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GEC Cathode-Ray Tube Screen Types

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Type B also known as P1

This is the ordinary green Willemite* screen with which the standard tubes are normally supplied. It is suitable for visual observation of the trace although it has a very slight persistence which can be troublesome when recording photographically on moving film.

Type E also known as P11

This screen is highly actinic with very short persistence and is therefore suitable for photographic recording of high speed transients particularly when used with a blue sensitive photographic emulsion.

Type C also known as P28

This screen should be used where it is desired to record high speed transients in which a relatively small amount of energy is available to excite the screen. The persistence enables the transient to be observed for several seconds after it has occurred. This type of screen is useful for reducing flicker with recurrent traces of low frequency, say 5-10Hz.

Type M also known as P7

This type of screen should be used where a relatively large amount of energy is available and a bright afterglow of considerable duration is required. It is useful in observing low speed phenomena which may have a duration of several seconds, eg electro-cardiography.

It is not possible to define the characteristics of the C and M screens in more precise terms unless the exact conditions are specified.

There is also a type N phosphor which by other classifications is known as p2.

* Willemite is a zinc silicate mineral. It is highly fluorescent (green) under UV light or electron bombardment.

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