ARI-MA: Cavity Resonance Kinetic Inductance Detectors (CaRKIDs)

University Of Colorado At Boulder, Boulder CO

Investigators

Abstract

1039309 Betz The objective of this proposal is to develop detectors with high efficiency and high resolution. Currently, the best high-purity germanium detectors (HPGe) used in nuclear spectroscopy provide a fractional energy resolution of only 0.5% in the 100 keV region important in nuclear spectroscopy. In many cases this resolution is inadequate to discriminate between threatening nuclear materials and more mundane substances which are part of the natural background. For example, the most common source of false alarms at US border crossings is the confusion between the naturally occurring emission of 226Ra (an element commonly found in clay-bearing materials and soils) at 186.211 keV and the185.715 keV emission of fissile 235U. Another spectroscopic challenge in nuclear materials analysis is separating the intense 104.2 keV line of 240Pu from the nearby 103.7 keV X-ray of Pu X. These and other line overlaps in the 100-200 keV region set the error budget for nondestructive analysis of mixed actinide samples. Determining the isotopic mix in a reactor fuel sample provides both a characteristic fingerprint and specific information about the intended purpose of the fuel (weapons production or electricity generation), the type of reactor, and the history of chemical processing, if any. Further, detectors with high efficiency and high resolution can provide new capabilities for detecting fissile material. Detectors with better resolution produce a better signal-to-noise ratio when measuring faint emission lines from trace quantities of radioactive material in the presence of background or overlapping lines. The new superconducting detectors proposed here offer the promise of 30 times better energy resolution than HPGe, and perhaps 1000 times greater cross-sectional sensitivity compared to cryogenic microcalorimeters. The intellectual merit of the proposed activity derives from its potential to produce more than an order of magnitude improvement in the energy resolution of gamma ray detectors, and the scientific fallout this advance would have, not only for nuclear security, but also in astrophysics and nuclear medicine. The detectors proposed rely on an effect called kinetic inductance, in which the macroscopic inductance of the surface of a superconductor can be influenced by the creation of unpaired electrons (quasiparticles) through the absorption of ionizing radiation. The change in inductance is picked up by a high-Q microwave circuit, and the signal event is counted as with any another photon counter, but with the difference that the pulse heights can be measured with 30 eV energy resolution in the gamma absorption. The broader impact of this effort will be felt in several areas. First in science the development of high-energy kinetic inductance detectors will influence the direction of gamma ray astronomy and perhaps even the search for dark matter. In technology, the impact will be felt in the development of non-contact nuclear assay methods of unprecedented sensitivity. Finally, in education, the participants in the research, the graduate student and postdoc, will be free to explore a wide open area as part of thesis and postdoctoral research. Finally the senior personnel will have something exciting to do, and something new to convey to the K-12 students in the science fair and outreach activities.