Mass‐Selective Photoionization Detector

Project # 23-002 | Year 1 of 2

^aManuel J. Manard, ^aRusty Trainham, ^bPaul Kemper

Special Technologies Lab (STL)^a, University of California, Santa Barbara^b
_{This work was done by Mission Support and Test Services, LLC, under Contract No. DE-NA0003624 with the U.S. Department of Energy, the NNSA Office of Defense Programs, and supported by the Site-Directed Research and Development Program. DOE/NV/03624–1917.}

Abstract

The objective of this feasibility study on a robotic system for radiation mapping of dispersal and point source was to constrict a couple of remote-controlled robotic platforms for radiation sensors deployment. In the aftermath of aerial dispersion of radiological materials and subsequent ground deposition, one of the important tasks for the emergency response team is to characterize the extent of the contamination and locate radiological debris that causes excessive dose rates (hotspots). Any radiological incident or accident can result in very complex emergency response operations and pose significant health and safety risks due to the potential for internal and external radiological exposure. The motivation and goal for this study were to address these issues with an interesting and challenging research and development project using innovative radiological detection devices integrated into advanced robotic systems with remote communications. Within the period of execution of the project, two modules were built and deployed for two notable measurement campaigns. The first campaign was at the University of Nevada, Las Vegas (UNLV) parking lot and involved making measurements on small, distributed radiation check sources on the ground using simultaneous ground robot systems and UNLV unmanned aerial systems (UAS) carrying radiating sensors. The measurement shows the efficacy of the robot platform providing ground truth measurement for the UAS. The second campaign involved dispersal of a radioactive compound, potassium bromide (KBr), by various means (exploded on the ground, from an aerial drone) and sprayed from a drone in aqueous form.

Background

The Nevada National Security Sites’s (NNSS) Remote Sensing Laboratory (RSL) at the Joint Base Andrews, Maryland, has assembled a remote-controlled robot to mount a 4 x 4 x 2″ sodium iodide scintillator 18″ above ground for measurement of ground deposition of gamma emitting particles after a radiological dispersion from explosions. The system uses a high-precision differential global positioning system (GPS) measuring device with sub-meter accuracy for radiation mapping. The device is most useful in large area contamination characterization and detecting invisible embedded sub-micron particulate debris with gamma radioactivity from the surface/subsurface up to a depth of 3″ underground.

The system employs a configurable four-wheel-drive all-terrain robot from SuperDroid Robots. The robot comes with a 24 x 24″ aluminum chassis to house the four motors, motor driver, wheels, and batteries. The 10″ all-terrain pneumatic wheels are powered by Model IG52-04 24 VDC 136 RPM gear motors from Shayang Ye Industrial Co. The motor drive is a Sabertooth 2×32 Dual 32A system by Dimension Engineering. The remote control for the robot system is a FlySky Digital Proportional Radio Control System FS-i6X dual antenna transmitter and a FS-iA6 6-channel dual antenna receiver operating at 2.4 GHz Automatic Frequency Hopping Digital System. The remote-control system operates via line of sight. The system is programmed for single stick operation. The robot is powered by two Interstate 12-volt, 18-amp-hour sealed lead acid batteries in series supplying 24 volts. The system is designed for weights up to 70 pounds. The total weight of the system is 45 pounds.

Technical Approach

Using vehicle mounted radiation sensors to rapidly characterize radiologically contaminated areas is a part of concept of operations in monitoring and sampling after a radiological explosion or a release from a nuclear power plant. Airborne systems have been successfully used in most recorded nuclear releases including the Fukushima accident in March of 2011. Ground vehicles moving with the traffic pattern anywhere between 25–55 mph are routinely used for highway search operations by radiological emergency response. The current device described in this article moves slowly (typically at human walking speed of 2.5 ft per second) and carries the detector at a low height above the local ground level. The low altitude, slower speed, and added collimation make this detector sensitive to hotspots created by small debris after radiological explosions. The methodology involves two processes – first localization of radiation point sources followed by long dwell measurements to identify the radioisotopes involved in the radioactive materials in the explosion.

Small particulate radioactive materials can be localized after a radiological dispersal device (RDD) explosion by these remote-controlled devices. The robot moves at a deliberate low speed of approximately 2.5 ft per second. RSL uses dynamic gamma background counts update to compare the net count rate to the standard deviation of the recently acquired background count rates over several data acquisition periods. The typical Gamut data acquisition period for normal search and localization operations is 3 seconds. If the instantaneous net count rate is much higher than the standard deviation of the background, the system creates an alarm condition to let the operator know that the device has located a radiation anomaly. The data acquisition system, Advanced Visualization and Integration of Data (AVID), creates a strip chart of gamma gross counts and gamma alarm levels.

Once a particulate radioactive debris is localized and isolated, the radiation sensor is positioned on top of the hotspot and a long dwell measurement of at least 5 minutes is made. The gamma gross count strip chart shows a persistent elevated reading. The spectral component can be extracted from these data by integrating the spectra under high count rates.

The data acquisition system consists of the RSL electronics coupled to the detector. The data collected is logged using the Gamut application on an Android phone. The Android phone telemeters the gamma gross count rate data and GPS coordinates once per second to the cloud-based AVID application. The AVID application is used to process and analyze the data. AVID performs the isotopic extraction from spectral data using an advanced algorithm. The robot traveled along parallel lines about 1 m apart.

UNLV deployed an octocopter capable of carrying a payload of 10 kg with an estimated flight time of ~20 minutes. The figure shows the octocopter that carried a GEMINI detector for gamma radiation detection. The UAS flown above the grid lines followed by the robotic system on the ground.

Results and Technical Accomplishments

• Two robots have been constructed complete with sodium iodide scintillators (3 x 3″ cylinder with tungsten collimator, 2 x 4 x 4″ rectangular slab with lead collimator).
• Programming for autonomous control is occurring so that the robot can follow a series of way points.
• The devices will be able to localize identify hotspots where it is unsafe for radiation workers to perform search operations; it will be able to detect subsurface embedded macro particles that are radioactive.
• New high resolution GPS system has been introduced.
• Two summer interns are partially working on this project.
• Strong collaboration with UNLV (Minority Serving Institution Partnership Program-Nuclear Security Science and Technology Consortium project on UAS) – measurements completed at Stan Fulton Stadium parking lot (UAS + robot).

Conclusions and Path Forward

There are challenges to the detection of surface/subsurface contaminated fragments in an explosively dispersed radioactive material. One of the critical components of nuclear forensics after an RDD incident is to locate and collect the contaminated fragments which are dispersed in a large, complex fragmentation field. The field is also contaminated with dispersed radioactive material from the ground zero and downwind plume deposition. Larger fragments which land on the ground surface can be visually located, marked, photographed, and bagged as evidence. The location of hot smaller and subsurface fragments requires a detection system and a mode to survey along parallel lines over a fragmentation field which can extend to 100 x 100′ or larger. The energetic fragments can bury in softer ground surfaces and may contain vital evidence such as identification numbers or identifying markings. The device would be able to locate embedded subsurface small radiologically hot particles.

The system is still under development. Programming the motor driver for autonomous speed and direction will require a Kangaroo x2 motion controller by Dimension Engineering. This component provides feedback input for the mechanical wheel parts of the robot by providing instructions to move at a specific speed or to a new position. The feedback generally must be calculated and then tuned but this unit is the first in its class of self-tuning motion controllers. Dimension Engineering also provides DELink2 USB Link to interface directly with the motor controller using their DEScribe software. The DELink2 can be connected to transmit and receive for radio control of the robot. This part of the project will allow autonomous command of speed, position, or a combination for motion and position changes.

Back to Enabling Technologies for Autonomous Systems and Sensing