RE: Cal Range Question

["Lavera, Ron" <Ron.Lavera@nypa.gov>]

In the days before we adopted calibration jigs ( instrument detector
supports ) for our calibration range, we noted that the response of some
instruments would change by as much as 10% when they were elevated 4 to 6
inches above the J. L. Shepherd supplied aluminum instrument platform.  

The HPS Laboratory Accreditation program had some stiff restrictions on the
use of Box type calibrators for tertiary labs and prohibited the use at the
secondary lab level.  It might be worth your while to give the HPS a call to
get a copy of the protocol.  

...  mine and mine alone  ...

Ron LaVera
Lavera.r@nypa.gov

		-----Original Message-----
		From:	Glen.Vickers@ucm.com [mailto:Glen.Vickers@ucm.com]
		Sent:	Tuesday, July 20, 1999 11:47 AM
		To:	Multiple recipients of list
		Subject:	RE: Cal Range Question

		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

			
	
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