Somewhere in the world on Oct. 9, 2006, a low-yield nuclear device exploded underground.
In 48 hours, the sensors of the Comprehensive Nuclear Test Ban Treaty’s (CTBT) International Monitoring System (IMS) — globally distributed — were able to pinpoint the location of the blast to an underground area in North Korea only 10 kilometers across.
The ability to detect and quickly pinpoint the location of the relatively small explosion — many times smaller than the Hiroshima bomb — suggests that any gaps in worldwide sensing capabilities have diminished greatly over the past decade, say Sandians involved in global efforts to detect nuclear explosions wherever they may occur.
Joe Sanders (5924) examines the shell of a next-generation airborne radionuclide particle collection pod designed at Sandia. The pods sensors detect short-lived radionuclides released into the atmosphere in the wake of an underground nuclear detonation. The modernized system replaces technology dating from the 1950s and 1960s. (Photo by Randy Montoya)
This year, in response to President Barack Obama’s April 5 speech in Prague in which he stated that his administration would seek CTBT ratification “aggressively and immediately,” a team of five Sandians journeyed to Vienna to the CTBT Organization’s (CTBTO) International Science Studies Conference. The Sandians presented three posters that demonstrated improved technical capabilities to detect underground nuclear blasts.
“We went there,” says Tim McDonald (5736), “to reestablish our presence in an international community rejuvenated since the president expressed his determination to get the CTBT ratified. I was surprised by the intensity of the reaction to President Obama’s outreach. The interest level was astounding.”
Tim was also “very pleased with the number and quality of scientific presentations.”
The Sandians were, besides Tim, Christopher Young (5527), Sandy Ballard (5527), Joe Damico (6723), and Jim Arzigian (6723).
In addition to showing the world computationally that global sensing of an underground nuclear explosion is a reality, Sandia also is responsible for ensuring the proper installation and testing of US-sponsored CTBT International Monitoring System stations. Randy
Rembold (5736), the US configuration manager in these efforts, has a personal letter of commendation from the CTBTO to prove it.
Finally, Sandians have actively worked to improve the keystone of nuclear test confirmation: airborne sampling of nuclear debris.
‘An impressive though unusual venue’
In what Tim McDonald described as “an impressive though unusual venue” — the (former) emperor’s palace in Vienna — 400 researchers, diplomats, and foreign service personnel from many countries convened to present or review the latest methods of detecting underground nuclear explosions.
The meeting’s technical exchanges were intended to advance efforts to develop more sensitive sensors and better data processing and analysis methods. The ultimate goal is to drive explosion detection to lower and lower thresholds.
“The idea is to combine computing, signal processing, and sensors to achieve the goal of making it impossible to explode a nuclear weapon anywhere in the world without it being sensed,” says Tim. “Sandia is very much a leader in this.”
While Sandia routinely assists the National Data Center (NDC), “We’re also exploring work with the International Data Center (IDC) to help them do as good a job as they can. It’s in our national interest,” says Tim.
One Sandia poster, sponsored by NNSA’s Office of Nonproliferation and International Security (NA24), titled “Simulations of IMS Detection Effectiveness as Deployed vs. Planned,” was a kind of map intended “to show the world that we could detect an illegal test,” says lead Jim Arzigian. “We made a map to show how well we can detect explosions around the world.”
The map program is simple enough to run on a laptop. It models information obtained from the four main vehicles of remote nuclear sensing. These are hydroacoustic (water), radionuclide (radioactive materials), seismic (earth), and infrasound rumble (air).
“We had a very benign statement on our poster that we wanted to make an announcement to the international community,” Jim says.
Says Joseph Damico, “Our model integrates all four main technologies and is portable. It doesn’t need a supercomputer. It was very effective in establishing the point that this can be done and be useful.” An earlier version of the model helped determine initial placements of IMS sensors.
While the Sandia team did not discuss the latest technologies, Joseph says, the model elicited positive responses by foreign representatives, including a nation that — like the United States — has signed but not ratified the pact. Signatories that have not yet ratified include China, Israel, and Iran. Countries that have neither signed nor ratified the CTBT include North Korea, Pakistan, and India.
The poster showed that for a 10-kiloton underground explosion “both the certified stations and the full complement of stations are predicted to detect the event. The addition of the auxiliary stations to the certified stations improves the location accuracy predicted.”
Eighty percent of the agreed-upon IMS stations are now deployed and certified. Demonstrating the effectiveness of the current distribution is important because requiring more sensors will require more money and possibly different locations than the 10-year-old treaty had specified. This would open the door to unwanted new negotiations.
The second and third posters, sponsored by NNSA’s Office of Nonproliferation Research and Development (NA-22), involved enhanced methods for seismic detection.
One, hosted by Sandy Ballard, discussed improved methods of correctly modeling seismic waves passing through the Earth.
“Locating seismic events [like nuclear tests] depends on accurate knowledge of the structure of the Earth and how waves travel to reduce uncertainties in interpretation,” he says. Today’s high-performance computing capability enables 3-D simulations that provide more accurate information on wave propagation than earlier 2-D models that overly simplify the true structure of the Earth by assuming it is laterally symmetric.
Accurate interpretation of seismic events is crucial because thousands of shocks a day pass through Earth’s crust. Within this background noise, sensors and programs have had to locate the only two detected nuclear explosions that occurred during the last decade.
A third poster, “Applying Machine Learning Methods to Improve Efficiency and Effectiveness of the IDC Automatic Event Detection System,” by Christopher Young, Michael Procopio (both 5527), and Jack Gauthier (6342), described a method to improve the rapidity and effectiveness of interpreting seismic data of interest.
Sandia helps install sensing stations
More than 300 monitoring stations around the world make up the International Monitoring System that collects data for verification of the CTBT. Of these, the US is responsible for 37: five primary seismic stations, 12 auxiliary seismic stations, 11 radionuclide stations, eight infrasound stations, and one hydroacoustic station.
Randy Rembold, configuration manager for all the International Monitoring System stations in the US, received an individual acknowledgement from CTBTO Radionuclide Engineering Officer Luis Cello for Randy’s service in installing and assisting in the certification of these sensing stations.
An integration configuration manager ensures that stations meet the technical requirements of the CTBT in Vienna, allowing these stations to be certified by the CTBTO. Once so certified, the data from an IMS station can be accepted and processed by the International Data Center (IDC).
The occasion for praise was the certification of a Midway Island radionuclide particulate station that was the final US agreed-upon station to monitor radionuclide particles, “making [the US] the first nuclear-weapon state and the second of those having four or more facilities to accomplish such a goal,” wrote Cello. “Congratulations to all for the excellent job, especially . . . Randy Rembold, who took part in all the certifications, always supporting the PTS [Provisional Technical Secretariat] staff before, during, and after the certification visits.”
Randy has visited almost every US station from Antarctica to the Arctic, including sensor sites on Guam, Midway Island, Wake Island, Alaska, and Hawaii.
“We’re in the shadows; our name doesn’t get mentioned,” he says of Sandia’s involvement. “We don’t run the stations, we just certify that the stations meet CTBT design and operation specs.”
As a part of the inspection, Sandia conducts both system and component testing, currently done by Darren Hart (5736) at each of the stations. Randy says that “Sandia is known all over the world among the seismic monitoring community for our FACT [Facility for Acceptance, Calibration, and Testing] test facility and the sensor, digitizer, and system evaluation performed there.” A digitizer is the heart of a data acquisition system that measures a voltage signal, converting it into a binary file consisting of ones and zeroes. Because seismic signals of interest may be quite small with respect to the background, the digitizers have very high resolution, usually with the capability of resolving one part in 16 million of the full-scale signal.
Airborne nuclear debris collection, analysis
The gold standard for confirming that an explosion observed by seismic, hydroacoustic, or infrasound sensors is of nuclear origin is by detection of short-lived radionuclides produced by the event.
Historically, aircraft equipped with special collection equipment have been the most effective at accomplishing this task. Aircraft have the mobility to fly “downwind” of the event, which may require searching over a broad ocean area. Fixed land-based radionuclide sensors do not have this option, and might not be located in the path of the debris plume.
Airborne evidence is difficult to mask, says Joe Sanders (5924). Even when the scrutinized nation goes to great lengths to contain the radioactive explosion products from an underground nuclear test, telltale radionuclides can still leak out and be detected downwind. Radioactive debris from poorly contained events often escapes immediately and in large quantities, making airborne collection and detection quite feasible.
Well into the current decade, the primary US aircraft nuclear collection capability consisted of nuclear debris collection and analysis equipment developed in the late 1950s and early 1960s. This equipment was installed on military aircraft, which underwent extensive fuselage modifications to carry the bulky equipment. This pre-computer era equipment used vacuum tubes and chart recorders and required pencil-and-paper data logging. In the late 1990s, Sandia was tasked to develop an upgraded airborne sampling suite to replace the still-operating 1960s-era system.
The fully computerized system, which went operational in 2004, represented a major modernization over the earlier system, but “it still required permanent modifications to the aircraft,” says Walt Caldwell (5923).
The modular solution
Recognizing that permanent modifications to aircraft are expensive and limit the number of platforms on which sampling systems can be flown, Sandia has been developing modular hardware since early this decade. The currently favored modular solution consists of pods that can be attached on hardpoints beneath the wings of manned or unmanned aircraft, says Joe. Research to develop and test these pods has been supported by NA-22 and DoD.
To date, Sandia and its Albuquerque industrial partner Mechtronic Solutions, Inc., have developed technology demonstration units for three types of pods: a particulate collection pod (known as ARCS), a whole air sampling pod (known as WASP), and a directional gamma sensor pod (known as DGRS) that can identify the direction of peak radiation intensity in the nuclear debris plume. “The ARCS pod has been successfully tested on both manned and unmanned aircraft,” says Joe.
Says Bob Huelskamp (5730), “Sandia is a great example of what a national lab can do in support of a presidential objective to improve world security.”