Pulsed fast neutron analysis

One of the most popular refinements of FNA involves the use of a pulsed neutron source. There are many options for the neutron accelerators used for PFNA. One representative approach is the use of a 300 0,A injector with a 6 MeV deuteron 

A proposal has been made for a PFNA-based system designed to detect illicit materials for air cargo inspection (ACI). This system is referred to as PFNA ACI. The PFNA ACI is a proprietary design that utilizes a tandem Van de Graff accelerator to accelerate deuterons. The neutron beam is collimated in a scan arm and focused on the front surface of the container. Testing has been conducted on aircraft LD3 container as well as truck cargo trailers. 

There is considerable momentum behind an investigation of the potential of a PFNA system. A prototype of a PFNA system has been tested at the Ysleta Port of Entry (located near El Paso, Texas) on truck cargo containers. Projects on ongoing to have a PFNA system tested in an airport environment. 

Filters are sometimes derived from test cargo calibration runs to optimize the explosive detection. The PFNA detection algorithm can be totally automated but previous demonstrations (prior to the 2005 Ysleta Port of Entry testing) have used operator intervention to evaluate the basic scan alarm regions before a directed scan is made of the selected basic scan alarm regions. 

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D. R. Brown, Cargo Inspection System Based on Pulsed Fast Neutron Analysis An Update, SPIE Vol. 2276, Cargo Inspection Technologies (1994) 449. 

D. R. Brown, T. Gozani, R. Loveman, J. Bendahan, P. Ryge,J. Stevenson, F. Liu, M. Sivakumar, Application of Pulsed Fast Neutrons Analysis to Cargo Inspection, Nuclear Instruments and... 

Terrorism and Drug Trafficking Testing Status and Views on Operational Viabihty of Pulsed Fast Neutron Analysis Technology, Report to the Subcommittee on Treasury and General Government, Committee on Appropriations, US Senate, GAO/GGD-99-54, April 1999. 

One of the most developed of these methods is the technique usually referred to as pulsed fast neutron analysis (PENA) [3,11-13], The operation is illustrated in Fig. 7 [11], Neutrons in the range of 8 MeV are generated by an accelerator (not shown) by the reaction D(d,n)He. The accelerator is pulsed with a 1 ns pulse width to produce 1 ns pulses of neutrons with a repetition rate of 1 MHz. Gamma rays are detected in a series of scintillation detectors. The time difference between the accelerator pulse and the... 

API, associated particle interogation FNA, fast neutron analysis PFNA, pulsed fast neutron analysis TNA, thermal neutron analysis. 

D.R. Brown and T. Gozani, Cargo inspection system based on pulsed fast neutron analysis, Nucl. Instrum. Methods Phys. Res. Sec. B, 99(1—4) (1995) 753-756. 

Panel on Assessment of the Practicality of Pulsed Fast Neutron Analysis for Aviation Security, National Research Council, Assessment of the Practicality of Pulsed Fast Neutron Analysis for Aviation Security, National Academies Press, Washington (2002)... 

A portable isotopic neutron spectroscopy (PINS) detector can be used to help eliminate an anomaly or munitions as being dangerous. The PINS detector is only effective for six inches, thus the object does not have to be completely excavated. A larger truck-mounted version called pulsed fast neutron analysis (PFNA) can penetrate to five feet, but it is extremely dangerous to drive a heavy vehicle over a munitions site. Still larger permanently mounted versions are available for customs work, which can look through an 8-ft wide steel shipping container or semitrailer. 

PENA Pulsed Fast Neutron Analysis (detector)... 

Fig. 9. Principles of pulsed fast neutron transmission analysis. No, open beam intensity with no material in...

P.C. Womble, G. Vourvopoulos, J. Paschal and P.A. Dokhale, Multi-element analysis utilizing pulsed fast/thermal neutron analysis for contraband detection, Proc. SPIE, 3769 (1999) 189-195. 

The increased incident flight-path has a second consequence. The intense feature at 13600 ps, in Fig. 3.22a, is the elastic line for TFXA, d = 12.1 m. As the flight path is increased, the elastically scattered neutrons reach the sample later and the elastic line occurs at later times. On TOSCA where di = 17.5 m, it occurs at 22600 ps. However, ISIS operates at 50 Hz and each time frame is only 20000 ps long. Thus the elastic line from one pulse of neutrons would occur in the next time frame frame overlap. An alternative viewpoint is that fast neutrons from the current frame have overtaken the slow neutrons from the previous frame. Frame overlap is catastrophic because the uniqueness of the time-stamp, so crucial to the analysis of the spectrum, is lost. 

The nanosecond pulsed beam with time gating at the detector and the associated particle method (APM) render the three-dimensional (3D) elemental analysis of solids possible (Overley 1987 Rynes et al. 1999). The APM is based mainly on the D-D and D-T reactions by the detection of He and He particles, respectively, emitted at 180° to the neutron direction. The 4-5 cm/ns travel time of the neutrons allows the imaging of the interrogated volume along the direction of the ns pulsed neutrons with a spatial resolution of 5 cm. Some 2D-3D fast neutron imaging principles and techniques are summarized by Gozani (1994), Mikerov et al. (1998, 2001), and Chen and Lanza (2001), while typical thermal neutron radiography systems are demonstrated by Balasko et al. 1998, 2001) and Shaikh et al. (1998, 2001). 

Although the pulse sequences used to study phase transitions are usually quite simple in the examples presented in this review (one to maximum four pulses), the interpretation may be subtle. Solid-state NMR nevertheless remains a difficult technique since quantitative interpretation of the spectra rely on a profound knowledge of the chemical composition and structure of the sample analysis of NMR results also requires a model to relate the observed NMR spectral shapes or relaxation behavior to hypothesis concerning the structure and dynamics of the atoms or molecules carrying spins. That NMR motionally average the atomic and molecular displacements that occur on a time-scale faster than 10—8 10—9s is an important point that should be considered in the interpretation of data. In particular, the difference in perception between NMR and X-ray diffraction with regard to fast and slow dynamical disorder in molecular crystals undergoing phase transitions between different polymorphs was illustrated. In fact, the interpretation of NMR data almost always needs the support of other data obtained by different techniques. Therefore, we emphasized the different complementarities with X-ray (or neutron) diffraction, IQNS and other spectroscopic methods to provide, by cross-correlation of the different data, consistent picture of the phase transition. 

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