Low Photon Numbers Research Articles

XUV Spectroscopy in Jet

The 2m extreme grazing incidence XUV Schwob-Fraenkel spectrometer has been described in detail [1]. Its use on the TFR tokamak is presented in a parallel paper [2], The instrument installed on JET differs in that it has two microchannel plates scanning independently two portions of the spectral range from 10 to 335Å. A full scan takes 164ms, due to the low number of photons. 127 spectra may be taken during a 20s tokamak discharge. The calculated and measured spectral resolution (FWHM) with a 600g/mm Bausch and Lomb grating and 20µm entrance slit is shown in Fig. 1 for detector positions, y, between 200 and 390mm (corresponding wavelengths of the central pixels are 85 and 310 Å, respectively).

Single-slit digital radiography: some practical considerations

Clinical evaluation of an experimental digital chest unit using a solid-state linear detector array has provided information regarding the postpatient photon flux required for clinically acceptable images. Results from computer simulation show that energy subtraction imaging of the chest by the method of x-ray-tube voltage switching will be unsuccessful unless it can be demonstrated clinically that a much lower number of photons per pixel is acceptable in energy subtracted images. In addition, x-ray-tube loading limitations preclude imaging of the abdominal and pelvic regions with this technology.

Television pick-up tubes for x-ray screen intensification.

This paper is primarily concerned with the application of television systems to X-ray screen intensification, in particular to systems built around the image-orthicon type of camera tube. One object of screen intensification in fluoroscopy is to present to the physician a display which is so much brighter than the normal fluoroscopic image that he does not need to become dark-adapted before making an examination. It takes 30 minutes or more for the eye to attain its maximum sensitivity after entering the darkroom and during this time the gain in sensitivity may be as much as 10,000 times. This gives an indication of the degree of image brightening required to compensate for dark adaptation. A further object is to obtain maximum information from the fluoroscope without exceeding the permissible X-ray dosage; indeed, it is desirable to lower the dosage if possible in order to reduce the probability of later harmful effects to the patient. The dark-adapted eye can resolve little detail, due partly to the physical structure of the retina and partly to the low number of photons usefully collected. The eye has very low resolution at the light levels experienced in fluoroscopy. By bringing the light level of the image into the photopic range of vision, screen intensification enables the eye to utilise all the information available at the fluoroscopic screen but, of course, no more.