Re:

[Keith Welch <welch@CEBAF.GOV>]

At 03:05 AM 10/2/96 -0500, you wrote:
> Dear Radsafers.......
>                

>What I am looking for, is an active method to measure such radiation fields.

I see this as two questions.  Measuring the prompt field is quite different
than doing area radiation monitoring.

For the prompt field, we employ ( in our machine protection system) PMTs
(with no scintilator) which respond via cherenkov.  I'm told that the key to
getting the best performance from a system like this is to synchronize the
analysis of teh signal to the pulse.  Our tubes are set up something like
this:  Output current goes to an I/V converter, voltage goes to an ADC, and
the ADC should be synchronized to the beam pulse (presently it is not which
makes for lots of slop in the system).  All this beam sync stuff needs to be
done with adequate attention given to the signal rise and processing times.

The main thing about any system used in these conditions is that if you want
to get anything other than qualitative information, you have to do some kind
of calibration or reference exposure as has been mentioned.

>How area radiation monitoring is acheived in such accelerators elsewhere?

We do our area monitoring with Nuc Research Corp ADM-610.  They use sealed
proportional tubes with energy compensation.  The tube also operates in a
variable HV mode, which gives it a very wide dose rate range - from
background readings in micro-R/hr up to about 10 R/hr (I may be wrong on the
max dose rate).  We also have a  neutron channel on these instruments with BF-3.
 
Keith Welch
Thomas Jefferson National Accelerator Facility
Newport News VA
welch@cebaf.gov