magnetic shields

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Even changing the orientation of a photomultiplier in the Earth’s field can show a detectable effect. We offer a selection of different types of magnetic shields to cover the entire range of Electron Tubes photomultipliers.

There is more than one type of shield available for some tube types and the final choice of shield will depend on the magnitude of shielding required. Magnetic fields affect the collection efficiency and the gain of a photomultiplier, to a degree dependent on the type of dynode structure. Performance curves for the four multiplier structures are given in the technical document: understanding photomultipliers. Information is also given in the individual data sheets.

integral magnetic shields

These are offered for all end-window photomultipliers up to 52 mm diameter. The photograph to the right shows a photomultiplier fitted with an integral magnetic shield. A 0.125 mm thick mumetal* sheet is wrapped around the envelope and protected by an insulating sleeve. There is direct electrical contact from the shield to the cathode pin. These are the most cost effective, but other options with a higher degree of shielding may be necessary in place of, or in addition to, an integral shield.

split cylinder magnetic shields

These are available for end window photomultipliers up to 52 mm in diameter. The shield is in the form of a split cylinder of thickness 0.5 mm. An internal grip pad that adheres to the photomultiplier is included. The range is listed in the table below.

shield type	length A mm	length B mm	Ø pmt mm
MS19A	75	22	19
MS25A	39	29	25
MS30A	76	33	30
MS30B	102	33	30
MS38A	83	41	38
MS52A	76	56	52
MS52B	102	56	52
MS52C	133	56	52
MS52D	152	56	52

contoured magnetic shields

These 0.5 mm thick magnetic shields are available for side-window, and end window photomultipliers with diameters in the range 52 mm to 200 mm.

The range is listed in the table below. To view an outline drawing click on the shield type number.

shield type	photmultiplier diameter mm	socket
MSSW	30 (side window)	B11A no lugs
MS52E	52	B14A, B21
MS52F	52	B15B, B19A
MS75/90	75	B15B, B19A
MS75/90	90	B15B, B19A
MS130A	130	B15B, B19A
MS130B	130	B14A
MS200A	200	B20

A comprehensive selection guide for individual photomultiplier types can be viewed on this page.

An insight into magnetic field theory is provided on this page.

It is important to connect the magnetic shield to the photocathode potential; this will prevent noise generation from potential gradients across the glass envelope of the photomultiplier.

* Mumetal is a registered trade mark of Magnetic Shield Corportion.