By David Phillips, James Barber
ISBN-10: 1860946607
ISBN-13: 9781860946608
ISBN-10: 1860948936
ISBN-13: 9781860948930
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Sample text
The main difference in design from the ordinary continuous source was in the pressure of the gas filling which must be high enough to prevent the discharge taking place until the triggering pulse is applied. Unless the lamp is to be flashed very frequently cooling is not necessary. I t may be constructed in the shape and length most suitable for the particular application, and the other factors which can be varied are gas filling, gas pressure, capacity, voltage, and the material of the tube and electrodes.
Duration of the flash Edgerton found that when high capacities were used the current passed by the discharge tube tended to a maximum corresponding to a resistance of 0-2 Q for a tube measuring 30 x 1-4 cm. That a corresponding maximum in light output is reached is shown by the oscillograph recordings in figure 1. These were taken by using a 1 P 28 photomultiplier cell which is sensitive over the whole region between 2000 and 8000 A. The lamp was 1 m. x 1 cm. in size, was krypton filled at a pressure of 5 cm.
The secondary pulse is probably due to the circuit inductance. The duration of the flash may be decreased by using shorter or wider tubes which decreases the resistance, but this reduces the power which can be dissipated per flash. For a given capacity the duration of the light pulse is proportional to the length * These seals were supplied by Messrs Siemens and I am indebted to Dr J. N. Aldington and Mr A. J. Meadowcroft for information about the construction of photographic flash tubes. The Biography of George Porter 45 G.
The Life and Scientific Legacy of George Porter by David Phillips, James Barber
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