Safety question re electron beam curing device

["Wayne F Johnston" <wjohnsto@dhhs.state.nh.us>]

Does anyone have any experience or information about electron "dark
current" or other radiation safety concerns with electron beam curing
devices?  One of our registrants has an Energy Sciences, Inc. electron beam
curing machine.  This thing is big and heavy-duty.  Manufacturer's
literature indicates an electron dose of about 4 Mrad at a product
throughput speed of 1300 ft/min. for example.

I am less concerned with radiation problems during operation than with the
possibility of "dark current" doses during maintenance or setup.  The front
end of the machine rolls forward and individuals can stand in front of the
beam port (a thin metal plate).  My concern is that the current source
could be turned off while the accelerating voltage could remain applied.
At 400 kV or more, it seems to me there could be enough stray electrons to
set up a substantial "dark current" and dose workers standing before the
beam port.  I cannot get out of my mind the 1993 report in Health Physics
(V. 65, no. 2) about the "dark current" incident at an industrial
accelerator facility in which the current source was turned off but the
accelerating voltage remained at operating levels.

Although I will speak to them again, the manufacturer was not able to tell
me much about the potential for this kind of occurrence the first time I
asked.  Any help appreciated.

(Usual disclaimers.)
wayne johnston
nh bur. rad. health
6 hazen drive
concord, nh  03301-6527
603-271-4842
wjohnsto@dhhs.state.nh.us