Eur. Phys. J. Plus (2014) 129: 239
https://doi.org/10.1140/epjp/i2014-14239-3

Regular Article

Detection of nuclear sources in search survey using dynamic quantum clustering of gamma-ray spectral data

¹ Quantum Insights LLC, 3845 Nathan Way, 94303, Palo Alto, CA, USA
² Stanford Linear Accelerator Center (Emeritus), 2575 Sand Hill Road, 94025, Menlo Park, CA, USA
³ Nuclear Engineering Division, Argonne National Laboratory, 9700 South Cass Avenue, 60439, Lemont, IL, USA

^* e-mail: aheifetz@anl.gov

Received: 18 June 2014
Revised: 19 September 2014
Accepted: 29 September 2014
Published online: 7 November 2014

Abstract

In a search scenario, nuclear background spectra are continuously measured in short acquisition intervals with a mobile detector-spectrometer. Detecting sources from measured data is difficult because of low signal-to-noise ratio (S/N of spectra, large and highly varying background due to naturally occurring radioactive material (NORM), and line broadening due to limited spectral resolution of nuclear detector. We have invented a method for detection of sources using clustering of spectral data. Our method takes advantage of the physical fact that a source not only produces counts in the region of its spectral emission, but also has the effect on the entire detector spectrum via Compton continuum. This allows characterizing the low S/N spectrum without distinct isotopic lines using multiple data features. We have shown that noisy spectra with low S/N can be grouped by overall spectral shape similarity using a data clustering technique called Dynamic Quantum Clustering (DQC). The spectra in the same cluster can then be averaged to enhance S/N of the isotopic spectral line. This would allow for increased accuracy of isotopic identification and lower false alarm rate. Our method was validated in a proof-of-principle study using a data set of spectra measured in one-second intervals with sodium iodide detector. The data set consisted of over 7000 spectra obtained in urban background measurements, and approximately 70 measurements of ¹³⁷Cs and ⁶⁰Co sources. Using DQC analysis, we have observed that all spectra containing ¹³⁷Cs and ⁶⁰Co signal cluster away from the background.