NIST Gamma Ray Detector System including a cryogen-free refrigerator with microcalorimeter detectors (left) and a rack of read-out electronics (right).
EEEL Researchers Deliver Microcalorimeter Gamma-ray Spectrometer to Los Alamos National Laboratory
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NIST Gamma Ray Detector System including a cryogen-free refrigerator with microcalorimeter detectors (left) and a rack of read-out electronics (right). |
Joel Ullom and Randy Doriese of EEEL’s Quantum Sensors Project traveled to Los Alamos National Laboratory (LANL) to successfully deliver an ultra-high resolution gamma-ray spectrometer for use analyzing nuclear materials. The ability to analyze and identify nuclear materials is an essential component of the international effort to prevent proliferation of nuclear weapons. This unique-in-the-world spectrometer consists of a 0.1 K refrigerator, an array of superconducting microcalorimeter detectors optimized for gamma-rays, a Superconducting Quantum Interference Device (SQUID) multiplexer for multichannel readout, and the necessary control electronics. All components were developed and fabricated by the Quantum Sensors Project. The refrigerator, which was designed by Joel Ullom and William Duncan, relies on closed-cycle refrigerators instead of liquid cryogens and is thus suitable for use outside cryogenics laboratories. Each pixel in the microcalorimeter detector array combines a micromachined thermal isolation structure with a superconducting bulk absorber and a highly sensitive, low-noise superconducting transition-edge thermometer. The delivered spectrometer has demonstrated world record energy resolution better than 25 eV full-width-at-half-maximum at 103 keV. The unmatched resolution of the microcalorimeters (better than 10x that of state-of-the-art germanium detectors) allows closely-spaced X- and gamma-ray lines to be easily separated. In the first experimental demonstrations at LANL the spectrometer has produced spectra from a mixture of plutonium isotopes of unprecedented clarity, revealing the different isotopic constituents. The entire system was designed to be “user-friendly,” and, after a short training period by the NIST staff, the Los Alamos personnel are operating the system independently.