[ RadSafe ] Re: attn. Landauer Customers

Wed Aug 24 12:54:12 CDT 2005

Yes, very good points, Neill. Plus there is a small neutron component to
the background radiation field, and many dosimeter designs include a
combination of neutron-sensitive and neutron-insensitive elements. With
TLD there is also usually some small, constant non-radiation induced
signal that is present but different for each element configuration. A
similar issue in TLD are the fading corrections, especially if more than
one phosphor type is present in the dosimeter. Since for low doses the
"background" is a non-trivial component of the total response, and since
element ratios are the key to correctly deciphering the incident
radiation fields, it's best make all of those corrections before running
the net data through an algorithm. 

Kim McMAHAN    ORNL External Dosimetry    865.576.1566

-----Original Message-----
From: radsafe-bounces at radlab.nl [mailto:radsafe-bounces at radlab.nl] On
Behalf Of Neill Stanford
Sent: Wednesday, August 24, 2005 1:07 PM
To: jblute at NITON.com; radsafe at radlab.nl
Subject: [ RadSafe ] Re: attn. Landauer Customers

This topic opens up an interesting and sometimes critical issue. In
subtracting background or transit response from a multi-element
dosimeter,
the correct method is to subtract element specific values, not
calculated
dose.
If you have a field dosimeter that is exposed say to low energy photons,
then add on some typical high energy background signal, the field
dosimeter
response is muddied with the background radiation response. The <gross>
dose
for the field dosimeter is calculated based on element readings that are
not
indicative of the field exposure, but on a mix with higher energy
photons.
Subtracting the dose calculated using the background dosimeter is not
accurate. If, on the other hand, you take the gross responses (field
plus
bkgd) and subtract the background responses, you are then left with just
what the dosimeter received in the field and the dose is accurately
calcualted.

This may seem nitpicky or impractical or both, but the reality is that
if
the field radiation and the background radiation are not the same
quality,
subtracting dose gives you the wrong answer. The solution is to use
shipment-specific background dosimeters and have the background element
responses subtracted, not the background dose. A second choice would be
to
have an estimated background element value subtracted and then simply
check
the actual background dosimeters to ensure that none showed a positive
result.

Neill Stanford, CHP
-----------------------------------------------------
Stanford Dosimetry, LLC
PO Box 935
921 S. Fourth St.
Suite B
La Conner, WA 98257

www.stanforddosimetry.com <http://www.stanforddosimetry.com/> 
360 466-1090 (voice/fax)
360 770-7778 (cell)
------------------------------------------------------

Original message ---------------
Date: Tue, 23 Aug 2005 18:11:14 -0400

From: "Jim Blute" <>

Subject: [ RadSafe ] Attn. Landauer Customers

To: <>

Message-ID:

<8EC7BA9EEA294F41B9EF5A1740B145D44C46D5 at chromium.NITON.com>

Content-Type: text/plain; charset="us-ascii"

I want to share with everyone a solution I found to a problem that has

bugged me for some time.

I have experienced frustration with administering a dosimetry program

and frequently having control badges not subtracted from personnel badge

results. I use Landauer and, admittedly, at times I was at fault by not

submitting the control badge for various reasons. Other times I came to

suspect that Landauer made the mistake. I have heard from other HPs who

use other companies for dosimetry services and they run into similar

problems so I am not writing this to criticize Landauer. Regardless of

root cause, fixing the problem was a not always easy. You can ask

Landauer to subtract any value you feel is appropriate after the fact,

but Landauer does not regularly report the control badge results so I am

left trying to choose an appropriate background without having knowledge

of what background to a badge might be for me. Not to mention that I

would rather not have to deal with a correction each time the problem

occurs. Often I would forget to do a correction or consciously decide

that I was too busy and the correction to minor for me to be bothered.

At these times I was left feeling guilty for not subtracting something

appropriate.

I spoke with Landauer today about it and for the first time I was made

aware of a reporting option that you have with them. If you ask them

to, they will automatically subtract 6 mrem per month from any reported

result that did not have a control badge associated with it. The 6 mrem

comes from a study they did of national average. Granted it may not be

perfect, but it is likely close enough for most applications. And it

keeps you from having to deal with the problem each time. 

I hope this info helps at least a few folks out there. If it is common

knowledge, then I missed the boat somewhere along the line.

Of course, I always seem to be at the airport when my ship comes in :-)

Jim Blute, CHP

Thermo Electron Corporation

Corporate Radiation Safety Officer

Portable Elemental Analysis

900 Middlesex Turnpike, Bldg. #8

Billerica, MA 01821-3926 USA

1-800-875-1578

Fax: 978-670-7430

e-mail: jblute at niton.com

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