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RE: Sandy's EPD Comments

To: radsafe@romulus.ehs.uiuc.edu
Subject: RE: Sandy's EPD Comments
From: mark sasser <duke99301@yahoo.com>
Date: Fri, 29 Jan 1999 00:44:02 -0800 (PST)

it seems some good points being an hp in the field.
I have  seen  some things you donot see in a lab.
the drop test from a steam genny platform...opps.and when I was at one
plant the labor force was usung there 
ED to check dose rates .. then I had a labor belive he had to leave
because when alarmed he was thinking it was full!!! but the big one
was when some workers found when you took a radio walkey talky. and
put the ant. right at the ED and keyed the mike it would pit the ED
off scale.. they thought this was funny. more papper work!!!!

that always wants me to say  why me ....

---Mike Lantz <mlantz33@cybertrails.com> wrote:
>
> 
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> I am shocked and saddened by the sudden passing of Charlie Willis. 
He =
> was a wonderful Health Physicist who will be missed by all.  His
support =
> of this list alone was amazing considering all of the efforts he was =
> involved in.  In that light, I can attempt to honor him by
increasing my =
> support of the Health Physics Society and this list.  And that I
will =
> do. =20
> 
> 
> I will quit lurking on this list and start supporting it.   I will
begin =
> by listing a few of the ways that ED's have measured doses low and =
> therefore could create the scenario that Sandy Perle had presented. 
He =
> certainly was not being an alarmist, simply an HP who has tested
ED's in =
> various situations.
> 
> 1) Exposure to high energy photons from underneath, such as standing
on =
> a high integrity container of rad waste, TLD =3D 600 mrem, SRD =3D
575 =
> mrem and ED =3D 250 mrem because of significant angular dependence.  =
> This factor of more than 2 increases to a factor of 4 underresponse
if =
> the transmitter is added to the ED.=20
> 
> 2) ED's have underresponded by a factor of 3 to noble gas submersion =
> (dominated by Xe-133) even though testing shows the ED responds =
> accurately to 80 kev photons at perpendicular incidence.  Again, a =
> serious angular dependence.
> 
> 3) Low energy photons from the side, top or underneath have been =
> measured to respond a factor of 14 low (!) in laboratory testing by
the =
> vendor.  In my article a few years ago, I worried if these ED's were =
> being used by flouroscopists because of the likelihood of
significant =
> underresponse.=20
> 
> 4)  The vast majority of ED's in use in the US will significantly =
> underrespond to any photons below approximately 60 keV at
perpendicular =
> incidence, and worsens dramatically as the angle moves from 0 degrees.
> 
> 5) ED's will saturate and underrespond in VHRA's; and the
underresponse =
> will be relatively unknown.  We recently tested a brand new
dosimeter =
> type that responded well at 90 R/hr, but at 120 R/hr indicated NO =
> response, nothing!  Its secondary dead time correction in its =
> complicated dose rate to dose conversion algorithm, which is known
to NO =
> users, failed and the dosimeter stopped working until the dose rate
was =
> reduced to below 100 R/hr!  We also tested ED's to NVLAP Proficiency =
> Testing and 2 dosimeters read 54% and 65% lower than expected
because =
> they were irradiated to a high dose rate.
> 
> 6) Drills, motors, and magnetic fields have placed ED's into a
latent =
> state where they are completely UNRESPONSIVE to radiation,
regardless of =
> the dose rate.
> 
> 7) The energy response characteristics of individual pin diode
detectors =
> have been documented to be much more variable than I have ever seen
in =
> TLD or film testing.  Variable responses, certainly more notable as
the =
> energy of photons is decreased, have been found, possibly related to =
> dopants in the pin diode materials; errors up to 60%.
> 
> 8) ED's have been found to change calibration factors by a factor of
2 =
> in the field; and then correct themselves.
> 
> 9) The current crop of ED's are fairly new.  I find this the hardest =
> part to swallow that people think they just work; and will continue
to =
> work or be supported by the vendor for years, even as the vendors
move =
> to newer designs.  As they have aged, loss and repair rates have
been =
> significant.  Speakers for the alarms fail.  And so little has been =
> published.=20
> 
> 10) Computer software and hardware that is not in a mature state yet =
> controls the tracking of all doses to be recorded by ED's.  Examples
of =
> data loss (ie, dose) include a recent situation where a terminal to =
> verify that the ED was turned on actually turned off random ED's. 
Other =
> software problems continue to lose dose by ED's.
> 
> This is part of the list of problems with EDs that I wrote about in =
> 1996.  One of our many duties must be to continue to set standards
for =
> personnel dosimetry that guarantee our facility personnel high
quality =
> dosimetry that works in all spectra, angles and environments that
they =
> will encounter.  The vendors have continued to improve their
products =
> and we should be proud that we were part of the push for that =
> improvement.
> 
> Mike Lantz, CHP
> 
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>
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==
mark sasser 
at duke99301@yahoo.com
pager# 888-768-7451 640 east ice harbor dr pasco wa. 99301
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