Venetian Blind Dynode Research Articles

Optimization of an ion-to-photon detector for large molecules in mass spectrometry.

Ion packets can be detected in time-of-flight mass spectrometry by collecting the photons that are produced during the impact of the packets with a scintillator. The photon yield is a function of the ion energy. It was found that post-acceleration of the particles in front of the scintillator was an efficient way of increasing signal intensities. For the same total ion energy, the intensities were larger with post-acceleration than when only increasing the initial ion kinetic energy. A venetian blind dynode, converting the primary ion beam into electrons/secondary ions, was also introduced. Positive or negative secondary particles produced on the dynode surface could be accelerated to the scintillator. Electrons were found to give the highest signals. Intensities similar to those measured with microchannel plates were found. The linearity and onset of saturation of the microchannel plates and the ion-to-photon detector were compared. At optimum operating conditions, the ion-to-photon detector gave around 10 times higher signals than the microchannel plates for heavy ions (150 kDa), with similar mass resolution. Copyright 1999 John Wiley & Sons, Ltd.

The effect of the photomultiplier nonuniformity on the performance of gas proportional scintillation counters

Abstract Experimental results are presented showing that the energy resolution of xenon filled gas proportional scintillation counters with large radiation windows depends not only on the radial but also on the azimuthal variation of the efficiency of the photomultiplier. The commonly used venetian blind dynode photomultipliers are found to present a strong azimuth dependent efficiency and so are not advisable for high performance detectors. With properly chosen 2 in. diameter photomultipliers energy resolutions of less than 9% can be achieved with 20 mm diameter radiation windows in nonfocused detectors.

State-of-The-Art Photomultipliers for Anger Cameras

A study was conducted to determine the state-of-the-art in PMT's (photomultiplier tubes) used in Anger scintillation cameras. These are end-window PMT's with transmission-mode photocathodes. Several hundred PMT's including venetian blind, box-and-grid, "tea-cup" and "gamma target" types were selected from a population of 20 000 and carefully studied. Typically the sample size for any given type exceeded 100. The best observed 57Co PHR (pulse height resolution) values were 8.0% for a two-inch PMT with box-and-grid dynodes and 8.6% for a three-inch PMT with venetian blind dynodes. No one multiplier structure was found to be superior overall. It was concluded that a small number of PMT's out of the typical population exhibit exceptionally good PHR, indicating that better PMT processing control coupled with new designs could improve the relative 57Co PHR average by as much as 10 to 20 percent. The impact of this potential improvement upon Anger camera performance is discussed.

A cathode-ray switch tube with 11 channels of electron multiplication

An 11-channel switch tube with 5 stages of electron multiplication has been developed. In some applications the switch tube will replace the camera-oscilloscope system for recording the rise times of electrical signals. This tube will be used to convert wide-band information from a single channel into eleven channels of lower bandwidth information which can be transmitted over standard telephone cables for telemetering operations. Venetian-blind dynodes are used for the multiplier structure. Each channel is defined by a pair of louvers on the dynode disk. U-shaped shields, which just straddle the louver edge of the preceding dynode, are used to minimize crosstalk. The channel width is 0.120 inch or a total length of 1.32 in for the 11 channels. The collector system provides a method for equalizing the gain of all the channels. The switch tube is 3 in in diameter and 24 in in length. Operating at a 4-kv beam potential with 2-µa beam current, the tube provides 20 ma of output current, with less than 5 per cent crosstalk to adjacent channels. The electron optics and the performance of the tube are described.

A cathode-ray switch tube with 10 channels of electron multiplication

A ten-channel switch tube with five stages of electron multiplication has been developed. The advantages are low crosstalk, low beam potential, electrostatic deflection, and light weight. This tube will be used to convert wide-band information from a single channel into ten channels of information that can be transmitted over standard telephone cables in telemetering operations. Venetian-blind dynodes are used for the multiplier structure. Each channel is defined by a louver on the dynode desk. U-shaped shields are Used to minimize crosstalk. The channel length is 0.120 inch, or a total length of 1.2 inches for the ten channels. The collector system provides a method for equalizing the gain of all the channels. Operating at a 2-kv beam potential with 5-µa beam current, the tube provides 20 ma of output current, with less than 5% crosstalk to adjacent channels. The electron optics and the performance of the tube are described.

New Rugged High-Temperature Photomultipliers

A new photomultiplier has been designed which, up to temperatures of 150°C, is suitable for scintillation counting of the natural radioactivity of sediments traversed by an oil well. It uses a special head-on photocathode which is a compromise of stability, sensitivity and noise. The tube envelope is made of a succession of parallel Kovar and glass rings fused together. Venetian-blind dynodes of the Lallemand type are welded to the inner side of the Kovar rings and bleeder resistors to the outer side. This structure combines excellent mechanical properties (ruggedness, freedom from microphonics) with the very high electrical insulation needed, even at elevated temperatures. Taking advantage of the great versatility of the multiplier structure, several other types of tubes were built with conventional photocathodes (S-11 and S-17) and 14 and 18 stages. They are intended for applications requiring good performance associated with ruggedness.