Newswise — Since the terrorist attacks of September 11, 2001, counterterrorism has been one of the nation’s top priorities. This counterterrorism effort includes programs to prevent terrorists from smuggling nuclear or radioactive materials into the country and from trafficking within the country to perpetrate an incident involving an improvised nuclear device or radiological dispersal device (also known as a “dirty” bomb). To address this threat, the U.S. Department of Homeland Security (DHS), through its Science and Technology Directorate (S&T), has made a substantial investment in preventive radiological and nuclear detection (PRND) equipment for law enforcement officers to monitor and interdict such materials before an incident occurs.
Over the past two years, four U.S. Department of Energy (DOE) national laboratories—Brookhaven, Lawrence Livermore, Savannah River, and the Nevada National Security Site Remote Sensing Laboratory—have been collaborating with DHS’ National Urban Security Technology Laboratory (NUSTL) to determine how PRND equipment can be repurposed for four consequence management missions: emergency worker radiation-exposure control, emergency worker radiation-dose monitoring, radiation survey, and contamination detection. In particular, this collaboration involves complementary efforts to evaluate archetype detectors representative of the main PRND equipment categories in the characteristic radiological environments that they would be used in following an incident. It also involves developing guidance for first responders on how to most effectively deploy the instruments in the different missions.
“The multilab project shows how this class of equipment can be repurposed to protect first responders and the public in the early hours to the first few days of an accident or intentional incident such as an act of terrorism,” said principal investigator Stephen Musolino, a health physicist in Brookhaven Lab’s Nonproliferation and National Security Department. “During this time, these instruments are the only tools that would be broadly available.” Musolino and Lab colleagues Charles Finfrock, Jose Gomera, Joseph Moskowitz, Thomas Roberts, and Charles Rose, and NUSTL physicist Gladys Klemic and intern Lance Schaefer carried out the Brookhaven-led instrument evaluation.
From prevention to emergency response
Among local and state agencies, PRND equipment is the most widely available and fielded instrumentation for detecting and identifying sources of nuclear and radiological material. Worn by police and other law enforcement officers, placed at fixed locations like bridges and tunnels, and incorporated into mobile-based platforms such as backpacks and vehicles, the detectors incorporate algorithms that identify unusual radiation signatures that deviate from the normal background radiation signatures. In general, PRND equipment is used as a deterrent—people and the environment are routinely being monitored for radiation signatures that should not be present.
If a nuclear or radiological event were to happen, it would be important to monitor the amount or “dose” of radiation that first responders and the general public are exposed to and determine the level of environmental contamination. However, in the early aftermath of such an event, most police officers and firefighters would not be equipped with standard health physics instruments such as radiation dosimeters, which are wearable devices that measure radiation dose to a person. Complete radiation monitoring capabilities would only become available upon the arrival of federal assets such as the Federal Emergency Management Agency and DOE-led Federal Radiological Monitoring and Assessment Center.
Brookhaven Lab health physicist Stephen Musolino describes the multi-lab project to demonstrate how equipment designed to interdict radiological and nuclear material could be repurposed to protect first responders and the public in the early aftermath of an incident that released such material.
Musolino, who has had a long-term relationship with the New York City Health, Fire, and Police departments, recognized this problem: how can the radiation dose to first responders be measured and monitored at the time of the incident, when dosimetry resources are not widespread? Following Musolino’s suggestion, the New York City Health Department contacted the National Council on Radiation Protection and Measurements (NCRP) for guidance. In turn, NCRP proposed a writing group be convened to develop a report on emergency response dosimetry, which was submitted to NUSTL’s Radiological/Nuclear Response and Recovery Research and Development Program for support.
“The outcome was an NCRP report that makes the observation that you do not need a dosimeter to do dosimetry,” explained Musolino, who is also a member of NCRP and co-chair of the NCRP scientific committee that developed the report. “For example, if you can measure the dose rate and multiply that rate by the time that a person or group of emergency workers spends in an affected area, you can estimate the dose.”
The NCRP report goes on to provide guidance on how the large inventory of PRND and other radiation detection equipment can be repurposed to estimate people’s radiation doses before resources from the federal government arrive to fully equip the emergency response with standard health physics instrumentation.
“The PRND equipment comes with manuals in which the manufacturers specify the purposes or missions for which the different pieces of equipment can be used,” said Richard Schlueck, a battalion chief in the Hazardous Materials Battalion of the New York City Fire Department who has been working with Musolino for the past 12 years on various projects relating to radiation safety. “As a firefighter and not a health physicist or a member of DOE’s RAP [Radiological Assistance Program] team, I find it very challenging to modify these specifications and use the equipment for additional missions other than those it was originally designed. But if I have the national labs and DHS giving their stamp of approval, I know it is appropriate. This project essentially expands the scope of missions for which we can use the equipment—a really good thing for the first responder community.”
For example, following a nuclear detonation, there could be highly contaminated areas for 10s of miles and detectable radiation above background levels on the order of 100 miles downwind. The PRND equipment could be used to document not only the relatively higher exposure doses of first responders performing life-saving and rescue operations close to the site of the incident but also the exposure doses of individuals who take on emergency response duties in areas with lower levels of contamination.
“We need to account for all of the doses to people, including those who may not expect to be emergency workers before an incident occurs,” said Musolino. “Bus drivers evacuating people, medical professionals caring for people, and other related groups who may find themselves providing humanitarian assistance and disaster relief. Even if their doses are very small, we need to document them.”
Measurements with PRND equipment would inform initial time-sensitive decisions about which protective actions should be taken. These decisions are based on guidance established by the U.S. Environmental Protection Agency (EPA) to protect both the general public and emergency responders. For example, the EPA guidelines recommend that people shelter in place or evacuate if the predicted radiation dose could exceed one to five rem (rem is a standard unit used to measure the dose equivalent, which accounts for the different types of radiation and risk of health effects) over the first four days. For first responders, who inherently take on more risk than average people when carrying out life-saving activities, a dose of 25 rem or greater (in situations where the benefits of the activities clearly exceed the risks) is permissible according to the EPA-issued guidance.
After the emergency, the data collected from the PRND instruments would also be used as one of the sources of data to complete a retrospective dose reconstruction for the entire area affected by the contamination. This method is used to conservatively estimate the radiation doses of exposed individuals and the possible long-term health risks on the basis of where people were at the time of the incident and how long they were there.
Instrument evaluation
This past summer, the Brookhaven team evaluated 19 models of instruments representing the most common types within the PRND equipment categories—body-worn personal radiation detectors (PRDs), body-worn extended-range PRDs, radioisotope identification devices (RIDs), human-portable detectors (backpacks), and mobile systems (vehicles, airplanes, and boats) with large-volume detectors.
The team members tested the instruments in simulated radiological environments to validate how responders can best deploy PRND equipment in emergency response scenarios. For example, to simulate the use of body-worn PRDs—which are typically clipped onto a belt or carried in pockets, and beep and/or vibrate when the wearer passes near a radiation source—for dose rate measurements, they placed the detectors on polycarbonate-slab phantoms. They also simulated the handheld use of PRDs and RIDs for dose rate measurements or contamination surveys by performing tests in the air.
All of the functional testing was performed at Brookhaven Lab’s calibration facility, with cesium-137—the standard radioisotope for calibrating radiation-detection instruments—as the radiation source for the irradiations. They evaluated the performance of each instrument according to its dynamic range (measure of instrument’s ability to generate a signal relative to the level of radiation) and capabilities as specified by the manufacturer. For instance, some PRDs have dual detectors—one that is sensitive to low-level radiation and a second to high-level radiation—and thus can operate in “cold” and “hot” radiation zones. In addition, some of the instruments have the capability to measure not only the dose rate but also the integrated dose, or the total amount of radiation.
“As expected, these instruments afford sufficient accuracy to measure radiation dose rates and thus can be used as survey instruments,” said Musolino. “Similarly, the instruments capable of measuring integrated doses can be used to accurately make such measurements.”
In another lab, the team simulated contamination screenings for people and objects. Brookhaven Lab research engineer Charles Finfrock assembled a conveyer belt system to move radiation sources past stationary detectors and detectors past stationary radiation sources. This system has a high-precision motor coupled with a shaft encoder, an electromechanical device that converts mechanical motion into electronic signals that can then be read out. With this system, the team can precisely control the speed at which the sources or detectors are transported across the 15-foot-long track.
“This system allows us to simulate either a line of people walking by a detector or a line of people standing in place as they are scanned by a detector,” said Finfrock.
Contamination monitoring would involve initial screenings to identify people and objects requiring immediate decontamination and people who may need medical evaluation, and contamination checks for lower levels of contamination if the initial results are negative. People who test negative after the initial screening process would be directed to secondary monitoring facilities such as Community Reception Centers, which are part of the plan that cities are putting in place to conduct population monitoring in the case that radiological terrorism occurs. At these centers, the PRND equipment could be used to monitor people or objects to see if they require decontamination before entering the facility or to localize low levels of contamination.
“Our evaluation shows the instruments can reliably be used for rapid initial screening for and detection of 20 microcuries—enough radioactivity to require decontamination of a person or object—from a source-detector distance of 12 inches and a speed no faster than 12 inches per second,” said Musolino. “The instruments can also reliably check for a spot of contamination that caused a portal monitor in a Community Reception Center to alarm—one microcurie on the surface of clothing, skin, or objects from a distance of two inches away and a speed of up to six inches per second.”
It is anticipated that the PRND equipment will be put into practice for the consequence management mission within the next few years, as part of a DHS-led nationwide rollout of a series of emergency response tools, including those for rapid assessment.
“Despite the fact that manufacturers designed and built this class of equipment for interdiction, our evaluation shows the instruments are suitable for monitoring and controlling radiation doses to responders and the public, and for screening people and objects for surface contamination in the early period of a radiological or nuclear incident,” said Musolino.
This work was supported by the DHS S&T Directorate.
Brookhaven National Laboratory is supported by the Office of Science of the U.S. Department of Energy. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.
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