Re: Re[2]: Questions on EBWs and EMs

[John Pickering <johnjp@email.sjsu.edu>]

EMs use a very low kV which determines the range of the x-rays.  The
enclosure is significant to shield the radiation generated in cases where I
surveyed using an Victoreen 471 calibrated to as low an energy as possible
(the instrument is not extremely linear at the low energies).  To maximize
the POTENTIAL of generating x-rays, use a high "Z" target in the chamber and
operate at the maximum kV.  Recommended to use a high "Z" target and the
normal kV for such targets.  This way a realistic exposure rate may be
achieved which will most likely be outside the range of the instrument
(little to nothing measured).  You also reduce the possibility of damaging
the EM.  Researchers get a little upset when you damage their EMs.

John Pickering
johnjp@email.sjsu.edu


At 04:04 PM 3/3/98 -0600, you wrote:
>Hi all
>
>I was the RSO at an Australian University a couple of years ago, and surveyed
>the electron microscopes used there. I also found no increase above background
>at the operator position, but I did find an appreciable increase immediately
>against the column in the vicinity of the electron gun. Unfortunately the
>instrument I was using was a simple ratemeter (reading in CPM/CPS) attached
to a
>scintillation detector and was not calibrated for doserate at the low
energies I
>was measuring. I found this surprising and asked the EM manager to inform the
>manufacturer of our findings and seek comment. I can't remember what the
outcome
>was, but in any case, it was not significant from a radiation protection
>viewpoint.
>
>Regards
>
>
>
>Alex Zapantis             
>Health Physicist
>Supervising Scientist Group
>
>Email : alex.zapantis@ea.gov.au
>Fax : (int+) 61 2  6217 2060
>Phone: (int+) 61 2 6217 2037
>
>PO Box E305
>Kingston ACT 2604
>AUSTRALIA
>
>The Supervising Scientist Group is Part of Environment Australia
>
>