We have developed a microchannel plate intensified, subnanosecond X-ray cathode, a microchannel plate, electrostatic focusing optics and a subnanosecond phosphor. The detector is used for one dimensional imaging and sional Reticon camera or a streak camera. The microchannel plates employ an X-ray photocathode (CUI or CsI) deposited on the front surface of the microchannel plate to enhance their soft X-ray efficiency. Electrostatic focusing of the electrons exciting the microchannel plate also enhances the gain of the detector by an order of magnitude. The electrons are accelerated to 20 kV tor output is coupled to a Reticon camera or a streak camera with a fiber optic array. We have built and calibrated more than twenty microchannel plate intensified detectors. Efficiencies in excess of 1000 (wjcm' output per wjcm? input) have been demonstrated. The time response of the detector is less than 500ps. The efficiency if the CUI and CsI X-ray photocathodes have been measured from 450eV to 1300eV at the Stanford Synchrotron Radiation Laboratory. Data are presented on the efficiency, time response, spectral response and the spatial resolution of the detectors.the electrons from the back of the MCP. This large electric field preserves the spatial resolution in the imaging direction detector for X-ray imaging experiments, It consists of an X-ray photo-(proximity focusing)' The phosphor is coated with a thin layer of A1 (about 0.1 Pm) to allow US to apply voltage to the phosphor and to block background light.Several other versions of this detector have been developed including a detector with a transmission photocathode in place Of the MCP' In the transmission photocathode version, the X-ray Photocathode is deposited on a thin PolYProPYlene film. The photocathode is placed at the MCP location. This flux is sufficiently large that the gain of the MCP is not spectroscopic measurements. Signals are recorded using either a one dimenbefore striking a fast phosphor (indium doped cadmium sulfide). The detecgeometry is useful in applications where the incident X-ray necessary* Many variations Of this generic detector geometry are Possible depending on the incident X-ray flux levels and the application. Microchannel plateTwo different sizes of MCP have been used, 75 mm diameter and 40" diameter. Both have 12pm pores and 15pm center to center spacing. The ratio of the length to diameter of the pores is approximately 40. The MCP bias angle is 5". An electrical conductor (0.2pm of gold over 0.05pm of niobium) is applied to the back surface of the MCP. The coatings are deposited on the back surface at an agle of 45". This results in a small amount of end spoiling of the plates. The front surface of the MCP is also coated with a 0.05 pm cathode. The niobium and gold are deposited on the front surface of the MCP at an angle of 15" from normal. The plate is continuously rotated during deposition of the conductors. The photocathodes are deposited at 45". The 45" angle is X-rays will strike the photocathode instead of bare channel
LLNL is developing an ultra-wideband, side-looking, ground-penetrating impulse radar system that can be mounted on an airborne platform for the purpose of locating buried mines. The radar system is presently mounted on an 1 8-meter boom. We have successfully imaged a minefield located at the Nevada Test Site. The minefield consists of real and surrogate mines of various materials and sizes placed in natural vegetation. Some areas have been cleared for non-cluttered studies. A technical description of the system will be presented, describing the wideband antennas, the video pulser, the receiver hardware, and the data acquisition system. The receiver and data acquisition hardware are off-the-shelf-components. The data was processed using LLNL-developed image reconstruction software, and has been registered against the ground truth data. Images showing clearly visible mines, surface reference markers, and ground clutter will be presented.
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