Available Technology

BSA 16-07: Long range detection and identification of special nuclear materials

In concentrated form the special nuclear materials (SNMs) can be the primary ingredients of nuclear explosives. These nuclear materials include plutonium, uranium-233, or uranium-238 enriched with uranium-233 or uranium-235 isotopes. Reliable detection and identification of SNMs is an important goal for nuclear nonproliferation, national security and nuclear safeguards. Historically, many of the tools used to safeguard SNMs have relied on measuring one or more of the inherent nuclear attributes or signatures of these SNMs. However, the presence of interferences, such as shielding and other high-Z profile materials, may influence these attributes or signatures to the degree that many of the historical tools and techniques used in nuclear safeguards must be modified or redesigned to be able to provide specificity in the presence of interference. This invention provides an active interrogation method for reliable detection and identification of SNMs that relies on the emission of delayed neutrons present in the decay of fission products (delayed neutron precursors) as a unique signature for the SNMs.
Patent Abstract: 
The analysis for SNM signatures by a long range interrogation method is activated by a single burst from an intense source. The long-range implies the distance between the target and the detection system of 10 m to 200 m. It is desirable for the active long range interrogation method to separate the signal of the SNMs from relatively benign fission material with high-Z value when the induced fission is used. The disclosed method for detecting and identifying SNMs follows the steps of (i) exposing a target to a high intensity particle or photon beam pulse to induce fission; (ii) detecting emission of prompt and delayed radiation from the target using a detection system including fast and thermal neutrons; (iii) recording fast neutrons induced by thermal neutron fission and gamma-rays from thermal neutron induced fission; (iv) analyzing a die away in the fast neutron yield induced by thermal neutron fission of the target; and (iv) comparing the fast neutron yield from the target to the fast neutron yield characteristic for a special nuclear material; where a close correlation of the fast neutron die away indicates the presence of the special nuclear material within the target. The die away yields of fast neutrons are recorded preferably in the 150-450 mu.s time regions after the induced fission.
By using pulsed radiation fields to stimulate fissionable material, active interrogation can, investigate time-correlated signatures, which passive signature techniques generally cannot by monitoring the induced radiation with appropriate nuclear detectors. Furthermore, since active interrogation measurements can be made without contacting SNMs directly, instrumentation maintenance and repair can be performed without the need to break into the SNM containers or impact subsequent operations.
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