Imploded Capsule Fuel Temperature and Density Measurement by Energy-Dependent Neutron Imaging Page: 4 of 5
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2 JOURNAL DE PHYSIQUE IV
3-D source 2-D image
(- 100 pm) (- 30 cm)
Figure 1. 3-D source projected onto 2-D image.
can reveal the spatial distribution of nonburning fuel that surrounds the hot burning core of the target
(see Figure 2)1. These measurements are possible because the optical emissions from modern fast
scintillators decay quickly enough that low-intensity late-arriving downscattered images can be
recorded after the initial 14-MeV peak.
14 MeV - 10-11 MeV
(n/ns) 11-12 MeV (MeV)
7-8 MeV 8
6-7 MeV. 5
-100 0 100 200 300 400 500 600 700
TOF-800 (ns, 40 m)
Figure 2. Neutron images versus neutron energy.
Another application that has been considered is fast gating of multiple 14-MeV neutron images. The
relative intensities of these images depend on the temperature-dependent spectral width of the 14-
MeV peak. A pixel-by-pixel map of the ratios of images at different energies near 14-MeV provides a
direct indication of the temperature distribution over the hot burning core.2 With a sufficiently long
line of sight (~ 40 m) and fast scintillators, the recorded ratios provide a good indication of the 14-
MeV spectral width, as illustrated in Fig. 3. Here, burn temperatures of 10 keV and 50 keV lead to
spectral widths of 560 keV and 1260 keV, respectively, for the 14-MeV peak. Gated images at
different times on the peak will have ratios that reflect the underlying spectral widths.
The independent images of emission intensity and burn temperature make it possible to study the
density distribution of a burning ICF target. This is because neutron emission dn/dt can be written
simply as dn/dt= N2sv(T), where N is the (equimolar) deuterium and tritium density and sv is the
known temperature-dependent Maxwell-averaged DT fusion cross section. With measurements of the
emission distribution (dn/dt) and temperature distribution (T), the equation can be inverted to provide
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Moran, M J; Koch, J; Landen, O L; Haan, S W; Barrera, C A & Morse, E C. Imploded Capsule Fuel Temperature and Density Measurement by Energy-Dependent Neutron Imaging, article, September 28, 2005; Livermore, California. (digital.library.unt.edu/ark:/67531/metadc892308/m1/4/: accessed December 16, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.