Development of a Centrifugal Tensioned Metastable Fluid Detector Array to Detect SNM using Active Neutron Interrogation

A novel, portable, and lightweight active neutron interrogation system is under development by our collaboration incorporating a man-portable IEC based D-D neutron generator and Centrifugal Tensioned Metastable Fluid Detector (CTMFD) panels to enable the detection of SNM in cargos less than 1 m3. Threshold Energy Neutron Analysis (TENA) techniques are utilized to discriminate the ~2.5 MeV interrogation neutrons used to induce fission in a SNM target while remaining sensitive to the 25% to 30% of the fission spectrum emitted at energies >2.5 MeV. CTMFDs are ideal for TENA applications due to their inherent ability to selectively discriminate lower energy neutrons by tailoring the tensioned metastable negative pressure (P
_neg
) state [1] and their proven gamma insensitivity (gamma intrinsic detection efficiency <;1×10
^-9
[2]-[4]). A small prototype panel of 6 CTMFD units, each with a ~16cm
³
SV, was developed, constructed and evaluated with D-D, D-T, and 252Cf neutron sources. Initial experimentation with the prototype panel highlighted several areas capable of targeted improvement, and as a result the Lightweight(LW)-CTMFD was developed to meet these challenges. The resultant LW-CTMFD was then configured into a portable modular configuration consisting of 5× ~16cm3 SV units. Each module was targeted for operation in a stacked configuration resulting in a total of 15 × ~16cm
³
SV LWCTMFD units per panel. Preliminary assessments indicate that an intrinsic detection efficiency ratio (ε
_Cf
:ε
_DD
) of >10
⁴
:1 is achievable with the LW-CTMFD at a Pneg of ~2.8 bar and becomes effectively infinite at lower Pneg indicating complete insensitivity to 2.5 MeV neutrons from the interrogation source. The construction of the LW-CTMFD module and the detailed results of experimentation indicate that the Modular LW-CTMFD system not only meets but also exceeds the design goals therefore enabling the detection of small quantities of HEU hidden in 1m
³
cargos within minutes.