[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: AW: X-ray dose
One thing to consider about the TLD. This was mentioned in a later post, but I
would like to add emphasis. If you are using a single chip TLD such as LiF,
portions of the the X-ray spectrum will over-respond significantly, as much as
60%, and other parts (less than 20 keV) tend to under-respond due to attenuation
by the TLD packaging. Multi-chip TLDs use varying filters to estimate field
composition allowing for a correction, but if there is only 1 chip it is
probably calibrated to Cs-137 and would overestimate the dose unless the vendor
was instructed about the effective E. Either way I would let the vendor know
the energy you were exposing it to.
I think a charge collecting instrument might shed some light. Maybe you have an
electometer (or pocket dosimeter) around that you could use to verify the dose
(correcting for material differences). This would probably not see the very low
E X-rays. To track down the TLD discrepancy, you might be able to filter the
beam with an Aluminum or Copper sheet to eliminate the low E component to see
it's significance. For 60 kV, NIST technique M60 uses1.5mm Al to yield an
average E of 35 keV (3mm Be), ISO uses .3mm Cu for and average E of 44 keV
(3.6mm Be) and .6mm Cu for an average E of 47 keV (3.6mm Be). The ISO beams
eliminate most of the photons less than 20 keV. This assumes a W target is
used.
Rob Gunter
----------------------------------------------------------------------------------------------------------
Robert J. Gunter Tel: (714) 545-0100
Sr. Technical Specialist Tel: (800) 548-5100 Ext. 2414
ICN Biomedicals, Inc. Fax: (714) 668-3149
Dosimetry Division Email: rjgunter@icnpharm.com
3300 Hyland Avenue
Costa Mesa, CA 92626
D J Hornsey <bssdjh@bath.ac.uk> on 09/23/99 06:47:10 AM
Please respond to radsafe@romulus.ehs.uiuc.edu
To: Multiple recipients of list <radsafe@romulus.ehs.uiuc.edu>
cc: (bcc: Robert Gunter/HQ/ICN)
Subject: Re: AW: X-ray dose
Thank you sunny Salzburg. The ICRP 33 data confirms the data I was using
to calculate the expected dose from this X-ray system. My TLDs were read
by an acredited dosimetry service, so no calibration needed. So I still
have a problem!!
David Hornsey
**************************************
* David J. Hornsey, Radiation Safety.*
* South Building, *
* University of Bath *
* Claverton Down, *
* Bath BA2 7AY. UK. *
* *
* tel:01225 826540 *
* fax:01225 826779 *
* e-mail: d.j.hornsey@bath.ac.uk *
**************************************
************************************************************************
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