Zone plate imaging of neutrons emitted from a laser fusion target

The authors report on zone plate coded imaging techniques, routinely used to image non-penetrating emissions from laser fusion targets. Only highly penetrating radiations like 14-MeV neutrons will escape the dense compressed core region of future targets to provide information about the burn region. A zone plate for 14-MeV neutrons must be several centimeters thick to produce adequate modulation in the coded image. Computer modeling of zone plate systems show that a thick, tapered zone plate acts like a thin zone plate for points within its field of view and depth of field. Equations developed for thin zone plate systems that describe quantities such as planar and tomographic resolution may be applied to thick zone plate systems. System simulations of a 100-zone, 5-cm-thick zone plate with 5-μ outer zone width constructed of alternating layers of gold and aluminum produce images with 10-μ resolution. The source strength required to image a 20-μ diameter source is 100 to 1000 times less than that needed with an equivalent pinhole system