Re: wrong DOT label

[William V Lipton <liptonw@dteenergy.com>]

The data is interesting, although I'm not sure of the practical implications.  A
look at a table of attenuation coefficients explains the loss of response below
approximately 30 kev.  For example, for water, the mass energy absorption
coefficient is 0.0669 cm2/g for 40 kev, 0.150 cm2/g for 30 kev, and 0.526 cm2/g
for 20 kev.  Thus, low energy photons tend to be attenuated by the instrument.
They would also be attenuated by shielding and packaging material.  I thus doubt
that low energy photons would be a problem for shipments (Although I'd be
interested if anyone knows of cases where they have been a problem.)

You quoted an error of 105% for N-16, but since the half life is 7.13 seconds, I
don't worry too much about shipping it.

Some other practical rules:

1.  Try to avoid shipping near a limit.

2.  If you must ship near a limit, use special care, such as multiple surveys with
different instruments.

3.  Try to use the  type of instrument used by the receiver.

4.  If you're right at the break point for a label category, eg. white-1 to
yellow-2, go with the higher category; I'll take my chances with a hit for
overlabeling, rather than risk a more serious hit for underlabeling.  I'd use
instrument tolerances as the justification, if called on this.

5.  Avoid "scab shielding," i.e. shielding which is not part of the package
design.  It is likely to shift during transport, changing the dose rate.  It may
also invalidate a package certification.

The  opinions expressed are strictly mine.
It's not about dose, it's about trust.

Bill Lipton
liptonw@dteenergy.com


Dave Derenzo wrote:

> Dear Glen and Irene,
>
> Using an energy compensated GM detector is certainly a good idea.  However,
> the following specs are interesting.
>
> Eberline HP-270 Energy Compensated GM Detector- There is scant information
> in their current catalog which simply states "Energy Range: 30 keV to 6
> MeV" with no mention of accuracy.  A much older catalog from the 1970s
> however indicates energy response of +/- 20% from 40 keV to 1.25 MeV.  It
> also includes an energy response curve that seems to indicate the detector
> under-responds by about 50% at 40 keV and drops off rapidly below that value.
>
> Ludlum 44-38 Energy Compensated GM Detector - The current catalog states
> "Within +/- 15% of true value from 50 keV -1.25 MeV.  There is no energy
> response curve.
>
> I am pretty sure that other energy compensated GM detectors have similar
> specs.  So, if you are measuring a bremmstrahlung spectrum with such a
> detector, you might expect a reading that is too low by maybe 50%.
>
> A similar look at the energy response info for ion chambers yields the
> following:
>
> Eberline RO-20 - +/- 30% from 8 keV to 6 Mev and +/- 15% from 33 keV to 6
> MeV, implying there is greater error in the range of 8 to 33 keV.  There is
> no energy response curve in the catalog.  A look at the old catalog for
> different models such as the RO-2 indicates a fairly flat response that
> drops off starting at about 15 keV with the slide open, and drops off
> starting at about 35 keV with the slide closed.
>
> Victoreen 471 - Within 10% for gamma and x-rays from 6 to 300 keV with beta
> cap off: within 10% from 25 keV to 2 MeV - and to 105% of N-16 gamma rays
> (most prominent gamma is 6.13 MeV) as tested at the University of
> Lowell.  The energy response curve shows under-response at low energies.
>
> So which is more conservative, the G.M. detector that you can get closer
> but that could significantly under-respond, or the ion chamber which is
> more accurate but cannot be brought close to the surface?  Tough call if
> you are trying to measure exposure rates from P-32 bremmstrhalung that is
> partially attenuated by the vial shield.  All things considered, I think
> that you could very easily get a +/- 50% to 100% difference in readings for
> such a situation, and that you need to interpret readings very carefully
> before making a report to a regulatory agency alleging
> non-compliance.  Both parties have probably made their best efforts to make
> the measurement.  Like my former boss used to say, "Where are the
> bodies?"  My opinion is that unless there was a significant safety problem
> caused by this difference, give the shipper the benefit of the doubt.
>
> Dave Derenzo
>
> At 09:28 PM 05/16/2000 -0500, you wrote:
> >The comments about the type of instrument used, large ion chamber vs. small
> >diameter compensated GM are certainly valid.  If someone were to be
> >non-conservative and use a large volume detector, aren't they taking risk
> >upon themselves?
> >
> >We use a small diameter, compensated GM detectors for all of our package
> >measurements.  I realize, that a small-diameter pulse counter may read higher
> >than an ion chamber in low energy fields and different geometries, but I
> >ensure that I never get any calls about exceeding dose rate limits.
> >
> >There is no cost difference in shipping White-I vs. Yellow-II, so I'd think
> >someone would use the most conservative meter?
> >
> >Glen Vickers
> >glen.vickers@ucm.com
> >************************************************************************
> >The RADSAFE Frequently Asked Questions list, archives and subscription
> >information can be accessed at http://www.ehs.uiuc.edu/~rad/radsafe.html
>
> Dave Derenzo, RSO (dave@uic.edu)
> UIC Radiation Safety Section, M/C 932
> Phones: Voice (312) 996-1177  Fax: (312) 996-8776
>
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> information can be accessed at http://www.ehs.uiuc.edu/~rad/radsafe.html

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