Idaho State University Pushes the Limits of Standoff Detection of Fissile Materials

Problem: Standoff detection of fissile isotopes at distances of ~100 m by active interrogation using radiation as a probe may be possible at high energies. Practical application in nuclear forensics will require characterization of the fission signatures. DTRA has funded basic research into fission signatures and interfering reactions from non-fissionable materials at energies greater than ~20 MeV with a goal of increasing the practical standoff distances to greater than 100 m.


Schematic of the experimental setup for fission signature determination and identification of interfering reactions. Thirteen detectors were fielded including 3He (to identify delayed neutron interference), BGO (to identify delayed γ-ray interference, and HPGe (to measure integral cross sections).

Results: Professor Alan Hunt of Idaho State University has examined secondary emissions to identify fission signatures and has identified over 170 possible interfering reactions, including neutron, high-energy γ-ray and electron emitting reaction products. Cross section measurements were made on 34 different targets with high bremsstrahlung endpoint energies between 19 and 45 MeV. DTRA has an interest in bremsstrahlung energies as high as 60 MeV for higher efficiency, better penetration, and better cross sectional overlap, all of which should lead to longer standoff distances. However, interfering reactions become more acute at higher energies.

Potential: The measurements of interfering reactions and integral cross section conducted in this program when combined with Monte Carlo models can be compared to available databases to improve standoff detection sensitivity and identify mitigation strategies to overcome interference from the most problematic isotopes (18O, 19F, and 13C).

Transition/Impact: Idaho Accelerator Center (IAC) received an award from Johns Hopkins University’s Applied Physics Laboratory to support upgrading, operating, and utilizing the Photonuclear Inspection and Threat Assessment System (PITAS) accelerator at the IAC’s long standoff detection range for projects including expanding the library of signatures and interfering reactions. This collaborative effort provides research and development support for DTRA’s Integrated Standoff Detection Inspection System project, led by Raytheon’s Integrated Defense Systems division. The PITAS accelerator is 25 MeV pulsed radiofrequency electron linac capable of delivering up to ~1 kW of electron beam power. This accelerator is located at the IAC-Airport facility’s long standoff detection range, providing a 15 acre site for performing active inspection experimentation at distances up to ~120 m.



RADIOLOGICAL – NUCLEAR STANDOFF DETECTION & WIDE AREA SEARCH (TA-1)
HDTRA1-08-1-0019: BASIC RESEARCH IN HIGH SENSITIVITY SNM FORENSICS VIA CORRELATED PHOTO-INDUCED EMISSION SIGNATURES
ALAN HUNT, IDAHO STATE UNIVERSITY