Re: Magnetic Field interference

["David Whitfill/Kdhe" <DWhitfil@kdhe.state.ks.us>]

Referencing Knoll's Radiation Detection and Measurement (2nd ed., ISBN
0-471-81504-7, p. 274-B.Magnetic shielding):

"The electron optics within a PM tube are particularly sensitive to stray
magnetic fields because of the low average energy (on the order of 100 eV)
of the electrons traveling from stage to stage...In situations in which the
tube is likely to be...brought near equipment with stray magnetic fields,
it is essential that a magnetic shield be provided to prevent gain shifts
of the PM tube. The most common form consists of a thin cylinder of
mu-metal which fits closely around the outside glass envelope of the PM
tube. For most tube designs, this shield must be held at photocathode
potential in order to avoid noise due to electroluminescence in the glass
envelope."

It would probably be best to contact the manufacturer of the PM tube for
their recommendations.

Here is link of interest:

http://magnetic-shield.com/faqs.html

The following is from the above site (Magnetic Shield Corporation):

What is Mumetal®? (or mu-metal or mewmetal, or moometal or newmetal?)

Mumetal® is one registered trade name for a high-permeability, magnetically
"soft" alloy used for magnetic shielding.
Hipernom®, HyMu-80®. Permalloy®, and other names refer to one of the two
typical formulas for this alloy. Both include about 80% nickel and 15%
iron, with the balance being copper, molybdenum or chromium, depending on
the recipe being used. The term mumetal is often used as a generic term, as
Kleenex® is used for any facial tissue. Magnetic Shield Corporation's
registered trademark for our shielding alloy is CO-NETIC AA® (Other
trademarks shown are
property of their respective owners).





Salladay John L PORT <SalladayJL@mail.ports.navy.mil>@romulus.ehs.uiuc.edu
on 11/08/99 12:48:37 PM

Please respond to radsafe@romulus.ehs.uiuc.edu

Sent by:  radsafe@romulus.ehs.uiuc.edu


To:   Multiple recipients of list <radsafe@romulus.ehs.uiuc.edu>
cc:

Subject:  Magnetic Field interference


RADSAFERS,

Has anyone run across interference on PMT's that was due to magnetic
fields?
If so,  I would appreciate any information you could forward to me.

Thanks in Advance



John L. Salladay, CHP
jlsalladay@mail.ports.navy.mil

************************************************************************
The RADSAFE Frequently Asked Questions list, archives and subscription
information can be accessed at http://www.ehs.uiuc.edu/~rad/radsafe.html



************************************************************************
The RADSAFE Frequently Asked Questions list, archives and subscription
information can be accessed at http://www.ehs.uiuc.edu/~rad/radsafe.html