Phosphor screen imaging

Compounds that are radioactive can be located on a preparative layer by contact film autoradiography, electronic autoradiography, and storage phosphor screen imaging [21-23]. These methods differ in terms of factors such as simplicity, speed, sensitivity, and resolution, and the method of choice depends on the available equipment, reagents, and instrumentation. All are nondestructive, and the detected compounds can be recovered without change for later studies. 

Storage phosphor screen imaging is often termed filmless autoradiography. The phosphor screens are sensitive to any source of ionizing radiation, e.g., " C, H, S,... 

Fig. 1. Schematic diagram of the multimass ion imaging detection system. (1) Pulsed nozzle (2) skimmers (3) molecular beam (4) photolysis laser beam (5) VUV laser beam, which is perpendicular to the plane of this figure (6) ion extraction plate floated on V0 with pulsed voltage variable from 3000 to 4600 V (7) ion extraction plate with voltage Va (8) outer concentric cylindrical electrode (9) inner concentric cylindrical electrode (10) simulation ion trajectory of m/e = 16 (11) simulation ion trajectory of rri/e = 14 (12) simulation ion trajectory of m/e = 12 (13) 30 (im diameter tungsten wire (14) 8 x 10cm metal mesh with voltage V0] (15) sstack multichannel plates and phosphor screen. In the two-dimensional detector, the V-axis is the mass axis, and V-axis (perpendicular to the plane of this figure) is the velocity axis (16) CCD camera.

Laser devices are the most sophisticated image-acquisition tools. They are particularly useful for gels labeled with fluorescent dyes because the lasers can be matched to the excitation wavelengths of the fluorophores. Detection is generally with photomultiplier tubes. Some instruments incorporate storage phosphor screens for detection of radiolabeled and chemiluminescent compounds (not discussed in this chapter). Resolution depends on the scanning speed of the illumination module and can be as low as 10 pm. 

In the optoelectronic X-ray image intensifier (Fig. 86), [5.427], the X-ray phosphor screen (input screen) is in direct optical contact with a photocathode that converts the luminance distribution of the X-ray screen into an electron-density distribution. The liberated electrons are accelerated in an electric field between the photocathode and an anode (20-30 kV) and are focused by electron lenses onto a second phosphor screen (output screen), where conversion of the electron image to a visible image takes place. 

Phosphors are an important, quality-determining component of cathode-ray tubes (Fig. 87). In the phosphor screen, modulated electrons are converted into a visible image. 

The optoelectronic image converter converts an image invisible to the human eye first into an electron image and the latter into a visible one on a phosphor screen [5.431]. It extends human vision into UV, IR, and X-ray regions. The phosphor... 

Figure 2. Schematic diagram of the imaging apparatus with ion lens. The detector is a dual microchannel plate/phosphor screen assembly (40 mm active diameter) coupled with a CCD camera. Electric field lines are shown to illustrate the ion lens. Equipotential surfaces in the repeller/extractor region are also included.

Besides space charge, image quality is limited by the combination of the number of pixels of the CCD camera and the size of a single ion event. The PSD usually employs two micro-channel plates (MCPs) mounted in a chevron configuration and backed by a phosphor screen. A product ion causes an electron cascade through the channel plates and onto the phosphor, which emits a pulse of diffuse light that must be focused properly onto the CCD array with a camera lens or fiber optic taper. In this process one product ion results in a signal on the CCD that is usually several pixels... 

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