FEATURE
Preserving Goddard’s Preeminence in Detector Technologies
For years, Goddard has invested in detector technologies that have maintained the Center’s preeminence in the field, leading to scientific discoveries literally across the electromagnetic spectrum. Here, we showcase a few of those technologies, including one that the Department of Homeland Security could use to prevent illicit nuclear material from being shipped into the country.
 This image shows one of three fully assembled kilopixel arrays that Goddard technologist Jay Chervenak developed for the Millimeter Bolometer Array Camera installed in a Chilean observatory. |
World’s Largest Bolometer Array Camera Debuts in Chile
Goddard technologists have tripled the size of a detector array that will fly on NASA’s Stratospheric Observatory for Infrared Astronomy (SOFIA) to create the world’s largest bolometer array camera, which is now observing the afterglow light — the so-called cosmic microwave background — that was created during the first moments of the universe’s creation billions of years ago.
The Millimeter Bolometer Array Camera (MBAC), which traces its heritage to SOFIA’s High-resolution Airborne Wideband Camera (HAWC), was installed in the Atacama Cosmology Telescope in Chile late last year and has produced high-resolution, high-sensitivity data that scientists are now analyzing, said Principal Investigator Jay Chervenak. Scientists are expected to report the results in scientific journals shortly.
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“It’s exciting,” Chervenak said, referring to the camera’s results. “This has been in development for a long time.”
Ideal for Observing Background Radiation
The bolometer camera is a radiant-heat detector. It is ideal for observing the changes in the microwave background radiation — the oldest light in the universe — as it passes through and around galaxy clusters that began to form in the early universe. When combined with optical and X-ray data, MBAC’s high-angular-resolution data will provide insights into the mechanics that drove their formation.
This particular camera-development effort is the result of a partnership involving Goddard, Princeton University, the National Institute of Standards and Technology, and the National Science Foundation. Under the collaboration, Chervenak and his team developed three detector arrays capable of making simultaneous observations in three microwave wavelength bands.
Advances in ‘Pop-Up’ Technology
Like HAWC, MBAC makes use of the Goddard-developed “pop-up” detector technology that a team led by technologist Christine Allen (see related story below) began developing in the late 1990s under R&D funding.
However, MBAC represents a significant advance over its predecessor. Using Internal Research and Development funding, Chervenak increased the size of the detector array to include 1,024 pixels, resulting in the largest array of pop-up detector bolometers ever fielded. In comparison, HAWC hosts a 384-pixel array. For microwave measurements, more pixels mean faster and a more detailed mapping of the sky.
The Big Challenge
“The big challenge for us was making the larger arrays,” Chervenak said. Array assembly was simplified by using low power and superconducting circuits that could be arrayed lithographically. Chervenak added that his team developed the techniques to produce the thousands of elements needed.
The Chilean observatory made its initial observations in November. Full science observations with the three detector arrays are expected to begin this summer.
Chervenak’s work does not end here. The next step is developing and demonstrating a “scalable” array that offers even higher sensitivity.
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It’s Not a Whachamacallit…It’s a GISMO!
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These two images, taken with the Hubble Space Telescope and the Goddard-developed GISMO, show the Orion Nebula, the closest region of massive star formation. Because GISMO views objects in the infrared, it is able to penetrate the dust to pinpoint the most active star-forming regions.
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A prototype camera that employs a large-format, faster and more efficient detector array developed in part with Internal Research and Development (IRAD) funding has gathered high-quality infrared data on nearby to very distant galaxies that formed less than a billion years after the creation of the universe.
The instrument, the Goddard-IRAM Superconducting 2-Millimeter Observer (GISMO), observed these objects in late 2007 after being installed in a 30-meter telescope operated by the Institut de Radio Astronomie Millimétrique (IRAM) in Spain. The instrument will do follow-up observations in June. Brainchild of Goddard Technologist
GISMO is the brainchild of Goddard technologist Christine Allen. Her team used NASA Headquarters funding to develop the instrument as a way to validate a next-generation detector architecture she created with Goddard IRAD funding. The detector architecture — called the backshort-under-grid (BUG) — allows easier assembly of the instrument’s bolometer array because the array’s three individual components are merged into a single working unit.
That contrasts sharply with the level of effort she invested into building a similar array now used in a bolometer camera at the Caltech Submillimeter Observatory in Hawaii.
The 384 detectors in the Caltech instrument were made using 12 individual rows of 32-pixel arrays, requiring a significant amount of handwork for assembly. “This was quite an undertaking,” Allen said. By constructing the pixels on a single silicon wafer bonded onto a read-out circuit, however, the new BUG architecture is scalable, which means she can easily increase the size of the detector array. The larger the detector array, the better the sensitivity and resolution of data.
The more efficient fabrication technique also contributed to GISMO’s relatively low cost and speedy development. It took Allen’s team just a year to build the entire instrument, which was designed specifically to observe in the 2-millimeter bands because this wavelength regime allows observations of objects in the distant universe.
‘On Our Way’
During the demonstration in Spain, GISMO observed in the far-infrared wavelength bands some of the oldest galaxies in the universe. Enshrouded in dust, they are of particular interest to scientists because they all experienced a phase of violent star formation and a large number of them host quasars, indicating the presence of super-massive black holes at their centers. GISMO’s observations are aimed at giving scientists insights into their evolution on cosmological time scales and the physical processes that formed them.
“With a successful ground-based demonstration, we hope to be on our way to building large-format arrays that can be tailored to operate at a wide range of wavelengths,” Allen said.
Although GISMO’s principal investigator for science, Johannes Staguhn, says he’s still processing the data, he is pleased with the results. “We got some real science out of our first observing run. They’re eager for us to come back and do more science with GISMO in June,” he added, referring to IRAM. “This is really saying something since getting an invitation (to install a new instrument and carry out observations at IRAM) is not common procedure at this observatory.”
“We’re hopeful that this opens the doors to other observing opportunities,” he said.
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BAT Technology Applied to Homeland Security Need
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Detecting gamma-ray bursts from space is really no different than finding and intercepting nuclear material illegally stowed inside shipping containers or even trains — at least that’s the view of the principal investigator who created Swift’s Burst Alert Telescope (BAT) that has detected hundreds of gamma-ray bursts from all directions in the sky.
To prove his point, Principal Investigator Scott Barthelmy received Department of Energy funding to cobble together a prototype system using leftover components from the BAT-development effort. Although his prototype would have to be smaller and more mobile to operate as a counter-terrorism tool, the same principles are at play, he said. He hopes to make the case and win Department of Homeland Security (DHS) funding to build a second-generation detection system equipped with even more capable detectors now being developed under Goddard’s Internal Research and Development (IRAD) program.
Scott Barthelmy believes this instrument prototype would be useful for detecting nuclear material hidden in shipping containers and trains. He built it using leftover components from Goddard’s Burst Alert Telecope.
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Inspired by Swift
The instrument that inspired the potential spin-off application is now flying aboard NASA’s Swift mission, which as it name implies, swiftly detects gamma-ray bursts and then targets itself toward the event in about one minute to make detailed observations. Gamma-ray bursts are the most powerful explosions in the universe — second only to the Big Bang in terms of total energy output. They occur randomly about once per day, lasting only a few milliseconds to tens of milliseconds in duration.
Scientists strongly believe these split-second flashes of gamma-ray light signal the collision of a black hole and a neutron star or the collision of two neutron stars that then create a black hole. Hypernova, the explosion of massive stars, also are believed to cause the bursts.
First Line of Defense
BAT is the instrument that detects and locates the burst. Developed with Goddard R&D funding several years ago, BAT carries out its job using a technique called a “coded aperture mask” that creates a gamma-ray shadow on its 32,768-pixel, cadmium-zinc-telluride (CZT) detector plane. The mask itself contains 52,000 randomly placed lead tiles that block some gamma rays from reaching the detectors. With each burst, some of the CZT detectors light up while others remain dark, shaded by the lead tiles. The angle of the shadow points to the direction of the gamma-ray burst.
The same instrument concept is ideal for homeland security, Barthelmy said. “We’ve already produced an instrument that has a 100-degree field of view and can pinpoint the location of a gamma-ray source,” Barthelmy said. “It’s what you would need to find and intercept nuclear material stowed inside shipping containers and trains.”
Next Step: Winning DHS Funding
A new generation of CZT detectors and electronics, which Barthelmy is developing under current IRAD funding for possible use on NASA’s proposed Energetic X-ray Imaging Survey Telescope (EXIST), would further improve the prototype. “They really need the ability to distinguish legitimate sources,” he said. The new CZT technology would do just that. It could distinguish isotopes and determine whether the detected nuclear material were medical in nature or posed a national security threat, he said.
His goal is to get DHS funding to develop a second-generation prototype using the EXIST detectors. “We really want to move into the second stage,” he said.
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