Penumbral imaging and numerical evaluation of large area source neutron imaging system

Abstract

The fusion neutron penumbral imaging system Monte Carlo model was established. The transfer functions of the two discrete units in the neutron source were obtained in two situations: Imaging in geometrical near-optical and real situation. The spatial resolutions of the imaging system in two situations were evaluated and compared. The penumbral images of four units in the source were obtained by means of 2-dimensional (2D) convolution and Monte Carlo simulation. The penumbral images were reconstructed with the same method of filter. The same results were confirmed. The encoding essence of penumbral imaging was revealed. With MCNP(Monte Carlo N-particle) simulation, the neutron penumbral images of the large area source (200 μm×200 μm) on scintillation fiber array were obtained. The improved Wiener filter method was used to reconstruct the penumbral image and the source image was obtained. The results agree with the preset neutron source image. The feasibility of the neutron imaging system was verified.penumbral imaging, reconstruction, unit source, spatial invariance, spatial resolution, MCNP codeIn inertial confinement fusion (ICF) experiment, through detecting the thermonuclear release, such as neutrons, protons and X-rays, a great deal of diagnostic information was obtained. A variety of methods were tried since 1970s and 1980s of the last century, a lot of experiences and results [1][2][3][4][5][6] accumulated in the last 40 years at the institutes in The United States, Japan, European countries [7][8][9][10] . Compared to the X-rays from the target capsule plasma, the fusion neutrons can bring out better information about spatial scale, shape, and uniformity of the implosion compression area of target pill. The detection efficiency is not high enough because the existing detector materials cross section to 14 MeV neutron between fast and ultra-fast neutrons is low. In order to obtain 14 MeV neutron image of thermonuclear fusion, reaction efficiency or neutron yield is improved in efforts, moreover, optimization design is also being made for the imaging aperture. As a result, the aperture diameter is larger than the fusion subject, and so pinhole imaging changes into penumbral imaging, which is the inheritance and development of pinhole image, and has the following advantages: Firstly, the neutron transports efficiency is much improved and appropriate for the diagnosis process at the low-yield neutrons; secondly, the detection limit of dynamic range can be reasonably as low as possible; thirdly, the penumbral image is larger than pinhole image, the resolution of source region can be upgraded moderately; lastly, the aperture is much larger than the fusion source, and so the mechanic requirements were reduced with respect to other encoding pinhole. The penumbral imaging geometric principle is shown in Figure 1. Penumbral image is a complex en-

Obtaining point spread function of penumbral encoding aperture with “expectation maximization” algorithm based on matched source-image pair experiment

“…The so-called penumbral encoded image is the overlap of all the projection spots formed by all the unit sources in the source plane through encoded aperture on the pixel array surface of detector. We have previously proved these points by calculation and digital projection test of the two methods 33 The middle highlighted area in Fig. 2 is the umbra and every point in the source projects to this area.…”

“…33, the general simulation software MCNP was used. First, the system Monte Carlo ͑MC͒ geometric optics model was established according to the mapping principle of the geometrical optics, as shown in Fig.…”

“…[23][24][25][26][27][28][29][30][31][32][33] A designed meaningful shaped "male mold" was reserved in the ropy polymer mixture, which was equally added into a certain ratio of microscale tungsten ͑or gold͒ powder. Before the mixture was going to be solidified completely, the male mold was removed off and the remained "female shell" is the encoded aperture used for experiments.…”

Visualization and quantification of water movement in porous cement-based materials by real time thermal neutron radiography: Theoretical analysis and experimental study

“…This method requires good experience and sophisticated analysis to fulfil its potential performance. 4) Radiation attenuation techniques: These include X-ray system [5], gamma ray system [6] and neutron radiography system [7][8][9][10][11][12][13][14][15]. Their attenuations can be related to water content within the materials.…”

An accurate solution of point kinetics equations of one-group delayed neutrons and an extraneous neutron source for step reactivity insertion

“…The whole process from the subcritical state to the critical and supercritical states is considered under the condition of step reactivity insertion. For other reactors, such as the metal organic chemical vapour deposition reactor [20], the hydride vapor phase epitaxy reactor [21,22], pulse reactor [23], and fusion neutron penumbral imaging system [24], there is the phenomenon that two or more parameters are coupled. The theoretical study of different reactors is important fundamental work, and although the objects differ, the methods and principles are similar.…”