Foundations: Gamma-ray technology
Livermore researchers have pioneered a family of portable, lightweight, extremely sensitive gamma-ray instruments with applications in national security and space science.
The ability to detect gamma rays is a vital tool for many areas of research. Because gamma rays provide a unique fingerprint of a material’s isotopic composition, gamma-ray detectors allow scientists to study celestial phenomena, diagnose medical diseases, and search for illicit radioactive sources.
Lawrence Livermore has a long history of studying nuclear debris and developing radiation detection technologies and other diagnostics, stemming from decades of research and experience with nuclear weapons design and explosive testing. Livermore’s expertise in this area is leading to innovative gamma-ray technologies that are improving detection capabilities for both national security and space science applications.
Challenges in gamma-ray technology
Over the years, two challenges have driven the development of gamma-ray technology. First, researchers needed to determine where gamma rays originated—sometimes from a small signal at great distances. This required high-resolution instruments that accurately distinguished a source of interest from background signals. In national security applications, this would be the difference between legitimate (medical isotopes used in hospitals or those that occur naturally in the environment) and illicit (radiation related to a nuclear explosion) sources of gamma rays.
Germanium has long been the detector material of choice for precision gamma-ray spectroscopy. Compared with other semiconductor materials used in detectors, such as silicon or cadmium telluride, germanium provides better detection efficiency, line-shape characteristics, and precision energy resolution, which are needed to produce the detailed gamma-ray spectra for accurately identifying radioactive materials.
Germanium’s cooling requirements contributed to the second challenge in gamma-ray technology—building high-resolution portable detection devices to withstand the various conditions in security, health, and space applications. Early precision detection devices were large and power-intensive and required a consumable liquid cryogen (like liquid nitrogen) to operate. These qualities made standard detectors awkward to transport, store, and handle and often inaccessible for many field applications.
Providing laboratory-scale precision in the field
In 2002, after more than a decade of focused research, Lawrence Livermore researchers overcame the size and accessibility problems by coupling a germanium detector with a commercially available mechanical device commonly used to cool low-noise cell phone antennas. The Cyro3 device, originally designed for the aerospace industry, weighed 4.5 kilograms and could operate for 7 to 8 hours on two rechargeable lithium-ion batteries. The technology represented a quantum leap forward in portable radiation detection and nearly replicated the precision energy resolution found in larger, less-portable laboratory units.
Leveraging this technology, Laboratory researchers developed a range of terrestrial radiation detection instruments, including detectors on buoys for customs agents at U.S. maritime ports, cargo interrogation systems, and high-resolution handheld instruments that emergency response personnel could use to search for a clandestine nuclear device. In 2003, LLNL signed a licensing agreement with ORTEC to commercialize the Livermore-developed RadScout detector, the next version to use the mechanical cooling technology.
New generations for Earth and space
On August 4, 2004, NASA launched the MESSENGER spacecraft to Mercury. Onboard was a Livermore-developed gamma-ray spectrometer optimized for Mercury’s harsh environment. To help the device survive the extremely high temperatures at its destination, the design incorporated a small, low-power cryogenic cooling mechanism with an infrared shielding mechanism developed at Livermore. The device collected the first-ever gamma-ray data from the planet Mercury and has prompted researchers to rethink how Mercury formed.
This next-generation detector significantly advanced the field of gamma-ray spectroscopy. Its features included rugged construction, low power consumption, automated operation, and small size—characteristics needed for both handheld devices and space applications. Livermore researchers transitioned the gamma-ray spectrometer on MESSENGER to the commercially fieldable GeMini, receiving an R&D 100 Award for the innovative technology. In 2009, the Laboratory again licensed the technology to ORTEC.
GeMini opened a wide range of new applications for high-resolution, gamma-ray spectroscopy. Its technology is evolving into new radiation detectors ready to assist security personnel, first responders, scientists, and nonproliferation experts in locating and identifying nuclear materials. Additionally, Livermore researchers are adapting GeMini technology for upcoming space missions.