Tham khảo tài liệu 'photodiodes communications bio sensings measurements and high energy part 14', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Quantitative Measurements of X-Ray Intensity 251 Methods for imaging The SXI s CCD camera was mounted on the diagnostic arm is shown Fig. 6. There was an extension between the camera and the Manson chamber of sufficient length that the X-ray beam uniformly illuminated the CCD. The camera calibration proceeded by the following steps 1. Locate the bad pixels so that they can be masked out for image analysis 2. Determine the linear range of the camera 3. Measure the camera sensitivity 4. Measure the uniformity of the CCD chip response over the area of the camera. The cameras had a large number of bad rows and hot pixels. The bad rows were associated with the readout and identified using closed shutter images with a 3 ms exposure time. The hot pixels were identified by taking an image using the Ti anode and no filter and using the same exposure time that was used for the experiments on the NIF target chamber experiments. A map was made that identified the bad rows and bad pixels. The photon intensity was measured with the photodiode in arm 1 as seen in Fig. 6. An exposure time was chosen to be as short as possible to give a reasonable signal. Photodiode readings were taken before and after acquiring each CCD image. During imaging the X-ray beam intensity was monitored continuously for beam fluctuations using the photodiode in arm 2. If there were beam intensity fluctuations observed during imaging that image was discarded. Flat field images are images where the CCD is uniformly illuminated in order to measure the uniformity of the camera response over its area. They were taken using the same anode voltage that was used for the camera efficiency measurements and maximum anode current. The exposure time was chosen to produce a signal that was 50 to 60 of saturation. Ten flat field images and ten background images were taken at each photon energy. Image analysis The camera images for the efficiency analysis had the background subtracted and the bad pixels .
