<p>This
dissertation addresses a key 21st Century Grand Challenge – "Combatting
Nuclear Terrorism”. A principal
component associated with addressing this challenge pertains to timely and near
real-time detection and tracking of small quantities of special nuclear
materials (SNMs); the isotopes of uranium (U-235), and Plutonium (Pu) which
constitute the key components of nuclear warheads. Such detection and tracking, especially for
shielded U-235 using passive means is virtually impossible due to the extremely
faint neutron-photon emission signals from radioactive decay which can be
readily masked. Active photon and/or neutron interrogation methods are the only
viable means for HEU detection but the field suffers from detector saturation
in extreme 10<sup>4</sup> R h<sup>-1</sup> radiation fields. Pu isotopes in multi-kg levels emanate
neutrons from spontaneous fission that offer a means for passive interrogation
with directionality, even at low levels assuming novel, high-efficiency
detectors are available. Both U-235 and
Pu isotopes also emit Rn gas (an alpha radiation emitter) at trace levels,
during decay - which offers a possible novel means for identifying the presence
of SNMs – from the faint multi Bq m<sup>-3 </sup>(pCi L<sup>-1</sup>) alpha
emitting gas and progeny in air - if only a real time sensitive enough detector
were available. </p>
<p> </p>
<p>This thesis work
was aimed at filling critical technology gaps, via researching and advancing
the field of metastable fluid detector (TMFD) technology pertaining to novel/transformational
passive and active (photoneutron) interrogation of SNMs. The results of R&D
from this dissertation provide evidence for rapidly and conclusively monitoring
for the presence of Rn-222 and progeny in air at ultra-trace (pCi L<sup>-1</sup>)
levels – even below the action levels mandated by the U.S. EPA by the
development of protocols for sampling and detection using centrifugally
tensioned metastable fluid detectors (CTMFD). </p>
<p> </p>
<p>For SNM neutron
emission (either spontaneous or induced) based active and passive interrogation
this dissertation presents evidence for advancing into novel designs, and
schemes resulting in 100-1000x enhancements in detection efficiency for the
acoustically driven ATMFD architecture in single and array forms. Novel drive
modes: a direct (fixed and sweep) resonance mode, and radically novel indirect
traveling wave mode were used to expand ATMFD capabilities and efficiencies
beyond previous iterations of ATMFD technology.
The experimentation work has been coupled with multi-physics theoretical
modeling and simulations benchmarked against experimental data. ATMFDs in single and array-based
architectures are being investigated for offering a novel, high-efficiency
means for passive interrogation of SNMs.
Coupled together with the Rn-alpha sensing approach, the ATMFD sensors
for neutron monitoring enable a first-of-a-kind transformational dual mode
architecture for monitoring both HEU (U-235) and Pu based SNMs.</p>
<p> </p>
<p>Successful
results were also demonstrated for rapid and convincing 9 MeV (end point x-ray)
photoneutron based active interrogation of 4.5 kg of depleted uranium in
ultra-high gamma background of ~10<sup>4</sup> R h<sup>-1</sup> using a single
CTMFD or ATMFD sensor. Under such intense gamma backgrounds, conventional
detectors are known to get saturated and have presented a major challenge. The
research from this thesis offers a novel solution for both passive and active
SNM interrogation. </p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/12249968 |
| Date | 21 June 2022 |
| Creators | Nathan M Boyle (8801081) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/thesis/Interrogation_Via_Alpha_and_Neutron_Signatures_of_Special_Nuclear_Material_Using_Acoustically_and_Centrifugally_Tensioned_Metastable_Fluid_Detectors/12249968 |
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