with a spread of energy from thermal up to the energy of the accelerated charged projectiles, prompt photons and other particles prevailing during cyclotron operation inside the bunkers, neutron and gamma survey meters with extended energy ranges attached to a robotic carrier have been used. The robotic carrier movement was controlled remotely from the control room with the help of multiple visible range optical cameras provided inside the bunkers and the wireless and wired protocols of communication helped its movement and data acquisition from the survey meters. Variable Energy Cyclotron Centre, Kolkata has positive ion accelerating facilities such as K-130 room Temperature Cyclotron, K-500 Super Conducting Cyclotron and a forthcoming 30MeV Proton Medical Cyclotron with high beam current. The dose rates data for K-130 Room Temperature Cyclotron, VECC were collected for various energies of alpha and proton beams losing their total energy at different stages on different materials at various strategic locations of radiological importance inside the bunkers. The measurements established that radiation levels inside the machine bunker dynamically change depending upon the beam type, beam energy, machine operation parameters, deflector condition, slit placement and central region beam tuning. The obtained inference from the association of dose rates with the parameters like beam intensity, type and energy of projectiles, helped in improving the primary beam transmission and minimizing the ambient radiation fields inside the bunkers.

Controlling sensitivity and stability of ferrous–xylenol orange–gelatin 3D gel dosimeters by doping with phenanthroline-type ligands and glyoxal

The ferrous–xylenol orange–gelatin (FXG) dosimeter is widely used for three-dimensional ionizing radiation field mapping through optical scanning. Upon irradiation, the ferrous iron (Fe2+) is oxidized to ferric iron (Fe3+), which forms an intensely coloured complex with xylenol orange (XO). XO also acts as a diffusion-limiting additive; however, its presence may cause rapid auto-oxidation of Fe2+ during storage and low stability of the dose response. In this work, phenanthroline-type ligands were added to FXG system in a bid to bind the ferrous iron in a stable complex and minimize the rate of the auto-oxidation, whereas glyoxal was used as a chemical cross-linker, aiming to minimize the ferric iron diffusion. It was found that addition of either 1,10-phenanthroline or 5-nitro-1,10-phenanthroline can improve the auto-oxidation behaviour of the gels. However, the initial background absorbance was slightly increased, and the sensitivity of the dosimeters was decreased. Doping with glyoxal led to a moderate decrease of the diffusion only in those gels that also contained a phenanthroline-type ligand, and did not affect the initial dose response. Glyoxal also afforded an extended period of stable background absorbance level after an initial period of bleaching of the gel. Following re-irradiation, most glyoxal-containing dosimeters showed an excellent linearity of the dose response, albeit at a decreased sensitivity. We recommend further testing of FXG dosimeters, doped with phenanthroline-type ligands and glyoxal as a means for controlling the dose response and improving the long-term storage properties of the gels and the potential for dose fractionation.

Low-cost Multi-UAV Technologies for Contour Mapping of Nuclear Radiation Field

Low cost UAVs are becoming more and more popular in both research and practical applications, and it leads to a new, potentially significant service product known as UAV-based personal remote sensing (PRS). Multi-UAV system with advanced cooperative control algorithms has advantages over single UAV system, especially in time urgent tasks such as detecting nuclear radiation before deploying the salvage. This paper considers two scenarios for nuclear radiation detection using multiple UAVs, of which contour mapping of the nuclear radiation is simulated. Then, for real applications, this paper presents a low-cost UAV platform with built-in formation flight control architecture together with a formulated standard flight test routine. Three experimental formation flight scenarios that imitate the nuclear detection missions are prepared for contour mapping of nuclear radiation field in 3D space.

Characterization of a CT ionization chamber for radiation field mapping

A pencil-type ionization chamber, developed at Instituto de Pesquisas Energéticas e Nucleares (IPEN), was characterized with the objective to verify the possibility of its application in radiation field mapping procedures. The characterization tests were evaluated, and the results were satisfactory. The results obtained for the X radiation field mapping with the homemade chamber were compared with those of a PTW Farmer-type chamber (TN 30011-1). The maximum difference observed in this comparison was only 1.25%, showing good agreement.

Radiation field mapping using a mechanical-electronic detector

A method of radiation field mapping of a scanned electron beam using a Faraday-type detector and an electromechanical linear translator is presented. Utilizing this arrangement, fluence and fluence rate measurements can be made at different locations within the radiation field. The Faraday-type detector used in these experiments differs from most as it consists of a hollow stainless steel sphere. Results are presented in two- and three-dimensional views of the radiation field.

Characterisation of the ferrous-xylenol orange-gelatin (FXG) gel dosimeter

Recent studies have used the ferrous-xylenol orange-gelatin (FXG) gel dosimeter for 3D radiation field mapping using the optical computed tomography technique. However the characterisation of the dosimetry performance of the FXG gel has not been detailed, such as the variation in dose-response of the FXG gel with changes in preparation techniques, constituent concentrations, pre-irradiation storage time, and concentrations of additives such as oxygen and saccharides. In this paper these issues are addressed with the aim of developing a standard FXG gel for future use in radiation dosimetry applications.

Laser-scanned agarose gel sections for radiation field mapping

Purpose : A dedicated laser scanning system has been applied to the measurement of optical density change in ferrous sulphate-xylenol orange dye-agarose gel mixtures for applications in radiation field mapping. Methods and Materials : The gels were poured, irradiated, and optically scanned in Lucite casts providing a uniform gel section thickness of 1 cm. The gel sections were optically scanned both pre- and postirradiation to determine the optical density change in the gel and consequently the absorved dose. Irradiation of the gel sections were performed with an orthovoltage unit and a linear accelerator. Results : For linear dose response up to 10 Gy, an appropriate gel mixture was found to be 0.4 mM Fe 2+, 0.2 mM xylenol orange dye, 25 mM sulphuric acid, and 1% by weight agarose gel with a mixing temperature of 60°C. In dosimetry of a 20 × 10 cm 6 MV wedged x-ray field, good agreement in terms or relative dose was found between the gel values and ionization chamber readings. However, in repeated experiments with the gel dosimeter involving calculation of absolute dose at various points in the wedge field, variations in absolute dose measurements of up to ± 5% were observed. Conclusions : The dosimetry technique involving laser scanning of agarose gel sections has potential for further applications in radiotherapy dosimetry.

An automated system for gamma radiation field mapping

Remote radiation survey equipment was sorely needed at Chernobyl but adequate systems did not exist. The current state of the art still consists of a survey meter mounted on a robotic carriage, which scans an area at many points on a grid. This process is both time consuming and somewhat inaccurate. The system we have developed will overcome these limitations, and would provide significant savings in man-hours and man-rem over manual survey techniques. The system we have developed consists of a collimated ionization chamber mounted in a scanning head. The measurement process is similar to that used in medical computed tomography (CT) imaging and consists of a series of collimator rotations and translations. The key to this work is the use of a collimator to provide position information with a position insensitive detector. In addition, an inverse filter image reconstruction technique has been used to reduce the distortion effects due to the scanner and scanning process in the resulting maps. This technique models the distortion as a linear, space invariant degrading function which is removed in a deconvolution process. We have constructed first- and second-generation prototype scanners, and developed software to produce three-dimensional radiation field “iso-dose” maps. The iso-dose maps will be superimposed on three-dimensional computer-aided design and drafting (CADD) drawings of the radiation area, aiding in the characterization of the source of radiation.

Image Reconstruction for a Radiation Field Mapping Device

A proof-of-principle device for producing isodose maps of the radiation field due to an arbitrary gamma-ray source distribution has been constructed. Borrowing methodology from medical computerized tomography imagining radiation fields are scanned with a pair of collimated ionization chambers by a series of rotations and translations. Experimental considerations limit each scan to two carriage positions, resulting in highly distorted maps. By modeling the map distortion as the result of a linear, space invariant degrading function, an inverse filter was used to remove the distortion. Application of the inverse filter has proved fruitful, and high-quality accurate maps have been produced.