Development of a semi-autonomous directional and spectroscopic radiation detection mobile platform

Abstract

This thesis presents a method for a small, inexpensive mobile robot equipped with a single high resolution scintillation detector to quickly survey an area and convey information about local sources of gamma radiation to a remote human operator. This is achieved by s urrounding the detector with a lead sheath that blocks all gamma rays except those incident along the detector's axial direction. A horizontal scan is performed by rotating the detector and a directional profile of gamma radiation is constructed. In addition a visual panorama of the local area is assembled using a camera mounted on the detector. A plot of the detector signal versus angle is then overlaid on top of the visual panorama and visible peaks clearly indicate the direction of local gamma radiation sources. Moreover, measuring the energy spectrum of gamma rays in each direction produces a 2D count frequency histogram where distinct peaks indicate the energy and direction of local gamma ray sources allowing the identification of different radio-isotopes.3

Development of a Low Cost Gamma-Ray Imaging System Using Handheld Scintillation Detectors for Visual Surveying of Radiation Fields with Robots

“…The result is shown in Figure 4(b). Figure 4(b) agrees very well with our MATLAB model presented in Figure 4(a) for both the bare detector and the collimated detector and these both agree with experimental results from our previous work [6] and with the work in [8] and [9]. The scale of the efficiency is less in Figure 4(b) because our MATLAB simulation uses the total attenuation coefficient (including photo-electric effect, Compton scattering and pair production) while the MCNP data is only effected by the photoelectric cross section (since only the 662keV bin is used) [5].…”

“…A photomultiplier tube (PMT) translates the light output into a measurable electric current pulse and a multi-channel analyzer places the current pulses into energy bins creating a spectrum [5]. In our previous work [6], [7] we developed a MATLAB program that uses an analytical model based on [8] and [9] to calculate the counting efficiency of cylindrical inorganic scintillation detectors while measuring point sources of gamma radiation. We incorporated the addition of a lead collimator into our model and developed a prototype mobile robot that can identify the direction of local gammaray sources, track and move towards them and triangulate source positions in a plane.…”

State-of-the-Art Mobile Radiation Detection Systems for Different Scenarios

“…During the Fukushima nuclear accident, radioactive isotopes (mainly 137 Cs, 134 Cs, and 131 I) were released to the atmosphere with formation of a radioactive plume that, afterwards, traveled and later deposited in the surface. Concentrations of these radionuclides still remain in the soils.…”

“…The use of unmanned helicopters allowed to carry a more reasonable payload weight and also perform measurements at lower altitudes (50-150 m) and speeds (8 m/s) than manned aircrafts, which allowed improved spatial resolution [78,151,155,156]. While Towler et al [155] used an NaI(Tl) scintillating detector for the mapping of the radiation distribution and localization of hotspots, Sanada et al [78,151] and Nishizawa et al [156] used three LaBr 3 :Ce (6.5 kg) to measure the distribution and variation along the time of the air dose rate and a single LaBr 3 :Ce to determine the ratio 134 Cs and 137 Cs, respectively. The choice of LaBr 3 was related to its higher efficiency and energy resolution compared to NaI crystals, allowing to distinguish the energy lines of the radioactive 134 Cs (796 keV) and 137 Cs (662 keV).…”

“…While Towler et al [155] used an NaI(Tl) scintillating detector for the mapping of the radiation distribution and localization of hotspots, Sanada et al [78,151] and Nishizawa et al [156] used three LaBr 3 :Ce (6.5 kg) to measure the distribution and variation along the time of the air dose rate and a single LaBr 3 :Ce to determine the ratio 134 Cs and 137 Cs, respectively. The choice of LaBr 3 was related to its higher efficiency and energy resolution compared to NaI crystals, allowing to distinguish the energy lines of the radioactive 134 Cs (796 keV) and 137 Cs (662 keV). Towler et al also used other sensors as a stereovision system to generate terrain maps and a gimbal camera with laser rangefinder to geo-locate points of interest.…”