RE: Cal Range Question

[Glen.Vickers@ucm.com]

If you use an ion chamber to certify your box calibrator.  Would a pulse
counting dose rate instrument over-respond on the low ranges?  Exposures for
the low dose rates typically involve many attenuators on the beam as well as
the scattering in the shielded box calibrator.  An ion chamber should tell
the truth and account for the reduced energy multi-scattered flux.  A pulse
counting instrument assumes all of the pulses are 662 keV for a Cs
irradiator.

Similarly, when the instruments are in the field, there is a different
energy spectrum than what was in the calibrator. There is a significant
amount of multi-scattered low energy photons in a power plant environment.
The ion chamber can account for the true energy deposited, while the
pulse-type instrument assumes each pulse is 662 KeV.  I would think the ion
chamber would once again tell the truth about the amount of energy deposited
and respond lower, while the pulse counting instrument thinks the dose rate
hasn't changed even though the energy of the flux is less.

Technicians will often times say the teletector over-responds compared to an
ion chamber.  I've heard most attribute this to geometry conditions and
active volume sizes of the detectors.  I'm tending to think the difference
is caused more the type of instrument, ion chamber vs. pulse counting.

Any comments or experiences?

Sincerely,
Glen Vickers
glen.vickers@ucm.com

	-----Original Message-----
	From:	Patrick Muldoon [SMTP:pmuldoon@mail.arc.nasa.gov]
	Sent:	Friday, July 16, 1999 10:07 AM
	To:	Multiple recipients of list
	Subject:	Cal Range Question

	Thank you to all who responded to my cal range question.  I will be
getting
	an ion chamber and electrometer that is certified to a NIST traceble
source
	to certify our range.

	Now, do any vendors out there want to e-mail me some quotes on an
	instrument that will do the trick?

	Thanks again.

	Patrick Muldoon
	pmuldoon@mail.arc.nasa.gov

	
************************************************************************
	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